Linear Technology Corp. v. International Trade Commission

United States Court of Appeals for the Federal Circuit
2008-1117, -1165

LINEAR TECHNOLOGY CORPORATION,

Appellant,

v.

INTERNATIONAL TRADE COMMISSION,

Appellee,

and

ADVANCED ANALOGIC TECHNOLOGIES,

Intervenor.

----------------------

ADVANCED ANALOGIC TECHNOLOGIES, INC.,

Appellant,

v.

INTERNATIONAL TRADE COMMISSION,

Appellee,

and

LINEAR TECHNOLOGY CORPORATION,

Intervenor.

Mark G. Davis, Weil, Gotshal & Manges LLP, of Washington, DC, argued for appellant
and intervenor Linear Technology Corporation. With him on the brief were Ronald J. Pabis
and Patricia E. Chow. Of counsel on the brief were Natalia V. Blinkova, McDermott Will &
Emery LLP, of Washington, DC, and Jimmy M. Shin, Sonnenschein Nath & Rosenthal LLP,
of Palo Alto, California. Of counsel were Matthew G. Cunninghan, McDermott Will & Emery
LLP, of Washington, DC, and Amalie M. Weber, Weil, Gotshal & Manges LLP, of
Washington, DC.
 Paul M. Bartkowski, Attorney, Office of the General Counsel, United States
International Trade Commission, of Washington, DC, argued for appellee. With him on the
brief were James M. Lyons, General Counsel, and Wayne W. Herrington, Assistant General
Counsel. Of counsel was Eric S. Frahm, Attorney.

Andrew N. Thomases, Dechert LLP, of Mountain View, California, argued for
intervenor and appellant Advanced Analogic Technologies, Inc. With him on the brief were
Chris Scott Graham, Jonathan D. Baker, Anthony B. Diepenbrock, III, and Philip Barilovits;
and George W. Webb, III, of Austin, Texas. Of counsel were Stephen J. Rosenman and
Ayumi Urabe, of Washington, DC.

Appealed from: United States International Trade Commission

2
United States Court of Appeals for the Federal Circuit

2008-1117, -1165

LINEAR TECHNOLOGY CORPORATION,

Appellant,

v.

INTERNATIONAL TRADE COMMISSION,

Appellee,

and

ADVANCED ANALOGIC TECHNOLOGIES,

Intervenor.

----------------------------------------

ADVANCED ANALOGIC TECHNOLOGIES, INC.,

Appellant,

v.

INTERNATIONAL TRADE COMMISSION,

Appellee,

and

LINEAR TECHNOLOGY CORPORATION,

Intervenor.
 On appeal from the United States International Trade Commission in
Investigation No. 337-TA-564.

_________________________

DECIDED: May 21, 2009
_________________________

Before MAYER, LOURIE, and SCHALL, Circuit Judges.

SCHALL, Circuit Judge.

Linear Technology Corporation (“Linear”) filed a complaint with the United States

International Trade Commission (“the Commission”) under section 337 of the Tariff Act

of 1930, 19 U.S.C. § 1337(a)(1)(B), alleging that Advanced Analogic Technologies, Inc.

(“AATI”) imported and/or sold for importation certain electronic voltage regulators that

infringe U.S. Patent No. 6,580,258 (“the ’258 patent”). See In re Certain Voltage

Regulators, Components Thereof and Products Containing Same, 71 Fed. Reg. 14,545

(Int’l Trade Comm’n Mar. 22, 2006) (“Notice of Investigation”). Linear now appeals the

Commission’s final determination, ruling that certain AATI imported voltage regulators

do not infringe asserted claims 2, 3, 34, and 35 of the ’258 patent and that claim 35 is

invalid as anticipated by a device made by Maxim Integrated Products, Inc. (“the

MAX782”). In re Certain Voltage Regulators, No. 337-TA-564, slip op. (Int’l Trade

Comm’n Oct. 19, 2007) (“Final Determination”). In addition, AATI cross-appeals the

Commission’s ruling that one of its imported voltage regulators infringes asserted claims

2, 3, and 34 and that asserted claims 2, 3, and 34 are not invalid as anticipated. Id. For

the reasons stated in this opinion, we affirm-in-part, reverse-in-part, vacate-in-part, and

remand.

2008-1117, -1165 2
 BACKGROUND

I

Linear is the owner of the ’258 patent. The ’258 patent is titled “Control Circuit

and Method for Maintaining High Efficiency Over Broad Current Ranges in a Switching

Regulator Circuit.” The ’258 patent is a continuation of U.S. Patent No. 5,481,178 (“the

’178 Patent”) of the same title. See ’258 patent. The ’258 patent describes voltage

regulators, which “provide a predetermined and constant output voltage to a load from a

poorly-specified and fluctuating input voltage source.” Id. col.1 ll.24–27. In other words,

because an input source—such as a battery—may supply either an unstable voltage or

a voltage level not usable by a device—such as a laptop computer—a voltage regulator

changes the input voltage level to an output voltage level that is both stabilized and at a

level usable by the device. More specifically, the ’258 patent is directed to switching-

type voltage regulators that, “[b]ecause of their improved efficiency[,] . . . are typically

employed in battery-operated systems such as portable and laptop computers and

hand-held instruments.” Id. col.2 ll.3–6.

The switching voltage regulators described in the ’258 patent employ a switch

that provides power to a device using “pulses” of current from the input source, rather

than a steady stream of power or current. See id. col.1 ll.29–43. The switch is formed

by two transistors 1 connected to the input source, e.g., a battery. Id. fig.2, items 16 &

17. The switch creates current pulses by alternatively turning the two transistors on and

off—when the top transistor is on, the bottom transistor is off, and vice versa—called

1
A transistor is a semiconductor component used in an electronic circuit. It
can act like an electronic switch, either allowing or preventing current passage through
it.

2008-1117, -1165 3
synchronous switching. See, e.g., id. col.1 ll.29–43; id. col. 7 ll.48–51. Because the

switch is either OFF—when the input source provides no power to the device—or ON—

when the input source provides only a small amount of power with a small current

“pulse”—switching regulators generally “result[ ] in reduced amounts of power

dissipation.” Id. col.1 ll.56–62.

While switching voltage regulators generally improve efficiency and battery life,

efficiency nonetheless decreases under certain operating conditions, such as during

“low output current.” Id. col.2 ll.3–18. Thus, to accomplish higher efficiency, the ’258

patent proposes two improvements that are pertinent to this appeal. In the first

improvement, the ’258 patent describes a “sleep mode,” where additional power is

saved, thereby increasing efficiency, by maintaining the regulated output voltage using

only the electrical charge in a capacitor. 2 See id. col.2 ll.40-50; col.6 ll.43–55. Because

the regulated output voltage is maintained by a capacitor, rather than the input power

source (e.g., a battery), the device “does not consume power from the input power

source.” Id. col.2 ll.47–49. The second improvement increases efficiency by preventing

“reverse current” situations. See, e.g., id. col.14 l.14-col.15 l.10. In “reverse current”

situations, efficiency is decreased because power is drawn from the load device back

into the voltage regulator circuitry and eventually dissipated. See id. col.14 ll.62–67.

Thus, otherwise usable power is not used by the load device, but is instead “wasted.”

AATI manufactures a variety of electronic components and products. Linear

instituted a section 337 action against AATI, alleging that numerous AATI voltage

regulator products imported or sold for importation infringe the asserted claims of the

2
A capacitor is a component used in electronic circuits that can store an
electric charge.

2008-1117, -1165 4
’258 patent. The parties agreed to designate four representative AATI voltage regulator

products: the AAT1143, AAT1146, AAT1151, and AAT1265. Linear alleged that all four

accused products infringe claims 2, 3, and 34, which cover an apparatus and method

for implementing the above described “sleep mode” of operation. The asserted “sleep

mode” claims, as well as claim 1 from which claims 2 and 3 depend, are reproduced

below:

1. A circuit for controlling a switching voltage regulator, the regulator
having (1) a switch coupled to receive an input voltage and including a
pair of synchronously switched switching transistors and (2) an output for
supplying current at a regulated voltage to a load which includes an output
capacitor, the circuit comprising:

a first circuit for monitoring the output to generate a first feedback signal;

a second circuit for generating a first control signal during a first state of
circuit operation, the first control signal being responsive to the first
feedback signal to vary the duty cycle of the switching transistors to
maintain the output at the regulated voltage; and

a third circuit for generating a second control signal during a second state
of circuit operation to cause both switchin[g] transistors to be OFF for a
first period of time during which the output capacitor maintains the output
substantially at the regulated voltage.

2. The circuit of claim 1 wherein the second control signal is generated in
response to the first feedback signal.

3. The circuit of claim 2 wherein the circuit changes from the second to the
first state of operation in response to the magnitude of the first feedback
signal falling below a first threshold level.

34. A method for controlling a switching voltage regulator, the regulator
having (1) a switch coupled to receive an input voltage and including a
pair of synchronously switched switching transistors and (2) an output for
supplying current at a regulated voltage to a load which includes an output
capacitor, the method comprising the steps of:

(a) monitoring the output to generate a first feedback signal;

(b) varying the duty cycle of the switching transistors in response to the
first feedback signal to maintain the output at the regulated voltage during
a first state of circuit operations;

2008-1117, -1165 5
 (c) turning both switching transistors OFF for a first period of time following
the first state of circuit operation so as to allow the output capacitor to
maintain the output substantially at the regulated voltage by discharging
during a second state of circuit operation; and

(d) turning at least one of said switching transistors ON to recharge the
output capacitor following the second state of circuit operation.

Id. col.16 ll.40–67; col.18 l.57–col.19 l.10.

In addition, Linear alleged infringement of claim 35 by AATI’s AAT1143 and

AAT1146. Claim 35 purportedly covers the above-described “reverse current”

protection and reads as follows:

35. A circuit for controlling a switching voltage regulator, the regulator
having (1) a switch coupled to receive an input voltage and including a
pair of synchronously switched switching transistors and (2) an output for
supplying current at a regulated voltage to a load which includes an output
inductor, the circuit comprising:

a first circuit for monitoring the output to generate a first feedback signal;

a second circuit for generating a first control signal during a first state of
circuit operation, the first control signal being responsive to the first
feedback signal to vary the duty cycle of the switching transistors to
maintain the output at the regulated voltage; and

a third circuit for monitoring the current to the load to generate a second
control signal during a second state of circuit operation to cause one of
said switching transistors to be maintained OFF when the magnitude of
the monitored current falls below a current threshold.

Id. col.19 l.11–col.20 l.15.

On May 22, 2007, the Administrative Law Judge (“ALJ”) to whom the

investigation was assigned issued an Initial Determination (“ID”), finding that AATI did

not violate section 337, either because its accused products do not infringe the asserted

claims or because asserted claim 35 is invalid. In re Certain Voltage Regulators, No.

337-TA-564, slip op. (Int’l Trade Comm’n May 22, 2007) (“Initial Determination”).

Subsequently, Linear petitioned the Commission for review. On July 24, 2007, the

2008-1117, -1165 6
Commission decided to review certain portions of the ID—specifically, relating to claim

construction, infringement, and validity of the ’258 patent.

Upon review, the Commission modified the ALJ’s construction of several

disputed claim limitations and reversed the holding that the AAT1143 does not infringe

claims 2, 3, and 34. See, e.g., Final Determination, slip op. at 43, 80. The Commission,

however, sustained the ALJ’s ID in all other respects. Specifically, the Commission held

that (1) all of the other accused products—the AAT1146, AAT1151, and AAT1265—do

not infringe claims 2, 3, 34, and 35; (2) claims 2, 3, and 34 are not anticipated by a

reference entitled “Application Note 35—Step Down Switching Regulators” (“AN35”);

and (3) claim 35 is invalid as anticipated by the MAX782 product. See, e.g., id. at 80.

The Commission declined to address indirect infringement. Based upon its rulings, the

Commission “exclude[d] from entry for consumption into the United States AATI’s

voltage regulators that infringe one or more of claims 2, 3, and 34 of the ’258 patent.”

Id. at 80. Linear has timely appealed, and AATI has cross-appealed, the Commission’s

rulings regarding claim construction, infringement, and validity. We have jurisdiction

pursuant to 28 U.S.C. § 1295(a)(6).

DISCUSSION

I

Before addressing infringement and validity, we must first turn to the parties’

arguments about the Commission’s claim constructions. Claim construction is a

question of law that we review de novo. Finnigan Corp. v. Int’l Trade Comm’n, 180 F.3d

1354, 1362 (Fed. Cir. 1999).

2008-1117, -1165 7
A. “switch . . . including a pair of synchronously switched switching transistors”

The first disputed claim construction concerns the language “switch . . . including

a pair of synchronously switched switching transistors,” which appears in claims 2, 3,

34, and 35. The Commission construed this language according to the explicit definition

in the ’258 patent to mean “a switch including two switching transistors that are driven

out of phase to supply current at a regulated voltage to a load.” Final Determination,

slip op. at 15. Because the Commission construed this limitation in accordance with the

express definition in the ’258 patent’s specification, both Linear and the Commission

argue that the Commission’s construction is correct. AATI, however, contends that,

because a single control signal controls both switching transistors, the proper

construction requires “a switch that includes a pair of transistors connected for

complementary switching and controlled as a single unit.”

Because the Commission construed this limitation according to the definition in

the specification, the Commission’s construction—“a switch including two switching

transistors that are driven out of phase to supply current at a regulated voltage to a

load”—is correct. See, e.g., 3M Innovative Props. Co. v. Avery Dennison Corp., 350

F.3d 1365, 1374 (Fed. Cir. 2003) (providing a definition in the specification controls the

meaning of the term). As pointed out by the Commission and Linear, this construction

is consistent with the definition in the ’258 patent’s specification, which reads “[a]s used

herein, the term ‘synchronously-switched switch’ refers to a switch including two

switching transistors that are driven out of phase to supply current at a regulated

voltage to a load.” ’258 patent col.7 ll.48–51. Thus, we see no error in the

2008-1117, -1165 8
Commission’s construction of the language “switch . . . including a pair of synchronously

switched switching transistors.”

B. “second circuit” and “third circuit”

We now turn to the “second circuit” and “third circuit” limitations, which appear in

apparatus claims 2, 3, and 35, but not method claim 34. The Commission modified the

ALJ’s initial construction because the ALJ “too narrowly construed the asserted claims

as requiring that the ‘second’ and ‘third’ circuits be entirely distinct without common

circuit elements, that every element in the second circuit be completely distinct from

every element in the third circuit, and as precluding shared use of the same circuitry by

the ‘second’ and ‘third’ circuits of the asserted sleep mode claims.” Final Determination,

slip op. at 46. Accordingly, the Commission found that “even a difference such as

having an additional [component] can cause the circuits to be different and distinct in

their topology and their operation.” Id. AATI does not appear to take issue with

allowing the second and third circuits to differ by merely including an additional

component, but instead contends that the proper construction requires that the

additional component must “participate[ ] in performing the claimed function.” More

specifically according to AATI, the additional component in the “third circuit” must at

least help perform the function of that circuit and cannot be an arbitrary component,

which is unrelated to the function of the “third circuit.” In contrast, both Linear and the

Commission advocate that the Commission’s construction is correct.

We agree with the Commission’s construction of “second circuit” and “third

circuit,” defining the terms broadly to not require entirely separate and distinct circuits.

Indeed, there is nothing in the claim language or specification that supports narrowly

2008-1117, -1165 9
construing the terms to require a specific structural requirement or entirely distinct

“second” and “third” circuits. Rather, the “second” and “third” circuits must only perform

their stated functions. For example, what is required is that the “second circuit”

“generat[es] a first control signal . . . to vary the duty cycle,” not that any particular

components make up this circuit. ’258 patent col.16 ll.48–52. In fact, the ’258 patent’s

specification expressly discloses that the “second circuit” and “third circuit” can share

common components. For example, figure 2 shows that components of the “second

circuit”—such as the reference circuit 37—can also be part of the “third circuit.” See id.

fig.2 (disclosing that the reference circuit 37 sends a signal to the hysteretic comparator

74, which can be a part of the “third circuit for generating a second control signal”).

Accordingly, we think the terms “second circuit” and “third circuit” should be accorded

their full scope. See, e.g., Home Diagnostics, Inc. v. LifeScan, Inc., 381 F.3d 1352,

1358 (Fed. Cir. 2004) (“Absent a clear disavowal or contrary definition in the

specification or the prosecution history, the patentee is entitled to the full scope of its

claim language.”); Linear Tech. Corp. v. Impala Linear Corp., 379 F.3d 1311, 1320

(Fed. Cir. 2004) (construing the term “circuit” in the parent ’178 patent of this case and

acknowledging that the term is normally recognized broadly as “the combination of a

number of electrical devices and conductors that, when interconnected to form a

conducting path, fulfill some desired function”); cf. In re Translogic Tech., Inc., 504 F.3d

1249, 1257–58 (Fed. Cir. 2007) (construing “input terminals coupled to receive” without

a specific structural requirement because “the claim terms [did] not specify any

structural connection for the input terminals . . . and the . . . figures show[ed] no

structural connection for the input terminals . . . or the control input terminals”).

2008-1117, -1165 10
 Moreover, AATI does not contest that the “second circuit” and “third circuit” can

contain overlapping components. Rather, it advocates that the distinct component must

aid in the function of the claimed circuit. 3 As pointed out by the Commission, however,

the claim language itself mandates that the components comprising the claimed second

and third “circuits” must aid in the claimed function—e.g., the “third circuit” must “cause

both switching transistors to be OFF.” ’258 patent col.16 ll.53–57. Thus, because the

claim language already requires the components to aid in the circuit’s function, AATI’s

proposed additional language is unnecessary. See, e.g., Linear Tech., 379 F.3d at

1320 (construing the nearly identical claim limitations “second circuit” and “third circuit”

of the ’178 patent, although under § 112 ¶ 6 analysis, to not require additional structural

clarification because the “limitations . . . are accompanied by . . . language [in the

claims] reciting their respective objectives or operations”). The Commission did not err

in its construction of the “second circuit” and “third circuit” limitations.

3
In particular, AATI argues that the Commission’s construction is erroneous
because it allowed “a difference such as having an additional ZC comparator” to
distinguish the second and third “circuits.” Final Determination, slip op. at 46 (a
comparator is an electronic device that can compare two voltages or currents and
subsequently output a signal to indicate which is larger). Accordingly, AATI apparently
does not contest that the second and third circuits can generally be distinguished by an
additional component, if that component aids in the function of the claimed circuit. In
contrast, AATI takes specific issue with identifying the “ZC comparator” as the
distinguishing component because, according to AATI, it does not aid in the function of
the “third circuit”—namely, causing both switching transistors to be OFF. This
argument—whether the ZC comparator aids in the function of the third circuit—however,
is one of AATI’s noninfringement positions and does not impact our claim construction
analysis. See Int’l Rectifier Corp. v. IXYS Corp., 361 F.3d 1363, 1369 (Fed. Cir. 2004)
(“Although IXYS’s arguments on claim construction often conflate with its arguments on
infringement, we address these issues separately, turning first to claim construction.”).

2008-1117, -1165 11
C. “a second control signal . . . to cause both transistors to be OFF”

AATI also contests the Commission’s construction of the language “a second

control signal . . . to cause both transistors to be OFF,” which is required by claims 2

and 3, but not method claim 34. The Commission construed this language as “broad

enough to cover a signal which causes, or ultimately results in, both switching

transistors being OFF.” Final Determination, slip op. at 50. AATI argues that the proper

construction of this language requires “the third circuit [to] produce[ ] a signal whose

transition necessarily leads to both transistors being OFF,” “without the intervention of

any other independently-generated signal.” According to AATI, this is because

including “ultimately results in” removes the concept of “causation” and, therefore, is

contrary to the claim language itself. Linear and the Commission defend the current

construction, contending that the language, and in particular “cause,” was correctly

given its broad ordinary meaning—to make happen, to result in, requiring neither a

“direct” nor immediate cause.

We hold that the Commission properly construed the limitation “a second control

signal . . . to cause both transistors to be OFF” as requiring the second control signal to

neither directly cause both transistors to be OFF nor be entirely distinct from the first

control signal. The ’258 patent’s specification does not indicate that the “second control

signal” must directly cause both transistors to be OFF. Indeed, a direct causation

requirement—without the intervention of other signals or components—would be nearly

unworkable to articulate or ascertain. Also, such a requirement would allow an accused

infringer to evade infringement by merely identifying an intermediary signal or

component that allegedly breaks the “chain of causation.” Cf. Resonate Inc. v. Alteon

2008-1117, -1165 12
Websys., Inc., 338 F.3d 1360, 1365 (Fed. Cir. 2005) (“The patentee’s . . . choice not to

specify a transmission path from the server to the client” did not require direct

transmission to the client because “such a rule likely would prove unworkable.”). In

addition, such a requirement would be contrary to the specification, which in fact

discloses components that are located between the generation of the second control

signal and the switching transistors. See, e.g., ’258 patent fig.2. Tellingly, in construing

the nearly identical, but more restrictive, claim limitations of the parent ’178 patent, we

held that “to cause both switching transistors to be simultaneously OFF for a period of

time” should not be construed to include a narrow causation requirement. See Linear

Tech., 379 F.3d at 1324 (holding that the district court construed the limitations too

narrowly “because simultaneously merely requires a condition to exist at the same time

or concurrently,” “encompasses the simultaneous state of both switching transistors

being disabled or held off,” and “does not require the switching transistors to be turned

off or disabled at the same instant”).

Nor does the specification indicate that the “second control signal” must be

entirely distinct from the claimed “first control signal.” In fact, the specification discloses

the contrary—that a portion of the “first control signal” impacts whether the “second

control signal” turns both transistors OFF. Indeed, figure 2 discloses that the signal

from hysteretic comparator 74 in combination with the signal 25A from constant off time

one-shot circuit 25—part of the disclosed “first control signal” that “var[ies] the duty

cycle of the switching transistors”—“cause[s] both switching transistors to be OFF.”

See, e.g., ’258 patent fig.2; id. col.6 ll.38–55. Thus, the patent shows that the first

control signal can be a part of the second control signal, precluding a requirement that

2008-1117, -1165 13
the two control signals must be entirely distinct. The Commission’s construction of “a

second control signal . . . to cause both transistors to be OFF” is correct.

D. “first state of circuit operation” and “second state of circuit operation”

We now reach the parties’ dispute concerning the claim limitations “first state of

circuit operation” and “second state of circuit operation,” which are required by claims 2,

3, 34, and 35. The Commission construed these terms to mean “that the first state of

operation can be linked to high load currents, and the second state can be linked to low

load currents, although the states of operation do not necessarily have to be linked to a

high or low load current.” Final Determination, slip op. at 24. AATI contends that the

“first state” should “occur[] at high load currents,” while the “second state” should

“occur[] only at low load currents.” AATI argues that its construction is supported by the

’258 patent’s specification and by statements Linear made in prosecuting similar claims

in the parent ’178 patent. Linear and the Commission contend that the current

constructions of these terms are correct, arguing that neither the specification of the

’258 patent nor the prosecution history of the parent ’178 patent clearly disavow any

claim scope.

We decline to disturb the Commission’s constructions of “first state of circuit

operation” and “second state of circuit operation.” While the ’258 patent specification

provides examples and embodiments where the “first state of circuit operation” may

occur at high load currents and the “second state of circuit operation” may occur at low

load currents, there is no “clear intention to limit the claim scope using ‘words or

expressions of manifest exclusion or restriction,’” which is necessary to further narrow

the claim language. Liebel-Flarsheim Co. v. Medrad, Inc., 358 F.3d 898, 906 (Fed. Cir.

2008-1117, -1165 14
2004) (quoting Telefex, Inc. v. Ficosa N. Am. Corp., 299 F.3d 1313, 1327 (Fed. Cir.

2002)); see also Brookhill-Wilk 1, LLC v. Intuitive Surgical, Inc., 334 F.3d 1294, 1301

(Fed. Cir. 2003) (“Absent a clear disclaimer of particular subject matter, the fact that the

inventor anticipated that the invention may be used in a particular manner does not limit

the scope to that narrow context.”). We have repeatedly held that, even in situations

when only one embodiment is disclosed, the claims generally should not be narrowed to

cover only the disclosed embodiments or examples in the specification. See, e.g.,

Liebel-Flarsheim, 358 F.3d at 906 (“Even when the specification describes only a single

embodiment, the claims of the patent will not be read restrictively unless the patentee

has demonstrated a clear intention to limit the claim scope . . . .”); Brookhill-Wilk 1, 334

F.3d at 1301 (“The statements from the description of the preferred embodiment are

simply that—descriptions of a preferred embodiment . . . [which] do not indicate that the

invention can only be used in such a manner.”). In fact, the ’258 patent specification

discloses situations contrary to AATI’s suggested construction—operating in the “first

state of circuit operation” at low load currents. For example, at low load current levels

when the output capacitor has fully discharged—thus being incapable of maintaining the

regulated voltage—the “first mode of circuit operation” is initiated to “vary the duty cycle

of the switching transistors” in order to turn the top transistor 16 ON long enough to

“recharge” the output capacitor. See, e.g., ’258 patent col.9 l.63–col.10 l.10.

Nor do the statements made during prosecution of the parent ’178 patent evince

a “‘clear and unmistakable’ disavowal of claim scope that would compel a result

different than the claim language.” ResQNet.com, Inc. v. Lansa, Inc., 346 F.3d 1374,

1383 (Fed. Cir. 2003). As an initial matter, the statements made in the prosecution of

2008-1117, -1165 15
the parent ’178 patent do not remotely relate to the “first state of circuit operation” and,

as such, do not narrow this limitation, as urged by AATI. See, e.g., id. (finding no “clear

and unmistakable” disavowal of claim scope where the prosecution history of the parent

patent did not address the same claim limitations); Advanced Cardiovascular Sys., Inc.

v. Medtronic, Inc., 265 F.3d 1294, 1305-06 (Fed. Cir. 2001) (declining to construe a

term more narrowly based on the parent patent’s prosecution history because common

claim terms were not in dispute). Moreover, while the prosecution history of the ’178

patent does mention “low output current levels,” it neither “clearly and unmistakably”

addresses the “second state of circuit operation” nor limits that state to occurring only at

low output load current. See, e.g., ResQNet.com, 346 F.3d at 1383; Advanced

Cardiovascular Sys., 265 F.3d at 1305–06. Indeed, the claim amendments do not

“clearly and unmistakably” modify “the second state of circuit operation,” but instead

more directly address claim language not disputed in this case. In addition, the

amendments do not “clearly and unmistakably” limit the second mode to operating at

only low load currents. Rather, the amendments address when the second mode is

activated—specifically, when the current to the load falls lower than a predetermined

threshold. In other words, the amendments specify entering the second state when the

load current drops below some value in comparison to a threshold value—a value that

could be relatively high or low. Thus, the amendments and statements in the parent

’178 patent are plainly different than the limitations in AATI’s proposed construction.

In any event, the remainder of the claim language that modifies the “first state”

and “second state” of circuit operations clearly describes the terms. See, e.g., Linear

Tech., 379 F.3d at 1324 (looking to the other portions of the claim language in finding

2008-1117, -1165 16
that further narrowing of a limitation was unnecessary). In particular, the claim

language states with specificity that the “first state of circuit operation” corresponds to

when the duty cycle of the switching transistors is varying “to maintain the output at the

regulated voltage.” ’258 patent col.16 ll.50–52. Similarly, the claim language clarifies

that the “second state of circuit operation” corresponds to when the “output capacitor

maintains the output substantially at the regulated voltage.” Id. col.16 ll.55–57; see id.

col.2 ll.42–46; id. col.6 ll.4–8 (“when the voltage at output is capable of being

maintained substantially at the regulated voltage by the charge on the output

capacitor”). We therefore affirm the Commission’s claim construction of the “first state”

and “second state” of circuit operation.

E. “monitoring the current to the load”

Lastly, we address the Commission’s ruling regarding the “monitoring the current

to the load” limitation in claim 35. See ’258 patent col. 20 ll.9–14 (“a third circuit for

monitoring the current to the load to generate a second control signal during a second

state of circuit operation to cause one of said switching transistors to be maintained

OFF”). During its infringement analysis, the Commission excluded “monitoring voltage”

from meeting this limitation. Final Determination, slip op. at 51–53. In effect, because a

device can indirectly monitor current by monitoring voltage, the Commission limited the

“monitoring current” limitation to instances of directly monitoring current. Thus, although

the Commission did not explicitly address the “monitoring current” limitation under its

claim construction section, it effectively construed the limitation. We thus address the

parties’ dispute regarding this limitation as a claim construction issue. See, e.g., Board

of Regents of Univ. of Tex. Sys. v. BenQ Am. Corp., 533 F.3d 1362, 1367 (Fed. Cir.

2008-1117, -1165 17
2008) (treating the parties’ dispute over a limitation as a claim construction issue

because the district court “effectively construed the claim phrase” in its summary

judgment order). Linear argues that the exclusion of indirectly monitoring current is

incorrect, arguing that the ’258 patent’s specification and Ohm’s Law 4 support the

proposition that “monitoring the current to the load” in claim 35 can be accomplished

either directly or indirectly. In response, AATI contends that the Commission properly

rejected Linear’s reliance on Ohm’s Law and, thus, correctly found that monitoring

current could not include monitoring a voltage.

We agree with Linear that the Commission improperly narrowed this claim

limitation to exclude indirectly monitoring current through the measurement of voltage.

The claim limitation does not state directly monitoring current. Rather, it simply reads

“monitoring the current to the load.” ’258 patent col. 20 ll.9–10. As such, this limitation

should be accorded a scope commensurate with the ’258 patent’s specification. See,

e.g., Tegal Corp. v. Tokyo Electron Am., Inc., 257 F.3d 1331, 1342 (Fed. Cir. 2001)

(construing a limitation broadly based on the specification). In this case, the ’258 patent

not only discloses monitoring current directly by using a current comparator, see, e.g.,

id. col.14 ll.43–61, but also indirectly by some other means. Explicitly, the specification

states that “other means of detecting current reversals in the inductor current could be

used as well,” id. col.15 ll.1-10, including “generating a feedback signal indicative of

current reversal in inductor current . . . (see, e.g., resistor Rsense in Fig. 7),” id. col.15

ll.8-10 (emphases added). Generating a feedback signal based on resistor Rsense

4
Ohm’s Law is a principle of electrical circuits and is represented by the
equation I (current) = V (voltage) / R (resistance). Thus, it states that the current
through a conductor between two points is directly proportional to the voltage across the
two points, and inversely proportional to the resistance between them.

2008-1117, -1165 18
measures the voltage across resistor Rsense, therefore indirectly “indicat[ing] [] current

reversal in inductor current” by measuring voltage. Thus, the ’258 patent expressly

contemplates indirectly monitoring current by using a voltage measurement as a proxy.

Moreover, once voltage is known, one skilled in the art would recognize that Ohm’s Law

easily allows current to be calculated, therefore monitoring current indirectly by

monitoring voltage. Without support for limiting this limitation as it did, we think the

Commission interpreted this limitation incorrectly when it excluded the accused devices.

See, e.g., Cohesive Tech., Inc. v. Waters Corp., 543 F.3d 1351, 1367–68 (Fed. Cir.

2008) (“[I]t is not appropriate for the court to construe a claim solely to exclude the

accused device.”). Thus, because there is no basis in the patent specification for

adding the negative limitation—excluding monitoring voltage—we hold that the

Commission erred in construing this limitation. See, e.g., Omega Eng’g, Inc. v. Rayteck

Corp., 334 F.3d 1314, 1323 (Fed. Cir. 2003) (“Our independent review of the patent

document reveals . . . there is no basis in the patent specification for adding the

negative limitation.” (citations omitted)). In contrast to the Commission’s ruling, this

limitation can encompass monitoring voltage to indirectly monitor current.

In sum, we affirm the Commission’s claim construction of “switch . . . including a

pair of synchronously switched switching transistors”; “second circuit” and “third circuit”;

“a second control signal . . . to cause both transistors to be OFF”; and “first state of

circuit operation” and “second state of circuit operation.” Regarding “monitoring the

current to the load” in claim 35, however, we disagree with the Commission’s narrow

construction; we hold that this limitation can be satisfied by monitoring voltage to

indirectly monitor current.

2008-1117, -1165 19
 II

Having determined the proper construction of the disputed claim limitations, we

now turn to the Commission’s infringement rulings regarding the “sleep mode” claims.

The Commission’s findings regarding infringement are questions of fact, which we

review under the substantial evidence standard. See 19 U.S.C. § 1337(c); 5 U.S.C.

§ 706(2)(E); Finnigan, 180 F.3d at 1361–62. “‘Substantial evidence’ has been defined

as ‘more than a mere scintilla’ and as ‘such relevant evidence as a reasonable mind

might accept as adequate to support a conclusion.’” Honeywell lnt’l, lnc. v. Int’l Trade

Comm’n, 341 F.3d 1332, 1338 (Fed. Cir. 2003) (quoting Consol. Edison Co. v. NLRB,

305 U.S. 197, 229 (1938)). To prove infringement, a patentee must show “that a

defendant has practiced each and every element of the claimed invention,” and may do

so by relying on either direct or circumstantial evidence. See, e.g., BMC Res., Inc. v.

Paymentech, L.P., 498 F.3d 1373, 1380 (Fed. Cir. 2007); Liquid Dynamics Corp. v.

Vaughan Co., 449 F.3d 1209, 1219 (Fed. Cir. 2006). “A method claim is directly

infringed only by one practicing the patented method.” Joy Techs., Inc. v. Flakt, Inc., 6

F.3d 770, 775 (Fed. Cir. 1993).

For clarity, we proceed with our infringement analysis of the “sleep mode” claims

by separately discussing the several accused devices. The parties’ dispute focuses on

the limitations: “switch . . . including a pair of synchronously switched switching

transistors”; “second circuit” and “third circuit”; “a second control signal . . . to cause

both transistors to be OFF”; and “first state of circuit operation” and “second state of

circuit operation.” However, because AATI’s infringement arguments regarding the

“switch . . . including a pair of synchronously switched switching transistors” limitation in

2008-1117, -1165 20
all asserted claims rely entirely on its proposed claim construction, which we have

already rejected, we have no need to further address this limitation.

A. AAT1143 device

We first address the AAT1143 accused device, which the Commission found to

infringe all of the asserted “sleep mode” claims—namely, claims 2, 3, and 34. AATI

argues that the Commission’s infringement finding is not supported by substantial

evidence because various claim limitations are not met. AATI contends that the

“second circuit” and the “third circuit” limitations are not satisfied because the

component identified by the Commission that distinguishes the two “circuits”—the ZC

comparator circuitry—plays no role in the claimed function of the “third circuit.” In

addition, AATI argues that the “second control signal . . . to cause both switching

transistors to be OFF” limitation is not met because the second control signal identified

by the Commission—the CMP signal—does not “cause” both transistors to be OFF.

Linear and the Commission assert that the Commission properly found claims 2, 3, and

34 infringed.

We hold that there is substantial evidence supporting the Commission’s finding

that the AAT1143 device infringes claims 2 and 3. This evidence consists of circuit

schematics, graphs of the device in operation, and explanatory expert testimony. We

therefore affirm the Commission’s ruling in this regard. Concentrating on the disputed

limitations, there is substantial evidence that the AAT1143 operates in a “first mode”

and “second mode” of circuit operation. 5 Substantial evidence indicates that the

5
As a reminder, the claim language describes the “first state of circuit
operation” as corresponding to when the duty cycle of the switching transistors is
varying “to maintain the output at the regulated voltage,” ’258 patent col.16 ll.50–52,

2008-1117, -1165 21
AAT1143 operates in two modes of operation—one when the switching transistors are

synchronously switching to maintain the output voltage, and the other when both

transistors are OFF maintaining the output voltage using an output capacitor (i.e., “sleep

mode”). Indeed, AATI does not contend that the AAT1143 does not go into a “sleep

mode,” as it seemingly acknowledges that “at high load current levels, the switching

transistors of the accused products sometimes happen to switch alternately, while at

low load current levels there can be a time period when both switching transistors

happen to be OFF.” AATI’s Reply Br. 71-72. Rather, AATI arguments focus on

limitations not required by the claims and rely on proposed claim constructions that we

have already rejected.

Regarding the “second circuit” and “third circuit” limitations, as well as the “a

second control signal . . . to cause both switching transistors to be OFF” limitation, AATI

does not contest how the AAT1143 device actually operates. Rather, it argues that the

AAT1143 does not infringe under its proposed narrow claim constructions. Under the

correct claim constructions, however, the presence of these limitations in the AAT1143

is supported by substantial evidence. As explained by expert testimony and supported

by circuit schematics, the ZC comparator circuitry distinguishes the claimed “third

circuit” from the claimed “second circuit” and aids in the function of the “third circuit”—

namely, causing both switching transistors to be OFF. Thus, under the proper claim

and the “second state of circuit operation” as corresponding to when the “output
capacitor maintains the output substantially at the regulated voltage” while both
switching transistors are OFF, id. col.16 ll.55-57. We have left undisturbed the
Commission’s construction of these terms, requiring neither the first state of circuit
operation to necessarily be linked to high load current nor the second state of circuit
operation to necessarily be linked to low load current.

2008-1117, -1165 22
construction, there is substantial evidence that the “second circuit” and “third circuit”

limitations are satisfied.

Similarly, under the correct construction, there is substantial evidence that the

“second control signal” causes “both switching transistors to be OFF.” According to the

circuit schematics, documents, and expert testimony, the CMP signal in the AAT1143

device—acknowledged as the “second control signal”—turns the top transistor OFF.

Turning the top transistor OFF consequently and necessarily causes the ZC comparator

circuitry to output a ZC signal, which then shuts the bottom transistor OFF and causes

the AAT1143 to maintain the regulated voltage using the output capacitor. Thus,

because the CMP signal turns the top transistor OFF, which sequentially and

necessarily causes the ZC signal to turn the bottom transistor OFF, there is substantial

evidence that the AAT1143 has a second control signal to cause both transitions to be

OFF.

AATI argues that Linear admits that the CMP signal—i.e., the “second control

signal”—does not directly turn OFF both transistors. AATI’s argument, however, relies

again on a claim construction that we have already rejected. Indeed, the correct

construction does not require the “second control signal” to directly cause both

transistors to shut OFF. Rather, according to the correct construction—neither requiring

direct causation nor precluding the use of intermediary signals or components—the

CMP signal nonetheless “causes” both transistors to be OFF.

Turning now to method claim 34, the substantial evidence discussed above

regarding the AAT1143’s operation similarly supports that the limitations of this claim

are also satisfied. AATI contends, however, that there is not substantial evidence that

2008-1117, -1165 23
AATI actually practiced the claimed method, which is required to prove infringement of a

method claim. Contrary to AATI’s contentions, substantial evidence supports that it

actually practiced the claimed method and, therefore, infringed claim 34. For example,

there is testimony that AATI tested all of the accused products and generated voltage

output graphs, as well as documentation and charts evidencing this testing. As such,

we affirm the Commission’s finding that the AAT1143 infringes claim 34.

For the foregoing reasons, there is substantial evidence that the AAT1143

infringes claims 2, 3, and 34. Accordingly, we affirm the Commission’s finding of

infringement of these claims.

B. AAT1146 device

We now address the second accused product, the AAT1146 device. Despite the

fact that the AAT1146 is extremely similar to the AAT1143, the Commission found that

the AAT1146 does not infringe claims 2, 3, and 34. Linear urges that, mainly because

of the extreme similarity between AAT1143 and AAT1146, not only is the Commission’s

finding of noninfringement unsupported by substantial evidence, but that we should find

infringement in its favor. Conversely, AATI and the Commission support the

Commission’s noninfringement finding, arguing that Linear failed to show that the

AAT1146—although having similar components to the AAT1143—functions in the same

way as the AAT1143.

We agree with Linear regarding the AAT1146. The Commission’s finding of

noninfringement is not supported by substantial evidence. Indeed, the evidence of

record compels a finding of infringement of claims 2, 3, and 34 by the AAT1146. We

2008-1117, -1165 24
therefore reverse the Commission’s ruling and hold that the AAT1146 infringes claims 2,

3, and 34.

As far as claims 2 and 3 are concerned, in addition to testimony and

documentation specific to how the AAT1146 operates, there is substantial evidence that

the AAT1146 is nearly identical to the AAT1143—whose infringement is supported by

substantial evidence. In particular, both the AAT1143 and AAT1146 are 400mA step-

down converters and share the identical circuit schematic. In addition to independent

graphs and tests demonstrating two states of operation—one when the transistors are

synchronously switching and the other during a “sleep mode”—there was testimony that

the AAT1146 functions almost identically to the AAT1143 with respect to each claim

limitation. Importantly, it is undisputed that the AAT1146 has CMP circuitry and ZC

circuitry, which, as in the case of the AAT1143 device, cause both transistors to be

OFF. Indeed, one of the only apparent differences between the two accused devices is

that the AAT1146 is capable of switching the two transistors at a higher frequency (i.e.,

1.4MHz compared to the 1MHz), which is irrelevant to the claims.

Substantial evidence likewise supports finding that the method of claim 34 is

practiced using the AAT1146 device. That evidence consists of testimony of AATI

testing, as well as voltage output graphs and documentation and charts evidencing this

testing. Not only do we think that the finding that the AAT1146 infringes claim 34 is

supported by substantial evidence, but we have difficulty discerning the Commission’s

rationale for its decision to the contrary. Specifically, although the Commission stated

that the AAT1146 does not infringe apparatus claims 2 and 3 because the product lacks

the requisite “third circuit” limitation, a finding we have rejected above, it simultaneously

2008-1117, -1165 25
emphasized that method claim 34 does not require such a limitation. Final

Determination, slip op. at 46 (“[T]he ALJ appears to have erred in interpreting claim 34

as requiring second and third circuits and first and second control signals.”). In other

words, the Commission apparently found that the absence of this limitation in the

AAT1146 device did not support a finding of noninfringement with respect to claim 34.

At the same time, the Commission apparently found all of the required claim limitations

present in the AAT1146. Id. at 44–46. However, it decided, without identifying a

missing claim limitation, that the AAT1146 does not infringe claim 34. Id. at 51. 6

For the foregoing reasons, the Commission’s decision is not supported by

substantial evidence. We reverse its determination that the AAT1146 does not infringe

claims 2, 3, and 34 and hold that it does infringe those claims.

C. AAT1151 and AAT1265 devices

As the last infringement ruling regarding claims 2, 3, and 34 of the ’258 patent,

the Commission found that the AAT1151 and AAT1265 do not infringe. Concerning

claims 2 and 3, despite admitting that the AAT1151 and AAT1265 do not contain the ZC

comparator circuitry, Linear contends that it sufficiently identified other circuitry that

maintains the two transistors OFF. Thus, according to Linear, it presented sufficient

evidence showing that the “third circuit” claim limitation is met and, therefore, the

Commission’s finding is not supported by substantial evidence. Linear makes an

6
The Commission’s noninfringement finding concerning claim 34 is noted in
an opinion from the Office of Unfair Import Investigations (“OUII”). Resp. of OUII to
Complainant’s Pet. for Recons. of the Comm’n’s Final Determination, In re Certain
Voltage Regulators, No. 337-TA-564 (Int’l Trade Comm’n Oct. 16, 2007) (“This section
of the Opinion discusses six claim elements, but only elements (1), (2), and (3) are
identified as relevant to claim 34, and the opinion explicitly states that these claim[ ]
limitations are met by the AAT1146 . . . .”).

2008-1117, -1165 26
additional argument specific to claim 34—that the Commission’s opinion is internally

inconsistent and provides no explanation why the AAT1151 and AAT1265 do not

infringe other than the absence of the “third circuit” limitation, which undisputedly is not

required by claim 34.

In response, the Commission and AATI argue that Linear made the same

argument below as it makes on appeal—an argument the Commission correctly

rejected. Specifically, the Commission and AATI point out that it is undisputed that both

the AAT1151 and the AAT1265 devices lack the ZC comparator circuitry. Next, they

contend that the other circuitry identified by Linear does not meet the required “third

circuit” limitation.

Because there is substantial evidence that neither the AAT1151 nor the

AAT1265 meet the “third circuit” limitation, we affirm the Commission’s finding of

noninfringement with regards to claims 2 and 3. As noted, Linear concedes that neither

accused product contains the ZC comparator circuitry of the AAT1143 or AAT1146,

which “causes” both transistors to be OFF. In contrast, Linear argues that the CLK

circuitry in the AAT1151 and the STPCLK circuitry in the AAT1265 cause both

transistors to be OFF. As pointed out by the Commission, however, not only did Linear

fail to provide specified testimony explaining how the CLK and STPCLK circuits meet

the claim limitations, there was also substantial evidence and testimony expounding that

those circuits were operably different from the ZC circuitry in marked ways. In short, in

addition to the absence of particularized evidence of infringement, there is evidence that

the CLK and STPCLK signals have nothing to do with the “third circuit.” We therefore

2008-1117, -1165 27
affirm the Commission’s finding that the AAT1151 and AAT1265 do not infringe claims 2

and 3.

At the same time, however, we think the Commission’s finding that the AAT1151

and AAT1265 do not infringe claim 34 is internally inconsistent and not supported by

substantial evidence. We therefore vacate its finding of noninfringement with regard to

claim 34.

As pointed out by Linear, the Commission first noted that method claim 34 was

broader than apparatus claims 2 and 3—namely, that method claim 34 “simply does not

contain the limitations of ‘a second circuit for generating a first control signal . . .’ and ‘a

third circuit for generating a second control signal.’” Final Determination, slip op. at 46.

Thus, the Commission stated that it was erroneous to “interpret[ ] claim 34 as requiring

second and third circuits and first and second control signals.” In addition, the

Commission also stated that all of the accused products had two different states of

circuit operation. Id. at 45. Inconsistently, on that same page the Commission ruled

that the AAT1265 does not infringe claim 34 because it does not have “two separate

states of operation.” 7 Id. Other than this contradictory statement, the Commission

failed to provide any further rationale explaining why the AAT1265 does not infringe

7
Attempting to explain this paradox, the Commission argues that it did not find
“two separate states of operation” present in the AAT11265 because Linear failed to
assert in its Review Brief to the Commission that the AAT1265 in fact met this limitation.
Instead, according to the Commission, Linear solely argued that the AAT1143,
AAT1146, and AAT1151 contained “two separate states of operation.” In is quite
apparent, however, that Linear did not specifically mention the AAT1265 as meeting this
limitation because the ALJ’s ID did not specifically find this limitation missing from the
AAT1265 device. Initial Determination, slip op. at 55-56. Tellingly, the ALJ explicitly
found only that “at least the AAT1143, AAT1146, and AAT1151 representative products”
do not meet this limitation. Id. Thus, because the ALJ did not find this limitation missing
from the AAT1265, it would have been irrational for Linear to contest the ALJ’s finding—
presumably finding this limitation satisfied in the AAT1265—in its Petition for Review.

2008-1117, -1165 28
claim 34, let alone any reason why the AAT1151 does not infringe claim 34. Indeed,

other than the ultimate conclusion of noninfringement, the Commission’s opinion is

devoid of any statement that the AAT1151 does not include a particular limitation

required by claim 34. The only other possible explanation as to why these products do

not infringe is the Commission’s statement that both the AAT1151 and the AAT1265 do

not meet the “third circuit” or “second control signal” limitations. Id. at 48–51. As noted

by the Commission itself, however, method claim 34 does not require these limitations

and therefore these omissions cannot be the basis for a finding of noninfringement. In

short, the Commission’s finding of noninfringement is not supported by substantial

evidence. We therefore vacate and remand for further proceedings to determine

whether the AAT1151 and AAT1265 infringe method claim 34. 8

For the foregoing reasons, we affirm the Commission’s finding that the AAT1151

and AAT1265 devices do not infringe claims 2 and 3. However, we vacate its finding

regarding claim 34 and remand for further consideration of whether the AAT1151 and

AAT1265 infringe claim 34. 9

8
In its briefing to this court, the Commission acknowledged that the
noninfringement finding of claim 34 was problematic. Comm’n Br. 48 (“A review of the
Commission’s opinion does indicate, as Linear argues, that the Commission’s separate
conclusions regarding the disputed limitations of the asserted claims could be read as
supporting the conclusion that all disputed limitations of claim 34 are met by the
AAT1146 and AAT1151 products . . . .”); id. 49 (“While there is an apparent
inconsistency as to the two conclusions as they relate to the AAT1265 . . . .”).
9
We acknowledge that evidence similar to the type supporting that two states
of circuit operation are present in the AAT1143 and AAT1146 devices—for example, the
ripple graphs—was also provided to prove that the AAT1151 and AAT1265 devices
meet that same limitation. Based on the record before us on appeal, however, we are
not prepared to rule that the AAT1151 and AAT1265 definitively meet all the limitations
of claim 34 and therefore infringe. In particular, we note that the other evidence that
supported infringement of claims 2 and 3 by the AAT1143 and AAT1146 also suggested
infringement of claim 34 by those devices. This additional supporting evidence,

2008-1117, -1165 29
 III

We turn now to the validity of claims 2, 3, and 34, which the Commission found to

be not invalid as anticipated by the AN35 reference. Final Determination, slip op. at 61-

62. “Whether a prior art reference anticipates a patent claim is a question of fact,”

which we review for substantial evidence. 19 U.S.C. § 1337(c); 5 U.S.C. § 706(2)(E);

Finnigan, 180 F.3d at 1362. “The burden is on the party asserting invalidity to prove it

with facts supported by clear and convincing evidence.” Finnigan, 180 F.3d at 1365

(quoting SSIH Equip., S.A. v. Int’l Trade Comm’n, 718 F.2d 365, 375 (Fed. Cir. 1983)).

In particular, the Commission found that claims 2, 3, and 34 were not invalid

because the AN35 discloses “an asynchronous switching voltage regulator as opposed

to a synchronous switching voltage regulator, and that the [AN35] therefore does not

disclose the second switching transistor required by the asserted claims.” Final

Determination, slip op. at 61. While AATI argued to the Commission that the AN35

reference anticipated, as well as rendered obvious, claims 2, 3, and 34, it did not do so

in its appeal to this court. Rather, AATI has only challenged the Commission’s finding

that the claims 2, 3, and 34 are not anticipated. Specifically, AATI argues that the

Commission ignored Appendices A and D, which are allegedly part of the AN35

reference and describe adding a second synchronous transistor. The Commission and

Linear contend that, as found by the Commission, the AN35 reference cannot anticipate

however, was not present regarding the AAT1151 and AAT1265, as there was
substantial evidence supporting noninfringement of claims 2 and 3 by those devices.
We also consider the fact that the Commission’s opinion was inconsistent and leaves
open the possibility that the AAT1151 and AAT1265 devices do not infringe because of
the absence of other limitations. Thus, in these circumstances, we believe remanding is
the appropriate course of action.

2008-1117, -1165 30
the claims because it does not show a synchronous switching voltage regulator

including two transistors, as required by the construed claims.

Because there is substantial evidence that the AN35 reference does not disclose

each limitation of claims 2, 3, and 34, we affirm the Commission’s ruling that the “sleep

mode” claims are not invalid. See, e.g., Finnigan, 180 F.3d at 1365 (“A prior art

reference anticipates a patent claim if the reference discloses, either expressly or

inherently, all of the limitations of the claim.”). For example, claims 2, 3, and 34 all

require a “switch . . . including a pair of synchronously switched switching transistors,”

which, according to the correct claim construction, means “a switch including two

switching transistors that are driven out of phase to supply current at a regulated

voltage to a load.” There is substantial evidence, however, that the AN35 reference

does not disclose a synchronous switching voltage regulator that includes two switching

transistors. Rather, it discloses an asynchronous switching voltage regulator with one

transistor.

Indeed, AATI admitted, through its expert, that the AN35 reference by itself does

not meet all of the claim limitations. Instead, it argues that the Commission failed to

consider Appendices A and D of the AN35 reference, which allegedly show using two

synchronously switched transistors. Even considering Appendices A and D in

combination with the AN35 disclosure itself, however, there is still substantial evidence

that claims 2, 3, and 34 are not anticipated. For example, assuming that the

components in Appendices A and D could be combined with the components in the

AN35, this combination still does not explicitly show the “identical invention” as required

by the claims—“two switching transistors that are driven out of phase to supply current

2008-1117, -1165 31
at a regulated voltage to a load.” Continental Can Co. v. Monsanto Co., 948 F.2d 1264,

1268 (“Anticipation . . . requires that the identical invention that is claimed was

previously known to others and thus is not new.”); see Net MoneyIn, Inc. v. VeriSign,

Inc., 545 F.3d 1359, 1370 (Fed. Cir. 2008) (“[A]n anticipatory reference [must] show all

of the limitations of the claims arranged or combined in the same way as recited in the

claims.”). Indeed, there is no explanation as to how substituting the components in

Appendices A and D would necessarily result in the exact operational circuit as claimed.

For the foregoing reasons, the Commission’s ruling that there is not clear and

convincing evidence of anticipation is supported by substantial evidence. We therefore

affirm the Commission’s determination that claims 2, 3, and 34 are not invalid.

IV

We next address the Commission’s ruling that claim 35 of the ’258 patent is not

infringed by the AAT1143 and AAT1146 devices, as well as its ruling that claim 35 is

invalid. 10

A. Infringement of claim 35 by the AAT1143 and AAT1146 devices

The Commission found that the AAT1143 and AAT1146 do not infringe, either

literally or by equivalents, because the accused products monitor voltage and

“monitoring voltage using a voltage threshold do[es] not meet the limitations of

‘monitoring the current to the load’ or ‘monitoring the current’ using a ‘current

threshold.’” Final Determination, slip op. at 51. We have already determined, however,

that construing claim 35 to exclude monitoring voltage to indirectly monitor current was

an error. See supra Discussion I.E. Thus, because this error caused the Commission

10
Linear asserted that only the AAT1143 and AAT1146 infringe claim 35.

2008-1117, -1165 32
to improperly conclude that the “monitoring the current to the load” limitation was not

met and because the Commission did not identify any other missing claim limitation in

the accused products, its finding of noninfringement is not supported by substantial

evidence. We therefore vacate its ruling that the AAT1143 and AAT1146 do not literally

infringe claim 35, as well as its decision relating to infringement of claim 35 under the

doctrine of equivalents. See, e.g., Transmatic, Inc. v. Gulton Indus., Inc., 53 F.3d 1270,

1275 (Fed. Cir. 1995) (“[T]he court clearly erred in finding no literal infringement. We

therefore vacate as moot that part of the court’s decision relating to infringement under

the doctrine of equivalents.”). Accordingly, we remand for a determination of

infringement according to the correct claim construction. See, e.g., Free Motion

Fitness, Inc. v. Cybex Int’l, Inc., 423 F.3d 1343, 1353 (Fed. Cir. 2005) (“We vacate the

district court’s grant of summary judgment of non-infringement and remand for a

determination of literal infringement and infringement under the doctrine of equivalents

under the correct claim construction.”).

B. Validity of claim 35

Regarding the validity of claim 35, the Commission found claim 35 invalid as

anticipated by the prior art MAX782 product. It did so because it was undisputed that

the MAX782 disclosed each claim limitation—a finding which remains undisputed on

appeal—and because it found that Linear had failed to sufficiently antedate the ’258

patent’s invention date prior to the MAX782 product. See Final Determination, slip op.

at 63-64. Citing circuit schematics and laboratory notebooks, Linear argues that claim

35 was reduced to practice August 22, 1991, which precludes the MAX782 from being

2008-1117, -1165 33
prior art. In response, the Commission and AATI contend that Linear did not show a

complete conception or reduction to practice of all of the limitations of claim 35.

As was the case with its finding of noninfringement, what we have held to be the

Commission’s incorrect construction of the “monitoring the current” limitation in claim 35

infected its validity analysis. For that reason, its invalidity finding is not supported by

substantial evidence. We therefore vacate the finding that claim 35 is invalid.

Specifically, focusing on the invention date of the ’258 patent, the Commission found

that claim 35 did not have a prior invention date solely because reducing to practice

“monitoring voltage” was not sufficient to show the claimed “monitoring the current to

the load.” Id. The Commission stated that “Linear at best established reduction to

practice of a circuit that monitors a voltage using a voltage threshold.” Id. As discussed

above, however, by monitoring voltage a device can indirectly monitor current and,

therefore, prior invention of monitoring voltage is sufficient to show a prior invention date

of the “monitoring the current” limitation. While the Commission did appropriately

acknowledge that “in order to establish actual reduction to practice, the inventor must

prove that he constructed an embodiment . . . that met all the limitations,” see, e.g., Slip

Track Systems, Inc. v. Metal-Lite, Inc., 304 F.3d 1256, 1265 (Fed. Cir. 2002), it did not

identify any other missing limitations. See Final Determination, slip op. at 63-64. As

such, although failing to prove the prior invention of some other limitation could support

that claim 35 is not entitled to an earlier invention date, the Commission solely relied on

its erroneous belief that the “monitoring the current” limitation was not previously

invented. Thus, we remand for further consideration of whether, despite the fact that

prior invention of the “monitoring the current” limitation can be shown by prior disclosure

2008-1117, -1165 34
of monitoring voltage, there is some other absent limitation that precludes a prior

invention date of claim 35. See, e.g., Slip Track Sys., 304 F.3d at 1269 (“On remand,

the district court should consider whether those features of the Second Prototype whose

dates have been corroborated meet the limitations of the interfering subject matter.”).

The Commission’s opinion regarding the noninfringement and invalidity of claim

35 is not supported by substantial evidence. We therefore vacate its decision and

remand for further proceedings, consistent with this opinion and our modified claim

construction, to determine both whether claim 35 is infringed and whether the claim is

entitled to an invention date prior to the MAX782 product.

CONCLUSION

To summarize, with the exception of the “monitoring the current” limitation in

claim 35, we affirm the Commission’s claim construction in all respects. We also affirm

its finding that the AAT1143 infringes claims 2, 3, and 34 and that claims 2, 3, and 34

are not invalid as anticipated. In addition, we affirm the Commission’s finding that the

AAT1151 and AAT1265 do not infringe claims 2 and 3. We, however, reverse the

Commission’s finding that the AAT1146 does not infringe claims 2, 3, and 34 and,

consequently, rule that the AAT1146 does infringe claims 2, 3, and 34. In addition, we

vacate the Commission’s findings that the AAT1151 and AAT1265 do not infringe claim

34 and remand for further proceedings. We also vacate its ruling that the AAT1143 and

AAT1146 do not infringe claim 35, as well as its finding that claim 35 is invalid, and

2008-1117, -1165 35
remand for further proceedings, consistent with this opinion and our modified claim

construction, to determine whether claim 35 is infringed and invalid. 11

COSTS

Each party shall bear its own costs.

AFFIRMED-IN-PART, REVERSED-IN-PART, VACATED-IN-PART, and REMANDED.

11
Linear also argues that the Commission erred by not reaching issues of
indirect infringement. We find no error with the Commission’s decision to not address
indirect infringement. See, e.g., Personalized Media Commc’n, LLC v. Int’l Trade
Comm’n, 161 F.3d 696, 708 (Fed. Cir. 1998) (acknowledging that “[i]t was the
Commission’s prerogative to review only questions of indefiniteness and
noninfringement”); Beloit Corp. v. Valmet Oy, 742 F.2d 1421, 1423 (Fed. Cir. 1984)
(reinforcing the Commission’s requirement to address only one dispositive issue).

2008-1117, -1165 36