Court Opinion

ID: 6116128
Source: CourtListenerOpinion
Date Created: 2022-02-03 17:00:55.625094+00
Date Added: 2024-06-11T08:22:00.030668
License: Public Domain

Case: 20-1558   Document: 82    Page: 1     Filed: 02/01/2022

   United States Court of Appeals
       for the Federal Circuit
                 ______________________

           QUALCOMM INCORPORATED,
                  Appellant

                           v.

                     APPLE INC.,
                       Appellee

   ANDREW HIRSHFELD, PERFORMING THE
    FUNCTIONS AND DUTIES OF THE UNDER
       SECRETARY OF COMMERCE FOR
 INTELLECTUAL PROPERTY AND DIRECTOR OF
 THE UNITED STATES PATENT AND TRADEMARK
                   OFFICE,
                   Intervenor
             ______________________

                  2020-1558, 2020-1559
                 ______________________

     Appeals from the United States Patent and Trademark
 Office, Patent Trial and Appeal Board in Nos. IPR2018-
 01315, IPR2018-01316.
                  ______________________

                Decided: February 1, 2022
                 ______________________

    JENNIFER L. SWIZE, Jones Day, Washington, DC, ar-
 gued for appellant. Also represented by ROBERT BREETZ,
 DAVID B. COCHRAN, DAVID MICHAEL MAIORANA, JOSEPH M.
 SAUER, Cleveland, OH; MATTHEW JOHNSON, JOSHUA R.
Case: 20-1558    Document: 82      Page: 2    Filed: 02/01/2022

2                       QUALCOMM INCORPORATED    v. APPLE INC.

 NIGHTINGALE, Pittsburgh, PA; ISRAEL SASHA MAYERGOYZ,
 Chicago, IL.

     LAUREN ANN DEGNAN, Fish & Richardson PC, Wash-
 ington, DC, argued for appellee. Also represented by
 MICHAEL JOHN BALLANCO, CHRISTOPHER DRYER; WHITNEY
 REICHEL, Boston, MA.

    MAUREEN DONOVAN QUELER, Office of the Solicitor,
 United States Patent and Trademark Office, Alexandria,
 VA, argued for intervenor. Also represented by THOMAS W.
 KRAUSE, ROBERT J. MCMANUS, FARHEENA YASMEEN
 RASHEED.
                  ______________________

    Before TARANTO, BRYSON, and CHEN, Circuit Judges.
 CHEN, Circuit Judge.
     Qualcomm Inc. (Qualcomm) appeals from two related
 inter partes review (IPR) decisions of the Patent Trial and
 Appeal Board (Board) finding several claims of Qual-
 comm’s U.S. Patent No. 8,063,674 (’674 patent) unpatenta-
 ble under 35 U.S.C. § 103. 1 To reach its unpatentability
 finding, the Board relied on a ground raised by Apple Inc.
 (Apple) that relied in part on applicant admitted prior art
 (AAPA)—here, statements in the challenged patent

     1    Congress amended §§ 102 and 103 when it passed
 the Leahy-Smith America Invents Act (AIA). Pub. L. No
 112-29, §§ 3(b), 3(c), 125 Stat. 284, 287 (2011). Because the
 application that led to the ’674 patent has never contained
 a claim having an effective filing date on or after March 16,
 2013 (the effective date of the statutory changes enacted in
 2011), or a reference under 35 U.S.C. §§ 120, 121, or 365(c)
 to any patent or patent application that ever contained
 such a claim, the pre-AIA §§ 102 and 103 apply. Id. §
 3(n)(1), 125 Stat. at 293.
Case: 20-1558     Document: 82      Page: 3    Filed: 02/01/2022

 QUALCOMM INCORPORATED      v. APPLE INC.                          3

 acknowledging that most of the limitations of the patent’s
 claims were already known—and a prior art patent. Qual-
 comm argues the Board’s reliance on AAPA runs afoul of
 35 U.S.C. § 311(b), which limits an inter partes review pe-
 titioner to challenge claims as unpatentable “only on a
 ground that could be raised under section 102 or 103 and
 only on the basis of prior art consisting of patents or printed
 publications.” § 311(b) (emphasis added). Because we
 agree with Qualcomm that the Board erred in concluding
 that AAPA constitutes “prior art consisting of patents or
 printed publications” under § 311(b), we vacate the Board’s
 decision. We remand for the Board to determine whether
 Apple’s petition nonetheless raises its § 103 challenge “on
 the basis of prior art consisting of patents or printed publi-
 cations.” § 311(b) (emphasis added).
                         BACKGROUND
                               A
     Qualcomm owns the ’674 patent, which is directed to
 integrated circuit devices with power detection circuits for
 systems with multiple supply voltages. See ’674 patent at
 Abstract, col. 1 ll. 6–8. According to the ’674 patent, mod-
 ern integrated circuits often contain multiple networks op-
 erating at different supply voltages. See id. at col. 1 ll. 22–
 25. For example, a core logic network may operate at a
 lower voltage, and an input/output network may simulta-
 neously operate at a higher voltage. See id. Such a system
 can save power by allowing the broader circuit to power
 down a network, like the core logic network, when it is not
 needed. See id. at col. 1 ll. 26–40.
     The patent describes “level shifters” that communicate
 between the input/output devices and the core devices. See
 id. at col. 1 ll. 28–29. When the core devices are powered
 down, the connection between the core and input/output
 network through the level shifters can lead to problems.
 One such problem is stray currents causing the level shift-
 ers to trigger the input/output devices for transmission
Case: 20-1558       Document: 82   Page: 4    Filed: 02/01/2022

4                       QUALCOMM INCORPORATED    v. APPLE INC.

 resulting in erroneous output signals from the circuit. See
 id. at col. 1 ll. 29–40.
     The ’674 patent describes a prior art method to remedy
 the stray current problem. The Background states that
 power-up/down detectors can be used to generate a power-
 on/off-control (POC) signal internally that instructs the in-
 put/output devices when the core devices are shut down.
 See id. at col. 1 ll. 55–58. Figure 1 of the patent depicts a
 “prior art” “standard POC system” with a power-up/down
 detector 100:

 Id. at Figure 1.
      The patent asserts that there are problems with the
 prior art solution in Figure 1. For example, when the in-
 put/output power supply 104 is on and the core power is off,
 powering up the core results in “a period in which all three
 transistors [M1-M3] within power up/down detector 100
 are on,” causing “a significant amount of current to flow
 from [input/output] power supply 104 to ground.” Id. at col.
 2 ll. 21–29. The ’674 patent recognizes that “decreas[ing]
 the sizes of the transistors M1-M3” can physically limit this
 “glitch current” or leakage but notes that smaller transis-
 tors may reduce detection sensitivity or result in “longer
Case: 20-1558    Document: 82     Page: 5    Filed: 02/01/2022

 QUALCOMM INCORPORATED    v. APPLE INC.                         5

 processing time for power-up/down events.” Id. at col. 2 ll.
 31–39; see also id. at col. 2 l. 63–col. 3 l. 11.
      The ’674 patent avoids these problems by adding a
 feedback network to increase detection speed. See id. at
 col. 6 ll. 25–28. Specifically, as depicted in Figure 4, the
 ’674 patent includes power-up transistor M8. Transistor
 M8 transitions from on to off during power-up and from off
 to on during power-down. See id. at col. 6 ll. 12–18, 21–28.
 When M8 is off, the current capacity of the power-up/down
 detector is reduced. When M8 is on, the power-up/down
 detector has increased current capacity resulting in
 quicker detection of the core powering down. See id.
      Claims 1, 2, 5–9, 12, 13, and 16–22 of the ’674 patent
 are at issue on appeal. Claim 1, reproduced below, is
 illustrative of the claimed invention:
    1. A multiple supply voltage device comprising:
    a core network operative at a first supply voltage;
    and
    a control network coupled to said core network
    wherein said control network is configured to
    transmit a control signal, said control network
    comprising: an up/down (up/down) detector config-
    ured to detect a power state of said core network;
    processing circuitry coupled to said up/down detec-
    tor and configured to generate said control signal
    based on said power state;
    one or more feedback circuits coupled to said
    up/down detector, said one or more feedback cir-
    cuits configured to provide feedback signals to ad-
    just a current capacity of said up/down detector;
    at least one first transistor coupled to a second sup-
    ply voltage, the at least one more first transistor
    being configured to switch on when said first
Case: 20-1558     Document: 82     Page: 6    Filed: 02/01/2022

6                      QUALCOMM INCORPORATED      v. APPLE INC.

     supply voltage is powered down and to switch off
     when said first supply voltage is powered on;
     at least one second transistor coupled in series with
     the at least one first transistor and coupled to said
     first supply voltage, the at least one second transis-
     tor being configured to switch on when said first
     supply voltage is powered on and to switch off when
     said first supply voltage is powered down;
     at least one third transistor coupled in series be-
     tween the at least one first transistor and the at
     least one second transistor.
 ’674 patent at claim 1.
                               B
     Apple filed two petitions for inter partes review 2 based
 on the same two grounds but each challenging different
 sets of claims in the ’674 patent. In ground 1, Apple chal-
 lenged the claims as unpatentable under § 103 in view of
 Steinacker 3, Doyle, 4 and Park. 5 In its final written deci-
 sion, the Board found that Apple had not proven with this
 ground the unpatentability of the challenged claims.
      Apple’s second ground relied on AAPA—Figure 1 and
 its accompanying description in the ’674 patent—in view of
 Majcherczak. 6 Like the ’674 patent, Majcherczak relates
 to “integrated circuit[s] using at least two power supply

     2   IPR2018-01315 and IPR2018-01316.
     3   U.S. Patent No. 7,279,943.
      4  U.S. Patent No. 4,717,836.
      5  J. C. Park and V. J. Mooney III, Sleepy Stack Leak-
 age Reduction, 14 IEEE Transactions on Very Large Scale
 Integration (VLSI) Systems 11, 1250–63 (2006) (J.A. 1247–
 60).
      6  U.S.    Patent    Application     Publication   No.
      2002/0163364.
Case: 20-1558    Document: 82     Page: 7    Filed: 02/01/2022

 QUALCOMM INCORPORATED    v. APPLE INC.                         7

 voltages.” Majcherczak ¶ 1. Majcherczak discloses a
 voltage detection device that detects, among other things,
 when the core voltage is powered down. Apple argued that
 a skilled artisan would have found it obvious to integrate
 Majcherczak’s feedback transistor into the POC system
 described as prior art by the ’674 patent, as shown below:

     Qualcomm conceded that the combination of AAPA and
 Majcherczak teaches each element of the challenged
 claims, see Apple Inc. v. Qualcomm Inc., IPR2018-01315, -
 01316, 2020 Pat. App. LEXIS 5250, *28 (P.T.A.B. Jan. 3,
 2020) (Board Op.); J.A. 385–86, but challenged Apple’s use
 of AAPA. Qualcomm argued that such patent owner
 admissions cannot be used to challenge the validity of a
 patent in inter partes review. See Board Op. at *15–17; J.A.
Case: 20-1558    Document: 82      Page: 8    Filed: 02/01/2022

8                      QUALCOMM INCORPORATED     v. APPLE INC.

 403. 7 The Board disagreed. See Board Op. at *18–19
 (“Because AAPA is admitted to be prior art and is found in
 the ’674 patent, it can be used to challenge the claims in an
 inter partes review.”). Underpinning the Board’s analysis
 was its conclusion that, under 35 U.S.C. § 311(b), “prior art
 consisting of patents or printed publications” includes
 AAPA because it is prior art contained in a patent. See id.
 at *19. Having decided that Apple’s use of AAPA was
 proper under the statute, the Board found that the AAPA
 with Majcherczak rendered the challenged claims
 unpatentable as obvious.
    Qualcomm timely appeals. We have jurisdiction under
 28 U.S.C. § 1295(a)(4)(A).
                         DISCUSSION
     This appeal concerns the use of AAPA in inter partes
 review. 8 Qualcomm, Apple, and the United States Patent
 and Trademark Office (PTO) each offer competing views of
 the propriety of AAPA’s role in inter partes review and
 differing interpretations of the phrase “prior art consisting
 of patents or printed publications” in § 311(b).
      Qualcomm initially argued that AAPA may not be
 considered in inter partes review. See Appellant’s Br. 20
 (“[A] purported admission in the patent that is the subject
 [of] an inter partes review cannot be used to challenge
 claims in the IPR.”). Qualcomm explained that § 311(b)

     7    Qualcomm also challenged Apple’s alleged motiva-
 tion to combine Majcherczak with AAPA. See Board Op. at
 *33. Qualcomm does not raise this challenge on appeal.
     8    Qualcomm initially raised a challenge to the con-
 stitutionality of the Board, see Appellant’s Br. 34–35, but
 after the Supreme Court issued its decision in United
 States v. Arthrex, Inc., 141 S. Ct. 1970 (2021), Qualcomm
 withdrew its request for relief on that basis, see ECF No.
 70.
Case: 20-1558     Document: 82     Page: 9    Filed: 02/01/2022

 QUALCOMM INCORPORATED     v. APPLE INC.                          9

 requires any ground in an inter partes review to be based
 only on prior art patents or prior art printed publications.
 See id. at 24. Finding no support in § 311(b) for the use of
 AAPA, Qualcomm posited that the statute precludes any
 and all use of a patent owner’s admissions in inter partes
 review. See id. at 24–25. Qualcomm, however, softened its
 position in reply, acknowledging that “general knowledge
 and non-Section 311(b) art [e.g., AAPA] may have a role to
 play in IPR proceedings,” Appellant’s Reply Br. 15, but
 Qualcomm maintained its position that AAPA may not
 form “the basis” of a ground in an inter partes review. See
 id. at 14–15.
     According to Apple, Qualcomm’s theory impermissibly
 rewrites “prior art consisting of patents or printed
 publications” as “prior-art patents” or “prior-art
 publications.” See Appellee’s Br. at 27. Apple read § 311(b)
 to permit the use of any “prior art” “consisting of patents or
 printed publications.” See id. at 24–25. In other words,
 Apple argued that any “prior art”—including AAPA—that
 is contained in any patent or printed publication,
 regardless of whether the document itself is prior art, can
 be used as a basis for a challenge in inter partes review.
     The PTO, for its part, asked us to remand so the Board
 may apply the Director’s guidance on the “Treatment of
 Statements of the Applicant in the Challenged Patent in
 Inter Partes Reviews Under § 311(b)” (Guidance). 9 See
 PTO Br. 8–9; see also J.A. 4530–38 (Guidance) The
 Guidance agrees with Qualcomm that AAPA does not fall
 within “prior art consisting of patents or printed
 publications” under § 311(b). See Guidance at 3–4. Yet the
 Guidance reads our caselaw to permit the use of AAPA in
 inter partes review as evidence of the general knowledge of
 a skilled artisan. See id. at 4–5. As the Guidance

     9   The Director issued the Guidance on August 18,
 2020, after the Board’s final written decisions in this case.
Case: 20-1558     Document: 82     Page: 10    Filed: 02/01/2022

 10                     QUALCOMM INCORPORATED     v. APPLE INC.

 understands permissible uses of that knowledge to include
 supplying a missing claim limitation or supporting a
 motivation to combine, it concludes that AAPA may
 likewise be used for these purposes. See id. at 6–7. The
 PTO, however, stops short of taking a position as to
 whether Apple’s reliance on AAPA in this case is
 impermissible, because, as argued by Qualcomm, the
 AAPA in this case plays such a large role in the validity
 challenge that it forms “the basis” of the ground. The PTO
 urges us to remand that inquiry to allow Board to address
 that question in the first instance.
                               A
     The parties’ main argument on appeal focuses on
 whether AAPA constitutes “prior art consisting of patents
 or printed publications” under § 311(b) such that it may
 form “the basis” of a ground in inter partes review. We hold
 that it does not.
     Our analysis begins with Section 311(b) of the Patent
 Act:
      Scope.—
      A petitioner in an inter partes review may request
      to cancel as unpatentable 1 or more claims of a
      patent only on a ground that could be raised under
      section 102 or 103 and only on the basis of prior art
      consisting of patents or printed publications.
 The language of § 311(b) limits “the basis” of any “ground”
 in an inter partes review to “prior art consisting of patents
 or printed publications.”
     We agree with Qualcomm and the PTO that the
 “patents or printed publications” that form the “basis” of a
 ground for inter partes review must themselves be prior art
 to the challenged patent. That conclusion excludes any
 descriptions of the prior art contained in the challenged
 patent. This interpretation is consistent with prior judicial
Case: 20-1558    Document: 82      Page: 11    Filed: 02/01/2022

 QUALCOMM INCORPORATED     v. APPLE INC.                          11

 interpretations of the statute and represents a more
 natural reading of § 311(b).
     Both the Supreme Court and this court have previously
 understood the “patents and printed publications”
 referenced in § 311(b) to themselves be prior art. See
 Return Mail, Inc. v. U.S. Postal Serv., 139 S. Ct. 1853, 1860
 (2019) (“First, the ‘inter partes review’ provision permits ‘a
 person’ other than the patent owner to petition for the
 review and cancellation of a patent on the grounds that the
 invention lacks novelty or nonobviousness in light of
 ‘patents or printed publications’ existing at the time of the
 patent application.” (emphasis added) (quoting § 311(b));
 Regents of the Univ. of Minn. v. LSI Corp., 926 F.3d 1327,
 1335 (Fed. Cir. 2019) (“Before IPR can be instituted, a
 person must file a petition challenging the validity of one
 or more patent claims under § 102 or § 103 on the basis of
 prior art patents or printed publications.” (emphasis
 added)), cert. denied, 140 S. Ct. 908 (2020).
     This understanding aligns with prior judicial
 interpretations of identical language—“prior art consisting
 of patents or printed publications”—in a similar statute, 35
 U.S.C. § 301(a), as excluding patents which themselves are
 not prior art. See In re Lonardo, 119 F.3d 960, 966 (Fed.
 Cir. 1997). In Lonardo, the parties disputed whether
 obviousness-type double patenting based on a non-prior art
 patent was available as a challenge in ex parte
 reexamination. See id. at 965. Lonardo held that it was
 permissible for the challenger to rely on a non-prior art
 patent in ex parte reexamination under § 303(a), not
 § 301(a), because § 303(a) permits the Director to institute
 a reexamination after “consideration of other patents or
 printed publications.” See id. at 966 (quoting § 303(a))
 (emphasis added). While Lonardo did not directly address
 AAPA, it distinguished § 303(a) from § 301(a) by noting
 that the former “is not specifically limited to prior art
 patents or printed publications,” and referred to the latter
 as describing “prior art submitted by a third party.” See id.
Case: 20-1558    Document: 82      Page: 12     Filed: 02/01/2022

 12                     QUALCOMM INCORPORATED      v. APPLE INC.

 at 966 (emphasis added). Other cases reflect Lonardo’s
 understanding of the meaning of “prior art consisting of
 patents or printed publications” in § 301(a) as referring to
 prior art documents. See e.g., Return Mail, 139 S. Ct. at
 1859 (noting that § 301(a) permits any person at any time
 to cite to the Patent Office certain prior art that may “bea[r]
 on the patentability of any claim of a particular patent”);
 Mikkelsen Graphic Eng’g, Inc. v. Zund Am., Inc., 541 F.
 App’x 964, 973–74 (Fed. Cir. 2013) (stating that § 301(a)
 limits “reexamination requests to arguments based on
 prior art patents or printed publications”); In re NTP, Inc.,
 654 F.3d 1268, 1276 (Fed. Cir. 2011) (“During
 reexamination, the examiner reviews the claims in view of
 various prior art patents and printed publications.”); In re
 Swanson, 540 F.3d 1368, 1375 (Fed. Cir. 2008) (“Any
 person may file a request for an ex parte reexamination of
 an issued patent based on prior art patents or printed
 publications.”); In re Freeman, 30 F.3d 1459, 1468 (Fed.
 Cir. 1994) (“The reexamination statute provides that
 anyone at any time may request reexamination of any
 claim of a patent based upon prior art patents and printed
 publications.” (citing 35 U.S.C. § 301)).
     Neither party argues that Congress, in enacting the
 America Invents Act, 10 intended a different meaning of
 “prior art consisting of patents or printed publications” in
 § 311(b) than that of § 301(a). We agree with Apple that,
 “[w]hen Congress enacted the ‘prior art consisting of
 patents or printed publications’ proviso for IPRs in section
 311(b), it is presumed to have done so with reference to the
 same specialized provision in the reexamination statute.”
 Appellee’s Br. 38 (citing Reno v. Koray, 515 U.S. 50, 57
 (1995)). Congress is also presumed to be aware of judicial
 decisions interpreting statutory language. See Guerrero-

      10 The AIA created inter partes reviews and enacted
 the language codified at § 311(b). AIA § 6(a).
Case: 20-1558    Document: 82      Page: 13    Filed: 02/01/2022

 QUALCOMM INCORPORATED     v. APPLE INC.                          13

 Lasprilla v. Barr, 140 S. Ct. 1062, 1072 (2020). Given
 Congress’s use of language identical to § 301(a), and the
 judicial interpretations of that statute at the time the AIA
 was enacted, the logical extension is that the patents and
 printed publications referenced in § 311(b) must
 themselves be prior art to the challenged patent. In other
 words, § 311(b) does not permit AAPA in this case to be the
 basis of a ground in an inter partes review, because it is not
 contained in a document that is a prior art patent or prior
 art printed publication.
                               B
     While, under § 311(b), AAPA contained in the
 challenged patent is not “prior art consisting of patents or
 printed publications,” it does not follow that AAPA is
 categorically excluded from an inter partes review. Indeed,
 Qualcomm concedes that our precedent permits
 consideration of AAPA, at least to some extent, to challenge
 patent claims in an inter partes review. See Appellant’s
 Reply Br. 15.
     We have held that “it is appropriate to rely on
 admissions in a patent’s specification when assessing
 whether that patent’s claims would have been obvious” in
 an inter partes review proceeding. Koninklijke Philips N.V.
 v. Google LLC, 948 F.3d 1330, 1339 (Fed. Cir. 2020) (citing
 PharmaStem Therapeutics, Inc. v. ViaCell, Inc., 491 F.3d
 1342, 1362 (Fed. Cir. 2007) (“Admissions in the
 specification regarding the prior art are binding on the
 patentee for purposes of a later inquiry into
 obviousness.”)). 11

     11  As recognized in PharmaStem, our precedent
 treats AAPA as binding on the patentee. See Constant v.
 Advanced Micro-Devices, Inc., 848 F.2d 1560, 1570 (Fed.
 Cir. 1998) (“A statement in a patent that something is in
 the prior art is binding on the applicant and patentee for
Case: 20-1558    Document: 82      Page: 14    Filed: 02/01/2022

 14                    QUALCOMM INCORPORATED      v. APPLE INC.

      That is because a petitioner may rely on evidence
 beyond prior art documents in an inter partes review, even
 if such evidence itself may not qualify as the “basis” for a
 ground set forth in a petition. See 35 U.S.C. § 312(a)(3)(B)
 (permitting the use of “affidavits or declarations of support-
 ing evidence and opinions, if the petitioner relies on expert
 opinions”); § 314(a) (requiring the Director to consider “the
 information presented in the petition” when determining
 whether to institute inter partes review) (emphasis added);
 § 316(a)(3) (requiring the Director “establish[] procedures
 for the submission of supplemental information after the
 petition is filed.”); Yeda Rsch. v. Mylan Pharms. Inc., 906
 F.3d 1031, 1041 (Fed. Cir. 2018) (affirming PTO’s reliance
 on a non-prior art document in inter partes review for
 limited purposes). Indeed, Koninklijke Philips specifically
 rejected an argument that the general knowledge of a
 skilled artisan may not be relied on in an inter partes
 review because it does not constitute “prior art consisting
 of patents or printed publications” under § 311(b). See 948
 F.3d at 1337 (“Regardless of the tribunal, the inquiry into
 whether any ‘differences’ between the invention and the
 prior art would have rendered the invention obvious to a
 skilled artisan necessarily depends on such artisan’s

 determinations of anticipation and obviousness.”); In re
 Fout, 675 F.2d 297, 300 (CCPA 1982) (“Valid prior art may
 be created by the admissions of the parties.”); In re Nomiya,
 509 F.2d 566, 571 (CCPA 1975) (“By filing an application
 containing Figs. 1 and 2, labeled prior art, ipsissimis ver-
 bis, and statements explanatory thereof appellants have
 conceded what is to be considered as prior art in determin-
 ing obviousness of their improvement.”); In re Rishoi, 197
 F.2d 342, 343–44 (CCPA 1952) (affirming the “refusal to
 allow [a] claim [] based upon an unequivocal admission in
 appellants’ specification of what was old and well known in
 the art”).
Case: 20-1558    Document: 82     Page: 15    Filed: 02/01/2022

 QUALCOMM INCORPORATED     v. APPLE INC.                         15

 knowledge.”). In other words, the assessment of a claim’s
 patentability is inextricably tied to a skilled artisan’s
 knowledge and skill level.
     As a patentee’s admissions about the scope and content
 of the prior art provide a factual foundation as to what a
 skilled artisan would have known at the time of invention,
 Randal Manufacturing v. Rea, 733 F.3d 1355, 1362–63
 (Fed. Cir. 2013), it follows that AAPA may be used in
 similar ways in an inter partes review, see McCoy v. Heal
 Sys., LLC, 850 F. App’x 785, 789 (Fed. Cir. 2021) (“The
 Board did not err by accepting the specification’s own
 assertions of what is well known in the art . . . . By
 characterizing certain parts as conventional in the
 specification, the patentee effectively admits that such
 things would be known to a POSA.”). Such uses include,
 for example, furnishing a motivation to combine, see
 Randal Manufacturing, 733 F.3d at 1363, or supplying a
 missing claim limitation, Koninklijke Philips, 948 F.3d at
 1337–38. Thus, even though evidence such as expert
 testimony and party admissions are not themselves prior
 art references, they are permissible evidence in an inter
 partes review for establishing the background knowledge
 possessed by a person of ordinary skill in the art.
     Moreover, the use of AAPA in an inter partes review
 proceeding is consistent with our understanding that
 Congress sought to create a streamlined administrative
 proceeding that avoided some of the more challenging
 types of prior art identified in 35 U.S.C. § 102, such as
 commercial sales and public uses, by restricting the “prior
 art” which may form a basis of a ground to prior art
 documents. In OddzOn Prods., Inc. v. Just Toys, Inc., 122
 F.3d 1396, 1401–02 (Fed. Cir. 1997), we held that “prior
 art,” as referenced in 35 U.S.C. § 103, includes § 102(f), in
 addition to subsections (a), (b), (e), and (g), which “are
 clearly prior art provisions.” We observed that § 102(a) and
 (b) identify, among other things, “prior patents and
 publications” as prior art. Id. As for other types of prior
Case: 20-1558    Document: 82     Page: 16    Filed: 02/01/2022

 16                    QUALCOMM INCORPORATED     v. APPLE INC.

 art identified in § 102, we have explained, in the context of
 the reexamination statute, that “questions of public use
 and on sale were explicitly excluded by statute from those
 issues on which reexamination could be obtained.” Quad
 Envtl. Techs. Corp. v. Union Sanitary Dist., 946 F.2d 870,
 875 (Fed. Cir. 1991).         That is so because “[t]he
 congressional purpose in restricting reexamination to
 printed documents, 35 U.S.C. § 301, was to provide a
 cheaper and less time-consuming alternative to challenge
 patent validity on certain issues.” Id. at n.7 (citing H.R.
 Rep. No. 1307 at 4). Holding a patentee to descriptions of
 the prior art made in its specification does not implicate
 the type of fact-intensive inquiries Congress was seeking
 to avoid.
                              C
     Having determined that (i) the Board incorrectly
 interpreted § 311(b)’s “prior art consisting of patents or
 printed publications” to encompass AAPA contained in the
 challenged patent, but (ii) the use of AAPA can be
 permissible in an inter partes review, the next contested
 issue is whether AAPA improperly formed the “basis” of
 Apple’s challenge. Because the Board did not address this
 question in its final written decision, we remand to allow
 the Board to address this issue in the first instance.
                          *   *   *
     At bottom, Section 311 provides a limit on what prior
 art can be the basis for an inter partes review challenge and
 both the courts and the PTO must adhere to that limit. As
 explained above, AAPA may not form the “basis” of a
 ground in an inter partes review, and it is therefore
 impermissible for a petition to challenge a patent relying
 on solely AAPA without also relying on a prior art patent
 or printed publication. Here, we remand to the Board to
 determine whether Majcherczak forms the basis of Apple’s
 challenge, or whether the validity challenge impermissibly
 violated the statutory limit in Section 311.
Case: 20-1558    Document: 82     Page: 17   Filed: 02/01/2022

 QUALCOMM INCORPORATED    v. APPLE INC.                         17

                              D
      Finally, we reject Apple’s alternative ground for
 affirmance (which the Board likewise rejected) asserting
 the challenged claims are unpatentable based on the
 combination of Steinacker and Doyle or the combination of
 Steinacker, Doyle, and Park. Apple failed to show that the
 Board abused its discretion in determining that Apple’s
 proposed motivation to combine Steinacker and Doyle
 based on “hysteresis” was untimely raised for the first time
 on reply.      See Intelligent Bio-Sys., Inc. v. Illumina
 Cambridge Ltd., 821 F.3d 1359, 1369 (Fed. Cir. 2016) (“It
 is of the utmost importance that petitioners in IPR
 proceedings adhere to the requirement that the initial
 petition identify with particularity the evidence that
 supports the grounds for the challenge to each claim.”). As
 the Board correctly noted, Apple’s petition contained a
 single paragraph discussing the motivation to combine
 Doyle with Steinacker, focusing on Doyle’s relatively stable
 trip point. See Board Op. at *66 (citing J.A. 224). Absent
 from that paragraph, and the entire petition, is any
 mention or argument related to hysteresis as a motivation
 to combine these references. See J.A. 214–240. Thus,
 Apple has failed to show that the Board’s decision to not
 consider its hysteresis theory was legal error. See Henny
 Penny Corp. v. Frymaster LLC, 938 F.3d 1324, 1330 (Fed.
 Cir. 2019) (“Board did not abuse its discretion in holding
 [Petitioner] to its word and disregarding its new theory
 first raised in reply.”).
     Moreover, the Board’s finding that Apple’s timely
 raised motivations to combine Doyle with Steinacker were
 insufficient to support an obviousness determination are
 supported by substantial evidence. We see no reversible
 error in the Board’s finding that Apple failed to explain
 why a skilled artisan at the time of the invention would
 have considered a relatively stable trip point important
 enough to combine Doyle with Steinacker. See Board Op.
 at *71–74.
Case: 20-1558    Document: 82     Page: 18    Filed: 02/01/2022

 18                    QUALCOMM INCORPORATED     v. APPLE INC.

     As we hold there was no error in the Board’s finding
 that Apple made an insufficient showing of a motivation to
 combine Doyle with Steinacker—a prerequisite to its
 proposed three-way combination of Doyle with Steinacker
 and with Park—we do not reach the Board’s determination
 that Apple failed to sufficiently show that a skilled artisan
 would be motivated to use the forced stack technique
 described in Park with Doyle.
                        CONCLUSION
      We have considered the parties remaining arguments
 and find them unpersuasive. For the reasons set forth
 above, we vacate the Board’s decisions finding the chal-
 lenged claims of the ’674 patent unpatentable and remand
 for further proceedings consistent with this opinion.
                VACATED AND REMANDED
                            COSTS
 Costs to Qualcomm.