  United States Court of Appeals
      for the Federal Circuit
                ______________________

             ATI TECHNOLOGIES ULC,
                    Appellant

                          v.

    ANDREI IANCU, UNDER SECRETARY OF
  COMMERCE FOR INTELLECTUAL PROPERTY
   AND DIRECTOR OF THE UNITED STATES
     PATENT AND TRADEMARK OFFICE,
                  Intervenor
            ______________________

           2016-2222, 2016-2406, 2016-2608
               ______________________

    Appeals from the United States Patent and Trademark
Office, Patent Trial and Appeal Board in Nos. IPR2015-
00325, IPR2015-00326, IPR2015-00330.
                 ______________________

                Decided: April 11, 2019
                ______________________

    AARON ROBERT FAHRENKROG, Robins Kaplan LLP,
Minneapolis, MN, argued for appellant. Also represented
by BRYAN MECHELL; DANIELLE ROSENTHAL, New York, NY.

    THOMAS W. KRAUSE, Office of the Solicitor, United
States Patent and Trademark Office, Alexandria, VA, ar-
gued for intervenor. Also represented by FARHEENA
YASMEEN RASHEED, ROBERT J. MCMANUS.
                ______________________
2                              ATI TECHNOLOGIES ULC    v. IANCU




    Before NEWMAN, O’MALLEY, and WALLACH, Circuit
                      Judges.
NEWMAN, Circuit Judge.
    ATI Technologies ULC (“ATI”) appeals three final deci-
sions of the Patent Trial and Appeal Board (“PTAB” or
“Board”) on petitions for Inter Partes Review filed by LG
Electronics, Inc. (“LGE”). 1 The Board held all but one of
the challenged claims unpatentable as anticipated or obvi-
ous, invalidating claims 1, 2, and 5–7 of U.S. Patent No.
7,742,053 (“the ’053 patent”); claims 1–3, 5, 6, 8–11, 13, 15, 2
17, and 18 of U.S. Patent No. 6,897,871 (“the ’871 patent”);
and claims 1 and 2 of U.S. Patent No. 7,327,369 (“the ’369
patent”). Claim 20 of the ’871 patent was held patentable.
The three patents are called the “Unified Shader Patents.”
    Petitioner LGE cited references against each of the
Unified Shader Patents, and ATI’s response was that the
invention in each of the three patents preceded the primary
reference dates for that patent. In conformity with 37
C.F.R. § 1.131 (“Rule 131”), ATI presented evidence of con-
ception, reduction to practice, and diligence for each pa-
tent.   The PTAB held separate trials, and received
testimony and argument from both sides. The antedating



    1    LG Electronics, Inc. v. ATI Techs., No. IPR2015-
00325 (PTAB April 14, 2016) (“the ’053 Op.”); LG Electron-
ics, Inc., v. ATI Techs., No. IPR2015-00326 (PTAB June 28,
2016) (“the ’871 Op.”); LG Electronics, Inc., v. ATI Techs.,
No. IPR2015-00330 (PTAB July 1, 2016) (“the ’369 Op.”).
The cases were consolidated for this appeal. LG Electron-
ics withdrew from the appeal and withdrew its cross-ap-
peal, and the PTO Director intervened in support of the
three PTAB decisions.
     2   Claim 15 of the ’871 patent is not challenged on ap-
peal.
ATI TECHNOLOGIES ULC   v. IANCU                            3



issue was treated in detail in the ’053 opinion, and applied
to the ’871 and ’369 patents in separate opinions.
    For all three Unified Shader Patents, the PTAB held
that conception was established before the primary refer-
ence dates, and that constructive reduction to practice oc-
curred on the filing date of each patent. However, the
PTAB held that ATI had not established actual reduction
to practice and had not established diligence to construc-
tive reduction to practice, for all three patents. The PTAB
then invalidated the Unified Shader Patents based on the
cited references.
    We conclude that the PTAB erred in its application of
the law of diligence, and that on the correct law, diligence
was shown, thereby antedating the relevant references.
The PTO’s decisions of unpatentability are reversed.
    The technology
    A “shader” as used in this field is a computer-imple-
mented system that specifies how a computer-graphics
three-dimensional image is generated and presented on a
two-dimensional screen. The prior art describes that com-
puter-graphics images are drawn on a screen by filling in a
grid of dots called “pixels.” Shapes are represented by a
collection of simple polygons such as triangles or squares,
called “primitives,” formed by the interconnection of pixels.
The corner of each primitive is called a “vertex,” with each
vertex defined by the spatial coordinates: x, y, and z.
    Color and texture are applied to the individual pixels
that comprise the shape, based on the location of the pixels
within the primitive and the primitive’s orientation rela-
tive to the generated shape. To orient the wireframe three-
dimensional model, matrix transformations applied to ver-
tices Vx, Vy, and Vz of the primitives generate new vertices
Vx’, Vy’, and Vz’, which are then translated into pixels. The
graphics processor interconnects the primitives and ap-
plies color and texture to the generated shapes. ATI
4                            ATI TECHNOLOGIES ULC   v. IANCU



presented the following illustration of the graphics of dis-
play of a three-dimensional object as a two-dimensional im-
age:




Dr. Wolfe Decl. at ¶¶ 44–45 (J.A. 5200–01); see ’871 patent,
col. 1, ll. 11–60.
     Prior art processors required separate shaders to spec-
ify how and with what attributes a final image is drawn, in
transforming primitives by adjusting the x, y, and z coordi-
nates of their vertices. Prior art graphics processors re-
quired both a vertex shader and a pixel shader, because
vertex operations and pixel operations have different pro-
cessing requirements and were required to be performed
separately and sequentially by separate shader systems.
The Unified Shader Patents describe novel systems that
perform both vertex operations and pixel operations,
thereby providing enhanced efficiency, reliability, and
speed.
   Following is an outline of the Unified Shader Patents,
and representative claims on appeal:
ATI TECHNOLOGIES ULC   v. IANCU                           5



   The ’053 patent, inventors Laurent Lefebvre,
   Andrew E. Gruber, and Stephen L. Morein,
   filed Sept. 29, 2003
    The ’053 patent is the first-filed of the Unified Shader
Patents. It describes a multi-thread (unified) graphics pro-
cessing system that processes both vertex and pixel opera-
tions. The system employs a memory device for storing
command threads and an arbiter for providing a command
thread to a command processing engine, based on a priority
plan whereby the command processing engine performs ei-
ther vertex or pixel operations based on the command
thread from the arbiter. The specification provides details
of the system and its operation. Claim 5 was deemed rep-
resentative for the ’053 patent:
   5. A graphics processing system comprising:
       at least one memory device comprising a first
   portion operative to store a plurality of pixel com-
   mand threads and a second portion operative to
   store a plurality of vertex command threads;
       an arbiter, coupled to the at least one memory
   device, operable to select a command thread from
   either of the plurality of pixel command threads
   and the plurality of vertex command threads; and
       a plurality of command processing engines,
   coupled to the arbiter, each operable to receive and
   process the command thread.
The PTAB cited three primary references against the ’053
patent: U.S. Patent No. 7,363,472 (“Stuttard”) having an
effective filing date of October 9, 2001; U.S. Patent No.
7,015,913 (“Lindholm”) having an effective filing date of
June 27, 2003; and U.S. Patent No. 7,233,335 (“Moreton”)
having an effective filing date of April 21, 2003.
    ATI presented evidence of conception before the earli-
est reference filing date of October 9, 2001 (Stuttard), and
6                             ATI TECHNOLOGIES ULC   v. IANCU



evidence of continuing activity until the ’053 patent’s effec-
tive filing date of September 29, 2003. The PTAB held that
“ATI has demonstrated by a preponderance of the evidence
that the named inventors of the ’053 patent conceived the
claimed system no later than August 24, 2001, prior to the
U.S. filing dates of Stuttard, Moreton, and Lindholm.” ’053
Op. at 16–17. The dates of conception and constructive re-
duction to practice are not disputed on appeal.
     However, the PTAB held that diligence and actual re-
duction to practice had not been shown, and on this basis
the PTAB held claims 1, 2, and 5–7 of the ’053 patent un-
patentable on the following grounds: (1) claims 5–7 as an-
ticipated by the Moreton reference; (2) claims 1 and 2 as
obvious over Moreton combined with Whittaker (U.S. Pa-
tent No. 5,968,167); (3) claims 1, 2, and 5–7 as obvious over
Lindholm in view of Admitted Prior Art; and (4) claims 1,
2, and 5–7 as obvious over Stuttard in view of Admitted
Prior Art.
    LGE has withdrawn from the appeal, and the PTO Di-
rector has intervened and argues in support of the PTAB’s
holdings that diligence and actual reduction to practice
were not established, and thus that the references were not
antedated.
    The ’871 and ’369 patents, inventors Steven
    Morein, Laurent Lefebvre, Andy Gruber, and
    Andi Skende, filed November 20, 2003
    The ’871 and the ’369 patents have a common specifi-
cation and priority filing date of November 20, 2003. Both
patents are directed to a graphics processor employing a
unified shader capable of performing both vertex opera-
tions and pixel operations, and describe and claim specific
embodiments. Figure 4A is a schematic of the overall pro-
cess, and is included in ’871 and the ’369 Patents:
ATI TECHNOLOGIES ULC   v. IANCU                           7




As described in the patents, the graphics processor 60 in-
cludes a multiplexer 66 with a first and a second input,
whereby vertex data are provided at a first input, and in-
terpolated pixel parameter data and attribute data from a
rasterization engine 74 are provided at a second input. The
arbiter 64 generates a control signal that is transmitted to
the multiplexer 66, determining the inputs transmitted to
the unified shader 62.
8                              ATI TECHNOLOGIES ULC    v. IANCU



    Lindholm is the only primary reference cited against
the ’871 and ’369 claims on appeal.
    The ’871 patent
    The ’871 patent adds to the ’053 patent the structural
elements of a unified shader architecture, including an ar-
biter and selector for determining which vertex or pixel in-
puts the unified shader will process. The shader is “more
computationally efficient because it allows the shader to be
flexibly allocated to pixels or vertices based on workload.”
’871 patent, col. 2, ll. 64–67. Claim 1 was deemed repre-
sentative:
    1. A graphics processor, comprising:
         an arbiter circuit for selecting one of a plurality
    of inputs in response to a control signal; and
        a shader, coupled to the arbiter circuit, opera-
    tive to process the selected one of the plurality of
    inputs, the shader including means for performing
    vertex operations and pixel operations, and per-
    forming one of the vertex operations or pixel oper-
    ations based on the selected one of the plurality of
    inputs, wherein the shader provides a appearance
    attribute.
The PTAB again held that ATI had established conception
before the applicable reference date, but had not estab-
lished actual reduction to practice and had not established
diligence to constructive reduction to practice, stating that
“Patent Owner relies [on] the same evidence and substan-
tially the same arguments in the present review and in
IPR2015–00325 in support of its efforts to antedate Lind-
holm.” ’871 Op. at 3.
    Thus the PTAB held claims 1, 2, 5, 8, 10–11, 13 and 15
of the ’871 patent unpatentable as anticipated by Lind-
holm, claims 3 and 6 unpatentable as obvious over the com-
bination of Lindholm and Open GL, and claims 9, 17, and
ATI TECHNOLOGIES ULC   v. IANCU                               9



18 unpatentable as obvious over the combination of Lind-
holm and Kizhepat. The PTAB alternatively held claim 15
unpatentable as obvious over a reference to Rich.
   The PTAB held claim 20 patentable, and LGE’s cross-
appeal on claim 20 has been withdrawn.
   The ’369 patent
    The ’369 patent adds a vertex storage block to the uni-
fied shader system. The ’369 patent further generates a
color associated with a specific pixel. Claims 1 and 2 are
the only claims in the ’369 patent:
   1. A graphics processor, comprising:
        an arbiter circuit for selecting one of a plurality
   of inputs in response to a control signal;
       a shader, coupled to the arbiter circuit, opera-
   tive to process the selected one of the plurality of
   inputs, the shader including means for performing
   vertex operations and pixel operations, and per-
   forming one of the vertex operations or pixel oper-
   ations based on the selected one of the plurality of
   inputs, wherein the shader provides a appearance
   attribute;
       a vertex storage block for maintaining vertex
   information;
       wherein the vertex storage block further in-
   cludes a parameter cache operative to maintain ap-
   pearance attribute data for a corresponding vertex
   and a position cache operative to maintain position
   data for a corresponding vertex; and
       wherein the appearance attribute is color, and
   the color is associated with a corresponding pixel
   when the selected one of the plurality inputs is
   pixel data.
10                            ATI TECHNOLOGIES ULC   v. IANCU



         2. The graphics processor of claim 1 wherein
     the appearance attribute is position, and the posi-
     tion attribute is associated with a corresponding
     vertex when the selected one of the plurality of in-
     puts is vertex data.
The PTAB again held that conception and constructive re-
duction to practice had been established, but that actual
reduction to practice and diligence had not been shown. On
this ground, the PTAB held the ’369 claims unpatentable
over Lindholm and OpenGL.
                        DISCUSSION
     Standard of review
    The PTAB’s findings of fact are reviewed for support by
substantial evidence, and plenary review is accorded the
PTAB’s conclusions of law. “‘[S]ubstantial evidence’ review
involves examination of the record as a whole, taking into
account evidence that both justifies and detracts from an
agency’s decision.” In re Gartside, 203 F.3d 1305, 1312
(Fed. Cir. 2000). “[T]he Board’s opinion must explicate its
factual conclusions, enabling us to verify readily whether
those conclusions are indeed supported by ‘substantial evi-
dence’ contained within the record.” Id. at 1314. “That rec-
ord, when before us, is closed, in that the Board’s decision
must be justified within the four corners of that record.” Id.
     Antedating a Reference — 37 C.F.R. §1.131
    Rule 131 is called the “swearing back” or “swearing be-
hind” provision. See generally Manual of Patent Examin-
ing Procedure (“MPEP”) § 715 (9th ed. Jan. 2018). It
applies to references that may be prior art, but that do not
claim the same invention. 3 The standards for whether the


     3 Prior to March 16, 2013, patents or applications on
the same invention were placed into “interference” for
ATI TECHNOLOGIES ULC   v. IANCU                              11



subject matter in a reference has been antedated are stated
in Rule 131:
    (a) When any claim of an application or a patent
    under reexamination is rejected, the applicant or
    patent owner may submit an appropriate oath or
    declaration to establish invention of the subject
    matter of the rejected claim prior to the effective
    date of the reference or activity on which the rejec-
    tion is based.
    (b) The showing of facts for an oath or declaration
    under paragraph (a) of this section shall be such, in
    character and weight, as to establish reduction to
    practice prior to the effective date of the reference,
    or conception of the invention prior to the effective
    date of the reference coupled with due diligence
    from prior to said date to a subsequent reduction to
    practice or to the filing of the application.
    Accordingly, pursuant to Rule 131(b), the applicant
bears the burden of proof to establish either: (1) prior re-
duction to practice; or (2) prior conception “coupled with
due diligence.” In re Steed, 802 F.3d 1311, 1316 (Fed. Cir.
2015). “Demonstration of such priority requires documen-
tary support, from which factual findings and inferences
are drawn, in application of the rules and law of conception,
reduction to practice, and diligence.” Id. Indeed, Rule
131(b) expressly provides that: “[o]riginal exhibits of draw-
ings or records, or photocopies thereof, must accompany
and form part of the affidavit or declaration or their ab-
sence must be satisfactorily explained.”
    It is undisputed that ATI conceived of the patent claims
before the primary reference filing dates. As explained


determination of the first inventor. Since March 16, 2013,
only the application with the earlier filing date is granted.
MPEP § 2301.04.
12                             ATI TECHNOLOGIES ULC    v. IANCU



below, we find that ATI demonstrated diligence through
constructive reduction to practice as to the three Unified
Shader Patents. Given this conclusion, we need not review
the PTAB’s rulings concerning actual reduction to practice.
These rulings are vacated.
     The Standard for Diligence
    The diligence requirement implements the principle
that, to antedate a reference, the applicant must not only
have conceived the invention before the reference date, but
must have reasonably continued activity to reduce the in-
vention to practice. The court summarized the law with
respect to “due diligence” for purposes of Rule 131:
     A patent owner need not prove the inventor contin-
     uously exercised reasonable diligence throughout
     the critical period; it must show there was reason-
     ably continuous diligence.         See, e.g., Tyco
     Healthcare Grp. v. Ethicon Endo-Surgery, Inc., 774
     F.3d 968, 975 (Fed. Cir. 2014); Monsanto, 261 F.3d
     at 1370. Under this standard, an inventor is not
     required to work on reducing his invention to prac-
     tice every day during the critical period. See Mon-
     santo, 261 F.3d at 1369. And periods of inactivity
     within the critical period do not automatically van-
     quish a patent owner’s claim of reasonable dili-
     gence.
Perfect Surgical Techniques, Inc. v. Olympus Am., Inc., 841
F.3d 1004, 1009 (Fed. Cir. 2016) (emphases original).
    “An inventor’s testimony regarding his reasonable dil-
igence must be corroborated by evidence.” Id. at 1007; see
Price v. Symsek, 988 F.2d 1187, 1194 (Fed. Cir. 1993). The
burden of proving diligence is on the party asserting the
benefit of diligent activity, in this case the benefit of the
Rule 131 “swearing back” provision. See In re Steed, 802
F.3d 1311, 1316 (Fed. Cir. 2015) (“Steed bears the burden
to establish ‘facts ... in character and weight, as to establish
ATI TECHNOLOGIES ULC   v. IANCU                              13



reduction to practice prior to the effective date of the refer-
ence, or conception of the invention prior to the effective
date of the reference coupled with due diligence from prior
to said date to a subsequent reduction to practice or to the
filing of the application.’ 37 C.F.R. § 1.131(b)”); In re Mag-
num Oil Tools Int’l, Ltd., 829 F.3d 1364, 1376 (Fed. Cir.
2016) (“[A] patentee bears the burden of establishing that
its claimed invention is entitled to an earlier priority date
than an asserted prior art reference.”); see also Perfect Sur-
gical, 841 F.3d at 1007 (Fed. Cir. 2016) (“Pre–AIA section
102(g) allows a patent owner to antedate a reference by
proving earlier conception and reasonable diligence in re-
ducing to practice.”); Mahurkar v. C.R. Bard, Inc., 79 F.3d
1572, 1578 (Fed. Cir. 1996) (“Where a party is first to con-
ceive but second to reduce to practice, that party must
demonstrate reasonable diligence toward reduction to
practice from a date just prior to the other party’s concep-
tion to its reduction to practice.”). “A ‘variety of activities’
may corroborate an inventor’s testimony of reasonable dil-
igence and such corroborating evidence is considered ‘as a
whole’ under a rule of reason.” Perfect Surgical, 841 F.3d
at 1007–08 (quoting Brown v. Barbacid, 436 F.3d 1376,
1380 (Fed. Cir. 2006)).
    ATI stated that the PTAB applied an incorrect defini-
tion of diligence, and LGE so conceded in its brief before it
withdrew from this appeal. The Director instead describes
as “boilerplate” the PTAB’s erroneous definition. However,
it was not boilerplate, for the PTAB appeared to find a dis-
positive difference between “continuous reasonable dili-
gence” and “reasonably continuous diligence,” despite the
documentary evidence of activity by ATI on “every business
day.” We conclude that the PTAB applied the wrong legal
standard for diligence. As explained below, under the
proper legal standard, the record is clear that ATI exer-
cised the requisite “reasonably continuous diligence.” See
Perfect Surgical, 841 F.3d at 1009.
14                           ATI TECHNOLOGIES ULC   v. IANCU



     Diligence — Declarations and Documents
    Inventor Laurent Lefebvre described conception and
activities developing the technology in the three Unified
Shader Patents. His 60-page Declaration describes his and
the other inventors’ and other ATI employees’ activities on
this project (designated the R400 project), and was accom-
panied by “almost 1300” pages of documentary records
showing the work done and by whom and when, including
metadata, document logs, and folder histories. J.A. 2628–
88; J.A. 2689–3943; J.A. 3994–4312.
     Mr. Lefebvre explained that as the Unified Shader pro-
ject evolved, ATI increased the number of employees until
“ATI assigned over one hundred project managers/design-
ers to implement and test the R400 . . . [and] at least one
person on the R400 project team worked on the R400 de-
sign every non-holiday business day.” ’053 patent Lefebvre
Decl. ¶¶ 38–43 (J.A. 2650–54). He explained the develop-
ment of the technology, and identified the records as the
project evolved. He explained that the employees were re-
quired to save their work in a revision-control system
called Perforce that maintains metadata, and he refer-
enced the relevant documentary records and provided sum-
maries of the various aspects to which employees were
assigned, and records in document logs and folder histo-
ries.
    “Metadata” are data about changes in files, source
codes, edits, logs of access of files, time and date stamps,
user, changes made, etc. Calvin Watson Decl. ¶¶ 7–10 (J.A.
7906–07). The metadata include information concerning
revisions, including who made the revision and the date
each revision was made. ’053 patent Lefebvre Decl. ¶ 39
(J.A. 2650). Mr. Lefebvre provided a calendar summariz-
ing the metadata documentation, showing what activities
were performed on what dates. Id. ¶¶ 41–43 (J.A. 2654);
Section V (J.A. 2660–85) (calendar summarizing Perforce
folder history entries).
ATI TECHNOLOGIES ULC   v. IANCU                             15



    Mr. Lefebvre explained that ATI employees used the
R400 Sequencer Specification to write emulation code and
RTL [register-transfer level] code for the R400’s functional
blocks, and testing the R400’s functional blocks. The doc-
umentation included documents recording metadata on the
R400 Sequencer Emulator Folder History, Ex. 2048 (18
pages) (J.A. 3994–4012); Sequencer Parts Development
Folder History, Ex. 2049 (33 pages) (J.A. 4013–46); R400
Document Library Folder History, Ex. 2050 (110 pages)
(J.A. 4047–4157); R400 Architecture Folder History, Ex.
2051 (26 pages) (J.A. 4158–84); and R400 Testing Folder
History, Ex. 2052 (127 pages) (J.A. 4185–4312). Mr.
Lefebvre stated that:
    This metadata is not exhaustive of all se-
    quencer/shader-pipe files that were edited during
    this timeframe. But this metadata shows work
    that was necessary for implementing the R400 de-
    sign. Specifically, this metadata shows the design,
    development, and testing of the R400 sequencer
    and graphics blocks.
’053 patent Lefebvre Decl. ¶ 42 (J.A. 2654).
     Summarizing the information in the documents, Mr.
Lefebvre classified the ongoing activities as they applied to
the three Unified Shader patents, for the following periods:
(1) from prior to the Stuttard reference’s filing date of Oc-
tober 9, 2001 to the ’053 patent’s filing on September 29,
2003; (2) from prior to the Moreton reference’s filing date
of April 21, 2003 to the ’053 patent’s filing date of Septem-
ber 29, 2003; (3) from prior to the Lindholm reference’s fil-
ing date of June 27, 2003 to the ’053 patent’s filing date of
September 29, 2003; (4) from prior to the Lindholm refer-
ence’s filing date of June 27, 2003 to the ’871 patent’s filing
date of November 20, 2003; and (5) from prior to the Lind-
holm reference’s filing date of June 27, 2003 to the ’369 pa-
tent’s filing date of November 20, 2003. ’053 patent
Lefebvre Decl. ¶¶ 41–43 and Part V (Ex. 2006) (J.A. 2654;
16                             ATI TECHNOLOGIES ULC    v. IANCU



J.A. 2660–85); ’871 patent Lefebvre Decl. ¶¶ 41–43 and
Part V (Ex. 2006) (J.A. 8001; J.A. 8007–34).
     Mr. Lefebvre testified that “[f]or me and many of the
other project managers/designers, the R400 was the only
project that most of us were assigned to—it was our full-
time responsibility. . . . [and] any time that we did work for
ATI between late 2001 and the end of 2003, that work
would have been on the R400.” ’871 patent Lefebvre Decl.
¶ 43 (J.A. 8001). Mr. Lefebvre further testified his “analy-
sis [of this metadata] shows that at least one person on the
R400 project team worked on the R400 design every non-
holiday business day from early 2002 (when we conceived
of the invention) until November 20, 2003 (the effective fil-
ing date of the ’871 patent).” Id. ¶ 41. Mr. Lefebvre states
that he updated the R400 Sequencer Specification every
two to three weeks as the team worked to add or remove
data. ’053 patent Lefebvre Decl. ¶ 36 (J.A. 2649).
    ATI’s expert witness, Dr. Wolfe, reviewed the records
and summarized their content, submitting a Declaration
and appearing as a witness before the PTAB. Dr. Wolfe’s
testimony concentrated on actual reduction to practice, and
included additional exhibits as well as some of the same
exhibits (e.g., Ex. 2010), as well as mapping the RTL Code
to the claims. Ex. 2106 (J.A. 4702–4882).
     During the trial and at the final hearing the PTAB
raised no question about any of the evidence as to any of
the claimed inventions; nor had LGE done so. No inquiry
was made to any witness as to any fact or date or statement
or document. However, in its Final Written Decision the
PTAB held that diligence had not been established as to
any of the three Unified Shader Patents, the PTAB ruling
that “ATI fails to provide evidence that is specific both as
to facts and dates for each of the three critical periods.” ’053
Op. at 43.
ATI TECHNOLOGIES ULC   v. IANCU                           17



    The PTAB Decision
    The PTAB decision mentions two aspects as showing
failure of proof of diligence: (1) that “Mr. Lefebvre rede-
signed the R400, after the conception date, to include an
optional feature that is not recited in the claims at issue,”
’053 Op. at 44; and (2) that “ATI fails to provide a reasona-
ble way for us to determine whether unexplained lapses
have not occurred.” Id. at 53.
     The “optional feature” aspect was focused on a “second
chip design,” the PTAB stating that Mr. Lefebvre had not
provided a “meaningful explanation as to which activities
listed in the metadata are directed to the second chip de-
sign,” ’053 Op. at 45. The PTAB criticized that “ATI’s cal-
endar, metadata, document logs, and folder histories
(nearly 1,300 pages) are not self-explanatory and do not ex-
plain meaningfully as to which tasks are reasonably neces-
sary for reducing the claimed elements to practice, and
which tasks are directed toward developing and testing
other chip designs and optional features.” Id. at 41–42.
The PTAB dismissed the entirety of the evidence, stating
that “work done for the entire R400 project includes devel-
oping and testing other chip designs and optional features
to improve graphic processing systems generally, and not
merely for the claimed elements.” Id. at 42.
     The trial record shows no inquiry of any witness, ask-
ing about lapses in activity related to the Unified Shader.
In its Final Written Decision the PTAB refers to Lefebvre’s
information that ATI worked to increase the capability of
the product to meet the criteria of a potential customer for
the Unified Shader, identified as Microsoft. The PTAB ap-
pears to have held that this work defeated diligence, alt-
hough the PTAB did not state or suggest that this work
was not within the Unified Shader patents. Nor does the
PTAB propose that any of the work documented in the 1300
pages of exhibits is outside of the claims. Rather, the PTAB
18                            ATI TECHNOLOGIES ULC   v. IANCU



complains that ATI did not identify “unexplained lapses”
in the shader activity. Id. at 53.
    Diligence is not negated if the inventor works on im-
provements and evaluates alternatives while developing
an invention. In re Jolley, 308 F.3d 1317, 1328 (Fed. Cir.
2002) (“[W]e decline to adopt a rule that evidence of dili-
gence must be excluded if there is any possibility that it
could be construed in support of an invention beyond the
reach of the count.” (emphasis original)). Here, neither
LGE (before its withdrawal) nor the PTAB points to even
such possibility — to the contrary, Lefebvre testified that
over 100 ATI employees worked on this project.
     Mr. Lefebvre’s Declaration traced the development of
this technology, and explained the significance of the vari-
ous stages. He testified that the first “triangle test” demon-
strated that they had successfully designed software that
performed the unified shader operations, but that addi-
tional effort was required to perfect the operations. He tes-
tified that “after you are done with the single triangle you
need to continue working . . . [because] it’s not a sign that
you can productize a chip. In order to have something you
can productize, you have to run these thousand other
tests.” Ex. 1035 at 143:20–144:22 (J.A. 2060–61) (Deposi-
tion Transcript of Mr. Lefebvre).
    The PTAB identified no delays, no gaps in activity. Ra-
ther, the PTAB complained that Lefebvre had not identi-
fied any “unexplained lapses.” It is correct that Mr.
Lefebvre identified daily activity, not lapses. The Director
as Intervenor quotes the PTAB statements that ATI was
working on “unclaimed features,” but the Director, like the
PTAB, does not explain or identify any such features. See
Power Integrations, Inc. v. Lee, 797 F.3d 1318, 1323 (Fed.
Cir. 2015) (the Board must “fully and particularly set out
the bases upon which it reached [its] decision”); In re
NuVasive, Inc., 842 F.3d 1376, 1382 (Fed. Cir. 2016) (“[T]he
PTAB must make the necessary findings and have an
ATI TECHNOLOGIES ULC    v. IANCU                               19



adequate ‘evidentiary basis for its findings.’”) (quoting In
re Lee, 277 F.3d 1338, 1344 (Fed. Cir. 2002)).
    On appeal, we are directed to no view of the evidence
that could support a conclusion that ATI set aside the de-
velopment of the Unified Shader. The PTAB cited no basis
for finding that this technology was not being diligently
pursued. The Director seeks to excuse the PTAB’s absence
of support for its holding, by stating that ATI bears the bur-
den of proof of diligence. However, the Director does not
explain where the burden of proof was not met, upon the
extensive evidence of daily activity. LGE provided no evi-
dence to the contrary; the LGE argument was that ATI
could have filed its patent applications at an earlier stage
of development, and that continuing activity to develop a
satisfactory product does not count as diligence. Precedent
is not in accord; the purpose of the diligence requirement is
to show that the invention was not abandoned or set aside.
See Perfect Surgical, 841 F.3d at 1009 (explaining that the
“point of the diligence analysis . . . is to assure that, in light
of the evidence as a whole, ‘the invention was not aban-
doned or unreasonably delayed’”). Here, the Director does
not point to the remotest suggestion of abandonment or set-
ting aside of the Unified Shader technology.
    The Director as Intervenor cites no support for the
PTAB’s decisions, but merely quotes the PTAB’s statement
that the testimony of Lefebvre is “vague and not suffi-
ciently corroborated by independent evidence,” ’053 Op. at
42. The Director does not mention the 1300 pages of cor-
roborative documents. Although the Director states in his
Intervenor’s brief that there is an “unexplained delay” be-
fore the ’053 application was filed, Dir. Br. 52, the Director
does not elaborate.
    Instead, the Director presses the argument that ATI
should have filed its patent applications sooner. The Di-
rector states that: “At bottom, the problem was ATI’s fail-
ure to ‘explain why the team of engineers and designers
20                             ATI TECHNOLOGIES ULC   v. IANCU



could not have designed, built, and tested a chip embodying
the claimed elements, without those optional features,’”
Dir. Br. 56, quoting PTAB ’053 Op. at 52–53. The Director
states that to show diligence “the work relied on must or-
dinarily be directly related to reduction to practice of the
invention.” Dir. Br. 56 (quoting Naber v. Cricchi, 567 F.2d
382, 385 (CCPA 1977)). The ensuing sentence states that
     work in preparation for filing related patent appli-
     cations may suffice (e. g., Rey-Bellet v. Englehardt,
     493 F.2d 1380, 181 USPQ 453 (Cust. & Pat. App.
     1974)), as may work required to develop a first in-
     vention in order to develop or reduce to practice a
     second invention (e. g., Keizer v. Bradley, 270 F.2d
     396, 47 CCPA 709, 123 USPQ 215 (1959); Thomp-
     son v. Dunn, 166 F.2d 443, 35 CCPA 957, 77 USPQ
     49 (1948)).
Id. The principles underlying the law of diligence have
long been recognized:
     No general standard, by which diligence can be es-
     timated, has been established by the law, nor, in
     the nature of things, is such a standard possible. It
     must be reasonable, under all the circumstances of
     the particular case in question. The character of
     the invention; the health, the means, the liberty of
     the inventor; his occupation upon kindred or sub-
     ordinate inventions, — are proper subjects for con-
     sideration. Such reasonable diligence does not
     involve uninterrupted effort, nor the concentration
     of his entire energies upon this single enterprise.
1 Robinson on Patents § 387, at 548–49 (1890).
    The Board criticized ATI for “fail[ing] to provide a rea-
sonable way for us to determine whether unexplained
lapses have not occurred.” ’053 Op. at 53. Neither LGE
nor the Board raised a question of “unexplained lapses” at
trial, or requested additional information concerning
ATI TECHNOLOGIES ULC   v. IANCU                          21



corroboration. Although the Board also faulted ATI’s
presentation as “not explain[ing] meaningfully the nature
of the work” that was being done, ’053 Op. at 51, the Board
did not inquire of any witness as to the nature of the work.
In contrast, for example, a Board member asked counsel
what a “tape out” is, as that usage appeared in the docu-
ments. Oral Hr’g. Tr. 76–78. The record does not show
objection by LGE to the adequacy of the documentation.
    The PTAB did not separately explain its ruling of ab-
sence of diligence for the ’871 and ’369 patents, where the
periods were three and six months, respectively. The
PTAB simply referred to its ’053 patent decision, and
stated that “Patent Owner relies [on] the same evidence
and substantially the same arguments in the present re-
view and in IPR2015–00325 in support of its efforts to an-
tedate Lindholm. . . . [I]n IPR2015-00325, the panel
determined that Patent Owner had not antedated Lind-
holm. . . . In view of the determination that Patent Owner
has not antedated Lindholm . . . we conclude that” the chal-
lenged claims are unpatentable. ’871 Op. at 3; see ’369 Op.
at 8–9 (“Patent Owner relies on the same evidence and sub-
stantially the same arguments in the instant proceeding
and in IPR2015-00325, in support of its efforts to antedate
Lindholm. . . . To the extent necessary, we incorporate here
the discussion of the antedating of Lindholm from the Final
Written Decision of IPR2015-00325 by reference.”).
    During the ’871 and ’369 patent trials, Mr. Lefebvre
again testified and analyzed the metadata that show dili-
gence from conception to the effective filing date, antedat-
ing the Lindholm reference. ’871 patent Lefebvre Decl.
¶ 41 (J.A. 8001); ’369 patent Lefebvre Decl. ¶ 41 (J.A.
8443).
     Mr. Lefebvre provided an annotated calendar for the
critical periods. J.A. 8007–34. The calendar summarized
the various documents that show “the design, development,
and testing of the R400 sequencer and graphics blocks . . .
22                            ATI TECHNOLOGIES ULC   v. IANCU



[which] was necessary to make progress on the sequencer
block and the shader pipe block.” ’871 patent Lefebvre
Decl. ¶ 42 (J.A. 8001). The documentation included docu-
ments recording metadata on the R400 Sequencer Emula-
tor Folder History, Ex. 2048; Sequencer Parts Development
Folder History, Ex. 2049; R400 Document Library Folder
History, Ex. 2050; R400 Architecture Folder History, Ex.
2051; and R400 GFX Testing Folder History, Ex. 2052. J.A.
8007.
    The PTAB did not provide full analysis for the ’871 and
’369 patents, and referred to the reasoning in the ’053 opin-
ion. The Board’s rulings as to diligence are in error, in all
three patents, for the same reasons. These rulings are re-
versed.
                       CONCLUSION
    The Board erred in holding that diligence had not been
shown for the three Unified Shader Patents. On the undis-
puted rulings that conception and constructive reduction to
practice were shown for the three patents, and on our hold-
ing that diligence was shown for the three patents, the
Board’s decisions of unpatentability of the ’053 patent, the
’871 patent, and the ’369 patent are reversed.
                       REVERSED
