Apple Inc. v. Zentian Ltd.

N OTE: This disposition is nonprecedential.
United States Court of Appeals
for the Federal Circuit
______________________
APPLE INC.,
Appellant
v.
ZENTIAN LTD.,
Appellee
______________________
2024-2207
______________________
Appeal from the United States Patent and Trademark
Office, Patent Trial and Appeal Board in Nos. IPR2023-
00036, IPR2023-01195.
______________________
Decided: July 21, 2026
______________________
BRIAN R OBERT MATSUI, Morrison & Foerster LLP,
Washington, DC, argued for appellant. Also represented
by SETH W. L LOYD; ALEXANDRA M. AVVOCATO, New York,
NY; BITA RAHEBI, REBECCA WEIRES SETRAKIAN, Los Ange-
les, CA.
K ATHERINE E. RHOADES , Bartlit Beck LLP, Chicago, IL,
argued for appellee. Also represented by J ESSICA R.
BERNHARDT , N EVIN M. G EWERTZ; K AYVAN B. N OROOZI, No-
roozi PC, Los Angeles, CA.
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APPLE INC. v. ZENTIAN LTD. 2
______________________
Before D YK, MAYER , and P ROST , Circuit Judges.
D YK, Circuit Judge.
Apple Inc. (“Apple”) appeals a decision of the Patent
Trial and Appeal Board (the “Board”) concluding that
claims 1, 2, 4, 6–9, 11, 24, and 29 of U.S. Patent
No. 10,839,789 (the ’789 patent) were not shown to be un-
patentable. We vacate the Board’s decision and remand.
BACKGROUND
I
Zentian Ltd. (“Zentian”) owns the ’789 patent, which is
directed toward systems, circuits, and coprocessors used in
speech recognition. Claims 1 and 29 are representative for
purposes of this appeal. Claim 1 recites:
An acoustic coprocessor for processing data associ-
ated with an audio signal, comprising:
a first interface for receiving at least one fea-
ture vector, wherein the feature vector is deter-
mined from the audio signal;
an acoustic model memory for storing an acous-
tic model defining a plurality of acoustic states;
a calculating apparatus for calculating dis-
tances indicating a similarity between the at
least one feature vector and respective acoustic
states of the acoustic model read from the
acoustic model memory; and
a second interface for sending at least one dis-
tance calculated by the calculating apparatus;
wherein the calculating apparatus and the
acoustic model memory are fabricated on a sin-
gle integrated circuit.
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APPLE INC. v. ZENTIAN LTD. 3
’789 patent, claim 1 (emphases added). Claim 29 claims a
“speech recognition system” wherein an “acoustic coproces-
sor” and “at least one [search] processor are fabricated on
a single integrated circuit,” and wherein the acoustic copro-
cessor contains “one or more result memories,” “a status
register,” and “a direct memory access (DMA) controller ca-
pable of copying [data] from the one or more result memo-
ries to a buffer memory.” See id. claim 29 (depending from
claims 18, 25, and 26).
The speech recognition circuit analyzes speech sounds
by breaking down an incoming digital audio stream into
short “frames,” or segments of the audio stream. Id. col. 12
ll. 55–57. The audio in each frame is then converted into a
“feature vector,” which represents the various characteris-
tics of the audio. Id. col. 12 ll. 58–65. A prototypical fea-
ture vector is a series of coordinates that “represents a
point in an N-dimensional space,” where each dimension
corresponds to an audio characteristic, such as a particular
audio frequency band. Id. col. 12 ll. 58–65, col. 13 ll. 22–
26. Each of these feature vectors is then compared against
an “acoustic model,” which is a library of many acoustic
“states” representing known and expected sounds in
speech. See id. col. 4 ll. 12–17. In a preferred embodiment,
each state contains a probability distribution mapped onto
the same N-dimensional space as the feature vectors. Id.
col. 13 ll. 26–40. This allows a “distance” calculation to be
performed between the feature vector and each state; the
shorter the distance, the more likely the audio represented
by the feature vector is the known speech sound repre-
sented by the state. See id. col. 14 ll. 1–10. Once likely
sounds have been identified, a “search stage” identifies
likely words reflecting what was said in the digital audio
stream. Id. col. 6 ll. 6–9.
Three disclosed memories perform different functions.
First, the “acoustic model memory” holds the acoustic
model to which feature vectors are compared. E.g., id.
col. 25 ll. 42–56. Second, the “results memories . . . stor[e]
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APPLE INC. v. ZENTIAN LTD. 4
[the] calculated distances” between the feature vectors and
the states of the acoustic model. Id. col. 25 ll. 58–61.
Third, the “buffer memory” is additional memory space for
holding the calculated distances if the results memories re-
quire additional storage space. Id. col. 6 ll. 9–15. Claim 29
also requires a “status register” that “indicate[s] the com-
pletion of calculation of [a particular] set of distances.” Id.
(depending from claim 25).
Relevant to this appeal, both claims 1 and 29 require
“a single integrated circuit.” Id. Claim 1 requires that the
integrated circuit contain both the claimed acoustic model
memory and the claimed “calculating apparatus” (i.e., the
processor that calculates distances between feature vectors
and the states of the acoustic model). Claim 29 requires
that the integrated circuit contain both the claimed “acous-
tic coprocessor” (also referring to a processor that calcu-
lates distances) and the claimed “at least one [search]
processor” (a separate processor that analyzes the calcu-
lated distances to identify likely words). Id. (depending
from claims 10 and 28). The acoustic coprocessor of
claim 29 contains “one or more result memories” and a “di-
rect memory access (DMA) controller” that connects to the
buffer memory. Id. (depending from claims 18 and 26).
Claim 29 also requires an acoustic model memory, but it is
not required to be part of the integrated circuit.
II
Apple petitioned for inter partes review of claims 1, 2,
4, 6–14, 16–18, 20–29, 35, 37–39, and 42–45 of the ’789 pa-
tent. In the petition, Apple argued that claim 1 was obvi-
ous over prior art reference U.S. Patent No. 5,819,222
(“Smyth”) or the combination of Smyth and U.S. Patent
No. 6,832,194 (“Mozer”) and that claim 29 was obvious over
Smyth, Mozer, and several other references.
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APPLE INC. v. ZENTIAN LTD. 5
A
Smyth teaches a similar speech recognition circuit
wherein a digital audio stream is broken into frames, each
frame is converted into a feature vector, and each feature
vector is compared with a set of acoustics states, contained
in the “state memory,” to determine their similarity for the
purpose of eventually identifying likely words. Smyth,
col. 5 ll. 19–67. Smyth’s “state memory” is a component of
its “classifier,” which also contains a “classifying processor”
that calculates the distances between feature vectors and
states in the state memory. Id. col. 5 ll. 55–57. As Smyth
describes, the classifying processor could be “a single suit-
ably programmed digital signal processor (DSP) device
(such as the Motorola DSP 56000 . . .) or similar device.”
See id. col. 5 ll. 49–53, col. 6 ll. 5–9. Smyth also discloses a
“sequencer,” which takes the calculated distances and uses
them to match the audio frames to likely words. Id. col. 6
ll. 10–12, 35–42.
Mozer teaches another similar speech recognition cir-
cuit wherein the feature vector being analyzed is stored in
a memory on the integrated circuit along with a “template
vector,” which functions similarly to a single state in an
acoustic model. Mozer, col. 7 ll. 53–58, col. 9 l. 22–col. 10
l. 20.
B
Smyth alone and the Smyth and Mozer combination
disclose most of the claim limitations. The parties’ dispute
concerns the “acoustic model memory” and “integrated cir-
cuit” limitations of claims 1 and 29. As to claim 1, the pe-
tition argued that Smyth’s state memory and disclosure of
the Motorola DSP56000 disclosed the claimed acoustic
model memory on an integrated circuit with a calculating
apparatus. Alternatively, the petition argued that the
combination of Smyth and Mozer disclosed the acoustic
model memory on an integrated circuit with a calculating
apparatus.
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APPLE INC. v. ZENTIAN LTD. 6
In response, Zentian raised two separate arguments.
First, as to Smyth alone, Zentian argued that the Motorola
DSP56000 could not hold Smyth’s large-vocabulary model,
as Apple’s expert testified that the “typical size” of such a
model would be “around 4,700 bytes,” J.A. 3804,1 whereas
the undisputed testimony was that the Motorola
DSP56000 only contained around 1,500 bytes of available
memory. In reply, Apple argued that the claims did not
require a large-vocabulary model and that an “abbreviated
model,” such as one that is “configured to recognise certain
phrases or words for example a string of digits,” would be
much smaller than a complete model. J.A. 368 (quoting
Smyth, col. 6 ll. 61–66). Apple argued that the
Smyth/Mozer combination, which disclosed a larger 4,000-
byte memory, also disclosed this claim limitation. As
pointed out in the reply, Zentian’s expert testified in depo-
sition that a model for something “like a digits recognizer
or something . . . like, I think, Smith [sic] was doing” would
be an “abbreviated model” and could be “very small,”
J.A. 3380.
Second, as to the Smyth/Mozer combination, Zentian
argued that the claims required fabrication of the inte-
grated circuit and that a person of ordinary skill in the art
was not capable of fabricating a new circuit. On reply, Ap-
ple argued that the patent does not require the skilled ar-
tisan to perform the step of fabricating the circuit and that
the skilled artisan could simply obtain “known already fab-
ricated integrated circuits” with the appropriate specifica-
tions. J.A. 387–88.
Implicitly construing the claimed acoustic model
memory to require holding a large-vocabulary model, the
Board found that Apple had failed to show that Smyth
1 In contrast, Zentian’s expert testified that an
acoustic model could “require more than 720 kBytes
[720,000 bytes] of memory.” J.A. 3846.
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APPLE INC. v. ZENTIAN LTD. 7
alone disclosed the claimed acoustic model memory on an
integrated circuit because the Motorola DSP56000 only
had 1,500 bytes of available memory, which was insuffi-
cient to hold Smyth’s state memory, even accepting Apple’s
expert’s assertion that a typical large-vocabulary model
would be around 4,700 bytes. The Board then concluded
that Apple’s argument that an abbreviated model would
have been smaller was untimely as not raised “in the Peti-
tion or in the Reply” and in any event, there was insuffi-
cient evidence to show that an abbreviated model could fit
on the 1,500 bytes of the DSP56000.
The Board then determined that the petition’s pro-
posed combination of Smyth and Mozer was also insuffi-
cient. First, the Board found that the proposed
combination required the skilled artisan to personally fab-
ricate the integrated circuit and that there was insufficient
evidence that the skilled artisan would be able to do that.
The Board concluded that “even if [Apple] had shown there
was a reason to combine Smyth and Mozer,” a proposed
combination that required fabricating a new circuit com-
bining the integrated circuit disclosed in Mozer with a
larger memory would have been “beyond the level of ordi-
nary skill.” J.A. 38–39. Second, even assuming that the
claims do not require fabricating a new circuit, the Board
found that there was insufficient evidence that the skilled
artisan would have been able to use a prefabricated circuit
because Mozer’s disclosure only included a memory of
4,000 bytes, which would not have been large enough to
hold a 4,700-byte large-vocabulary acoustic model. The
Board therefore found claim 1, as well as several depend-
ent and similar claims,2 not unpatentable for the same rea-
sons.
2 These are claims 2, 4, 6–9, 11, and 24.
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APPLE INC. v. ZENTIAN LTD. 8
C
As to claim 29, the petition argued that the claim was
disclosed over a combination of several prior art references,
including Smyth and Mozer. The petition mapped Smyth’s
classifier onto the claimed acoustic coprocessor and
Smyth’s sequencer onto the claimed at least one search pro-
cessor. Zentian did not defend the patentability of claim 29
in either its response or sur-reply.
Nevertheless, the Board found that Apple had not
shown that claim 29 was unpatentable, finding that the in-
tegrated circuits in the prior art were not capable of hold-
ing Smyth’s classifier because Smyth’s classifier contained
the acoustic model memory, which the Board had deter-
mined was too large to fit on either the Motorola DSP56000
or Mozer’s 4,000-byte memory.
Apple appeals the Board’s conclusion that claims 1, 2,
4, 6–9, 11, 24, and 29 of the ’789 patent were not shown to
be unpatentable. We have jurisdiction under 28 U.S.C.
§ 1295(a)(4)(A).
D ISCUSSION
On appeal, Apple argues that the Board erred in its
analysis of claim 1 and that each of the remaining claims
is unpatentable as obvious. Zentian agrees that the
Board’s decision as to claim 29 must be set aside if the de-
cision as to claim 1 is set aside and does not advance any
alternative arguments to support the Board’s decision as to
that claim.3 We therefore solely address Apple’s argu-
ments as to claim 1, which we find sufficient to resolve the
issues on appeal.
3 To the extent the Board found that the petition’s
proposed combination did not disclose the claimed status
register, results memories, or buffer memory of claim 29,
those findings were not supported by substantial evidence.
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APPLE INC. v. ZENTIAN LTD. 9
“We review the Board’s factual findings for substantial
evidence and review its legal conclusions de novo.” Uber
Techs., Inc. v. X One, Inc., 957 F.3d 1334, 1337 (Fed. Cir.
2020) (internal quotation marks omitted). As obviousness
is a question of law, we review the Board’s ultimate obvi-
ousness determination de novo. Fed. Express Corp.
v. Qualcomm Inc., 174 F.4th 910, 913–14 (Fed. Cir. 2026).
I
As the Board found, the limitation that allegedly dis-
tinguishes claim 1 from the prior art is that it stores the
acoustic model on chip, that is, in an integrated circuit with
the processor. The prior art disclosed similar speech recog-
nition circuits that had on-chip memory but nonetheless
utilized off-chip memory to store the acoustic model. The
theory of the petition was that it would have been obvious
to use on-chip memory to store the acoustic model. The
Board made no finding that a standard memory of the ap-
propriate size would be unable to serve as the acoustic
model memory. Neither did the Board find that storing
data on the on-chip memory rather than off-chip memory
was anything other than routine. Instead, the Board found
that amongst the commercially available circuits presented
by Apple, none had an on-chip memory large enough to ac-
commodate a large-vocabulary acoustic model.
Apple argues that the Board erroneously required the
use of a large-vocabulary model when a smaller model
would have fit on an integrated chip at the time of the in-
vention. Zentian concedes that claim 1, which only re-
quires an “acoustic model,” does not require a large-
vocabulary model and would be satisfied by an abbreviated
model such as a digits recognizer model that can recognize
spoken numbers but not other words. The claim language
only requires that the acoustic model “defin[e] a plurality
of acoustic states,” which would include an abbreviated
model that contains fewer states than what would be
needed to model an entire language. See ’789 patent,
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APPLE INC. v. ZENTIAN LTD. 10
claim 1. In requiring that Apple show that a large-vocabu-
lary model—rather than a smaller abbreviated model—
would have fit on the integrated circuit in the prior art, the
Board committed legal error. An abbreviated model such
as a digits recognizer model satisfies the claim limitation.
The question remains whether the on-chip memory dis-
closed in Smyth and Mozer would be sufficient to store an
abbreviated acoustic model.
Apple argues that the abbreviated model of a digits rec-
ognizer would fit on the Motorola DSP56000 chip disclosed
in Smyth. Contrary to the Board, Apple raised this re-
sponse to Zentian’s argument in its reply. J.A. 368 (“[T]he
Motorola DSP56000 included a memory size sufficient to
store an ‘abbreviated model’ as would be required for
Smyth’s digit recognizer . . . .” (emphasis omitted)). The
Board erred in concluding that the argument was not made
in Apple’s reply.
However, the Board also concluded that Apple failed to
prove that an abbreviated model would fit onto the
Motorola DSP56000’s 1,500-byte memory. We need not de-
termine whether this conclusion was supported by sub-
stantial evidence because Apple made alternative
arguments concerning Mozer, which discloses a larger on-
chip memory than the Motorola DSP56000.
Apple argues that the Board erred with respect to its
theory based on a combination of Smyth and Mozer. We
agree. As to the Smyth/Mozer combination, the Board
again erroneously required a large-vocabulary model.
While the Board addressed the question of whether Mozer’s
disclosed 4,000-byte memory could hold a large-vocabulary
model, it did not address whether it could hold an abbrevi-
ated digits recognizer model. As a result, while the Board
found that an abbreviated digits recognizer model would
not fit on the Motorola DSP56000’s 1,500-byte memory, the
Board made no findings as to whether it would fit on
Mozer’s memory. Mozer’s 4,000-byte memory is much
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APPLE INC. v. ZENTIAN LTD. 11
larger than the Motorola DSP56000 and is nearly large
enough to store the 4,700-byte large-vocabulary model de-
scribed by Apple’s expert. Given that Zentian’s expert tes-
tified that an abbreviated model could be “very small”
compared to a large-vocabulary model, J.A. 3380, there is
evidence in the record that Mozer’s 4,000-byte memory was
large enough to store an abbreviated model. On remand,
the Board must address this factual question in the first
instance and consider whether the combination of Smyth
and Mozer would result in the claimed abbreviated acous-
tic model on an integrated circuit.
In this connection, Apple presented evidence that inte-
grated circuits combining processors and memory were
well known and Zentian does not argue otherwise. Apple
also presented undisputed evidence that there were known
benefits to using on-chip memory rather than off-chip
memory. See J.A. 3395 (Zentian’s expert acknowledging
that “it was known that . . . one way of making a system
more efficient[] was to reduce the off-chip memory ac-
cesses” by placing memory on chip). The patent indicates
that the claimed acoustic model memory is generically de-
scribed and does not require unique features. See, e.g.,
’789 patent, col. 34 ll. 52–66 (noting that while the acoustic
model is “typically held in a non-volatile memory” it can
also be stored in “on[-]chip” RAM memory); id. col. 35
ll. 35–39 (“There is no requirement for a memory that is
large enough to hold the entire decompressed acoustic
model . . . .”).
II
Zentian argues that the Board rejected the
Smyth/Mozer combination for another reason that Zentian
argues sustains the Board’s decision. The Board held that
Apple was required to show that the ordinarily skilled ar-
tisan could personally fabricate a new circuit implementing
the combination of a memory and processor. The relevant
claim language requires that “the calculating apparatus
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APPLE INC. v. ZENTIAN LTD. 12
and the acoustic model memory are fabricated on a single
integrated circuit.” ’789 patent, claim 1. While the peti-
tion argued that a skilled artisan would have found it obvi-
ous to apply “Mozer’s teachings to fabricate a calculating
apparatus and acoustic model memory on a single inte-
grated circuit,” the petition did not argue that a skilled ar-
tisan would be capable of fabricating the circuit without
assistance. J.A. 171. Nothing in the patent indicates that
fabrication is required to be performed as a step in the
claims. The Board’s own description of the level of skill in
the art assumes fabrication is not required because, as the
Board found, the ordinarily skilled artisan was not shown
to know how to fabricate a circuit with a generic memory
on it. See Liquid Dynamics Corp. v. Vaughan Co., 449 F.3d
1209, 1224 (Fed. Cir. 2006) (patent must enable the ordi-
narily skilled artisan to use the claimed invention). There
is therefore nothing to suggest that the skilled artisan
must personally fabricate the circuit rather than obtaining
a prefabricated circuit. The Board’s reading of the claims
was erroneous and incorporated an unclaimed requirement
into its analysis.
CONCLUSION
We vacate the Board’s decision as to claims 1, 2, 4, 6–
9, 11, 24, and 29 and remand for further proceedings con-
sistent with this opinion.4
VACATED AND REMANDED
COSTS
Each party to bear its own costs.
4 We note that Apple raises on appeal other alleged
errors with respect to the Board’s claim 29 determination
that are not addressed in our opinion and would have to be
addressed on remand if the Board were to conclude that
claim 1 was not unpatentable.
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