NOTE: This disposition is nonprecedential.

United States Court of Appeals 

for the Federal Circuit ______________________

PROMOS TECHNOLOGIES, INC.,

Appellant

v.

SAMSUNG ELECTRONICS CO., LTD.,

Appellee

______________________

2019-1343

______________________

Appeal from the United States Patent and Trademark 

Office, Patent Trial and Appeal Board in No. IPR2017-

01412.

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

PROMOS TECHNOLOGIES, INC.,

Appellant

v.

SAMSUNG ELECTRONICS CO., LTD.,

Appellee

______________________

2019-1344

______________________

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2 PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD.

Appeal from the United States Patent and Trademark 

Office, Patent Trial and Appeal Board in No. IPR2017-

01413.

______________________

Decided: April 6, 2020

______________________

KEVIN CHRISTOPHER JONES, TechKnowledge Law 

Group LLP, Redwood City, CA, argued for appellant. Also 

represented by CRAIG R. KAUFMAN. 

 NAVEEN MODI, Paul Hastings LLP, Washington, DC, 

argued for appellee. Also represented by CHETAN BANSAL,

STEPHEN BLAKE KINNAIRD, JOSEPH PALYS. 

 ______________________

Before O’MALLEY, REYNA, and WALLACH, Circuit Judges.

Opinion for the court filed by Circuit Judge O’MALLEY.

Dissenting opinion filed by Circuit Judge REYNA.

O’MALLEY, Circuit Judge.

In two inter partes review proceedings requested by 

Samsung Electronics Co. (“Samsung”), the U.S. Patent 

Trial and Appeal Board (“the Board”) invalidated all challenged claims of U.S. Patent No. 6,069,507 (the “’507 patent”), which is assigned to ProMOS Technologies, Inc. 

(“ProMOS”). J.A. 3; J.A.II. 3. 1 The Board found the challenged claims unpatentable as anticipated and obvious. 

1 This opinion primarily cites to the briefing and appendix from the -1343 appeal because the briefing and appendices for the two appeals are substantially identical on 

the claim construction issue. Any citations to the -1344 

briefing and appendices will use the modifier “II,” e.g., 

“J.A.II.,” “Appellant Br. II,” “Appellee Br. II”

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ProMOS appeals the Board’s final written decisions, arguing that the Board’s invalidity findings are erroneous because its construction of the “maintaining” limitation is 

erroneous. Because we agree with the Board’s construction, we affirm the Board’s decisions.

I. BACKGROUND

A. The Technology

A clock signal is a type of periodic signal that oscillates 

between low and high voltages, and is often used to coordinate or synchronize different parts of a circuit. J.A. 227. 

The most common type of clock signal is in the form of a 

square wave, usually with a fixed, constant frequency:

J.A. 227. The period (or cycle) of a clock signal is the duration between one LOW-to-HIGH transition, also called a 

“rising edge,” and the next LOW-to-HIGH transition. 

J.A. 227. The HIGH-to-LOW transition is similarly called 

a “falling edge.” One period of a clock signal spans a 360 ̊ 

phase. J.A. 228. When the rising and falling edges of two 

clock signals do not occur at the same time, the two signals 

are not “phase-aligned.” J.A. 228. This difference is known 

as a “phase difference.” 

One challenge associated with digital circuits is “clock 

skew”—that is, when a clock signal originating from a 

given source arrives at different components in a circuit at 

different times. J.A. 229–30. Clock skew may be caused 

by a variety of spatial or physical conditions, e.g., differing 

lengths of wire for conducting clock signals to respective 

components. J.A. 230. When circuit components have different perceptions of timing due to clock skew, this may

lead to undesirable circuit behavior. J.A. 230. For example, if two circuit components—which are designed to 

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execute actions simultaneously—receive copies of a clock 

signal that are not phase-aligned due to clock skew, the actions will occur sequentially.

One way to address this issue is through a system 

known as a “delay locked loop” (“DLL”). A DLL, via a 

“phase detector,” determines how much of a phase difference there is between two clock signals: a reference (or input) clock and an output (or feedback) clock. The DLL then 

employs a “voltage variable delay line” to delay the input 

data until it is synchronized with the reference clock.

B. The ’507 Patent

The ’507 patent, entitled “Circuit and Method for Reducing Delay Line Length in Delay-Locked Loops,” relates 

to DLLs and “more particularly to reducing delay line 

length in DLLs.” ’507 patent, col. 1 ll. 12–13. Figure 1 of 

the patent provides an example of a “typical digital DLL” 

at the time of the invention.

In this “typical digital DLL,” a phase detector 12 determines if a phase difference exists between the buffered input and feedback clock signals, “CKI” and “CKF.” ’507 

patent, col. 1 ll. 19–33. If there is a nonzero phase difference between the two signals, the system shifts the 

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buffered input clock signal by adjusting the shift register 

14 to select sufficient delay through delay line 16. ’507 patent, col. 1 ll. 29–33. This added delay synchronizes the 

input and feedback clock signals. Id.

Although DLLs can resolve the problems associated 

with clock skew, they generally require long delay lines to 

achieve sufficient coverage of frequency ranges and guarantee desired resolution. ’507 patent, col. 1 ll. 16–18. This 

increased delay line length may demand larger silicon area 

requirements and higher power consumption. ’507 patent, 

col. 1 ll. 42–44. Increased delay line length may also cause 

other problems, such as a longer lock-in time and greater

high frequency signal distortion. ’507 patent, col. 1 ll. 44–

46.

The ’507 patent proposes a “more elegant and cost effective” solution for reducing delay line length in a DLL. 

Figure 2, the only embodiment described in the written description, illustrates a “digital DLL 24 in accordance with 

the present invention.” ’507 patent, col. 2 ll. 49–50. 

The DLL 24 has an additional phase detector 30, which 

determines a phase difference between the buffered input 

clock signal CKI and a feedback clock signal CKF. ’507 patent, col. 2 ll. 61–67. If the second phase detector 30 

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determines that the difference between the feedback clock 

signal CKF and the buffered input clock signal CKI is 

within a 180 ̊ phase difference, the second phase detector 

controls the switch 28 to be at position (1), as seen above. 

Under this configuration, clock signal CKI is provided as 

an input to the delay line 16. ’507 patent, col. 2 l. 61–col. 

3, l. 6. But if the phase difference between the two clock 

signals is greater than 180 ̊, the second phase detector controls switch 28 to be at position (2). Under this new configuration, the clock signal CKI is inverted by inverter 26 and 

then provided as an input to the delay line. ’507 patent, 

col. 3 ll. 8–15. “Through the inversion, the phase difference 

needing to be compensated by the delay line 16’ is made 

less than 180 ̊” which decreases the length of the delay line 

by “approximately one-half the length that a typical DLL 

would require for comparable clock deskewing needs.” ’507 

patent, col. 3 ll. 11–18.

Independent claim 10 recites:

A method for reducing delay line length in a digital 

delay locked loop (DLL), the method comprising:

determining a phase difference between an 

input clock signal and a feedback clock signal;

maintaining the phase difference between 

the input clock signal and the feedback 

clock signal [within2] approximately 180 ̊, 

2 Both the Board and the parties agree that the word 

“within” is missing from the “maintaining” limitation and 

neither party challenged the Board’s decision to read the 

claim to include “within.” J.A. 7. During prosecution, the 

applicant amended the language of what became claim 10 

to include, inter alia, the limitation “within approximately 

180 ̊.” J.A. 7. In addition, the examiner acknowledged that 

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including adjusting the input clock signal 

with a loop comprising a phase detector, 

shift register, and delay line when the determined phase difference is less than approximately 180 ̊; and

delaying the input clock signal to compensate for the phase difference, wherein a 

number of delay cells utilized is reduced by 

approximately one-half. 

’507 patent, col. 4 ll. 47–59.

Dependent claim 11 recites:

The method of claim 10 wherein the phase detector 

comprises a phase difference detector with a first 

resolution.

’507 patent, col. 4 ll. 60–61.

C. The Prior Art

1. Donnelly (U.S. Patent No. 5,945,862)

Donnelly, a U.S. patent entitled, “Circuitry for the Delay Adjustment of a Clock Signal,” relates to providing “adjustable delays” to an incoming periodic signal, like a clock 

signal. J.A. 451. Donnelly discloses a DLL system. J.A. 

453, col. 5 ll. 32–34. The DLL system determines a phase 

difference between an input clock signal and a feedback 

clock signal via its phase detector. Donnelly explains that 

the DLL operates as follows: (1) the phase detector detects 

a nonzero difference between the two clock signals and instructs a counter to determine this difference; (2) the circuit block receives information which instructs the selector 

to switch consecutively through the taps from the output of 

the blender circuit to reduce the phase error; and (3) the 

the maintaining step recites “within approximately 180 degree[s].” J.A. 7. 

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selector switches consecutively through the taps until it 

eliminates the phase difference. J.A. 453, col. 5 l. 39–col. 6

l. 1. Donnelly explains that this process of constantly adjusting the value in the counter causes the output signal to 

“jitter” around the desired phase relationship between the 

input clock signal and the feedback clock signal. J.A. 453,

col. 6 ll. 1–8. 

2. Kim (U.S. Patent No. 5,875,219)

Kim, a U.S. patent entitled “Phase Delay Correction 

Apparatus,” discloses a digital DLL with an improved 

phase delay correction apparatus. J.A.II. 668, col. 1 ll. 5–

10. The DLL includes a phase detector for outputting a 

comparing signal, a shift register that can sequentially 

shift data bit values in both directions in accordance with 

the comparing signal, a phase delay unit for delaying and 

outputting the system clock signal, a domain selecting controller, and a domain selector for adjusting the phase of a 

driving signal from one region comprising approximately 

0–180 ̊ to another area comprising approximately 180–

360 ̊. J.A.II. 668, col 2 ll. 38–64.

D. The Board’s Decisions

As relevant to this appeal, Samsung filed two IPR petitions asserting that claims 10 and 11 of the ’507 patent 

are unpatentable because they would have been obvious in 

view of Donnelly and Iwamoto (U.S. Patent No. 5,875,219)3

and are anticipated by Kim. J.A. 133; J.A.II. 115. In its 

petitions, Samsung asserted that Donnelly and Kim disclose “maintaining the phase difference between the input 

clock signal and the feedback clock signal [within] approximately 180 ̊” (the “maintaining limitation”), as required by 

claim 10. J.A. 157–187; J.A.II. 129–55. Samsung and its 

expert, Dr. R. Jacob Baker, explained that the input and 

3 The disclosures of Iwamoto are not relevant to this 

appeal.

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feedback clocks in Donnelly and Kim have the same frequency and the same period. Under this assumption, the 

clock signals disclosed in the two references “always have 

a phase difference within 180 ̊.” J.A. 277–80; J.A.II. 217–

27. To illustrate Samsung’s point, Dr. Baker offered the 

following example:

J.A. 279 (annotated). The figure above shows two clock signals, an input clock signal and a feedback clock signal, with 

the same frequency and period. In this example, the later 

rising edge of the feedback clock signal (3) lags behind the 

rising edge of the input clock signal (2) by more than 180 ̊. 

The phase difference between the two signals is more than 

180 ̊. But the earlier rising edge of the feedback clock signal (1) is less than 180 ̊ ahead of the same rising edge of 

the input clock signal (2). The phase difference between 

these two signals is within approximately 180 ̊. Therefore, 

regardless of how the feedback clock signal is shifted, a rising edge of the feedback clock signal will always be within 

approximately 180 ̊ of the input clock signal. J.A. 279.

In its Patent Owner Preliminary Responses, ProMOS 

did not dispute that a feedback clock signal is always 

within either 180 ̊ ahead or 180 ̊ behind an input clock signal with the same period and frequency. Instead, ProMOS 

1

2

3

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argued that the “maintaining” limitation should be construed as meaning “ensuring that the feedback clock signal 

follows behind the input clock signal by less than 180 ̊.” 

J.A. 833 (emphases added). ProMOS asserted that a reading of the limitation that covered a variation in either direction is inconsistent with the intrinsic record and would, 

in effect, render the limitation meaningless. J.A. 831–33.

In its Institution Decisions, the Board agreed with ProMOS’s construction of the “maintaining” limitation. J.A. 

867–69. The Board accepted ProMOS’s characterization of 

the prosecution history and agreed with ProMOS that 

Samsung’s interpretation would render the claim term 

“meaningless.” J.A. 867–69. Accordingly, the Board initially did not institute IPRs on challenged claims 10 and 

11, but instituted the IPRs based on other unpatentability 

grounds, involving other claims (claims 13 and 15) that are 

not at issue in this appeal. J.A. 892–93. 

After the Supreme Court’s decision in SAS Inst., Inc. v. 

Iancu, 138 S. Ct. 1348 (2018), the Board issued orders in 

both IPRs, instituting on claims 10 and 11. J.A. 1042–43. 

Due to the limited scope of the original institution, however, ProMOS’s Patent Owner Responses only addressed 

claims 13 and 15. Accordingly, the Board asked the parties 

if further briefing was necessary for claims 10 and 11. J.A. 

1042–43. In response, ProMOS “indicated that it has nothing to add, for claims 10 and 11, and would be satisfied if 

[it] could simply rely on arguments made in [the] Patent 

Owner’s Preliminary Response for claims 10 and 11.” J.A. 

1047–48. Samsung, however, requested that it be allowed 

to file replies that addressed the arguments for claims 10 

and 11 in ProMOS’s Preliminary Responses. J.A. 1048. 

The Board granted Samsung’s request. J.A. 1048–49.

In its reply, Samsung argued that the Board should 

adopt the plain and ordinary meaning of the “maintaining” 

limitation—one without a directionality requirement—because the claim language, specification, and prosecution 

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history cut against ProMOS’s proposed construction. J.A. 

1074–85. Samsung argued that: (1) there was no “clear and 

unmistakable disavowal” of the full scope of the “maintaining” limitation; (2) the specification and the language of 

claim 13 demonstrated that the patent applicant deliberately chose not to inject a directionality requirement into 

the “maintaining” limitation; and (3) as confirmed by ProMOS’s own declarant, the specification itself does not support ProMOS’s construction. J.A. 1074–80. Samsung 

explained that the sole embodiment describes a phase difference between the input and feedback clock signals that 

oscillates between less than 180 ̊ and more than 180 ̊. J.A. 

1080–83. Samsung also pointed out that ProMOS’s Preliminary Response had misrepresented the prosecution 

history that had led the Board to originally deny institution 

on claims 10 and 11. J.A. 1083–85.

The Board rejected ProMOS’s proposed construction of 

the “maintaining” limitation the second time around. In 

its Final Written Decisions, the Board stated that it had 

changed its mind after reviewing “the complete trial record,” noting that the intrinsic evidence supported a finding 

that the limitation imposes no directionality requirement, 

such that one signal must follow the other by within approximately 180 ̊. J.A. 16–22. In particular, the Board explained that ProMOS’s interpretation of the prosecution 

history was “internally inconsistent and self-contradictory,” and found no disavowal by the applicant with regard 

to the subject matter of claim 10. J.A. 19–21. The Board 

concluded that the “maintaining” limitation “imposes no directional [sic] requirement, so either signal can be ahead or 

behind the other by within approximately 180 ̊.” J.A. 22. 

Based on this construction, the Board determined that 

Donnelly and Kim both disclose the “maintaining” limitation. J.A. 40–45; J.A.II 32–38. The Board found that Samsung had established, by a preponderance of the evidence,

that the challenged claims are anticipated by Kim and 

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would have been obvious over the combined teachings of 

Donnelly and Iwamoto. J.A. 45

ProMOS timely appealed the Board’s final decisions. 

We have jurisdiction under 28 U.S.C. § 1295(a)(4)(A).

II. DISCUSSION

ProMOS appeals: (1) the Board’s construction of the 

“maintaining” limitation; and (2) the Board’s anticipation 

and obviousness findings based on its construction of the 

“maintaining” limitation. Both parties agree that the claim 

construction dispute is dispositive to the Board’s anticipation and obviousness findings. Appellant Br. 10 (“Claim 

construction is dispositive in this appeal.”); Appellee Br. 38 

(“It is undisputed that if the Board’s construction is upheld, 

then there can be no error in the Board’s finding of unpatentability.”); Appellant Reply Br. 9. Accordingly, we address the claim construction dispute inquiry first.

A. Claim Construction

This court reviews the ultimate construction of a claim 

de novo. Teva Pharm. USA, Inc. v. Sandoz, Inc., 574 U.S. 

318 (2015). The court reviews subsidiary factual findings 

for substantial evidence. Knowles Elecs. LLC v. Iancu, 886 

F.3d 1369, 1374 (Fed. Cir. 2018). When we review the 

claim construction of a patent term in an IPR appeal after 

the patent has expired, such as in this case, we apply the 

standard established in Phillips, not the “broadest reasonable interpretation.” See In re CSB-Sys. Int’l, Inc., 832 F.3d 

1335, 1342 (Fed. Cir. 2016). That is, the words of a claim 

“are generally given their ordinary and customary meaning,” as the term would have been understood by a person 

of ordinary skill in the art at the time of the invention. 

Phillips v. AWH Corp., 415 F.3d 1303, 1313 (Fed. Cir. 

2005).

ProMOS argues that the Board’s construction of the 

“maintaining” limitation is erroneous because it does not 

include a directionality requirement. According to 

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ProMOS, the “maintaining” limitation should be construed 

as “ensuring that the feedback clock signal follows behind

the input clock signal by less than 180 ̊.” Appellant Br. 11

(emphasis added). In support of this argument, ProMOS 

relies on certain language from the written description and 

the prosecution history. As described in further detail below, however, ProMOS misinterprets the intrinsic evidence 

and attempts to import the narrower characteristics of an 

embodiment into an unrelated claim term.

1. The Plain Language of the Claims and the 

Written Description Do Not Support 

Importing a Directionality Restriction 

into the “Maintaining” Limitation

The plain text of the claim does not place a directionality restriction on the “maintaining” limitation. Claims 8

and 10, the only two claims reciting the limitation, simply

require that the phase difference between the input and 

the feedback clock signals is maintained within 180 ̊. ’507 

patent, col. 4 ll. 51–53 (“maintaining the phase difference 

between the input signal and the feedback clock signal 

[within] approximately 180 ̊”). Neither claim states or implies that the phase difference between the two signals is 

calculated by how much the feedback signal “follows” or 

lags behind the input signal. ’507 patent, col. 4 ll. 33–39, 

51–53. Accordingly, unless “the patentee has chosen to be 

his own lexicographer in the specification or has clearly disclaimed coverage during prosecution,” we must interpret 

claims according to their plain language. See E-Pass 

Techs., Inc. v. 3Com Corp., 343 F.3d 1364, 1370 Fed. Cir. 

2003). But there is no such explicit definition or disclaimer. 

Outside of claims 8 and 10, the ’507 patent only refers to 

the “maintaining” limitation in two instances: in the Abstract and in the Summary of the Invention. ’507 patent, 

Abstract; ’507 patent, col. 2 ll. 3–11. In both cases, the limitation is described broadly, without a directionality modifier such as “behind.” Id. 

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ProMOS argues that one of the statements in the written description, “CKF is more than 180 ̊ behind CKI,” indicates that the “maintaining” limitation calculates the 

phase difference based on how much the feedback signal 

lags the input signal. Appellant Br. 12. The written description, however, supports no such inference. In discussing the sole embodiment, depicted in Figure 2, the ’507 

patent recites:

When the second phase detector 30 determines 

that CKF [the feedback clock signal] is more than 

180 ̊ behind CKI [the input clock signal], the second 

phase detector 30 controls switch 28 to be at position (2). The inverted buffered clock signal is thus 

selected, so that the input clock signal CKI is reversed by 180 ̊[.] Through the inversion, the phase 

difference needing to be compensated by the delay 

line 16’ is made less than 180 ̊ and within the normal operation capabilities of the phase adjusting 

loop formed by phase detector 12, shift register 14’, 

and delay line 16’.

’507 patent, col. 3 ll. 7–15. This discussion of the preferred 

embodiment does not address the “maintaining” limitation. 

This passage explains that the phase detector “select[s]” 

the inverted buffered clock signal when it “determines” 

that the feedback signal is more than 180 ̊ behind the input 

signal. ’507 patent, col. 3 ll. 7–15. It does not state that 

this directionality requirement should also apply when the 

DLL is “maintaining” the phase difference between the two 

signals. ’507 patent, col. 3 ll. 7–15. 

ProMOS conflates the “determining” and “selecting” 

steps with the separate “maintaining” limitation. As disclosed in claims 8 and 10 of the patent, the “maintaining” 

limitation does not involve “determining” whether a phase 

difference exists or “selecting” an inverted buffered clock 

signal. Read plainly, the claim language states that the 

DLL maintains the phase difference between the two 

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signals within approximately 180 ̊ by adjusting the input 

clock signal with a loop comprising a phase detector, shift 

register, and delay line when the determined phase difference is less than approximately 180 ̊. ’507 patent, col. 4 ll. 

51–57. We need not construe the “maintaining” limitation 

so narrowly simply because an embodiment describes other 

steps, namely, the “determining” and “selecting” steps, 

which do have directional restrictions. In fact, this directionality restriction is captured by claim 13 of the ’507 patent, which includes the “determining” and “selecting” 

limitations:

A method for reducing delay line length in a digital 

delay locked loop (DLL), the method comprising:

determining whether a feedback clock signal in the 

DLL follows within a 180 ̊ phase difference behind

an input clock signal; and

selecting a switch position according to the determining step, including selecting a first switch position when the feedback clock signal follows behind

the input clock signal with 180 ̊. 

’507 patent, col. 4 l. 66–col. 5 l. 10 (emphases added). Like

the discussion of the preferred embodiment, claim 13 

acknowledges that these two steps include a directionality

restriction. If the patentee wanted to import that same restriction—“follows behind”—into the “maintaining” limitation of claim 10, he could have used similar language. But 

he did not. The written description further confirms that 

the patentee understood how to describe the relationship 

between two clock signals in a manner that makes clear 

which clock signal leads or lags the other in phase. ’507 

patent, col. 2, ll. 63–66 (“When the second phase detector 

30 determines that the feedback clock signal CKF from the 

DLL 24 is behind the buffered input clock CKI within a 

180 ̊ phase difference . . . .”). We decline to adopt a narrower construction in contravention of the plain language 

of the claims. 

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And, even if we were to determine that the above passage pertains to the “maintaining” limitation, it is well established that claims may be broader than described 

embodiments. See, e.g., Innogenetics, N.V. v. Abbott Labs., 

512 F.3d 1363, 1370 (Fed. Cir. 2008). 

2. The Prosecution History Does Not Support 

ProMOS’s Narrower Proposed Construction

of the “Maintaining” Limitation

ProMOS argues that the examiner allowed claim 10 

over Butcher (U.S. Patent No. 4,789,996), another prior art 

reference, because Butcher did not teach “maintaining the 

phase difference between the input clock signal and the 

feedback signal within 180 degrees.” Appellant Br. 13 (citing J.A. 393). According to ProMOS, “Butcher teaches a 

phase locked loop having input and feedback clock signals 

with equal frequencies.” Id. ProMOS insists that, if the 

examiner had understood the “maintaining” limitation under the Board’s construction, “he could not have reached 

the conclusion he did—that the DLL in Butcher did not 

teach the claimed ‘maintaining’ step.” Id.

ProMOS’s argument requires several logical leaps. In 

order to arrive at the same conclusion as ProMOS, the record must establish that: (1) the input and feedback clock 

signals disclosed in Butcher have the same frequencies; 

(2) the examiner knew that these clock signals have equivalent frequencies; and (3) the examiner’s allowance of the 

“maintaining” limitation was directed to the “within 180 ̊” 

part of the maintaining step, and not to the overall step 

itself. But whether the record supports these factual hurdles is irrelevant because ProMOS mischaracterizes the 

prosecution history. The patentee did not add the “maintaining” limitation to claim 10 in order to overcome rejection.

During prosecution, the examiner rejected pending 

claim 8, which included the “maintaining” limitation, as obvious in view of Butcher. J.A. 393. Although the examiner 

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admitted that Butcher did not disclose the “maintaining” 

limitation, he concluded that the step would have been obvious to a person of ordinary skill in the art. J.A. 393 (“It 

would have been obvious to one skilled in the art to maintain a delay of 180 degrees by selecting a proper number of

registers without changing the scope of the Butcher reference.”). Pending claims 9 and 11 (now claim 10), which depended from pending claim 8 and had additional 

limitations on top of the “maintaining” limitation, were 

found to include allowable subject matter. J.A. 394. Accordingly, the patentee rewrote claims 9 and 11 in independent form, incorporating the features of claim 8 from 

which they depended. J.A. 406–07. 

The record is clear: the “maintaining” limitation was 

not added to pending claim 11/now claim 10 in order to 

overcome the prior art, as argued by ProMOS. J.A. 33–34. 

Pending claim 11 already included the “maintaining” limitation based on its dependency on pending claim 8. These 

facts do not imply that the examiner somehow interpreted 

the “maintaining” limitation to include a directionality restriction, as ProMOS contends.

3. The Board’s Construction Does Not Render 

the “Maintaining” Limitation Superfluous

Finally, ProMOS argues that the Board’s construction 

of the “maintaining” limitation renders the limitation superfluous. Appellant Br. 16. Under the Board’s construction, any two clock signals with identical frequencies (and 

therefore, identical periods) are always “within 180 ̊ of each 

other.” ProMOS concludes that the limitation has “no real 

meaning” under this construction because the limitation is 

always satisfied.

The Supreme Court has stated that “[e]ach element 

contained in a patent claim is deemed material to defining 

the scope of the patented invention.” Warner-Jenkinson 

Co., Inc. v. Hilton Davis Chem. Co., 520 U.S. 17, 29 (1997). 

Consistent with this philosophy, we have determined that 

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it is generally improper to construe a patent claim so that 

express claim limitations or elements are rendered superfluous. See Biocon, Inc. v. Straumann Co., 441 F.3d 945, 

950–52 (Fed. Cir. 2006). The distinction here, however, is 

that claims 8 and 10 of the ’507 patent are not necessarily 

rendered “superfluous” by the Board’s construction. 

The plain language of the claims does not require the 

input clock signal and the feedback clock signal to have the 

same frequency and period. J.A. 131 at 4:47–59. Therefore, the Board’s construction does not render the claimed 

maintaining step superfluous because a pair of clock signals with different frequencies would not satisfy the limitation. These facts are distinct from those present in our 

“superfluous” precedent, where the erroneous claim construction ignored the ordinary meaning of explicit claim 

limitations or read out limitations in their entirety. See, 

e.g., Biocon, 441 F.3d at 950–52 (“In sum, the effect of 

adopting Diro’s proposed claim construction would be to 

read limitations [a], [b], [e], and [h] out of the claim. Not 

only would that be contrary to the principle that claim language should not be treated as meaningless, but it would 

be contrary to the specification, which describes the features of the claimed abutment in detail . . . .”); Elektra Instrument S.A. v. O.U.R. Sci. Int’l, Inc., 214 F.3d 1302, 1307 

(Fed. Cir. 2000) (claim language “only within a zone extending between latitudes 30 ̊–45 ̊” does not read on a device with radiation sources extending between 14 ̊–43 ̊ 

because “[a]ny other conclusion renders the reference to 30 

degrees superfluous”).

ProMOS contends that a DLL, such as the one disclosed in the ’507 patent, always has clock signals with the 

same frequency because it is a necessary characteristic of 

a DLL circuit. Appellant Br. 16–17. But neither party presented evidence on this issue. J.A. 21–22 (“Patent Owner 

has not, either in its Preliminary Response or its Patent 

Owner Response, asserted in a DLL the input clock signal 

and the feedback clock signal necessarily would have the 

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PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD. 19

same frequency. Petitioner has not had a full opportunity 

to respond to this new argument. Accordingly, the new argument, raised for the first time in Patent Owner’s SurReply, will not be considered.”). ProMOS relies on deposition testimony from Samsung’s expert stating that, “in the 

engineering sense,” two synchronized DLL clock signals 

have the same frequencies and the same signals. J.A. 959 

at 9:12–22. This, however, is not an admission that DLL 

clock signals always have the same input and feedback signals. In that context, Samsung’s expert may have been defining “synchronization” instead of opining on the 

fundamental characteristics of clock signals in DLL circuits. We decline to adopt ProMOS’s proposed construction 

without any supporting evidence in the record.

B. The Board’s Unpatentability Determinations 

Both parties agree that the claim construction dispute 

over the “maintaining” limitation is dispositive to the 

Board’s anticipation and obviousness findings. Appellant 

Br. 10 (“Claim construction is dispositive in this appeal.”); 

Appellee Br. 38 (“It is undisputed that if the Board’s construction is upheld, then there can be no error in the 

Board’s finding of unpatentability.”); Appellant Reply Br. 

9. Accordingly, because the Board correctly construed the 

“maintaining” limitation, we conclude that there is no error 

in the Board’s findings of unpatentability.

III. CONCLUSION

The Board correctly construed the “maintaining” limitation. As both parties agree that our determination with 

respect to the Board’s construction of that limitation is dispositive as to whether substantial evidence supports the 

Board’s anticipation and obviousness findings, we affirm 

the Board’s decisions in both IPRs.

AFFIRMED

Case: 19-1343 Document: 43 Page: 19 Filed: 04/06/2020
20 PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD.

COSTS

No costs.

Case: 19-1343 Document: 43 Page: 20 Filed: 04/06/2020
NOTE: This disposition is nonprecedential.

United States Court of Appeals 

for the Federal Circuit ______________________

PROMOS TECHNOLOGIES, INC.,

Appellant

v.

SAMSUNG ELECTRONICS CO., LTD.,

Appellee

______________________

2019-1343

______________________

Appeal from the United States Patent and Trademark 

Office, Patent Trial and Appeal Board in No. IPR2017-

01412.

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

PROMOS TECHNOLOGIES, INC.,

Appellant

v.

SAMSUNG ELECTRONICS CO., LTD.,

Appellee

______________________

2019-1344

______________________

Case: 19-1343 Document: 43 Page: 21 Filed: 04/06/2020
2 PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD.

Appeal from the United States Patent and Trademark 

Office, Patent Trial and Appeal Board in No. IPR2017-

01413.

______________________

REYNA, Circuit Judge, dissenting.

The ’507 patent concerns an improvement to the operation of a delay locked loop—a circuit used to synchronize

digital clocks by delaying the signal of one clock (here, an 

input clock signal) relative to the signal of another (here, a

feedback clock signal) to compensate for the “phase difference” between the signals. At issue is whether this “phase 

difference,” as used in the claim term “maintaining the 

phase difference between the input clock signal and the feedback clock signal [within] approximately 180 ̊” is to be 

measured in only one direction, i.e., as the lag of the feedback signal behind the input signal, or whether “phase difference” refers to the variance between the clock signals in 

either direction, i.e. as either the lag or the lead of the input 

signal relative to the feedback signal. 

A careful analysis of the way “phase difference” is used 

in the claims, and the way the invention is described in the 

specification, makes clear that the phase difference recited 

in the ’507 patent is unidirectional. Neither the majority 

nor the Board, however, engage in this analysis. Instead, 

they begin with the assumption that the “plain meaning” 

of the term “phase difference” is bi-directional. Only then 

do they turn to the intrinsic evidence to assess whether a 

“directional limitation” should be “imported” into the 

claims under the exacting criteria for lexicography and express disavowal.

This is contrary to the framework we set forth in Phillips, which dictates that the relevant plain meaning of a 

claim term is its meaning in the context of the patent, to be

discerned at the outset in the context of the specification 

and other intrinsic evidence. Because the majority 

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PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD. 3

embraces a construction of “phase difference” divorced 

from its usage in the patent and affirms the invalidation of 

the challenged claims based on that erroneous construction, I respectfully dissent. 

I

It is well-established that we generally give claim 

terms their plain and ordinary meaning to a skilled artisan

when read in the context of the specification and prosecution history. Thorner v. Sony Computer Ent. Am. LLC, 669 

F.3d 1362, 1365 (Fed. Cir. 2012); Phillips v. AWH Corp., 

415 F.3d 1303, 1315-17 (Fed. Cir. 2005). The doctrines of 

lexicography and disavowal are narrow exceptions to this 

rule that are applied when we limit claim scope in contradiction to the claim language. Thorner, 669 F.3d at 1365 

(citing Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 

1580 (Fed. Cir. 1996)). 

The intrinsic evidence is therefore integral at the outset of claim construction for discerning the plain and ordinary meaning of claim terms in the context of the patent. 

See Lexion Med., LLC v. Northgate Techs., Inc., 641 F.3d 

1352, 1356 (Fed. Cir. 2011). (“The customary meaning of a 

claim term is not determined in a vacuum and should be

harmonized . . . with the intrinsic record, as understood 

within the technological field of the invention.”); Abbott 

Labs. v. Andrx Pharms., Inc., 452 F.3d 1331, 1336 (Fed. 

Cir. 2006) (“Where claim terms are ambiguous or disputed, 

then we turn to the specification as . . . the single best 

guide to the meaning of a disputed term”) (quoting Phillips, 

415 F.3d at 1315)). In Phillips, we specifically cautioned 

against construing claims by first developing a broad definition of claim terms divorced from the context of the patent and then turning to the specification only to look for 

grounds for limiting the claim scope. Phillips, 415 F.3d at

1320 (discussing Texas Digital Sys., Inc. v. Telegenix, Inc., 

308 F.3d 1193 (Fed. Cir. 2002)). Such an approach, we 

noted, posed a “risk of systematic overbreadth,” which “is 

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4 PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD.

greatly reduced if the court instead focuses at the outset on 

how the patentee used the claim term in the claims, specification, and prosecution history, rather than starting with 

a broad definition and whittling it down.” Id. at 1321. 

Thus, we have rejected a proposed claim construction 

where it relies on an initial “assumption” that a claim term 

has a broad “ordinary meaning” unsupported by the intrinsic or extrinsic evidence. Ruckus Wireless, Inc. v. Innovative Wireless Sols., LLC, 824 F.3d 999, 1003 (Fed. Cir.

2016). When the plain meaning of a claim term does not 

clarify whether and how a restriction applies, we have said 

that such ambiguity is to be resolved in the first instance 

by reviewing the claim language as a whole, the other intrinsic record, and any extrinsic evidence. See Uship Intellectual Props., LLC v. U.S., 714 F.3d 1311, 1315 (Fed. Cir. 

2013). 

Fundamentally, when construing claims in light of the 

specification, we do so “with a view to ascertaining the invention.” United States v. Adams, 383 U.S. 39, 49 (1966). 

Even when applying the broadest reasonable interpretation standard, which is broader than the standard applicable here, we have held that “[t]he correct inquiry . . . is not 

whether the specification proscribes or precludes some 

broad reading of the claim term adopted by the examiner.” 

In re Smith Int’l, Inc., 871 F.3d 1375, 1382–83 (Fed. Cir. 

2017). Rather, a correct construction is one “that corresponds with . . . how the inventor describes his invention in 

the specification, i.e., an interpretation that is consistent 

with the specification.” Id. at 1383 (citation and internal 

quotation marks omitted); see also PPC Broadband, Inc. v. 

Corning Optical Commc’ns RF, LLC, 815 F.3d 747, 752 

(Fed. Cir. 2016).

II

Because the digital clock signals described in the ’507 

patent are periodic, i.e. they repeat at a regular interval, 

the variance or “phase difference” between two signals, A 

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PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD. 5

and B, can in theory always be measured in one of two 

ways: (1) from a certain point on signal A to the next corresponding point on signal B (i.e., as the lag of signal B behind signal A), or (2) from a point on signal B to the next 

corresponding point on signal A (i.e. as the lead of signal B

ahead of signal A). The question of whether a reference is 

referring to either or both of these measurements as the 

“phase difference” will depend on the context.

This is not unlike the ambiguity presented when we 

talk about the “time difference” between two analog clocks:

The time difference between Clock A, which reads 1 o’clock,

and Clock B, which reads 8 o’clock, could be 7 hours or 5

hours, depending on whether we are looking at the lag or 

the lead of Clock A relative to Clock B. If one is instructed 

to determine the time difference between these two clocks,

and to maintain the time difference within 6 hours, that 

person would first need to understand what “time difference” means in the full context of the instruction. 

Here, the Board recognized in its initial Institution Decision that the phrase, “maintaining the phase difference 

between the input clock signal and the feedback clock signal [within] approximately 180°,” was facially ambiguous 

in that it “does not specify whether the input clock signal 

must be ahead of the feedback clock signal or the feedback 

clock signal must be ahead of the input clock signal.” J.A.

867. Consistent with its obligations under Phillips, the 

Board looked to the specification for guidance, and determined that the patent’s written description of the limitation at issue indicated that “phase difference” referred to 

the lag of the feedback clock signal behind the input clock 

signal:

the Specification of the ’507 patent makes a distinction between feedback clock signals that are more 

than 180° behind the input clock signal and feedback clock signals that are less than 180° behind 

the input clock signal. [’507 patent, col. 3 ll. 8-15]. 

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6 PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD.

Indeed, when the feedback clock signal is determined to be more than 180° behind the input clock 

signal, a step is applied to invert it, effectively 

shifting it by 180°. Id. That is the disclosed implementation for the limitation at issue, i.e., “maintaining the phase difference between the input 

clock signal and the feedback clock signal [within] 

approximately 180°.”

J.A. 868-889 (emphasis added).

This unidirectional understanding of “phase difference” is consistent with the usage of the term throughout 

the claims. Claim 10 recites the following steps:

determining a phase difference between an input 

clock signal and a feedback clock signal;

maintaining the phase difference between the input 

clock signal and the feedback clock signal [within] 

approximately 180 ̊, including adjusting the input 

clock signal with a loop comprising a phase detector, shift register, and delay line when the determined phase difference is less than approximately 

180 ̊; and

delaying the input clock signal to compensate for 

the phase difference, wherein a number of delay 

cells utilized is reduced by approximately one-half. 

’507 patent, col. 4 ll. 49–59 (emphasis added). The “phase 

difference” determined in the first step is the antecedent 

for the “phase difference” in the subsequent steps, and thus 

the claim term should be construed to have a consistent 

meaning, including with respect to directionality, in each 

step. See Phonometrics, Inc. v. Northern Telecom Inc., 133 

F.3d 1459, 1465 (Fed. Cir. 1998) (“A word or phrase used 

consistently throughout a claim should be interpreted consistently.”). The steps of determining a phase difference, 

maintaining a phase difference within a given range, and 

adjusting the input signal based on the determined 

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PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD. 7

difference all indicate that the “phase difference” recited in 

the claim is meant to be a single measurable value: the 

term should not be construed to encompass two different 

“phase differences.” Moreover, the phrase “delaying the input clock signal to compensate for the phase difference” indicates that the phase difference refers to the lag of the 

feedback clock behind the input clock. As a matter of common usage, if I say that I am delaying Clock A to compensate for the time difference between Clock A and Clock B, I 

am implying that Clock B is behind Clock A. 

Additional intrinsic evidence supports the construction 

of “phase difference” as unidirectional. In particular, the 

’507 patent teaches that maintaining the phase difference 

within 180 ̊ by inverting (or shifting by 180 ̊) the input signal when the phase difference is greater than 180 ̊ reduces

the length of the delay line needed to compensate for the 

phase difference. ’507 patent, col. 3 ll. 7-18; col. 4 ll. 35-42. 

This only makes sense if the “phase difference” at each step 

is consistently measured in one direction.

III

Neither the Board nor the Majority refute or even engage with this analysis in arriving at the plain meaning of

the claim language. Indeed, when the Board revised its 

construction of “maintaining a phase difference . . . [within]

approximately 180 ̊” in its Final Written Decision, the 

Board pointed to nothing in the ’507 patent that indicated

a bi-directional usage of “phase difference.” Rather, the decision reframed the facial ambiguity identified in its institution decision as linguistic clarity: “The words of the claim 

are clear in not specifying which signal leads or lags.” J.A. 

17 (emphasis added). The Board then proceeded to explain 

why the intrinsic evidence supporting a directional limitation does not amount to “express disavowal” justifying “rewriting” of the claims. Id.

The majority relies on essentially the same reasoning. 

Citing only to the text of the “maintaining” limitation, and 

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8 PROMOS TECHS., INC. v. SAMSUNG ELECS. CO., LTD.

without any further discussion, the opinion concludes in a 

single sentence that neither claim 8 nor claim 10 “states or 

implies that the phase difference between the two signals 

is calculated by how much the feedback signal ‘follows’ or 

lags behind the input signal.” Slip op. 13. The opinion then 

proceeds to search the intrinsic evidence for lexicography 

or disavowal, and ultimately finds none. But if the skilled 

artisan would understand the plain and ordinary meaning 

of “phase difference” in the context of the patent to be unidirectional, then the patentee need not include additional 

verbiage to narrow the scope of its claims from some other 

broader meaning. Ultimately, nowhere does the majority 

conduct the principal analysis of determining the plain and 

ordinary meaning of the claim language, including the 

words “phase difference,” in the context of the patent. This 

is error. 

Nothing in the majority’s remaining analysis mitigates 

this deficiency. The mere fact that another independent 

claim, claim 13, recites “determining whether a feedback 

clock signal in the DLL follows within a 180° phase difference behind an input clock signal” does not contradict the 

consistent directionality of the “phase difference” described 

throughout the patent. Slip op. at 15 (quoting ’507 patent, 

col. 4 l. 66–col. 5 l. 10). We have previously acknowledged 

that a patentee’s choice to use different, though similar, 

words for corresponding limitations in different claims 

“does not mandate different interpretations of the two limitations . . . .” Kraft Foods, Inc. v. Int’l Trading Co., 203 

F.3d 1362, 1368 (Fed. Cir. 2000) (internal quotations and 

citation omitted). Here, in particular, the use of the words 

“follows” and “behinds” in one claim and not others does 

not implicate the doctrine of claim differentiation because 

the claims contain different steps that confer different 

claim scope separate and apart from the language at issue. 

Cf., id. at 1366 (noting that the doctrine of claim differentiation is based on the presumption that two claims in the 

same patent have different claim scope). 

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Likewise, a bi-directional construction of “phase difference” cannot rest on the conclusion that the construction 

does not always render the “maintaining” limitation superfluous and meaningless. Slip Op. 17-19. More relevant 

here is the canon that in cases of genuine ambiguity, claims 

are to be construed in favor of preserving validity. Ruckus, 

824 F.3d at 1004 (citing Phillips, 415 F.3d at 1327). Here, 

except in those circumstances where the “maintaining” 

limitation is functionally meaningless, the majority’s bi-directional reading of “phase difference” renders the claims 

at issue indefinite because it encompasses two different 

ways of determining the phase difference with no guidance 

on which to apply for any given claim, precluding a skilled 

artisan from discerning with “reasonable certainty” 

whether the “maintaining” limitation is satisfied. See Teva 

Pharms. USA, Inc. v. Sandoz, Inc., 789 F.3d 1335, 1345 

(Fed. Cir. 2015).

Ultimately, there is sometimes a fine line between “using the specification to interpret the meaning of a claim 

and importing limitations from the specification into the 

claim.” Phillips, 415 F.3d at 1323; Intervet Am., Inc. v. 

Kee–Vet Labs., Inc., 887 F.2d 1050, 1053 (Fed. Cir. 1989) 

(cautioning against confusing “interpreting what is meant 

by a word in a claim” with “adding an extraneous limitation 

appearing in the specification”). Here, the Board avoided 

its obligation to engage in the former task by mistaking it 

for the latter. The majority joins the Board in misjudging 

the line. 

For these reasons, I would reverse the Board’s claim 

construction. Because Samsung has made no argument

that the invalidation of the claims at issue could be affirmed under ProMOS’s construction, I would reverse the 

invalidation of those claims as well. 

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