PTAB

IPR2020-00556

NXP USA Inc v. Impinj Inc

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Petition

1. Case Identification

2. Patent Overview

  • Title: Interference Rejection in RFID Tags
  • Brief Description: The ’504 patent describes methods and circuits for Radio Frequency Identification (RFID) tags that filter out interference. The technology aims to reject distortion in a received RF signal by identifying and removing "artifact features" (e.g., spurious digital pulses caused by noise) from the demodulated signal before processing.

3. Grounds for Unpatentability

Ground 1: Obviousness over Shanks in view of Breimesser - Claims 1-2, 4, 7, and 13 are obvious over Shanks in view of Breimesser.

  • Prior Art Relied Upon: Shanks (Application # 2002/0152044) and Breimesser (Patent 3,997,798).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Shanks discloses an RFID tag circuit that receives and demodulates a wireless RF signal into a sequence of digital pulses. However, Shanks’s design is susceptible to interference, as it interprets all pulses below a certain duration, including short noise pulses, as valid data bits. Breimesser was cited for its teaching of an interference rejection circuit that "gates out" (i.e., filters) digital pulses whose duration is shorter than a predetermined minimum test period. Petitioner asserted that the combination involves feeding the digital output from Shanks's demodulator into Breimesser's filtering circuit. This combined circuit would derive a second, filtered output signal by removing pulses with durations (represented by "artifact numbers") less than a "first low number" corresponding to Breimesser's test period, while retaining valid pulses longer than that threshold.
    • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine Shanks and Breimesser to solve a known problem in Shanks—its susceptibility to misinterpreting short noise pulses as valid data, which degrades performance. Breimesser provides a known, off-the-shelf solution by explicitly teaching a circuit for "gating out interference signals of shorter duration than the useful signal." The combination represents the use of a known technique to improve a known device, addressing a specific need in Shanks to filter spurious short pulses.
    • Expectation of Success: Petitioner contended that a POSITA would have had a reasonable expectation of success. Combining the circuits was described as a straightforward modification that would predictably yield improved performance by eliminating noise pulses that Shanks's circuit would otherwise fail to filter.

Ground 2: Obviousness over Shanks, Breimesser, and Lichtblau - Claims 8-10, 14–15, 17–19, and 21 are obvious over Shanks in view of Breimesser and in further view of Lichtblau.

  • Prior Art Relied Upon: Shanks (Application # 2002/0152044), Breimesser (Patent 3,997,798), and Lichtblau (Patent 4,779,077).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground builds upon the Shanks and Breimesser combination by adding Lichtblau to address limitations related to filtering pulses that are too long. While Breimesser teaches filtering pulses shorter than a minimum threshold, Lichtblau discloses a "pulse train processor" that is responsive to both a minimum and a maximum pulse duration. Petitioner argued that Lichtblau teaches adding a second test period to filter out pulses longer than a maximum expected duration. This corresponds to the challenged dependent claims, which require removing pulses with artifact numbers greater than a "first high number" (corresponding to a second, maximum time duration threshold).
    • Motivation to Combine: A POSITA, having addressed the problem of short interference pulses by applying Breimesser's teachings, would also be motivated to filter longer pulses arising from interference to make the system more robust. Lichtblau provides a known solution for filtering pulses that exceed a maximum duration. A POSITA would have found it obvious to modify the Shanks/Breimesser circuit to incorporate Lichtblau's teachings to create a more comprehensive band-pass filter for pulse durations, thereby rejecting noise pulses that are either too short or too long.
    • Expectation of Success: Petitioner argued that a POSITA would have reasonably expected success in this combination. The modification involves combining known prior art elements (a minimum duration filter and a maximum duration filter) according to conventional methods to yield a predictable result: a circuit that rejects a wider range of interference signals and offers improved performance.

4. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1–2, 4, 7–10, 13–15, 17–19, and 21 of the ’504 patent as unpatentable.