PTAB

IPR2020-01336

Xilinx Inc v. Analog Devices Inc

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Common-Mode Circuits with Error Correction
  • Brief Description: The ’463 patent discloses common-mode circuits, such as differential amplifiers, that employ a switched-capacitor feedback circuit to reduce common-mode error gain. The invention adds an "error correcting" or "impedance matching" circuit to compensate for errors like charge injection and common-mode error gain variation introduced by the feedback components.

3. Grounds for Unpatentability

Ground 1: Claims 1, 2, 4, 6, 11, 13, and 29 are obvious over Oliaei.

  • Prior Art Relied Upon: Oliaei (Patent 6,697,001).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Oliaei alone discloses every element of the challenged claims. Oliaei teaches a differential amplifier with a switched-capacitor common-mode feedback circuit (circuit 500) that operates in two clock phases, functionally identically to the "common-mode corrector circuit" of the ’463 patent. During a first phase, feedback capacitors are connected to the amplifier output, and precharging capacitors are charged to a reference voltage. In a second phase, the precharging and feedback capacitors are connected in parallel to adjust the feedback signal. Furthermore, Petitioner asserted that Oliaei’s Figure 6 discloses a symmetric version of this circuit (circuit 600) which constitutes the claimed "error correcting circuit." This symmetric circuit adds balancing capacitors (608, 609) and switches to maintain a constant capacitive load across both clock phases, thereby minimizing common-mode error gain variation and adjusting the signal offset level as claimed.
    • Motivation to Combine (for §103 grounds): This ground is based on a single reference. However, Petitioner argued that a person of ordinary skill in the art (POSITA) would have been motivated to use Oliaei's symmetric circuit from Figure 6 in the system of Figure 10 because Oliaei expressly teaches they are interchangeable embodiments ("Embodiments 500, 600...are shown in FIG. 5 and FIG. 6") and notes the advantage of the symmetric circuit is maintaining a constant amplifier capacitive load, a known goal for improving stability and bandwidth.

Ground 2: Claims 1-7, 10-17, and 29 are obvious over Oliaei in view of Vittoz.

  • Prior Art Relied Upon: Oliaei (Patent 6,697,001) and Vittoz ("Design of VLSI Circuits for Telecommunications and Signal Processing," a 1994 publication).
  • Core Argument for this Ground:
    • Prior Art Mapping: As an alternative to Ground 1, Petitioner argued that even if a POSITA did not recognize Oliaei's symmetric circuit as a complete "error correcting circuit," it would have been obvious to combine Oliaei's base circuit with the teachings of Vittoz. Oliaei provides the foundational common-mode circuit with a switched-capacitor feedback loop (circuit 500). Vittoz, which Petitioner characterized as providing "textbook knowledge," explicitly teaches methods to compensate for charge injection in switched-capacitor circuits. These methods include adding balancing capacitors on either side of a switch to equalize impedance and using half-sized "dummy switches" to absorb injected charge. Petitioner contended that applying Vittoz's well-known error correction techniques to Oliaei's circuit results in a configuration that meets all limitations of the claimed "error correcting" and "impedance matching" circuits.
    • Motivation to Combine (for §103 grounds): A POSITA would combine these references for several reasons. Oliaei expressly states its circuit should be "immune to the large amount of noise inherent to the switching environment," providing a clear motivation to seek a solution. Vittoz provides that solution, teaching established techniques to mitigate charge injection, a primary source of such noise. The combination involved applying a known technique (from Vittoz) to a known device (Oliaei's circuit) to solve a known problem, yielding predictable results. Petitioner also framed this as an "obvious to try" scenario, as there was a recognized need and a finite number of well-documented, predictable solutions for charge injection compensation.
    • Expectation of Success: A POSITA would have had a high expectation of success. The principles of charge injection and the efficacy of compensation techniques like balancing capacitors and dummy switches were well-understood and documented long before the ’463 patent's priority date. Applying these standard techniques from Vittoz to the conventional switched-capacitor circuit in Oliaei would predictably reduce noise and improve circuit performance.

4. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1-7, 10-17, and 29 of the ’463 patent as unpatentable.