NXP USA Inc v. Impinj Inc

1. Case Identification

• Patent #: 8,344,857
• Filed: February 10, 2020
• Petitioner(s): NXP USA, Inc.
• Patent Owner(s): Impinj, Inc.
• Challenged Claims: 1-15

2. Patent Overview

• Title: RFID Tags with Synchronous Power Rectifier
• Brief Description: The ’857 patent relates to power rectifier circuits for Radio Frequency Identification (RFID) tags. The disclosed invention is a multi-stage synchronous power rectifier constructed from complementary MOS transistors, designed to harvest energy from an RF signal and convert it to a DC voltage to power the tag.

3. Grounds for Unpatentability

Ground 1: Claims 1-15 are obvious over the Mandal Thesis

• Prior Art Relied Upon: Mandal Thesis (Soumyajit Mandal, Far Field RF Power Extraction Circuits and Systems, M.S. thesis, June 2004).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that the Mandal Thesis teaches every element of the challenged claims. The thesis discloses designing high-frequency, low-power RFID circuits with a focus on efficient power harvesting. It explicitly teaches cascading multiple four-transistor rectifier cells (Fig. 3-3) in series to create a multi-stage rectifier that obtains larger DC voltages (Fig. 3-6). The thesis also teaches using floating-gate transistors (Fig. 3-17) as an alternative to standard MOS transistors to improve rectifier performance by reducing threshold voltages. Petitioner contended that combining these teachings, along with the disclosed antenna design (Fig. 4-10), results in the apparatus claimed in the ’857 patent. The arguments for dependent claims followed this logic, asserting that features like a "third transistor" (zeroth stage) or parasitic "averaging-node" capacitors are inherent or obvious modifications of the core disclosed circuit.
  • Motivation to Combine (for §103 grounds): Petitioner asserted that the Mandal Thesis itself provides the motivation for a person of ordinary skill in the art (POSITA) to combine its teachings. The primary motivations stated were the explicit goals of creating an efficient method for DC power extraction, the express suggestion to cascade rectifier cells to "obtain large DC voltages," and the teaching that floating-gate structures can be used to improve rectifier performance.
  • Expectation of Success (for §103 grounds): Petitioner argued that a POSITA would have had a reasonable expectation of success because the Mandal Thesis provides a detailed roadmap, including design theory, circuit diagrams, and experimental results for creating the very type of power extraction system claimed.

Ground 2: Claims 1-15 are anticipated by the Mandal ’947 Patent

• Prior Art Relied Upon: Mandal ’947 Patent (Patent 8,045,947).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that the Mandal ’947 patent, which shares an inventor with the Mandal Thesis, anticipates every limitation of claims 1-15. The ’947 patent discloses a far-field power extraction circuit for RFID tags that includes a multi-stage rectifier (Fig. 18). This rectifier is composed of rectifier cells that may be the four-transistor type (Fig. 24) or, critically, a floating-gate version (Fig. 25) that improves performance. Petitioner contended that the ’947 patent’s figures and description disclose the complete claimed structure, including the specific arrangement of complementary NMOS and PMOS transistors, antenna inputs, and capacitive coupling. The petition also argued that a POSITA would understand how to "unzip" the disclosed differential rectifier into two single-ended rectifiers, thereby disclosing all claimed configurations. It was asserted that any minor inconsistencies, such as a typo in a circuit diagram (Fig. 18), would be recognized and understood by a POSITA.

4. Arguments Regarding Discretionary Denial

• Petitioner argued that an inter partes review (IPR) should not be foreclosed under 35 U.S.C. §325(d). While a related patent (Mandal ’090 Patent) was before the examiner during prosecution of a parent application, Petitioner asserted that the Mandal Thesis and the Mandal ’947 patent relied upon in this petition contain additional and different information. Specifically, it was argued that these references disclose every element of the challenged claims, unlike the reference previously considered by the examiner.

5. Relief Requested

• Petitioner requests the institution of an IPR and cancellation of claims 1-15 of Patent 8,344,857 as unpatentable.