Greenthread, LLC v. Cirrus Logic, Inc.

Greenthread, LLC v. Cirrus Logic, Inc. is a patent infringement lawsuit filed in the U.S. District Court for the Western District of Texas. The plaintiff, Greenthread, LLC, is identified as a Texas-based non-practicing entity (NPE) or patent assertion entity (PAE) that primarily asserts semiconductor fabrication patents originating from inventor G.R. Mohan Rao, who is also a director of Greenthread. These assertions are reportedly backed by a funder new to patent monetization, Empyrean Capital Partners, LP. The defendant, Cirrus Logic, Inc., is a Texas-based chip designer specializing in low-power, mixed-signal processing technology and components. The litigation targets Cirrus Logic's semiconductor products, specifically identifying the CLI1793B1 power management integrated circuit as an accused product in related PTAB proceedings. The lawsuit asserts U.S. Patent No. 11,316,014, among others. This patent, like others in Greenthread's portfolio, generally relates to "graded junction semiconductor components for improved performance" or "semiconductor devices with graded dopant regions" that create electric fields for managing carrier movement within integrated semiconductor devices.

The case, filed on March 31, 2023, is pending in the Western District of Texas under Judge David Counts, with Magistrate Judge Derek T. Gilliland also assigned. The Western District of Texas has been a popular venue for patent litigation, often noted for its plaintiff-friendly docket and speed to trial, though the specific judge (Judge Counts) might influence procedural timelines.

This case is notable due to Greenthread's broader pattern of asserting its semiconductor patent portfolio against major technology companies. Greenthread has initiated multiple lawsuits against companies like Intel, Samsung, Texas Instruments, ON Semiconductor, Western Digital, and Monolithic Power Systems, making it a significant player in semiconductor patent assertions. A key development in this specific litigation is that Cirrus Logic successfully challenged the asserted patents at the Patent Trial and Appeal Board (PTAB). Between October and November 2025, the PTAB issued seven Final Written Decisions in Inter Partes Reviews (IPRs) filed by Cirrus Logic, finding all challenged claims from six of Greenthread's patents, including U.S. Patent No. 11,316,014, to be unpatentable. Greenthread intends to file requests for Director Review of these PTAB decisions. This IPR linkage and the subsequent invalidation of claims significantly impact the trajectory and noteworthiness of the district court litigation. The district court case had been stayed pending the IPR outcomes.

Legal Developments and Case Outcome

As of the present date, the district court litigation between Greenthread and Cirrus Logic is effectively neutralized, pending a long-shot appeal by Greenthread. The case has been stayed since September 2025, following the complete invalidation of all asserted patent claims by the U.S. Patent Trial and Appeal Board (PTAB).

Here is a chronological summary of key legal developments:

Filing and Initial Pleadings

• 2023-03-31: Greenthread, LLC files its patent infringement complaint against Cirrus Logic, Inc. in the U.S. District Court for the Western District of Texas. The case is assigned to Judge David Counts. The suit initially asserts seven patents, including U.S. Patent No. 11,316,014.
• 2023-06-09: Cirrus Logic files its Answer, denying infringement and asserting counterclaims for non-infringement and invalidity of the asserted patents.

Parallel PTAB Proceedings and Motion to Stay

• 2023-10-11 to 2023-10-27: Cirrus Logic files seven Inter Partes Review (IPR) petitions with the PTAB, challenging the validity of all asserted claims across the six patents remaining in the case. The petition challenging U.S. Patent No. 11,316,014 was filed on October 27, 2023, and assigned case number IPR2024-00019. Other defendants in Greenthread's broader litigation campaign, such as OmniVision and ON Semiconductor, also filed IPRs against Greenthread's portfolio.
• 2023-11-09: Citing its filed IPR petitions, Cirrus Logic files a motion to stay the district court case pending the PTAB's decisions on whether to institute the reviews.
• 2024-05-03: The PTAB institutes trial on all seven of Cirrus Logic's IPR petitions, including IPR2024-00019 against the '014 patent, finding a reasonable likelihood that Cirrus Logic would prevail in showing the claims were unpatentable.
• 2025-09-16: Following the PTAB's institution decisions, the district court grants the motion to stay the case pending the outcome of the IPR proceedings. This order effectively pauses all district court activity, including claim construction and discovery, pending the PTAB's final written decisions.

Claim Construction (Markman)

• The case was stayed before a formal Markman hearing or ruling occurred. However, the parties had exchanged claim construction briefs. For instance, on December 14, 2023, Greenthread filed a responsive claim construction brief (Dkt. 37), referencing prior constructions of similar terms from other litigations involving its patent portfolio, notably against Intel. The parties' arguments and proposed constructions were also presented within the context of the IPR proceedings.

PTAB Final Decisions and Current Posture

• 2025-10-29 to 2025-11-07: The PTAB issues seven Final Written Decisions (FWDs) covering all pending IPRs between Cirrus Logic and Greenthread. The Board finds all challenged claims of the six asserted patents, including claims 1–9 and 12–28 of the '014 patent, to be unpatentable.
• 2025-11-14: The parties file a Joint Status Report in the district court, notifying Judge Counts of the PTAB's decisions. In this filing, Greenthread states its intention to request Director Review of all seven adverse FWDs.
• Late Nov / Early Dec 2025: Greenthread's deadlines to file for Director Review of the PTAB decisions fall in this period.
• 2026-01-16 to 2026-01-26 (Anticipated): In the November 14 status report, the parties jointly estimate that decisions on the Director Review requests could be expected in mid-to-late January 2026. They request that the court-ordered stay remain in place and ask for a deadline to request a status conference seven days after the first Director Review decision is issued.

Outcome and Current Status
The litigation is currently stayed and has been rendered largely moot by the PTAB's wholesale invalidation of the asserted patent claims. Unless Greenthread succeeds in overturning the PTAB's decisions through the highly discretionary Director Review process or a subsequent appeal to the Federal Circuit, the district court case will likely be dismissed with prejudice. Cirrus Logic has achieved a comprehensive victory at the PTAB, which has effectively halted Greenthread's litigation campaign against it and other semiconductor companies on this portfolio of patents. The case remains technically pending but is inactive, awaiting the final resolution of the PTAB appeals.

Plaintiff's Counsel of Record: Greenthread, LLC

Greenthread, LLC has retained a team of attorneys from several law firms, a common strategy in patent assertion campaigns. The team combines attorneys from firms known for representing non-practicing entities (NPEs) with local counsel fulfilling the court's admission requirements.

LEAD COUNSEL

• Name: Jonathan K. Waldrop (Lead Attorney)

  • Firm: Kasowitz Benson Torres LLP (Redwood Shores, CA)
  • Note: Waldrop is a prominent patent litigator and managing partner of Kasowitz's Silicon Valley office, known for representing patent owners in high-stakes technology cases.

• Name: Darcy L. Jones

  • Firm: Kasowitz Benson Torres LLP (Redwood Shores, CA)
  • Note: Jones is a partner at Kasowitz who frequently litigates alongside Jonathan Waldrop, focusing on complex patent cases in district courts and the ITC.

• Name: Chad N. Pahnke

  • Firm: Kasowitz Benson Torres LLP (Redwood Shores, CA)
  • Note: Pahnke is a partner at Kasowitz with extensive experience in patent litigation involving semiconductor technology, software, and telecommunications.

• Name: Marcus A. Barber

  • Firm: Kasowitz Benson Torres LLP (Redwood Shores, CA)
  • Note: Barber is a partner at Kasowitz specializing in intellectual property litigation, with a focus on patent disputes.

ADDITIONAL COUNSEL

• Name: Stamatios Stamoulis

  • Firm: Stamoulis & Associates LLC (Wilmington, DE)
  • Note: Stamoulis's firm specializes in representing patent holders in infringement litigation, often on a contingent-fee basis, and frequently appears in major patent venues.

• Name: Richard C. Weinblatt

  • Firm: Stamoulis & Associates LLC (Wilmington, DE)
  • Note: Weinblatt is an attorney at Stamoulis & Associates, regularly appearing in patent cases alongside Stamatios Stamoulis.

LOCAL COUNSEL

• Name: S. Calvin Capshaw (Local Counsel)

  • Firm: Capshaw DeRieux LLP (Longview, TX)
  • Note: Capshaw is a well-known and prolific local counsel in Texas patent litigation, having represented numerous plaintiffs in the Eastern and Western Districts of Texas.

• Name: Elizabeth L. DeRieux (Local Counsel)

  • Firm: Capshaw DeRieux LLP (Longview, TX)
  • Note: DeRieux is a founding partner of the firm and frequently serves as local counsel with S. Calvin Capshaw in Texas patent infringement cases.

Defendant's Counsel of Record: Cirrus Logic, Inc.

Cirrus Logic, Inc. is represented by a team of attorneys from Morrison & Foerster LLP, a large international law firm known for its intellectual property practice, and Darrow Mustafa PC, an IP specialty firm. They also utilize local Texas counsel from Kelly Hart & Hallman LLP.

Notably, while one of the local counsel attorneys of record, J. Stephen Ravel, passed away in early 2023, he has not been formally terminated from the docket as of the most recent filings.

LEAD COUNSEL

• Name: Brian C. Nash

  • Firm: Morrison & Foerster LLP (Austin, TX)
  • Note: Nash co-chairs the firm's global IP Litigation Group and is the Austin office's managing partner, with extensive experience in over 250 IP cases, including many in the Western District of Texas.

• Name: Mark A. Hannemann

  • Firm: Troutman Pepper (formerly Kenyon & Kenyon) (New York, NY)
  • Note: While court filings may not explicitly designate him as lead, Hannemann has over 25 years of experience leading high-stakes patent litigation for major technology companies and has first-chair trial experience.

ADDITIONAL COUNSEL

• Name: John A. Lingl

  • Firm: Darrow Mustafa PC (Northville, MI)
  • Note: Lingl is an executive partner at his firm with significant experience in patent prosecution and litigation involving semiconductor, software, and automotive technologies.

• Name: Harry Vartanian

  • Firm: Darrow Mustafa PC (Northville, MI)
  • Note: Vartanian is a registered patent attorney and former USPTO patent examiner whose practice focuses on patent prosecution and litigation support in telecommunications and software.

LOCAL COUNSEL

• Name: J. Stephen Ravel (Deceased)
  • Firm: Kelly Hart & Hallman LLP (Austin, TX)
  • Note: Ravel was a highly experienced Texas trial lawyer who specialized in defending technology companies in patent litigation within the Western District of Texas; he passed away in February 2023.

IN-HOUSE COUNSEL

• Name: G. Scott Thomas
  • Role: Senior Vice President, General Counsel, and Corporate Secretary
  • Firm: Cirrus Logic, Inc. (Austin, TX)
  • Note: Thomas has served as General Counsel since 2003 and has a background as an electrical engineer at Texas Instruments and AT&T Bell Labs and as an IP litigator at major firms.