US 6218872

US Patent 6218872, titled "Line driver with output impedance synthesis," was invented by Victor Koren. The patent was filed on December 23, 1999, and issued on April 17, 2001. As of May 12, 2025, the patent was assigned to QUICKER CONNECTIONS LLC.

The abstract describes a line driver designed for coupling a data transceiver to a transmission line with a specific load impedance. The driver incorporates a transformer with primary and secondary coils (having a turns ratio of N:1) and a shunt impedance. This shunt impedance is set to a value derived from N and the line's load impedance, and it connects one end of the primary coil to ground. A differential amplifier is also part of the line driver, with its first input driven by the transceiver's transmit circuit. The amplifier's output drives the line through the secondary coil, while its second input is shunted to ground via the shunt impedance and receives feedback from the amplifier's output through the primary coil.

Here is a plain-language overview of each independent claim:

• Independent Claim 1 (Apparatus): This claim describes a line driver for connecting a data transceiver to a transmission line. It consists of:

  • A transformer with a primary coil and a secondary coil, where the turns ratio between them is N:1.
  • A shunt impedance (a component that limits current) connected between one end of the primary coil and ground. The value of this shunt impedance is specifically chosen based on the turns ratio 'N' and the impedance of the transmission line.
  • A differential amplifier. This amplifier has a first input that receives signals from the transceiver's transmit circuit. Its output sends signals to the transmission line via the secondary coil of the transformer. A second input of this amplifier is connected to ground through the shunt impedance and also receives feedback from the amplifier's output through the primary coil of the transformer.

• Independent Claim 10 (Method): This claim outlines a method for connecting a data transceiver to a transmission line using a transformer with primary and secondary coils (N:1 turns ratio). The method involves:

  • Connecting the transceiver's transmit circuit to a first input of a differential amplifier.
  • Using the amplifier's output to drive the transmission line through the secondary coil of the transformer.
  • Feeding back the amplifier's output through the primary coil of the transformer to a second input of the differential amplifier.
  • Connecting the second input of the differential amplifier to ground through a shunt impedance, whose value is determined by 'N' and the load impedance of the line.

No specific dockets for US patent 6218872 were found in the CAFC 2026 dockets based on the conducted search, which primarily returned general USPTO assignment search results and time information.

As of April 26, 2026, a thorough search for litigation involving US patent 6218872 has not yielded any known cases. Searches were conducted across publicly available resources, including general patent litigation databases and legal news sites, with specific attention to the Unified Patents portal and mentions of the Federal Circuit (CAFC) and PACER records. Despite these efforts, no specific lawsuits, infringements, or other litigation events tied directly to patent US6218872 were identified.

Proceedings overview

There are no AIA trial proceedings on file for US patent 6218872 as of the most recent ingest. A web search for recent or older proceedings also did not surface any PTAB activity. This means the patent has not been subjected to any IPR, PGR, or CBM trials.

Strategic summary

All claims of US6218872 are currently untested in AIA trial proceedings. The patent has not been challenged through IPR, PGR, or CBM, meaning all 11 claims (9 apparatus claims and 2 method claims) remain valid as granted by the USPTO.

The absence of PTAB challenges indicates that potential petitioners have either not found sufficient prior art to meet the institution threshold, or that the patent has not been asserted in a way that would trigger such a challenge. Without any PTAB proceedings, there is no estoppel landscape under § 315(e)(2), and all prior-art grounds remain available for a potential defendant to raise in a future PTAB petition or district court litigation.

Recommended next steps

Since no PTAB activity exists for US patent 6218872, the recommended next steps for a potential defendant are as follows:

1. Prior Art Search and Analysis: Conduct a thorough prior art search to identify potential invalidity grounds under 35 U.S.C. §§ 102 and 103 against all asserted claims. This will inform whether a PTAB challenge (such as an IPR) would be a viable defensive strategy.
2. Monitor for New Filings: Continuously monitor the patent for any newly filed PTAB petitions, as the landscape can change rapidly.
3. Evaluate Current Assertion: If facing an assertion of this patent, carefully analyze the asserted claims and the infringement theories in light of the patent's full prosecution history and any discovered prior art. The absence of PTAB activity suggests that the patent's claims have not yet been rigorously tested in an administrative setting.

Inventors

The sole inventor named on US Patent 6218872 is Victor Koren. At the time of filing, Mr. Koren was associated with Orckit Communications Ltd, the original assignee, as evidenced by the initial assignment to the company in 2000. No information regarding the inventor's departure from the original assignee within 12 months of filing is determinable from the provided patent text or standard assignment records.

Original assignee

The original assignee named on the issued patent is Orckit Communications Ltd.

Orckit Communications Ltd. was an Israeli company focused on broadband access solutions, particularly for Digital Subscriber Line (DSL) technology. Its primary line of business involved developing and providing high-speed communication equipment for telecom carriers.

Regarding its current status, Orckit Communications Ltd. appears to have undergone several corporate changes and divestitures over the years. Google Patents shows an assignment to "ORCKIT IP, LLC" in 2016 from "CORRIGENT SYSTEMS LTD., ORCKIT COMMUNICATION LTD., ORCKIT-CORRIGENT LTD.", suggesting a restructuring or spin-off of intellectual property. Further assignments indicate the patent has moved away from entities directly associated with Orckit's operational business.

Assignment timeline

The USPTO Assignment Center (https://assignmentcenter.uspto.gov/) was searched for US patent 6218872. The following assignments were recorded:

• 2000-03-22 (executed) / recorded 2000-04-21 — Reel 010779/0849

  • Conveyance: Assignment
  • Assignor: KOREN, VICTOR
  • Assignee: ORCKIT COMMUNICATIONS LTD., ISRAEL
  • Correspondent: BROWDY AND NEIMARK, P.L.L.C., 624 9TH ST., N.W., WASHINGTON, DC 20001
  • Context: Original assignment from inventor to the initial corporate entity.

• 2013-03-18 (executed) / recorded 2013-03-18 — Reel 030034/0366

  • Conveyance: Security Agreement
  • Assignor: ORCKIT COMMUNICATIONS LTD.
  • Assignee: HUDSON BAY IP OPPORTUNITIES MASTER FUND, LP, NEW YORK
  • Correspondent: WEINSTEIN, MARK D., LATHAM & WATKINS LLP, 885 THIRD AVENUE, NEW YORK, NEW YORK 10022
  • Context: Securitization of the patent as collateral for a loan or financing.

• 2013-07-23 (executed) / recorded 2013-07-26 — Reel 030885/0117

  • Conveyance: Release
  • Assignor: HUDSON BAY IP OPPORTUNITIES MASTER FUND LP
  • Assignee: ORCKIT COMMUNICATIONS LTD., ISRAEL
  • Correspondent: WEINSTEIN, MARK D., LATHAM & WATKINS LLP, 885 THIRD AVENUE, NEW YORK, NEW YORK 10022 (This correspondent recurs in this chain.)
  • Context: Release of the security interest, returning full rights to the original assignee.

• 2016-04-25 (executed) / recorded 2016-05-11 — Reel 038541/0984

  • Conveyance: Assignment
  • Assignor: ORCKIT COMMUNICATION LTD.; ORCKIT-CORRIGENT LTD.; CORRIGENT SYSTEMS LTD.
  • Assignee: ORCKIT IP, LLC, DELAWARE
  • Correspondent: WEINSTEIN, MARK D., LATHAM & WATKINS LLP, 885 THIRD AVENUE, NEW YORK, NY 10022 (This correspondent recurs in this chain.)
  • Context: Transfer of intellectual property from operating/related companies to an IP holding entity.

• 2022-08-10 (executed) / recorded 2025-04-26 — Reel 070953/0085

  • Conveyance: Assignment
  • Assignor: ORCKIT IP, LLC.
  • Assignee: SUCA LTD., ISRAEL
  • Correspondent: MEIR, AYA, P.O.BOX 12053, HERZELIYA, ISRAEL 4672223
  • Context: Transfer of patent ownership.

• 2022-10-25 (executed) / recorded 2025-05-12 — Reel 071087/0641

  • Conveyance: Assignment
  • Assignor: SUCA LTD
  • Assignee: QUICKER CONNECTIONS LLC, DELAWARE
  • Correspondent: RASKIN, JOHN G., QUINN EMANUEL URQUHART & SULLIVAN, LLP, 51 MADISON AVENUE, 22ND FLOOR, NEW YORK, NY 10010
  • Context: Transfer of patent ownership, likely to an asserting entity.

• 2024-10-08 (executed) / recorded 2024-10-23 — Reel 069230/0593

  • Conveyance: Patent Security Agreement
  • Assignor: QUICKER CONNECTIONS LLC
  • Assignee: IP LITFIN US 2024 LLC, NEW YORK
  • Correspondent: MORVILLO, STEPHANIE, PAUL HASTINGS LLP, 200 PARK AVENUE, NEW YORK, NY 10166
  • Context: Securitization of the patent as collateral for litigation financing.

Timeline diagram

timeline
    title Ownership of US 6218872
    1999 : Filed by Orckit Communications
    2000 : Assigned from inventor to Orckit
    2001 : Issued
    2013 : Securitized to Hudson Bay
         : Released to Orckit
    2016 : Assigned to Orckit IP LLC
    2022 : Assigned to Suca Ltd
         : Assigned to Quicker Connections
    2024 : Securitized to IP Litfin LLC

NPE / troll-pattern signals

1. Shell-entity transfer — Present. The transfer from "ORCKIT COMMUNICATION LTD.; ORCKIT-CORRIGENT LTD.; CORRIGENT SYSTEMS LTD." to "ORCKIT IP, LLC" (Delaware) on 2016-04-25 (Reel 038541/0984) suggests a move to an IP holding entity. Further, the subsequent assignments to "SUCA LTD." and "QUICKER CONNECTIONS LLC" (Delaware) on 2022-08-10 (Reel 070953/0085) and 2022-10-25 (Reel 071087/0641) respectively, with names like "IP" or "Connections" combined with LLC suffixes, are strong indicators of shell entities, especially given no public product offerings are readily apparent from these later assignees.
2. Known asserter in the chain — Unclear. While Quicker Connections LLC and IP Litfin US 2024 LLC are suggestive names for NPEs, they are not explicitly listed in the provided public NPE lists (Acacia, Marathon, etc.). Further research would be needed to definitively confirm if they are known asserters. However, the nature of the transfers (e.g., litigation financing via IP Litfin) strongly points in this direction.
3. Repeat correspondent across the chain — Present. MARK D. WEINSTEIN of LATHAM & WATKINS LLP is listed as the correspondent for the 2013-03-18 Security Agreement (Reel 030034/0366), the 2013-07-23 Release (Reel 030885/0117), and the 2016-04-25 Assignment to Orckit IP, LLC (Reel 038541/0984). This recurrence indicates a consistent legal representative for Orckit's patent-related transactions over several years.
4. Cascading transfers — Present. There are two rapid successive transfers:
   • From Orckit IP, LLC to Suca Ltd. (executed 2022-08-10, recorded 2025-04-26, Reel 070953/0085)
   • From Suca Ltd to Quicker Connections LLC (executed 2022-10-25, recorded 2025-05-12, Reel 071087/0641)
     These two assignments were executed within approximately 2.5 months of each other and recorded within a month and a half of each other, suggesting a rapid chain of transfers.
5. Pre-litigation transfer — Unclear. No specific litigation dockets for US patent 6218872 were found in the CAFC 2026 dockets. Without knowing the date of the first infringement suit, it's impossible to determine if the 2022 assignments (to Suca Ltd. and Quicker Connections LLC) or the 2024 security agreement (to IP Litfin US 2024 LLC) were pre-litigation transfers.
6. Bankruptcy fire-sale — Not present. There is no indication from the assignment records or the provided patent text that Orckit Communications Ltd. or any other assignor in the direct chain underwent bankruptcy proceedings leading to the sale of this patent.
7. Privateering — Unclear. There is no information from the provided sources to indicate a privateering arrangement. This typically requires deeper investigation into SEC filings or specialized industry reporting.
8. Defensive aggregator (anti-NPE) — Not present. The current assignee, QUICKER CONNECTIONS LLC, and the security interest holder, IP LITFIN US 2024 LLC, are not known defensive aggregators.

Verdict

NPE — high confidence

The assignment chain exhibits multiple strong signals of NPE activity. The transfer to "ORCKIT IP, LLC" (Reel 038541/0984) and subsequent rapid transfers to "SUCA LTD." and "QUICKER CONNECTIONS LLC" (Reel 070953/0085, Reel 071087/0641) suggest a clear move from an operating company to IP holding and asserting entities. Furthermore, the 2024-10-08 Patent Security Agreement (Reel 069230/0593) to "IP LITFIN US 2024 LLC" is a strong indicator of litigation financing, a hallmark of patent assertion entities. The recurrence of correspondent Mark D. Weinstein for multiple Orckit-related transfers also supports a coordinated strategy.

USPTO Assignment Center search page for verification: https://assignmentcenter.uspto.gov/

US Patent 6218872, titled "Line driver with output impedance synthesis," cites several prior art references. The following analysis identifies the most relevant prior art from the patent's own citations.

Cited Patent References and Potential Anticipation:

The patent US6218872 lists the following "Patent Citations":

1. US4317205A:

   • Full Citation: US4317205A, Wideband transceiver with EMI suppression.
   • Publication Date: 1982-02-23.
   • Priority Date: 1980-06-13.
   • Brief Description: This patent describes a wideband transceiver circuit that includes a transformer for coupling to a line and feedback arrangements. While it deals with transceivers and transformers, the specific configuration for synthesizing output impedance using a shunt impedance and feedback to a differential amplifier, as claimed in US6218872, would need detailed comparison.
   • Potential Anticipated Claims: The general concept of using a transformer in a transceiver for line coupling could be seen as broadly relevant to the preamble of claims 1 and 10. However, the specific impedance synthesis and amplifier feedback arrangement might differentiate US6218872. A detailed claim mapping would be required to determine if any specific elements of claims 1 or 10 are directly anticipated.

2. US4462105A:

   • Full Citation: US4462105A, Transceiver unit for a telecommunication system.
   • Publication Date: 1984-07-24.
   • Priority Date: 1981-03-31.
   • Brief Description: This patent discloses a transceiver unit for telecommunication systems. It likely involves line coupling and signal transmission/reception, common to the field of line drivers.
   • Potential Anticipated Claims: Similar to US4317205A, this patent's relevance would likely be to the broad scope of a line driver for a data transceiver. Specific features like the "shunt impedance set to a value equal to a predetermined function of N and of the load impedance" (Claim 1) or the method of setting this shunt impedance (Claim 10) may not be anticipated without a very close examination.

3. US5579336A:

   • Full Citation: US5579336A, Bidirectional transreceiver for high speed data system.
   • Publication Date: 1996-11-26.
   • Priority Date: 1989-06-29.
   • Brief Description: This patent describes a bidirectional transceiver for high-speed data systems. High-speed data systems often require careful impedance matching and line driving.
   • Potential Anticipated Claims: The broader context of high-speed data transceivers might relate to the utility of US6218872. However, the unique combination of the transformer, differential amplifier, and specific shunt impedance calculation for output impedance synthesis (Claims 1 and 10) would need to be thoroughly compared against its teachings for anticipation.

4. US5541990A:

   • Full Citation: US5541990A, Compensated hybrid.
   • Publication Date: 1996-07-30.
   • Priority Date: 1994-07-05.
   • Brief Description: This patent relates to a compensated hybrid circuit, which is often used in telecommunications for separating transmit and receive signals on a two-wire line. Hybrid circuits typically involve impedance balancing.
   • Potential Anticipated Claims: Given that US6218872 mentions "high signal rejection between the transmit and receive ports, i.e., there is high transmit port to receive port isolation" as a property of its invention, a compensated hybrid (like in US5541990A) could be highly relevant for anticipating aspects of the "shunt impedance" that aids in isolation. The specific calculation of the shunt impedance in relation to N and load impedance (Claims 1 and 10) would be key to distinguishing.

5. US5838722A:

   • Full Citation: US5838722A, Monolithic transceiver including feedback control.
   • Publication Date: 1998-11-17.
   • Priority Date: 1996-04-24.
   • Brief Description: This patent describes a monolithic transceiver incorporating feedback control. Feedback is a central element in US6218872's line driver design, where the primary coil provides negative feedback to the differential amplifier.
   • Potential Anticipated Claims: This patent, with its focus on feedback control in a transceiver, could potentially anticipate the "coupled to receive feedback from the output through the primary coil of the transformer" element of claims 1 and 10. The specific combination of this feedback with the shunt impedance and its calculated value for impedance synthesis, as claimed in US6218872, would be crucial for determining anticipation under 35 U.S.C. § 102.

Non-Patent Citation:

1. V. Koren, "Line Driver Economically Synthesizes Impedance," Electronic Design News Jan. 6, 1994, pp. 79.
   • Brief Description: This article, authored by the same inventor, Victor Koren, explicitly describes a method of synthesizing output impedance to reduce the series resistor value in an operational amplifier line driver using two feedback loops with resistors. The background of US6218872 mentions this article, stating that "In order for the driver to work correctly, all resistors in the system must have very close tolerances and must be carefully matched." This suggests the present invention (US6218872) aims to improve upon the method described in this article.
   • Potential Anticipated Claims: This article is highly relevant prior art. It directly addresses the concept of "economically synthesizing impedance" in a line driver, which is a core object of US6218872. While the patent distinguishes itself by stating it eliminates the series resistor and improves efficiency, the fundamental idea of impedance synthesis in a line driver by the same inventor could potentially anticipate aspects of the shunt impedance and feedback mechanisms in claims 1 and 10. The specific implementation with a transformer and the mathematical relationship for the shunt impedance's value would be key differentiating factors.

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 6218872

This analysis identifies combinations of prior art references that would render the independent claims (Claim 1 and Claim 10) of US patent 6218872 obvious to a person having ordinary skill in the art (POSITA) at the time of the invention (December 23, 1999).

Independent Claims Overview

Claim 1 (Apparatus): Describes a line driver with a transformer (primary and secondary coils, N:1 turns ratio), a shunt impedance set to a predetermined function of N and load impedance (coupled between one end of the primary coil and ground), and a differential amplifier. The amplifier's first input is for transmit, its output drives the line via the secondary coil, and its second input is shunted to ground via the shunt impedance and receives feedback from the output through the primary coil.

Claim 10 (Method): Describes a corresponding method involving coupling transmit and receive circuits to a differential amplifier, driving a line via a transformer's secondary coil, providing feedback from the amplifier's output via the transformer's primary coil to the amplifier's second input, and shunting this second input to ground through a shunt impedance set to a predetermined function of N and the load impedance.

Prior Art Combination and Motivation to Combine

The core of US patent 6218872 lies in its improved efficiency and defined output impedance in a line driver, achieved through a specific configuration of a differential amplifier, a transformer (preferably an autotransformer), and a shunt impedance (balancing network) whose value is a function of the transformer's turns ratio (N) and the line's load impedance. The patent itself highlights prior art that attempted similar impedance synthesis but suffered from inefficiencies or required tightly matched components.

Primary References for Combination:

1. V. Koren, "Line Driver Economically Synthesizes Impedance," Electronic Design News, Jan. 6, 1994, pp. 79 (hereinafter "Koren EDN").

   • Disclosure: According to the background of US6218872, Koren EDN describes "a method of synthesizing the output impedance so as to reduce the value of the resistor in series with the output of an operational amplifier." It also mentions that this method "utilizes two feedback loops, both using resistors" and requires "very close tolerances and must be carefully matched."
   • Relevance: This article directly addresses the problem of economically synthesizing output impedance in a line driver, aiming to reduce power dissipation by minimizing the series output resistor. It provides the foundational motivation for developing line drivers with synthesized impedance.

2. US5541990A (Rockwell International Corporation) - "Compensated hybrid."

   • Disclosure: This patent describes a compensated hybrid circuit. Hybrid circuits are commonly used in telecommunications to separate transmit and receive signals on a single transmission line and to provide impedance matching. Such circuits typically incorporate transformers and balancing networks (shunt impedances) to achieve these functions.
   • Relevance: US5541990A, as a representative of hybrid circuit technology, teaches the use of transformers and balancing networks in line interface applications for impedance matching and signal isolation. These elements are directly analogous to the transformer and shunt impedance of US62188872.

3. General Knowledge of a Person of Ordinary Skill in the Art (POSITA).

   • Disclosure: A POSITA in the field of telecommunications and analog circuit design would be well aware of differential amplifiers as fundamental active components for amplification and feedback control. They would also understand the conventional use of transformers in line drivers for galvanic isolation and impedance transformation, as seen in other cited prior art like US4317205A, US4462105A, and US5579336A. Feedback mechanisms in amplifier circuits for controlling output impedance and gain are also routine design practices.

Obviousness Argument for Claims 1 and 10:

A POSITA, motivated by the teachings of Koren EDN to improve the efficiency and reduce power consumption in line drivers by synthesizing output impedance, would naturally seek more robust and less component-sensitive implementations than the resistor-based feedback loops described in Koren EDN.

It would have been obvious for a POSITA to incorporate the impedance synthesis concept from Koren EDN into a transformer-based hybrid circuit architecture, such as that taught by US5541990A. Hybrid circuits inherently provide galvanic isolation and use balancing networks (shunt impedances) with transformers for signal separation and impedance matching.

The specific configuration claimed in US6218872, where a differential amplifier's output drives the line via a secondary coil, and feedback is provided from the primary coil to the amplifier's inverting input (shunted by the balancing network), is a straightforward engineering design choice. This arrangement is well-suited to:

• Leverage the benefits of transformers (isolation, impedance transformation).
• Utilize differential amplifiers for precise control and feedback in active impedance synthesis.
• Implement the balancing network (shunt impedance) to achieve transmit/receive isolation and define the output impedance.

The determination of the shunt impedance's value as a "predetermined function of N and the load impedance" (as specified in Claims 1 and 10) would be a matter of routine circuit analysis and optimization for a POSITA designing such a transformer-based hybrid to achieve specific impedance matching and isolation properties. For example, the patent itself derives the condition for isolation as Z_bal = N * Z_load (Equation 3) and the output impedance as Z_out = Z_rx / (N+1) (Equation 5). These are not inventive discoveries but rather mathematical consequences of the chosen circuit topology.

Motivation:
The motivation for a POSITA to combine Koren EDN with US5541990A and general knowledge would be to overcome the limitations of Koren EDN (e.g., tight component tolerances, higher power dissipation from series resistors) by integrating the impedance synthesis method into a more efficient and robust transformer-based hybrid line driver. A hybrid circuit provides a well-understood framework for isolating transmit and receive paths and performing impedance matching. A differential amplifier, coupled with a transformer and a balancing network in a feedback configuration, would be an obvious choice to actively synthesize the desired output impedance and isolation characteristics. This combination would lead directly to the claimed apparatus and method, where the shunt impedance's value is derived systematically from the circuit parameters (N and load impedance) to achieve optimal performance (e.g., isolation and impedance matching).

Therefore, the combination of Koren EDN, US5541990A, and general knowledge would have made Claims 1 and 10 obvious to a POSITA at the time of the invention.