DCT
5:20-cv-01650
Xiaohua Huang v. We Buy Used It Equipment
Key Events
Complaint
I. Executive Summary and Procedural Information
- Parties & Counsel:
- Plaintiff: Xiaohua Huang (California)
- Defendant: We Buy Used IT Equipment (California)
- Plaintiff’s Counsel: Pro Se
- Case Identification: 5:20-cv-01650, C.D. Cal., 08/17/2020
- Venue Allegations: Plaintiff alleges venue is proper in the district because Defendant generates revenues and profits within California by selling networking switches that infringe the patent-in-suit.
- Core Dispute: Plaintiff alleges that Defendant’s sale of refurbished Juniper Networks networking switches infringes a patent related to high-speed, low-power Ternary Content Addressable Memory (TCAM) circuits.
- Technical Context: TCAMs are specialized high-speed memory used in networking devices for rapid search operations, such as packet forwarding and access control list enforcement, which are critical for modern internet infrastructure.
- Key Procedural History: The complaint references and attaches an "Expert Report" as an exhibit, which is an unconventional procedural step for a complaint and forms the primary basis for the infringement allegations.
Case Timeline
| Date | Event |
|---|---|
| 2001-10-04 | Earliest Priority Date for U.S. Patent No. 6,999,331 |
| 2006-02-14 | U.S. Patent No. 6,999,331 Issues |
| 2020-08-17 | Complaint Filed |
II. Technology and Patent(s)-in-Suit Analysis
U.S. Patent No. 6,999,331 - CAM cells and differential sense circuits for content addressable memory (CAM)
- Patent Identification: U.S. Patent No. 6,999,331, CAM cells and differential sense circuits for content addressable memory (CAM), issued Feb. 14, 2006.
The Invention Explained
- Problem Addressed: The patent describes conventional Content Addressable Memory (CAM) designs as suffering from performance limitations related to speed and power consumption. Specifically, when checking for a data match, a "match line" for each row of memory cells must be discharged if a mismatch occurs. In large memory arrays, this process can be slow and consume excessive power, particularly when many rows result in a mismatch (’331 Patent, col. 1:57-2:16).
- The Patented Solution: The invention proposes a differential sensing architecture to improve speed and power efficiency. This is achieved by adding a "dummy line" and a column of "dummy CAM cells" to the memory array, which act as a reference (’331 Patent, Fig. 1B). Instead of waiting for a full voltage drop on the match line to signal a mismatch, the patented circuit can quickly detect a small voltage difference between the match line and the dummy line to determine the result. This "low voltage swing" sensing enables faster and lower-power operation (’331 Patent, col. 2:20-40, Abstract).
- Technical Importance: This differential sensing approach addresses a fundamental bottleneck in high-speed networking hardware, allowing for faster and more energy-efficient parallel search operations critical for routers and switches (’331 Patent, col. 2:12-16).
Key Claims at a Glance
- The complaint asserts at least Claim 1 of the ’331 Patent (Compl. ¶13).
- Independent Claim 1 requires:
- An array of ternary content addressable memory (TCAM) cells arranged in a plurality of rows and columns
- A plurality of match lines, one for each row, coupled to output transistors of the TCAM cells
- A plurality of dummy lines, one for each row, coupled to dummy transistors of the TCAM cells
- A plurality of match data bit lines and their complements for each column
- A column of dummy TCAM (DTCAM) cells, connected to the match line and the dummy line in each row
- A pair of dummy match data bit lines and its complement for the column of DTCAM cells
- A sense amplifier connected to the match line and the dummy line in each row
- Current sources connected to each of the match line and the dummy line in each row
III. The Accused Instrumentality
Product Identification
- Juniper Network EX Series Switches, including models EX2200, EX3300, EX4200, EX4300, EX4500, EX4550, EX4600, EX6200, EX8200, and EX9200 (Compl. ¶¶11, 13). The complaint states that Defendant "has refurbished and sold" these products (Compl. ¶13).
Functionality and Market Context
- The complaint alleges that these networking switches contain and use TCAM components to perform critical table look-up functions for features such as access control lists (ACL), Quality of Service (QoS), VLAN, and packet forwarding (Compl. ¶10). An exhibit to the complaint, a Juniper Networks technical article, describes how TCAM entries are used for firewall filters in its switches (Compl. Ex. E, p. 39).
- The complaint identifies specific features of the TCAMs within the accused products, allegedly determined through "Data sheet, reverse engineering and information obtained," including the use of a differential sense amplifier and a dummy line as a reference (Compl. ¶¶11, 11(b)-(c)). The "TCAM micro architectural diagram" included in the expert report shows a structure of CAM cells organized in rows and columns connected to a "Sensing Amplifier Column" (Compl. Ex. T, p. 54).
IV. Analysis of Infringement Allegations
The complaint does not contain a formal claim chart. The infringement theory is presented in a narrative list of features (Compl. ¶11) and an attached expert report (Compl. Ex. T). The following table summarizes the allegations from the expert report, which maps features of the accused TCAM to Claim 1 of the ’331 Patent.
U.S. Patent No. 6,999,331 Infringement Allegations
| Claim Element (from Independent Claim 1) | Alleged Infringing Functionality | Complaint Citation | Patent Citation |
|---|---|---|---|
| A ternary content addressable memory (TCAM) comprising: an array of TCAM cells arranged in a plurality of rows and a plurality of columns; | The accused products contain a TCAM with a micro-architectural diagram showing CAM cells arranged in rows and columns. A "TCAM micro architectural diagram" depicts this structure (Compl. Ex. T, p. 54). | Ex. T, p. 55 | col. 18:20-22 |
| a plurality of match lines, one match line for each row of TCAM cells and operatively coupled to a plurality of output transistors for the TCAM cells in each row; | The accused TCAM schematic and diagram show match lines (labeled "Out1," "Out255," etc.) for each row. A "circuit schematic" shows a "match" line (Compl. Ex. T, p. 53). | Ex. T, p. 55 | col. 18:23-26 |
| a plurality of dummy lines, one dummy line for each row of TCAM cells and operatively coupled to a plurality of dummy transistors for the TCAM cells in each row; | The accused TCAM is alleged to use a dummy line to be a reference to the match line. The "circuit schematic" explicitly labels a "dummy" line (Compl. Ex. T, p. 53). | Ex. T, pp. 52, 55 | col. 18:27-30 |
| a column of dummy TCAM (DTCAM) cells, each connected to the match line and the dummy line in each row; | The accused TCAM schematic allegedly shows a "CAM cell 1" column that corresponds to the claimed DTCAM column. | Ex. T, p. 56 | col. 18:40-42 |
| a sense amplifier connected to the match line and the dummy line in each row; and current sources connected to each of the match line and the dummy line in each row. | The accused TCAM uses a differential sense amplifier to sense the match line signal. The micro-architectural diagram shows a "Sensing Amplifier Column having current" connected to the array (Compl. Ex. T, pp. 54, 56). | Ex. T, pp. 52, 56 | col. 18:49-54 |
- Identified Points of Contention:
- Scope Questions: Claim 1 requires very specific circuit elements, including "current sources connected to each of the match line and the dummy line." A potential dispute is whether the "sense amplifier column having current" alleged in the expert report (Compl. Ex. T, p. 56) meets this specific limitation, or if it constitutes a different structure.
- Technical Questions: The complaint's infringement theory relies on schematics allegedly obtained from reverse engineering (Compl. ¶11; Ex. T). A central question will be whether discovery confirms that these schematics accurately represent the TCAMs within the specific refurbished Juniper products sold by the Defendant.
V. Key Claim Terms for Construction
The Term: "dummy line"
Context and Importance: The "dummy line" is the cornerstone of the patent’s differential sensing solution, providing the reference signal against which the "match line" is compared. The definition of this term is critical to determining whether the accused products, which allegedly use a "dummy line to be reference to match line" (Compl. ¶11(c)), infringe.
Intrinsic Evidence for Interpretation:
- Evidence for a Broader Interpretation: The claim language requires the dummy line to be "operatively coupled to a plurality of dummy transistors" (’331 Patent, col. 18:28-30), which could be argued to cover any reference line generated by transistor-based circuits.
- Evidence for a Narrower Interpretation: The specification repeatedly links the dummy line to a "column of M dummy CAM cells" (’331 Patent, col. 4:33-35) and describes its specific role in generating a reference signal that "mimic[s] the loading observed on match line" (’331 Patent, col. 8:27-28). This may support a narrower construction requiring a structure that closely mirrors the architecture of the primary CAM array.
The Term: "current sources"
Context and Importance: This term appears in the final limitation of Claim 1, requiring "current sources connected to each of the match line and the dummy line in each row." Practitioners may focus on this term because the complaint's evidence points to a "sense amplifier column having current" (Compl. Ex. T, p. 56), which may or may not be structurally and functionally equivalent to the claimed element.
Intrinsic Evidence for Interpretation:
- Evidence for a Broader Interpretation: The term is not explicitly defined, which may support giving it its plain and ordinary meaning as any component that supplies electrical current.
- Evidence for a Narrower Interpretation: Claim 7, which depends from Claim 1, specifies that the current sources are "P type transistors." While this appears in a dependent claim, language from the specification describing embodiments with P-channel transistors used to pre-charge the lines could be used to argue for a more limited construction of the term in Claim 1 (’331 Patent, col. 8:12-14).
VI. Other Allegations
- Indirect Infringement: The complaint alleges that Defendant induced infringement by its customers "through accessing and using the TCAM function of the equipment it has bought and sold" (Compl. ¶14). It also alleges contributory infringement by selling networking equipment that contains the allegedly infringing TCAMs for use in the "Internet system" (Compl. ¶14).
VII. Analyst’s Conclusion: Key Questions for the Case
- A core issue will be one of evidentiary proof: Can the pro se plaintiff obtain and present technical evidence sufficient to demonstrate that the specific TCAM circuits within refurbished networking equipment sold by the Defendant meet every limitation of the asserted claim, especially given the detailed architectural requirements?
- A key question will be one of claim scope: Does the accused TCAM’s sensing circuitry, described in the expert report as a "sense amplifier column having current," satisfy the distinct claim limitations requiring both a "sense amplifier" and separate "current sources connected to each of the match line and the dummy line"?
- A final question relates to liability: Can infringement be established against a seller of refurbished or used equipment, and what level of knowledge must be proven, particularly for the allegations of indirect infringement?