PTAB

IPR2024-00802

ElMOS Semiconductor Se v. Texas Instruments Inc

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1. Case Identification

2. Patent Overview

  • Title: Light-Emitting Diode (LED) Driver System with Slew-Rate Control
  • Brief Description: The ’432 patent discloses a driver system for LEDs that manages power dissipation. The system uses two current driver paths for an LED load, with one path including an external shunt resistor, and shifts current to the shunt path as supply voltage increases to transfer heat losses to the resistor. The system also incorporates a slew-rate controller to prevent current overshoot during this transition.

3. Grounds for Unpatentability

Ground 1: Claims 1-3, 6, 10-11, and 16-17 are obvious over Sudhaus.

  • Prior Art Relied Upon: Sudhaus (Patent 10,136,496).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Sudhaus disclosed all key limitations of the challenged claims. Sudhaus teaches a controller (RG) that manages total current to an LED load through two distinct current paths. The second path includes an external resistor (R_4), analogous to the claimed shunt resistor. Petitioner asserted that Sudhaus’s teaching of gradually shifting a portion of the total current from the first path to the second path as the system supply voltage increases inherently discloses or renders obvious the claimed slew-rate control functionality.
    • Motivation to Combine (for §103 grounds): This ground relies on a single reference. Petitioner argued that all claimed elements were present in Sudhaus, and a person of ordinary skill in the art (POSITA) would have found it obvious to configure its components to achieve the claimed system.

Ground 2: Claims 1-4, 6-7, 10-12, and 15-18 are obvious over Sudhaus in view of Ryoichi.

  • Prior Art Relied Upon: Sudhaus (Patent 10,136,496) and Ryoichi (JP 2012160287).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground used Sudhaus for the base two-path LED driver architecture with power dissipation management. Petitioner argued that Ryoichi was then used to supply the explicit, transistor-level implementation details for the error amplifier and slew-rate controller elements, which may only be implicitly disclosed in Sudhaus. Ryoichi describes multiple methods for controlling slew rate in an LED driver, including adjusting bias currents, switching transistor pairs in an amplifier output stage to add parallel offset currents, and using a variable capacitor.
    • Motivation to Combine (for §103 grounds): A POSITA would combine these references because Sudhaus provides a high-level system architecture for managing power in an LED driver, while Ryoichi provides well-known, specific circuit implementations for the functional blocks within that system, such as the error amplifier and slew-rate controller. Ryoichi’s detailed circuits represent known solutions to the problems of current control and slew rate management that a POSITA would naturally apply to the Sudhaus system.

Ground 5: Claims 1-20 are obvious over Sudhaus in view of Ryoichi, Praxis, Provost, TI Paper, and UK Paper.

  • Prior Art Relied Upon: Sudhaus (Patent 10,136,496), Ryoichi (JP 2012160287), Praxis (an Oct. 2016 article by Sudhaus), Provost (a Mar. 2003 IEEE article), TI Paper (a Dec. 2019 Texas Instruments white paper), and UK Paper (an Apr. 2011 University of Kansas white paper).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground extended the arguments from previous grounds to cover all 20 claims, presenting an alternative method for implementing slew-rate control. The combination of Sudhaus, Ryoichi, and Praxis was argued to teach the complete dual-path driver with error amplifier and slew-rate control. The combination of Provost, TI Paper, and UK Paper was presented as an obvious alternative for implementing the slew-rate controller recited in claims 5, 8, 13, and 19. Provost teaches an on-chip ramp generator using a charging current and capacitor to create a ramp voltage. The TI Paper teaches a voltage-to-current (V-I) converter that a POSITA would use to convert Provost's ramp voltage into an offset current. The UK Paper discloses standard current mirrors a POSITA would use to apply this offset current to control a transistor’s input voltage.
    • Motivation to Combine (for §103 grounds): A POSITA tasked with designing a slew-rate controller would look to well-known circuit building blocks. Combining a ramp generator (Provost) with a V-I converter (TI Paper) and current mirrors (UK Paper) represents a predictable and standard engineering design choice for creating a time-varying control signal (the offset current) to precisely manage the turn-on characteristics of a power transistor.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including Ground 3 (Sudhaus, Ryoichi, and Praxis) and Ground 4 (Sudhaus, Ryoichi, Praxis, and Wu), which relied on similar logic but introduced Praxis for its disclosure of an error amplifier with two outputs and Wu (Patent 11,599,132) as another alternative for slew-rate control.

4. Key Claim Construction Positions

  • Petitioner proposed plain and ordinary meaning constructions for several terms, arguing they are readily understood by a POSITA. Key proposed constructions included:
    • “amplifier output stage”: an electrical circuit that receives at least one input and outputs a signal based on that input.
    • “error amplifier”: an electrical circuit that detects a difference between two input signals and outputs a signal based on the difference.
    • “slew-rate controller”: an electrical circuit that controls a rate of change of an electrical signal over time.

5. Relief Requested

  • Petitioner requests institution of an inter partes review (IPR) and cancellation of claims 1-20 of Patent 11,653,432 as unpatentable.