Radent Licensing LLC v. Rohm Semiconductor USA LLC

I. Executive Summary and Procedural Information

• Parties & Counsel:
  • Plaintiff: Radent Licensing LLC (Texas)
  • Defendant: ROHM Semiconductor U.S.A., LLC (Delaware)
  • Plaintiff’s Counsel: Chong Law Firm PA; SAND, SEBOLT & WERNOW CO., LPA
• Case Identification: 1:20-cv-00579, D. Del., 04/28/2020
• Venue Allegations: Venue is alleged to be proper in the District of Delaware because the Defendant is a Delaware corporation and therefore resides in the district for purposes of patent venue.
• Core Dispute: Plaintiff alleges that Defendant’s fan motor driver integrated circuit infringes three patents related to methods and circuits for generating Pulse-Width Modulation (PWM) signals for improved motor efficiency.
• Technical Context: The technology concerns the electronic control of motors, specifically using PWM signals derived from analog sensors to manage motor speed and power consumption efficiently, a critical function in countless electronic devices.
• Key Procedural History: The three patents-in-suit constitute a patent family, with U.S. Patent No. 8,310,184 being a continuation of the application for U.S. Patent No. 8,018,184, and U.S. Patent No. 8,541,966 being a continuation of the application for U.S. Patent No. 8,310,184. This shared prosecution history may be relevant for claim construction. No other procedural history is mentioned in the complaint.

Case Timeline

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 8,018,184 - PWM CONTROL CIRCUIT AND PWM CONTROL METHOD, Issued Sep. 13, 2011

The Invention Explained

• Problem Addressed: The patent addresses a demand for PWM control circuits that can achieve higher motor efficiency than conventional designs, which typically compare a sine wave signal from a motor sensor with a reference signal ('184 Patent, col. 1:18-25).
• The Patented Solution: The invention describes a method where an analog signal from a motor's sensor is first converted into a full-wave rectified signal. This rectified signal is then adjusted (e.g., by altering its offset or gain) to create an "adjusted waveform signal." This adjusted signal is compared against a fixed-frequency carrier signal (e.g., a sawtooth wave) to generate an initial PWM signal. Finally, this initial PWM signal is shaped using a polarity signal (derived from the original sensor output) to produce separate PWM drive signals for the positive and negative polarity sections of the motor's operation ('184 Patent, Abstract; col. 2:30-49). This process is illustrated in the circuit block diagram of Figure 1 and the signal waveform charts of Figure 4.
• Technical Importance: By generating a full-wave rectified signal and then adjusting it, the circuit can create a signal with a "desirable waveform" for PWM generation, which in turn allows for "more efficient PWM control" ('184 Patent, col. 2:53-57).

Key Claims at a Glance

• The complaint asserts independent method claim 11 (Compl. ¶14).
• The essential elements of Claim 11 are:
  • judging positive and negative polarity sections of an analog sensor output to generate a polarity signal;
  • generating a full wave rectification signal from the analog sensor output;
  • generating an adjusted waveform signal by adjusting the waveform of the full wave rectification signal;
  • generating a fixed frequency carrier signal;
  • generating an original PWM signal by comparing the adjusted waveform signal and the carrier signal; and
  • generating a first and second PWM signal for the positive and negative polarity sections, respectively, by shaping the original PWM signal according to the polarity signal.

U.S. Patent No. 8,310,184 - PWM CONTROL CIRCUIT AND PWN CONTROL METHOD, Issued Nov. 13, 2012

The Invention Explained

• Problem Addressed: Like its parent, this patent seeks to provide "PWM control with better efficiency" than was available with conventional circuits ('0184 Patent, col. 1:29-30).
• The Patented Solution: The method is similar to that of the ’184 Patent, involving the generation of polarity, full-wave rectified, and adjusted waveform signals. However, asserted claim 5 includes a key distinguishing feature in a "wherein" clause, which specifies that the step of generating the adjusted waveform signal includes "setting only part of the full wave rectification signal as valid and the other part as invalid" ('0184 Patent, col. 10:13-17). The specification describes this being performed by an "excitation interval setting unit" which can, for example, make the signal invalid near the zero-cross point to avoid applying drive voltage when it would not produce a valid drive force ('0184 Patent, col. 5:20-29; Fig. 5A).
• Technical Importance: This technique of invalidating portions of the control signal is disclosed as a way to improve motor efficiency and reduce vibration and noise that can occur when drive voltage is applied near the zero-cross point of the sensor signal ('0184 Patent, col. 5:25-29).

Key Claims at a Glance

• The complaint asserts independent method claim 5 (Compl. ¶21).
• The essential elements of Claim 5 are:
  • judging positive and negative polarity sections of an analog sensor output to generate a polarity signal;
  • generating a full wave rectification signal from the analog sensor output;
  • generating an adjusted waveform signal by adjusting the waveform of the full wave rectification signal; and
  • generating a first and second PWM signal for the positive and negative polarity sections, based on the polarity signal and the adjusted waveform signal;
  • wherein the step of generating the adjusted waveform signal includes setting only part of the full wave rectification signal as valid and the other part as invalid.

U.S. Patent No. 8,541,966 - PWM CONTROL CIRCUIT AND PWM CONTROL METHOD, Issued Sep. 24, 2013

• Technology Synopsis: This patent, a continuation in the same family, also describes a technology for more efficient PWM motor control (Compl. ¶27). The claimed method involves generating polarity, full-wave rectified, and adjusted waveform signals from a sensor output, with the key step being that the "adjusted waveform signal includes a part of the full wave rectification signal and excludes the other part," which is then used to generate the final PWM drive signals ('966 Patent, Abstract; Compl. ¶29).
• Asserted Claims: The complaint asserts independent method claim 6 (Compl. ¶28).
• Accused Features: The complaint alleges that the Accused Product practices the method of claim 6 by performing the sequence of signal generation and adjustment steps, including generating an adjusted waveform that includes one part and excludes another part of a full wave rectified signal (Compl. ¶¶49-54).

III. The Accused Instrumentality

Product Identification

• The "Rohm Fan Motor Driver BU69099NUX" is identified as the Accused Product (Compl. ¶31).

Functionality and Market Context

• The complaint alleges the Accused Product is a "solution" that "practices a method of generating PWM signals based on an analog sensor output from a sensor provided in a device to be controlled" (Compl. ¶31). The infringement allegations are based on the Accused Product's use "at least in internal testing and usage" (Compl. ¶33). The complaint does not provide further technical details about the product's operation or its specific market positioning. No probative visual evidence provided in complaint.

IV. Analysis of Infringement Allegations

8,018,184 Infringement Allegations

8,310,184 Infringement Allegations

Identified Points of Contention

• Evidentiary Questions: The complaint's allegations are conclusory, stating the Accused Product "practices" the claimed method steps "at least in internal testing and usage" (e.g., Compl. ¶33, ¶42). A primary point of contention will be what evidence Plaintiff can produce from discovery to demonstrate that the internal logic of the BU69099NUX chip actually performs the specific, sequential signal processing steps recited in the method claims.
• Technical Questions: A technical question for the court will be whether the Accused Product's signal processing architecture maps onto the specific sequence claimed (e.g., generating a discrete "full wave rectification signal" which is then "adjusted" to create a separate "adjusted waveform signal"). The defense may argue that the accused chip employs a different, more integrated, or non-sequential method to achieve a similar result.
• Scope Questions: For the '0184 Patent, a central dispute will be the functional limitation of "setting only part of the full wave rectification signal as valid and the other part as invalid." The analysis will raise the question of whether this language reads on the specific signal gating or blanking functions, if any, employed by the Accused Product.

V. Key Claim Terms for Construction

• For the '184 Patent:

  • The Term: "adjusted waveform signal"
  • Context and Importance: This term describes the intermediate signal that is compared to the carrier signal to generate the ultimate PWM output. The definition of what constitutes an "adjusted" signal is critical to determining the scope of the claim, as it forms the bridge between the raw rectified sensor signal and the final PWM signal.
  • Intrinsic Evidence for Interpretation:
    • Evidence for a Broader Interpretation: The claim itself defines this step broadly as "generating an adjusted waveform signal by adjusting waveform of the full wave rectification signal" ('184 Patent, col. 10:1-3). This suggests any form of adjustment could suffice.
    • Evidence for a Narrower Interpretation: The specification's primary embodiment discloses adjusting the waveform via a specific combination of an "offset adjustment unit" and a "gain adjustment unit" ('184 Patent, col. 4:16-23, Fig. 3). A party could argue the term should be construed as limited to these types of electronic adjustments.

• For the '0184 Patent:

  • The Term: "setting only part of the full wave rectification signal as valid and the other part as invalid"
  • Context and Importance: This functional language in the "wherein" clause of claim 5 is a key limitation. Its construction will be dispositive for infringement, as it defines the specific mechanism by which the patented method claims to improve efficiency. Practitioners may focus on this term because its functional nature makes it susceptible to disputes over what accused actions meet the definition.
  • Intrinsic Evidence for Interpretation:
    • Evidence for a Broader Interpretation: The claim language itself is functional and does not recite a specific structure. The specification describes the purpose is to avoid vibration and noise near the zero-cross point, which could support a construction covering any technique that achieves this result by selectively ignoring parts of the signal ('0184 Patent, col. 5:25-29).
    • Evidence for a Narrower Interpretation: The only embodiment that teaches this function uses an analog comparator (245a) to compare the signal against a threshold voltage (Vth), which in turn generates an enable signal (Enb) to control a buffer circuit (245b) ('0184 Patent, col. 4:60-65; Fig. 5A). A party may argue this is the only disclosed way of performing the function, potentially limiting the claim's scope to this or an equivalent implementation.

VI. Other Allegations

• Indirect Infringement: The complaint includes a conclusory allegation of induced infringement, stating Defendant encouraged infringement with knowledge ('59). The pleading does not, however, allege specific facts to support this claim, such as identifying specific instructions in user manuals, datasheets, or other materials that would instruct a third party to operate the Accused Product in an infringing manner.
• Willful Infringement: The complaint alleges that Defendant had knowledge of its infringement "at least as of the service of the present Complaint" (Compl. ¶57). This allegation on its own would only support a claim for post-filing willfulness and does not assert that Defendant had any knowledge of the patents-in-suit prior to the lawsuit being filed.

VII. Analyst’s Conclusion: Key Questions for the Case

• A core issue will be one of evidentiary proof: The complaint makes conclusory allegations that the accused chip "practices" the claimed methods. A key question for the case will be whether discovery reveals that the actual, internal operation of the Rohm fan motor driver mirrors the specific, sequential signal-processing steps recited in the asserted method claims.
• The case will also turn on a question of functional claim scope: A central legal dispute will be the construction of the phrase "setting only part of the full wave rectification signal as valid and the other part as invalid" from the '0184 patent. The key question for the court will be whether this functional language is limited to the specific comparator-and-threshold embodiment disclosed in the specification, or if it can be construed more broadly to cover any signal-gating technique used in the accused device.
• A third significant question relates to secondary liability: Given the bare-bones allegation for inducement, a key question will be whether the Plaintiff can develop facts to show that Defendant took affirmative steps with the specific intent to encourage its customers to infringe, as opposed to merely selling a multi-purpose component.