PTAB

IPR2014-00947

RPX Corp v. ParkerVision Inc

Key Events

Petition

Title: Method and System for Down-Converting an Electromagnetic Signal
Brief Description: The ’551 patent relates to radio frequency (RF) down-conversion circuits. The technology purports to distinguish itself from prior art "under-sampling" techniques by using sampling apertures of non-negligible duration to achieve a "non-negligible" transfer of energy from an input signal to a storage module, typically a capacitor.

Prior Art Relied Upon: Estabrook ("The direct conversion receiver: Analysis and design of the front-end components," Ph.D. diss., Stanford University, 1989).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner argued that Estabrook disclosed a method and apparatus for a direct conversion receiver that anticipates every limitation of the challenged claims. Estabrook’s circuit, which uses a diode as a switch controlled by a local oscillator, explicitly teaches maximizing current transfer by using an “ON time” of approximately 50% of the control signal’s period. Petitioner asserted this long, non-negligible aperture inherently results in the "non-negligible" energy transfer required by the claims. Estabrook’s output is a “sawtooth” voltage waveform resulting from the capacitor charging and then discharging into a low-impedance load, which Petitioner contended satisfies the claim limitation of "generating a lower frequency signal from the transferred energy," particularly under a narrow construction requiring discharge that Patent Owner previously advanced in litigation. The apparatus claims were met by Estabrook’s disclosure of a diode switch (switch module), a local oscillator (energy transfer signal generator), and a capacitor (storage module).

Prior Art Relied Upon: Avitabile et al. (“S-band digital downconverter for radar applications based on a GaAs MMIC fast sample-and-hold,” IEE Proc. On Circuits, Devices and Systems, 1996).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner contended that Avitabile, which describes a sub-harmonic sampling downconverter, also taught all claimed elements. Avitabile disclosed using sampling apertures of 400 ps and 100 ps, which represented 40% and 10% of the carrier period, respectively. Petitioner argued these are squarely within the ’551 patent’s description of "non-negligible" apertures. The down-converted signal in Avitabile is the voltage across the storage capacitor, which necessarily results from the energy transferred and stored. Petitioner further noted that Avitabile disclosed energy discharging from the capacitor during the hold period (termed "droop off"), which anticipates the claims even under a restrictive interpretation requiring discharge to "generate" the signal.

Prior Art Relied Upon: Weisskopf (“Subharmonic Sampling of Microwave Signal Processing Requirements,” Microwave Journal, May 1992).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner asserted that Weisskopf anticipated the claims by teaching a sub-harmonic sampling circuit designed to maximize energy transfer. Weisskopf explicitly taught that maximum energy is transferred when the sampling aperture is one-half the period of the sampled carrier—a duration the ’551 patent itself described as a "preferred embodiment." Weisskopf disclosed optimizing the capacitor size to maximize this energy transfer. Critically, Weisskopf described embodiments using both a high-impedance load (minimizing discharge, akin to a sample-and-hold circuit) and a low-impedance load (maximizing discharge). Petitioner argued that this dual disclosure anticipated the claims regardless of whether the "generating" step is interpreted broadly (voltage exists on the capacitor) or narrowly (voltage is generated by discharge).

"(Generating a lower frequency signal)...from the transferred energy": This was the most disputed phrase. Petitioner argued for the plain meaning: the down-converted signal is generated using the transferred energy, which manifests as a voltage across the storage capacitor regardless of discharge. Petitioner heavily criticized Patent Owner's litigation-induced position that this phrase requires the discharge of energy from the storage module. Petitioner argued this narrow construction was an improper attempt to avoid prior art, was contradicted by the ’551 patent's own "preferred embodiment" (a sample-and-hold circuit with minimal discharge), and would render dependent claims (e.g., claim 85, reciting a "sample and hold system") nonsensical under the doctrine of claim differentiation.
"Transferring non-negligible amounts of energy": While a district court construed this as "transferring energy in amounts distinguishable from noise," Petitioner argued the broadest reasonable interpretation, grounded in the specification, is that this limitation is a direct result of using a "non-negligible sampling aperture." The specification consistently links negligible energy transfer to negligible apertures and non-negligible energy transfer to non-negligible apertures. Dependent claim 98 objectively defines a non-negligible aperture as at least "one tenth of one percent of approximate half cycles of the carrier signal."

Petitioner requested the institution of an inter partes review and the cancellation of claims 1, 23, 25, 161, 193, and 202 of the ’551 patent as unpatentable.