Fenner Investments, Ltd. v. Microsoft et al.
United States District Court for E.D. Tex.
Filed 1/5/07, Decided 3/16/09 (Opinion issued 6/3/09)

This case revolved around Fenner Investment’s U.S. Patent No. 6,297,751, which describes a low-voltage joystick port interface.

Prior art joysticks used resistor-like devices called potentiometers to produce analog signals. These analog signals had to be transformed into digital signals to be read by a computer. An interface circuit interpreted the joystick’s analog signal to produce a responsive digital pulse which had a pulse width that corresponded to the joystick position. The computer would measure the width of the digital pulse to figure out the position.

Newly developed computer and video game systems require lower voltage (prior art joysticks and computers were electronically compatible, both operating at 5 volts), so they didn’t work with the interface circuits/joysticks anymore. Fenner’s patent solved that problem by creating an interface circuit that allowed the old, higher voltage joysticks to be used with the newer, lower voltage systems.

The “Pulse Width” Limitation
Fenner’s patent contains a limitation that requires an infringing product to produce ‘a single cycle of variation in the logical level of a signal, a width of the single cycle of variation, assessed in time or distance, represents a coordinate position of said joystick device.”

Fenner alleged that Microsoft’s Xbox controller and Nintendo’s Wii and GameCube controllers infringed on its patent. These controllers contain thumbsticks that operate by initial analog signals being translated into 8- or 10-bit digital signals (or “words”) that get sent to the console processor which interprets the digital word to calculate the corresponding thumbstick position.

Basically, Fenner’s invention works so that analog signals are represented by the width of a variation (pulse) in a digital signal, whereas defendants’ products require the full 8- or 10-bit digital word (made up of 1’s and 0’s) to give the joystick position. As an example of a digital word, “01100000” shows a two cycle “pulse” occurring toward the beginning of the 8-bit word.

Fenner argued that the defendants infringed simply because the accused products create a pulse with a width that can be measured and, based on the pulses, a joystick position can be determined. The defendants argued that the pulse widths alone are irrelevant and instead the entire digital word is necessary to determine the joystick position.

Claim Construction
The main issue here turned on the claim construction of the pulse width “representing” joystick position and whether that meant providing some information about the position (Fenner’s argument) or providing all information necessary to determine the position (Defendants’ argument). Relying on intrinsic evidence (i.e., the patent claims, specification, and its prosecution history before the United States Patent & Trademark Office), the court found that the claim required that the pulse must communicate all the necessary information to determine the specific joystick coordinate position.

Fenner also argued that “represent” meant that pulse width could be combined with other data, such as the position of the pulse in the 8- or 10-bit word, to indicate joystick position. The court rejected this argument based on the prosecution history and claim amendment language which indicated that only pulse width, not other data, was to be used to determine joystick position.

Summary Judgment – Direct Infringement
Using the above claim construction, the court found summary judgment appropriate because there was no genuine issue of material fact. Because Fenner’s patent relied on a pulse width alone to relate the joystick position, the defendants had not infringed on the patent. This is because, in the accused devices, the pulse widths alone are meaningless and say nothing about joystick position. The pulse widths simply describe the bits. It’s the 8 or 10 bits, read together, that actually give the position. A signal representing the series of two, three, or more “1's” in a row does express “a single variation of the logical level of a signal,” but it doesn’t give any position information without the accompanying “0's” that also make up the digital word.

Summary Judgment – Doctrine of Equivalents
Generally, patent protection is limited to what’s written in the patent claims. However, to ensure fair protection of patents, the doctrine of equivalents states that a patent may be protected even when another product or process does not literally infringe on the patent, as long as the infringing product or process is deemed to be equivalent. The doctrine of equivalents was formed so that copycats could not avoid patent infringement simply by making minor or trivial variations to the claims. For the doctrine to apply, the accused product must perform “substantially the same function in substantially the same way with substantially the same result” (referred to as the function-way-result, or FWR, test).

Fenner argued that the doctrine applied because the production of binary encoded numbers was equivalent to the production of pulse widths for determining joystick position. The court determined that Fenner’s interpretation wrongly wrote the “pulse limitation” out of the claim and disregarded the “way” part of the test by being so broad that it would include any digital signal no matter what “way” that it communicated position. The court further found that Fenner failed to show equivalence in the “way” the devices operate because in Fenner’s device, only the pulses, or “cycles of variation,” are used to determine joystick position whereas in the defendants’ devices the periods of no variation are just as necessary as the periods of variation (for creating an 8- or 10-bit digital word) to determine position.

The “Lower Source Voltage” Limitation
The court also faced a second issue of claim construction concerning the definition of the device parts, because certain parts of the accused products had to operate at a lower voltage in order to be infringing.

Claims 1, 9, and 14 of the ‘751 patent call for “[a]n interface between a joystick device having a first source voltage and a processor, comprising . . . an interface circuit having a second source voltage that is lower than the first source voltage. . .” The Court’s claim construction defined “interface circuit” as “a circuit that connects the joystick and the processor.”

The ‘751 patent claims required the interface circuit between the joystick and processor to operate at a lower voltage than the joystick. In the defendants’ accused products, only the processor core, or central processing unit (CPU), operates at a lower voltage than the joystick. Fenner argued that the periphery of the processor could be included in the interface circuit, while the defendants argued that the processor included the CPU and its peripherals, both separate from the interface circuit. The claim construction then turned on whether “processor” meant the entire processor chip or just the processor core. Using extrinsic definitions as well as the context of the claim, the court held that “processor” should be defined as “the CPU along with its peripheral circuitry.” Fenner had agreed that such a definition would preclude any issues of triable fact, so summary judgment was appropriate.