Detrola Radio & Television Corp. v. Hazeltine Corp.

Citations: 313 U.S. 259; 61 S. Ct. 948; 85 L. Ed. 1319; 1941 U.S. LEXIS 1276; 49 U.S.P.Q. (BNA) 337Docket: 666

Court: Supreme Court of the United States; May 12, 1941; Federal Supreme Court; Federal Appellate Court

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Harold A. Wheeler filed a patent application on July 7, 1927, for a circuit designed to control the amplitude of amplified signal voltage in modulated carrier current signaling systems, which was granted as Patent No. 1,879,863 on September 27, 1932, to Hazeltine Corporation, the assignee. A lawsuit for infringement of specific claims was initiated in the Eastern District of New York, where the District Court deemed the claims invalid for lack of invention. This ruling was upheld by the Second Circuit Court of Appeals. 

While the appeal was pending, Hazeltine applied for a reissue patent on September 26, 1934, and after the appeal's decision, redrafted the claims, resulting in a reissue patent (No. 19,744) granted on October 29, 1935. A subsequent infringement suit was filed against Detrola Radio & Television Corporation based on the reissue patent, excluding Claim 8. The District Court found the patent valid and infringed, a decision which was affirmed by the Circuit Court of Appeals.

The case raised questions regarding potential conflicts with the Second Circuit's earlier ruling. Wheeler's invention aimed to control amplification in both transmitting and receiving apparatus, focusing on its application in receivers to regulate loudspeaker volume. The technology involved modulating a high-frequency carrier wave with a low-frequency wave, which is amplified through triode tubes, eventually producing sound through a loudspeaker. Issues in the art included signal variations leading to loudspeaker distortion or fading. Wheeler's solution involved automatically adjusting the negative potential on the grid of the amplifying tubes in response to the strength of the incoming signal, thus stabilizing amplification levels through a feedback mechanism.

A method for signal amplification involves using a diode as a detector, where the output voltage matches the amplified signal's voltage. By coupling the detector's cathode and anode with a resistance, the anode remains slightly negative, maintaining a consistent potential with the amplifier's cathode. As signal strength increases, the rectified current raises the negative voltage at the detector's output, which in turn reduces the amplifier's gain. Conversely, a decrease in signal strength lowers the negative potential, enhancing amplification.

An alternative method utilizes a triode detector, maintaining a negative voltage on the grid using a battery and potentiometer. The output circuit connects the detector's anode to the amplifier's grid, transmitting the developed potential.

Both methods have pros and cons: the diode detector requires no additional battery but offers no amplification, while the triode requires a battery and voltage adjustment. Both setups include protections against unwanted electrical energy and manage the timing of negative potential transmission, though these features are not claimed to be novel.

Wheeler's specifications indicate that both methods operate similarly. His claims did not specify the detector type, leading to the cancellation of specific diode claims. After nearly five years, he submitted additional claims, including one that described a high resistance between the detector and amplifier. These were allowed, with one claim ultimately specifying no particular detector type or resistance, becoming Claim 1 of the patent.

In the Abrams lawsuit, Claims 1, 5, 6, and 10 were contested, centered on the broad principle of automatic volume control through any circuit type. The defendant argued that the patent lacked invention based on prior art, citing several earlier patents related to transmission and receiving systems, including those for automatic amplification control. Hazeltine attempted to differentiate Wheeler's patent by asserting it was limited to receiving systems, arguing that prior art related to transmission did not anticipate it. The District Court countered that Wheeler's patent was applicable to any modulated wave carrier signaling system and found no significant distinctions between Wheeler's claims and the prior art. Hazeltine also claimed the prior art did not include a time constant device, but the District Court ruled any differences did not constitute invention and would require rewriting the claims. 

The Circuit Court of Appeals viewed Wheeler's patent more liberally, assuming it was limited to receivers, yet found no inventive contribution in the changes made by Wheeler, describing them as obvious steps in a crowded field. Both courts concluded that Claim 10's mention of a diode detector did not introduce a novel element, as prior art had already disclosed similar technology. In response to these findings, Hazeltine revised its application for reissue, removing references to a triode detector and focusing on a diode detection system while retaining some claims that did not differentiate between diode and triode. Notably, the specifications were modified to emphasize a high resistance, which had been part of an unlit Claim 11, suggesting that Hazeltine's original claims for a broad monopoly on automatic volume control circuits were abandoned in favor of claiming a specific improvement. The petitioner argued that the reissued patent still did not disclose any invention in light of the prior art.

Automatic amplification control was recognized as existing technology prior to Wheeler's claimed invention, which necessitated a demonstration of improved means for such control. The lower courts identified invention in Wheeler's combination of a diode detector with a high resistance linked to the anode of the detector and the cathode of the amplifier, creating a negative potential that allows for a linear response to signal variations. However, this conclusion is seen as conflicting with previous rulings, particularly in the Abrams case, and does not adequately consider prior art disclosures.

The Circuit Court of Appeals differentiated between automatic amplification control in receivers and transmitters, as well as various methods that do not achieve a linear response. It acknowledged that prior art patents illustrate the ability to achieve a linear response, suggesting Wheeler may only have achieved an existing result through new means, rather than a novel invention. The prior art also established the utility of automatic amplification control across both receiving and transmitting devices, indicating that limiting Wheeler's claims to radio signal receivers does not imply invention.

Respondents assert that Wheeler's reissue patent is confined to a specific combination of a diode detector and high resistance, yet many cited patents already incorporate similar configurations for controlling amplification. The court found distinctions made by the lower court regarding Heising and Slepian's patents unfounded, as they also utilized automatic amplification control despite differing objectives. The lower court erred in stating that prior art relied solely on external batteries for control potential, as both Heising and Slepian achieved this from signal energy.

Wheeler cannot claim novelty for his linear response production, as the court found that Friis had already disclosed a similar linear response derived from battery energy. The insertion of a high resistance between the detector's anode and the amplifier's cathode, which Wheeler asserts is central to his invention, is also found in prior disclosures from inventors including Heising, Friis, Slepian, Affel, and Evans, many of whom describe it as a 'high resistance.' The court concludes that Wheeler's approach merely combines existing means that were already known in the art, and despite his lack of knowledge of earlier applications that predated his claimed invention date, he was not the first inventor. His contributions, if any, only required the application of existing skills. Consequently, the judgment is reversed and the case is remanded for further proceedings. Wheeler's conception date was noted as December 17, 1925, with several relevant patents cited, indicating that the claims did not materially differ from prior applications.