US 5304856

Patent Overview: US 5,304,856

Title: "Article comprising a balanced driver circuit with less power dissipation than conventional circuit"

Patent number / application: US 5,304,856 A; application US 07/992,514.

Inventor: Attilio J. Rainal.

Assignee: Original assignee AT&T Bell Laboratories Inc.; the source also lists American Telephone and Telegraph Company (assignment recorded 1992-12-17) and current assignees Nokia Bell Labs USA and AT&T Inc. (Google notes assignee listings may be inaccurate and were not legally analyzed.)

Key dates: Priority/filing date 1992-12-17; granted and published 1994-04-19. Related filings: EP 0609619 A3 (1993-12-02), JP 2991918 B2 (1993-12-13), KR 100269741 B1 (1993-12-16). Anticipated expiration 2012-12-17; status listed as "Expired - Lifetime."

Purpose: To provide a low-power balanced driver circuit that "essentially eliminates inductive noise" while reducing power dissipation versus conventional balanced or unbalanced drivers. The stated motivation is inductive noise when high-speed, high pin-out ICs have many drivers switching simultaneously, causing transient currents through ground/power inductance and possible false switching.

Plain-language scope: A balanced driver has two emitter follower output stages on an IC driving a pair of signal leads (primary and secondary), terminated by two resistors whose center tap connects to a supply −V_T; a receiver sits in parallel. Current in the secondary lead has equal amplitude but opposite sign to the primary, so negligible current returns through common ground leads. The invention lies in on-chip modification of voltage swing ΔV and levels V₁, V₂ for a special range of V_T: ΔV approximately 0.125–0.375 V and −V_T approximately −1.0 to −1.5 V, keeping minimum collector current above 1 mA. The excerpt reports roughly 50% less dissipation than a conventional balanced driver and about 25% less than a conventional unbalanced driver, applicable to point-to-point and bused interconnections, in ECL, BiCMOS, GaAs, or CMOS technologies, with "no modifications" needed to the differential line receiver.

Source: https://patents.google.com/patent/US5304856/en

Not established by the excerpt: the full text of the claims and their exact wording/scope; the complete figures and equations; whether the noted numerical benefits are claimed or only described; and any other prior art beyond the October 1992 IEEE Spectrum article and a "'767 application" mentioned in the text. Litigation, ownership transfers, validity, and prior-art analysis are outside this overview.