Differential line driver

Details Differential line driver Differential line driver

1996-07-08

1999-02-16

Pham, Chi H.

Pulse or digital communications

Cable systems and components

375258, 326 89, 326 90, 326126, 333109, 333116, H04B 300, H03K 190175, H03K 19086, H01P 512

Patent

active

058728112

ABSTRACT:
A differential line driver having a pair of transistors arranged as a differential pair for driving a transmission line with a differential logic output signal produced in accordance with a differential logic input signal fed to the base electrodes of the pair of transistors. The differential line driver includes circuitry for suppressing EMI emissions generated by common mode voltage switching transients produced at the collector electrodes of the pair of transistors in response to changes in the differential logic input signal. The common mode voltage switching transient suppression circuitry includes a pair of additional transistors. The differential logic input signal is fed to base electrodes of the additional transistors, and through such additional transistors, to the base electrodes of the pair of transistors of the differential pair. In one embodiment of the invention, the additional transistors are connected in a Darlington pair arrangement with the pair of transistors of the differential pair. While switching transients is the common mode voltage is still present because of the transient base current produced in the pair of transistors of the differential pair, the magnitude of the base current is attenuated by a factor .beta.+1, where .beta. is the beta of the additional (i.e., Darlington pair) of transistors. In another embodiment of the invention, the pair of transistors of the differential pair are NPN transistors and the additional, Darlington connected, pair of transistors are PNP transistors.

REFERENCES:
patent: 4760282 (1988-07-01), Kuo et al.
patent: 4791314 (1988-12-01), Kuo et al.
patent: 5049763 (1991-09-01), Rogers
patent: 5051609 (1991-09-01), Smith
patent: 5065050 (1991-11-01), Fernandez
patent: 5321575 (1994-06-01), Shilo
patent: 5457406 (1995-10-01), Takada et al.
patent: 5506521 (1996-04-01), Collins

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