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Differential Amplifier

IP.com Disclosure Number: IPCOM000074573D
Original Publication Date: 1971-May-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR

Abstract

A differential amplifier has a low-input impedance and a high common-mode rejection. Transmission line 10 is connected to input network 11 consisting of a voltage divider, having its extremities connected to the emitter electrodes of amplifier transistors 12 and 13. The composite impedance of the voltage divider and the emitter-base impedance are equal to the transmission line impedance. Output signals E0 and E0' are taken from the collectors of transistors 12 and 13 through load resistors 14 and 15.

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Differential Amplifier

A differential amplifier has a low-input impedance and a high common-mode rejection. Transmission line 10 is connected to input network 11 consisting of a voltage divider, having its extremities connected to the emitter electrodes of amplifier transistors 12 and 13. The composite impedance of the voltage divider and the emitter-base impedance are equal to the transmission line impedance. Output signals E0 and E0' are taken from the collectors of transistors 12 and 13 through load resistors 14 and 15.

Unity-gain amplifier 16 connects input node 17 to the base electrodes of transistors 12 and 13. Any common-mode signal supplied from cable 10 is unattenuated at 17. As a result, the voltages from base to emitter of transistors 12 and 13 for the differential signal are unattenuated. The common-mode voltage between the base and emitter of transistors 12 and 13 is completely attenuated when amplifier 16 has unity gain. If amplifier 16 has other than unity gain, attenuation will be high, but less than complete. The capacitor 20 provides AC coupling.

The transistor in amplifier 16 may be a Darlington connected pair for obtaining independence of line impedance from amplifier 16 operation.

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