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Four Level Gain Control Stage

IP.com Disclosure Number: IPCOM000076295D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Millican, DL: AUTHOR

Abstract

Shown is a differential amplifier having four possible levels of gain controlled by a two-bit binary word. The gain control stage could typically be used to go directly from the output of a digital register to a gain control stage, without the necessity of going through a digital-to-analog converter.

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Four Level Gain Control Stage

Shown is a differential amplifier having four possible levels of gain controlled by a two-bit binary word. The gain control stage could typically be used to go directly from the output of a digital register to a gain control stage, without the necessity of going through a digital-to-analog converter.

The input to the gain control stage is at terminals 10 and 11, while the output is taken from terminals 12 and 13. Only one of the transistors in the set 14 and 15 or the set 16 and 17 are operative at a given time. As configured, either transistors 14 and 17 are operative simultaneously, or transistors 15 and 16 are operative simultaneously.

The selection of the operative pair of transistors is controlled by transistors 18 and 20. If a binary 0 is applied at terminal 22, the voltage representative of binary 0 is such that transistor 18 will be off and transistor 20 will be on. Therefore, transistor pair 15 and 16 will be operative. For this pair, the emitter resistances are RE3 and RE4. On the other hand, if a binary 1 is applied at node 22, the voltage is such that transistor 18 is on and transistor 20 is off. In this configuration, transistors 14 and 17 are the operative transistors in the differential amplifier and the emitter resistances are RE1 and RE2.

Thus, the binary input 0 or 1 to node 22 will control the emitter resistance of the differential amplifier and can select two different resistances. Of course, as is well known, the...