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Browse Prior Art Database

AC Amplifier Having Digitally Controlled Gain

IP.com Disclosure Number: IPCOM000079915D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR

Abstract

This amplifier selectively provides variable amplification of an alternating input signal, in digitally controlled steps, and provides a constant DC level in the output signal, independent of the selected gain. A common-base configuration is shown, but the same technique can be applied to a common-emitter configuration.

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AC Amplifier Having Digitally Controlled Gain

This amplifier selectively provides variable amplification of an alternating input signal, in digitally controlled steps, and provides a constant DC level in the output signal, independent of the selected gain. A common-base configuration is shown, but the same technique can be applied to a common-emitter configuration.

The alternating signal to be amplified is connected to input 10, where it is processed by emitter-follower 11 and applied to conductor 12. This conductor connects to a number of similar networks, for example the three networks 13, 14 and 15. The gains of these networks may be any convenient weighting such as binary. The output of each of these networks is applied to summing resistor 16 and to output 17. The amplification is selectively determined by digital input control 18. This control is effective to render one or more of the networks 13, 14 and 15 operable to amplify the input signal.

With reference to network 13, transistors 19 and 20 form a current mode switch. If network 13 is to amplify the input signal, transistor 19 is turned on by input 18, and transistor 20 is turned off. With transistor 19 conducting, only transistor 21 of the pair 21, 22 conducts and an amplified alternating signal, with a DC component, is applied to resistor 16. When network 13 is not selected for operation, transistor 19 is turned off by input 18. As a result, transistor 20 conducts. This in turn causes only transistor...