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Digitally Controlled Amplifier Circuits

IP.com Disclosure Number: IPCOM000081086D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Ottesen, HH: AUTHOR

Abstract

It is advantageous to employ digital controls for controlling the signal gain of amplifiers, particularly operational amplifiers. Such digital controls should not detract or alter the operation of the amplifier, such as introduce nonlinearities and loading into its operation. Further, for simplifying the digital-to-amplifier interface, it is desirable to have a linear relationship between each digital control step and amplifier gain. These results are achieved for inverting and noninverting amplifiers, as shown in the figures. In the inverting or inverter configuration, the digitally controlled resistive network R3 in the gain equations is in the denominator. Substitution of R3 into the gain equation yields a summation in the numerator, resulting in linear resistance changes proportional to the digital input.

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Digitally Controlled Amplifier Circuits

It is advantageous to employ digital controls for controlling the signal gain of amplifiers, particularly operational amplifiers. Such digital controls should not detract or alter the operation of the amplifier, such as introduce nonlinearities and loading into its operation. Further, for simplifying the digital-to-amplifier interface, it is desirable to have a linear relationship between each digital control step and amplifier gain. These results are achieved for inverting and noninverting amplifiers, as shown in the figures. In the inverting or inverter configuration, the digitally controlled resistive network R3 in the gain equations is in the denominator. Substitution of R3 into the gain equation yields a summation in the numerator, resulting in linear resistance changes proportional to the digital input.

For the inverter, the overall gain is (R2+R4)/R1; while the adjustable gain factor is in increments of R(p)/R. In the noninverting amplifier, overall gain is (R1+R2+R4)/R1; while the adjustable gain factor is in increments of R(g)R. In addition to providing a linear gain relationship with respect to the digital input, the two illustrated amplifier configurations completely isolate the digital input control from the signal input at E(i), input impedance is constant, there is no added capacitance to the amplifier circuit signal flow because of the digital input, there is no shunting effect in the feedback network from cl...