Design and Performance Analysis of a Digitally Programmable Op-Amp

In this paper, the design and simulated response of a digitally programmable operational amplifier (op-amp) is discussed. The purpose of this programming capability is to allow for the op-amp DC gain and frequency response to be controlled. This is attained by programming the transistor tail current in the differential input stage of the op-amp operating at an analog power supply voltage of +3.3 V. Serial peripheral interface (SPI) communications is used here to provide control of the op-amp from an external digital host processor. The design is considered as a particular implementation of digital control of analog circuits. Examples of such digital control strategies of analog circuits are identified to create a context for this work before discussing and analyzing the op-amp design of concern.