Analysis and Design of Bipolar Programmable-Gain Amplifiers Using Digital Potentiometers

This paper presents a theoretical analysis and design procedure of versatile programmable amplifier circuits with bipolar gain. In particular, under analysis are two basic electronic circuits of single- and two-stage bipolar program-mable-gain amplifiers employing monolithic CMOS digital potentiometers. For both circuits, a single digital potentiometer is connected as a voltage divider in the negative feedback network of an op-amp. As a result of adjusting the position of the wiper of the potentiometer, the depth of the feedback changes, and hence the voltage gains change. Based on theoretical analysis of the circuits, analytical expressions for the basic static and dynamic parameters are derived. Moreover, using those formulas, approaches for selecting an appropriate circuit configuration and recommendations for selecting passive and active component values are proposed. The workability of the presented design recommendations is proved by computer simulations and experimental testing of sample analog circuits. The comparative analysis between simulation and measured results shows that the maximum relative error is up to 10%, which ensures a sufficient degree of accuracy in comparison to the tolerances of the electrical parameters.