Simple, Stable and Reliable Transistorized DC Amplifiers

A transistor dc feedback voltage amplifier using a differential input stage followed by a single common emitter stage is analyzed to obtain the gain and drift rate dependence on temperature. It is found that under typical restraints on allowable input terminal current, the open loop gain of such an amplifier is restricted to a value only somewhat greater than twenty (q/2kT) times the voltage across the collector load of the common emitter stage. The drift rate is found to depend on the common emitter stage transistor and on the signal source resistance as well as on the differential stage. A conservative design philosophy which limits each of the factors contributing to drift rate is found to be necessary if predictable, parameter independent performance is to be obtained.