On the performance of the differential cascode amplifier

Analysis is made of the differential cascode amplifier stage, an amplifier made of a differential common-emitter input pair driving a differential common-base output pair referenced to the emitter potential of the input pair. The analysis shows the differential cascode amplifier to have one or more orders of magnitude increase in common-mode input resistance and common-mode rejection ratio compared to that of a conventional differential pair. Consideration is also given to the use of junction field-effect transistors for either pair in the differential cascode stage. The frequency response of the stage is studied, and a potentially troublesome common-mode complex pole pair is identified as the one disadvantage of the differential cascode circuit.