Cascode amplifier: A cautionary tale

The cascode amplifier has the potential of providing high gain and high bandwidth simultaneously. However, the design is not as intuitive as one might at first think. In this paper we present a detail analysis of the single cascode amplifiers. The relationship between gain and bandwidth is important. When used to achieve maximum bandwidth the voltage gain of the common-source stage is close to unity. However when the cascode is designed to obtain a high voltage gain, then the gain-bandwidth trade-off, typical in the common source amplifier, re-appears. This analysis is used to provide the basis for practical cascode amplifier design.