On the Fulfilment of the Gain and Matching Specifications in the Design of a Single-Stage High-Frequency Amplifier

The first issue that needs to be addressed when designing a high-frequency amplifier is whether the circuit performance specifications can be met with the selected technology. In case the termination on one of the ports of the active device is fixed, the problem is usually solved using the gain and mismatch limits available in the literature. Otherwise, when the loads at the ports of the active device are not constrained, an analytical criterion is available in the literature to address the problem. However, it is not well known, so it is little exploited. Moreover, a proof of the criterion is not available in the literature. This paper presents a simple geometric proof of the criterion referenced. Closed-form expressions of the terminations determining the fulfilment of the amplifier design goals are determined and the stability of the amplifier in relation to the fulfilment of the performance specifications is addressed. Finally, it is shown that the criterion and the analysis developed in the paper are useful tools for the development of design methodologies of microwave amplifiers operating in more general conditions.