Stability Safety Margin Based Design of Low Noise Microwave Amplifiers
In low noise microwave amplifier design, particularly when using conditionally stable transistors, it is impossible to simultaneously achieve maximum gain, minimum noise figure and maximum port match. Hence it is necessary to trade-off these performance parameters which is usually accomplished with the aid of stability, gain, noise figure and mismatch (or VSWR) circles described on the reflection coefficient planes. However, use of these graphical aids is often subjective, necessitating final optimisation using circuit design software. In this paper, we propose a different approach whereby the functional behaviour of two objective functions involving gain, noise figure and port mismatch are described as functions of the stability safety margin. This approach leads to an optimum design without requiring sophisticated optimisation algorithms and includes stability safety margin as a design parameter.