The design of optimal phase tracking current controlled attenuators

Multi-channel receivers often require good phase tracking between channels. If a PIN diode current controlled attenuator (CCA) is needed in each channel, the individual CCAs should track in phase over the full control range. Variations in PIN diode complex impedance as well as component tolerances will cause phase tracking errors in a family of CCAs. A method to compare CCA topologies in terms of phase tracking performance is developed. By using sensitivity analysis and defining a single root sum square measure for comparing attenuator topologies, an optimum topology is identified for implementing an electronically controlled variable attenuator. The results clearly show that the cascade parallel quarter-wave attenuator topology will have the smallest phase tracking error within a family of CCAs.