Phase detectors for detecting a mutual phase difference between two

Abstract

A phase detector for detecting a mutual phase difference between two signals, such as first and second microwave signals, comprises first and second signal paths for being supplied with first and second input signals of the same frequency, respectively, and providing with a predetermined additional mutual phase difference between the first and second input signals at their output ends and a field effect transistor having a pair of input electrodes connected to the output ends of the first and second signal paths, respectively, and an output electrode from which an output signal representing a mutual phase difference which the first and second input signals have originally therebetween is derived. The first and second input signals at the input electrodes of the field effect transistor have the original mutual phase difference which is to be detected and the predetermined additional mutual phase difference added by the first and second signal paths therebetween. The field effect transistor is biased to operate with a gate bias voltage nearly equal to a pinch-off voltage thereof. In order to establish such biasing state without reducing the operational gain of the field effect transistor, a biasing resistance connected to the source of the field effect transistor is selected to be low and a current source is provided for supplying an external biasing current to the biasing resistance, thereby to produce the gate bias voltage required.