Abstract

A dual mode quadrature detector (15) uses the same components for both narrow band and wide band operation and provides an output amplitude which is independent of the mode of operation selected. A multiplier (32) provides a demodulated output signal (16) which is responsive to the phase difference between a signal (14) at one input (32A) and a phase shifted version of the signal at the other input (32B). A capacitor (30) and a phase shifting circuit (31) provide the phase shifted version of the signal. The phase shifting circuit (31) is responsive to a mode control signal (24) for determining the phase shift which is provided. The phase shift at the maximum frequency deviation of the narrow band signal is the same as the phase shaft at the maximum deviation of the wide band signal so that the output amplitude from the detector (15) is the same for both narrow band and wide band operation. The phase shift provided is controlled by varying the quality factor (Q) of the phase shifting circuit (31). This is achieved by controlling the amount of resistance placed in parallel with a tuned circuit (33, 34) in the phase shifting circuit (31). A higher Q is obtained by using a higher resistance, and a lower Q is obtained by using a lower resistance.