FREQUENCY CONTROL IN AN FSK RECEIVER

摘要

An RF receiver (1) comprises an antenna (2) for receiving radiated RF signals and for providing an FSK electrical signal. The receiver further comprises a first mixer (31) in which a signal from a local oscillator is mixed with an input signal from the FSK signal to provide an output signal. The mixer is controlled by local oscillator (32). The output from the first mixer is a version of the signal derived from the FSK signal at input (3). The second mixer (33) is controlled by clock signal and outputs a signal which is a frequency shifted version of the signal on output (3). The receiver further comprises detector circuit (36) for receiving a second signal and providing a third electrical signal having an amplitude representing an instantaneous logic level of the digital frequency modulating signal. The receiver further comprises the feedback resistor (12) providing a tuning voltage to the voltage controlled oscillator of the first mixer.