Low rate, direct conversion FSK radio-frequency signal receivers

摘要

The receiver (1) picks up low rate FSK radio frequency signals. This receiver includes an antenna (2) for receiving FSK radio frequency signals, a low noise amplifier (3) connected to the antenna, a local oscillator (7) for supplying oscillating signals (LO), a phase shift circuit (16) for performing a 0° to 90° phase shift, and vice versa, in the oscillating signals (LO) or the incoming FSK radio frequency signals in each semi-period of a phase switching cycle (1/fs). The phase shift circuit alternately and successively generates in-phase and quadrature oscillating signals, or in-phase and quadrature incoming FSK radio frequency signals. The receiver includes a single mixer (4) for mixing the oscillating signals successively with the incoming FSK radio frequency signals, so as to generate alternately intermediate in-phase and quadrature baseband signals (INT) as a function of the phase shift circuit. The receiver further includes a low-pass filter (8) for filtering the intermediate in-phase and quadrature signals, and a demodulation stage (20) for demodulating the data (DOUT) from the filtered intermediate signals. The receiver is arranged such that the phase shift circuit (16) is switched by a phase selection signal (SEL) to a phase switching cycle frequency (fs) which is lower than the frequency deviation (Δf) of the modulated data in the FSK radio frequency signals and higher than the data rate frequency. Magic circuits (14, 15) in the demodulation stage reconstruct the intermediate signals during each switch operation for continuous demodulation in the demodulator (12).

主权项

1. A low rate radio frequency signal receiver for frequency shift key (FSK) modulation, said low rate receiver including:
an antenna to receive FSK radio frequency signals, a low noise amplifier to amplify and filter the signals picked up by the antenna, a local oscillator to supply oscillating signals having a substantially identical frequency to the carrier frequency of the incoming FSK radio frequency signals, a phase shift circuit to perform a 0° to 90° phase shift and vice versa in the oscillating signals or the incoming FSK radio frequency signals, in each semi-period of a phase switching cycle, so as to generate, alternately and successively, in-phase and quadrature oscillating signals, or in-phase and quadrature incoming FSK radio frequency signals, a mixer to successively mix the in-phase and quadrature oscillating signals with the amplified and filtered incoming FSK radio frequency signals, or the oscillating signals with the in-phase and quadrature FSK radio frequency signals, so as to generate alternately intermediate in-phase and quadrature baseband signals, at least one low-pass filter to filter the intermediate in-phase and quadrature baseband signals, and a demodulation stage to demodulate data from the filtered intermediate in-phase and quadrature baseband signals, wherein the receiver is arranged such that the phase shift circuit is switched by a phase selection signal to a phase switching cycle frequency which is lower than a frequency deviation of the modulated data in the FSK radio frequency signals and higher than a frequency of a modulated data rate, and wherein the demodulation stage input includes a demultiplexer to receive the filtered intermediate in-phase and quadrature signals, said demultiplexer being controlled by the phase selection signal so as to supply cyclically the filtered intermediate in-phase signals at a first output and the filtered intermediate quadrature signals at a second output, and a data demodulator receiving the filtered intermediate in-phase and quadrature signals from the demultiplexer, to supply data signals.