| 摘要 |
A differential FM detection of signals uses in-phase and quadrature phase signal components of a received signal in the detection process, wherein the in-phase and quadrature phase signal components are at a low intermediate frequency (IF). The in-phase and quadrature phase signal components are each amplitude limited, sampled at a prescribed sampling rate and filtered in a prescribed manner. Delayed versions of the filtered in-phase and quadrature phase signal components are generated and, then, signal products are generated of the delayed in-phase signal component and quadrature phase signal component, and the delayed quadrature phase signal component and in-phase signal component. The algebraic difference of the generated signal products is obtained to yield the desired data signal, e.g., symbols. Specifically, a FIR (finite impulse response) filter is employed to filter the limited and sampled versions of the in-phase and quadrature phase signal components to alleviate the interference caused by the limiter. In an embodiment of the invention, the detector is a differential Continuous Phase Frequency Shift Keyed (CPFSK) FM detector. In a GFSK differential FM detector, employing a post detection compensation arrangement significantly reduces distortion caused by ISI. Specifically, the absolute value of the detected data signal is obtained and compared to a prescribed threshold value. If the threshold is exceeded no compensation is required. However, if the threshold is not exceeded, it is assumed that prescribed data symbol transitions have occurred and that the currently received data symbol is the inverse of the last preceding detected data symbol. Consequently, the current data symbol is replaced by the inverse of the preceding data symbol.
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