| 摘要 |
The receiver includes input means comprising an antenna and blocking filter, the output of which is connected to an amplifier. The input signal is split and mixed with an in-phase and quadrature phase signal generated by an oscillator in a mixer circuit, respectively. An output from each mixer circu it is applied to a low pass filter and to an input of a limiting circuit. The output from each low pass filter is applied to an input of a summator circui t respectively, a first of which is arranged to sum the in-phase and quadratur e phase signals, and the second of which is arranged to subtract the in-phase and quadrature phase signals to generate a respective output signal having a n axis intermediate of the in-phase and quadrature phase signal axes. These signals, together with the in-phase and quadrature phase signals are passed through a limiting circuit respectively, to a decoder circuit for recovering the data. The output of the limiting circuits represents signals quantised t o eight possible phase states separated by 45~. When the input signal is GFSK modulated the vector will always cross at least one axis, so the direction o f rotation can be established prior to data recovery. In an alternative embodiment a ratiometric combiner may be used instead of the summator circuits, and this is particularly useful for .pi./4-DQPSK modulation, where the phase excursion per symbol is ~ 45~ or ~ 135~ depending upon the bit pai r combination, and in this embodiment a minimum of eight axes are generated giving sixteen sectors and 22.5~ phase resolution.
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