Qpsk demodulator

Abstract

A receiver including two optimizers for demodulation, sampling and quantization of received QPSK digital data. One optimizer adjusts the phase of a reference signal used for demodulating the QPSK data into baseband in-phase and quadrature channels and another optimizer adjusts a sampling clock used to sample and quantize the baseband channels. The reference signal and the sampling clock are dithered in quadrature. Variations in the amplitude of the quantized data extracted by an eye quality monitor. Each optimizer multiplies the eye quality monitor output by a corresponding dither clock and integrates to form an error signal. Phase shifters, responsive to corresponding error signals and dithered clocks, adjust the phase of the demodulation reference signal and sampling clock. The data quality signal monitor translates the magnitude of the quantized data signals to a common set of signals for each state of the data signal. These common signals are translated into a voltage representing the degree to which the data signal amplitude corresponds to a predetermined value. Additionally, a phase shifter is shown which splits its input signal into two signals in quadrature. Theses two signals, when multiplied by two corresponding values and the products summed, form a phase shifted version of the input signal. The two values correspond to a nominal phase shift and vary to impart a linear phase change to the input signal proportional to a control voltage.