QPSK signal performance in the presence of phase spurious signals

When a wideband signal consisting of multiple carriers which may be either modulated or unmodulated, the latter case also including approximately a narrow band modulation signal case, is input to a nonlinear device such as an analog-to-digital converter, the output of the device may contain many spurious signals. An earlier analysis presented the number and power levels of various spurious signals generated due to the nonlinear characteristics Of the quantizer, which is an integral part of any A/D converter. Such a spur may also arise due to power supply fluctuations. Another possible source of such a spur is the frequency synthesizer generating the local oscillator signal in any communication system. Note that any spurious signal present in the desired signal band may be converted to a phase spur in the process of bandpass limiting of the signal at the receiver. This paper presents the degradation in the performance of the desired modulated signal such as a QPSK signal in the presence of multiple phase spurs.