Demodulators

A high quality demodulator uses software techniques to recover digital data from an FSK or PSK modulated signal. A Software Costas loop is utilised to convert representative samples of the incoming signal to a baseband signal which is further software processed by a second software loop to provide 'I' and 'Q' output signals with associated timing information. The representative signal samples are derived by Sub Nyquist sampling under control of a microprocessor (100) which provides control values to a digitally controlled oscillator (102). The digitally controlled oscillator (102) controls a sample and hold circuit (103) to select representative signal samples of the in-phase and quadrature phase modulation.