A single chip if FM/Am decoder using a sigma-delta analog-digital converter

This paper describes a digital radio demodulator for broadcast AM/FM receiver applications. The IC is comprised of a Sigma-Delta A/D converter and a digital AM/FM demodulator. The Sigma Delta modulator converts the standard 10.7 MHz IF signal, allowing the use of digital channel-select filtering, providing improved performance over analog filtering. Subsequent demodulation and signal processing are performed digitally, allowing flexibility in the algorithms employed and greater integration with other digital circuitry in the system. There is also a software element to the system, as the stereo decoder and RDS decoding functions are implemented by DSP off-chip rather than on dedicated hardware. Behavioural-level simulations of the system are presented, which show it meets the requirements of 80 db SNR for stereo FM input signals over a 150 kHz bandwidth.