25th IEEE International Conference on Electronics, Circuits and Systems
The paper entitled “A Tracking Quantizer for Continuous Time Quadrature Bandpass Sigma-Delta Modulators”, by T. Saalfeld, M. Scholl, C. Beyerstedt, R. Wunderlich and S. Heinen, has been included in the proceedings of the 25th IEEE International Conference on Electronics, Circuits and Systems!
The paper presents a quadrature bandpass sigma-delta modulator with a tracking quantizer consisting of only two comparators for each signal path. It is designed for a low IF narrow band receiver front end. Two comparators follow the input signal with a resistive D/A converter which supplies a variable and stable reference voltage. The frequency limitations introduced by this quantizer concept are discussed and solutions are presented. Additionally, the fragile loop stability of a tracking quantizer based modulator is enhanced by a fast digital control based on selection of precomputed A/D converter sampling values. For a highly linear feedback a non-return-to-zero current steering D/A converter is controlled by a low complexity dynamic element matching algorithm. The modulator has been designed and layouted in a 130 nm RF CMOS technology occupying an area of 0.87 mm 2 . System level simulations show 86 dB SNR at 1 MHz bandwidth with 96 MHz clock frequency. Furthermore, a low power consumption of 3.8 mW at 1.2 V supply voltage is achieved.