Cascading bandpass sigma-delta A-D converters

This paper describes an extension of the technique of cascading of two bandpass sigma-delta converters to provide a higher dynamic range converter. As these converters operate in the continuous time mode, matching of the two feedforward signal paths must be controlled to a high degree of accuracy in both phase and amplitude. In general this is beyond the stability of the analogue circuits involved and an automatic calibration procedure becomes necessary. Practical results are described for a converter of this type