A 4-channel, 18 b /spl Sigma//spl Delta/ modulator IC with chopped-offset stabilization

Switched-capacitor /spl Sigma//spl Delta/ modulation presents special problems for high DC precision applications where offsets and offset drifts must be minimized. Traditional chopper stabilization techniques can have the adverse effect of aliasing the large amount of high-frequency quantization noise into baseband. One solution is to chop at integer multiples of the sampling frequency where the quantization noise spectrum is quiet. However, chopping at multiples of the sampling rate can increase the speed and power requirements on the amplifiers since it may be required to settle full output swings several times in each sampling interval. Alternatively, offset compensation has been used in /spl Sigma//spl Delta/ modulators with the same offset and 1/f noise reduction effects as chopping, and with the additional benefit of opamp gain enhancement. Offset compensation effectiveness is limited by switch charge injection. Fully-differential circuit topologies help suppress errors caused by charge injection by rejecting common-mode charge injection but are still limited by switch mismatches. The author presents a /spl Sigma//spl Delta/ modulator which uses offset compensation to suppress the amplifier offset and 1/f noise, and chopping of switches to average out mismatched charge injection effects. Chopping on the switches alone, unlike chopping the amplifier, does not substantially increase the demands on the amplifier, which is particularly important in high-speed, low-power applications.