A 92-dB DR, 24.3-mW, 1.25-MHz BW Sigma-Delta Modulator Using Dynamically Biased Op Amp Sharing

A 2-2 cascaded switched-capacitor Sigma Delta modulator is presented for design of low-voltage, low-power, broadband analog-to-digital conversion. To reduce power dissipation in both analog and digital circuits and ensure low-voltage operation, a half-sample delayed-input feedforward architecture is employed in combination with 4-bit quantization, which results in reduced integrator output swings and relaxed timing constraint in the feedback path. The integrator power is further reduced by sharing an op amp in the two integrators in each stage and periodically changing the op amp bias condition between a high-current and a low-current mode using a fast low-power high-precision charge pump circuit. Implemented in a 0.18-mu m CMOS technology, the experimental prototype achieves a 92-dB dynamic range, a 91-dB peak signal-to-noise ratio, and an 84-dB peak signal-to-noise plus distortion ratio, respectively for a signal bandwidth of 1.25 MHz. Operated at a 40-MHz sampling rate, the modulator dissipates 24.3 mW from a 1 V supply.