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Power Reduction in Continuous-Time Delta-Sigma Modulators Using the Assisted Opamp Technique

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2 Author(s)
Pavan, S. ; Dept. of Electr. Eng., Indian Inst. of Technol., Chennai, India ; Sankar, P.

The opamp in the first integrator of a high resolution single-bit continuous-time modulator has stringent slew rate requirements, which increases power dissipation. We introduce the “assisted opamp” integrator, which is a way of achieving low distortion operation with low power consumption. We present circuit implementations of our technique for single-bit modulators using NRZ and switched-capacitor-resistor (SCR) feedback DACs. Audio modulators designed in a 0.18 μm CMOS technology are used as vehicles to demonstrate the effectiveness of our techniques. The modulator with an NRZ DAC achieves a dynamic range of 92.5 dB in a 24 kHz bandwidth and dissipates 110 μW from a 1.8 V supply. A second design, which employs an SCR-DAC, achieves a dynamic range of 91.5 dB and dissipates 122 μW. The figures of merit (FOM) of these modulators, 175.9 dB and 174.4 dB respectively, are comparable with those of state-of-the-art multibit designs.

Published in:

Solid-State Circuits, IEEE Journal of  (Volume:45 ,  Issue: 7 )