A continuous-time (CT) sigma-delta modulator (SDM) for condenser microphone readout interfaces is presented in this paper. The CT SDM can accommodate a single-ended input and has high input impedance, so that it can be directly driven by a single-ended condenser microphone. A current-sensing boosted OTA-C integrator with capacitive feedforward compensation is employed in the CT SDM to achieve high input impedance and high linearity with low power consumption. Fabricated in a \(0.35\)-\(\upmu\)m complementary metal-oxide-semiconductor (CMOS) process, a circuit prototype of the CT SDM achieves a peak signal-to-noise-and-distortion ratio of 74.2 dB, with 10-kHz bandwidth and \(801\)-\(\upmu\)W power consumption.
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Du, D., Odame, K. A microphone readout interface with 74-dB SNDR. Analog Integr Circ Sig Process 81, 241–252 (2014). https://doi.org/10.1007/s10470-014-0383-0