A low power sigma-delta modulator using charge-steering Opamp for Bluetooth application

The conventional current-steering Opamp is the building block of sigma-delta modulator circuits. It is also the major power consuming part of the circuit. The charge-steering concept can be applied to Opamps to obtain minimum power consumption. The two-stage charge-steering Opamp has been designed using 0.18um TSMC CMOS technology that consumes 0.23 mW power at a 48 MHz sampling frequency. A 2nd order, 1-bit, SC sigma-delta modulator is used to prove the applicability of the charge steering concept in sigma-delta modulators. The system achieves a SNR of 46 dB and a DR of 60 dB over a 1 MHz BW. The total power consumption of the circuit is 1.3 mW at 1.2v power supply.