A 12-bit 4-kHz incremental ADC with loading-free extended counting technique

In this design, a low-power incremental ADC employing the loading-free architecture for the extended counting technique is proposed. The proposed topology uses a multi-bit SAR ADC to complete the extended counting conversion, but the integrator of the preceding incremental ADC is not loaded by the DAC array of the SAR ADC, which means the opamp power can be reduced. This work adopts an incremental ADC to convert the first 5-bit MSB and a synchronous SAR ADC to convert the last 7-bit LSB, and thus totally 12-bit resolution can be obtained without calibration. The proposed topology is capable of achieving high resolution, and furthermore holds the power efficient advantage of SAR ADCs. The proposed ADC is implemented in a 0.18-μm 1P6M CMOS process. Under 4-kHz input signal bandwidth and 23.07-μW power consumption, the peak signal-to-noise and distortion ratio is 69.38 dB. The active core area including clock generator occupies of 0.33 mm².