A new17-bit 105.5-dB dynamic range 2-1 cascaded SAR-based [formula omitted] modulator using single-bit DAC for audio applications

Abstract

A new multi-bit ΔΣ modulator using a single-bit DAC based on an improved successive approximation register (SAR) quantizer is presented. Therefore, it eliminates the requirement for a dynamic element matching circuit that is used in the conventional multi-bit ΔΣ modulators. Although the improved SAR quantizer uses a single-bit DAC to generate multi-bit outputs, the conversion time is the same in the proposed quantizer and the conventional SAR ADCs. Utilizing a single-bit DAC also reduces the number of capacitors in the modulator structure which results in reducing the power and area consumption. In addition, the proposed quantizer uses the feedback DAC of the modulator to predict the output of the integrator, which results in elimination of the internal DAC of the SAR quantizer. To study the performance of the proposed method, a 2-1 cascaded discrete-time delta sigma modulator with 4-bit proposed quantizer is designed in 180 nm CMOS technology. The proposed SAR quantizer predicts its input signal in six clock pulses. The simulation results show an SNDR of 98.94 dB and dynamic range of 105.5 dB. The proposed modulator achieves FOM of 0.2pJ/conv.-step and effective number of bit of 17bits with an input bandwidth of 20 KHz.