2‐1 Switched‐current multi‐stage noise‐shaping delta–sigma modulator with a digital noise‐cancellation circuit

Abstract

This study focuses on the design of a 2-1 switched-current (SI) multi-stage noise-shaping delta–sigma modulator with a digital noise-cancellation circuit. The noise-cancellation circuit is designed by employing various algorithms for designing the logic circuits and constructing a delay block with an inverter and a transmission gate. It can eliminate the higher-order quantisation noise from the first stage of the modulator completely. In the proposed differential current-mode sample-and-hold circuit, low-input impedance is presented with feedback and width-length adjustment in SI feedback memory cell, a coupled differential replicate with the common-mode feed-forward (CMFF) circuit is used to stabilise the common-mode bias voltage at input terminal, and a differential cross-connected CMFF circuit is utilised to fix the bias voltages. Post-layout simulations reveal that the simulated signal-to-noise-and-distortion ratio (SNDR) was 90.4 dB and the effective number of bit (ENOB) was 14.73 bits. Measurements show that the SNDR was 59.13 dB and the ENOB was 9.53 bits at a sampling rate of 10.24 MHz, an oversampling ratio of 256, and a signal bandwidth of 20 kHz. This design has a power requirement of 12.99 mW from a supply voltage of 1.8 V and occupies a core area of 0.14 mm2.