TY  - EJOU
AU  - Li, Sha 
AU  - Meng, Qiao 
AU  - Tariq, Irfan 
AU  - Chen, Xi 

TI  - A 78-MHz BW Continuous-Time Sigma-Delta ADC with Programmable VCO Quantizer
T2  - Computers, Materials \& Continua

PY  - 2022
VL  - 72
IS  - 3
SN  - 1546-2226

AB  - This article presents a high speed third-order continuous-time (CT) sigma-delta analog-to-digital converter (SDADC) based on voltage-controlled oscillator (VCO), featuring a digital programmable quantizer structure. To improve the overall performance, not only oversampling technique but also noise-shaping enhancing technique is used to suppress in-band noise. Due to the intrinsic first-order noise-shaping of the VCO quantizer, the proposed third-order SDADC can realize forth-order noise-shaping ideally. As a bright advantage, the proposed programmable VCO quantizer is digital-friendly, which can simplify the design process and improve anti-interference capability of the circuit. A 4-bit programmable VCO quantizer clocked at 2.5 GHz, which is proposed in a 40 nm complementary metal-oxide semiconductor (CMOS) technology, consists of an analog VCO circuit and a digital programmable quantizer, achieving 50.7 dB signal-to-noise ratio (SNR) and 26.9 dB signal-to-noise-and-distortion ration (SNDR) for a 19 MHz − 3.5 dBFS input signal in 78 MHz bandwidth (BW). The digital quantizer, which is programmed in the Verilog hardware description language (HDL), consists of two-stage D-flip-flop (DFF) based registers, XOR gates and an adder. The presented SDADC adopts the cascade of integrators with feed-forward summation (CIFF) structure with a third-order loop filter, operating at 2.5 GHz and showing behavioral simulation performance of 92.9 dB SNR over 78 MHz bandwidth.
KW  - Sigma-delta ADC; oversampling converter; VCO; noise-shaping; programmable quantizer

DO  - 10.32604/cmc.2022.027404