Linearity Enhancement of VCO-Based Continuous-Time Delta-Sigma ADCs Using Digital Feedback Residue Quantization

A linearity enhancement scheme for voltage-controlled oscillator (VCO)-based continuous-time (CT) delta-sigma (& UDelta;sigma) analog-to-digital converters (ADCs) is proposed. Unlike conventional input feedforwarding techniques, the proposed feedforwarding scheme using digital feedback residue quantization (DFRQ) can avoid the analog summing amplifier, allow intrinsic anti-aliasing filtering (AAF) characteristic, and cause no switching noise injection into the input. A VCO-based CT & UDelta;sigma ADC adapting the proposed DFRQ enables residue-only processing in the quantizer, avoiding the degradation of signal-to-noise and distortion ratio (SNDR) due to VCO nonlinearity. The use of DFRQ also reduces the voltage swing of integrators without the drawbacks caused by conventional input feedforwarding techniques. The performance evaluation results indicate that the proposed VCO-based CT & UDelta;sigma ADC with DFRQ provides 30.3-dB SNDR improvement, reaching up to 83.5-dB in 2-MHz signal bandwidth.

Automated summary

This study proposes a linearity enhancement scheme for VCO-based CTΣ ADCs, which enables residue-only processing using DFRQ to avoid degradation of SNDR caused by VCO nonlinearity and improve the ADC performance.