A VCO-Based Continuous Time Delta-sigma ADC with An Alternative Feedforward Scheme VCO

A Voltage Controlled Oscillator (VCO) based continuous-time Delta-Sigma analog-to-digital converter (ADC) with an alternative new feedforward VCO scheme contributing to higher oscillation frequency within VCO-Based quantizer is explored in this paper. Fourth-Order noise shaping is achieved using three operational transconductance amplifiers (OTAs) and VCO acting as integrator and quantizer. Meanwhile, the excess loop delay (ELD) introduced by the finite gain-bandwidth product of OTAs is compensated by zero-order path in the loop filter to reduce the power consumption further. The simulation results indicate that this prototype achieves a SNDR of 72.17 dB over 10MHz bandwidth sampling at 400MHz while consumes 24mW for a 1.8V supply in 180nm CMOS technology.