A current-mode VCO-based amplifier-less 2nd-order ΔΣ modulator with over 85dB SNDR

In this paper, a new current-mode VCO-based delta-sigma modulator is presented to avoid the need to use operational-transconductance amplifiers (OTAs), which are usually the most power hungry building-blocks. The proposed hybrid structure doesn´t require an explicit high-gain block in the loop filter in order to achieve high resolution with second order noise shaping. Simulation results show the proposed current-mode VCO-based ADC performance is able to achieve to SNDR/SNR of 85/85.4dB with 5MHz bandwidth with only 2dB gain in the front-end current-mode integrator. The circuit architecture uses two 4-bit pseudo-differential VCO-based quantizers, operating in parallel, and two current-steering DACs providing intrinsic dynamic element matching (DEM).