Enhanced circuit for linear ring VCO-ADCs

Recently an extremely linear voltage-controlled ring-oscillator for use in VCO-ADCs was proposed by Babaie-Fishani and Rombouts. In this current Letter, a circuit-level technique to improve the bandwidth and noise performance of such a linear VCO is proposed. The key element is the modified delay cell, where the traditional cross-coupled inverters are modified into ` feed-forward' coupling inverters that pre-charge the subsequent elements in the ring. The resulting circuit maintains the excellent linearity, but has greatly enhanced bandwidth (up to 3 times higher) and considerably reduced power for the same circuit noise level (up to 2.5 times lower).