Level-Shifting variable current charging technique for high-speed Comparator-Based Switched-Capacitor circuits

The utilization of variable current sources, in Comparator-Based Switched-Capacitor (CBSC) circuits, instead of the traditional constant current sources, reveals itself as one of the effective ways to increase speed while maintaining the accuracy. In this paper, a Level-Shifting Variable Current Charging Technique is proposed to implement variable current sources for CBSC circuits. The CBSC gain stage obtained with the proposed technique is applied to a 2-1 Cascaded Multi-Stage (MASH) ΔΣ modulator implemented in 90 nm CMOS for WCDMA applications. Simulation results show that the modulator achieves 75 dB of dynamic range while consuming 2.7 mW.