Sequential Correlated Level Shifting: A Switched-Capacitor Approach for High-Accuracy Systems

Analog circuit accuracy is severely limited by finite and nonlinear opamp gain. For switched-capacitor circuits, correlated level shifting (CLS) is an effective technique to improve system accuracy with negligible additive noise. A modification of this method, called sequential CLS, is introduced in this brief, which provides dramatic increases in the effective accuracy of a switched-capacitor structure. Measurements of prototype sample-and-hold structures utilizing simple single-stage opamps in an LP 90-nm CMOS technology show that at the same power and area consumption, the proposed modification can improve the settling accuracy of simple CLS from 5.8 to 8.8 bits with two additional sequential steps.