The Correlated Level Shifting as a Gain Enhancement Technique for Comparator Based Integrators

This paper shows that correlated level shifting (CLS) technique can be successfully used in the comparator based integrators with the same benefits as in the conventional integrators. With help of CLS technique the signal dependent variation reduces by making current source work in the more voltage headroom region thus an output impedance of the current source is increasing. The latter leads to high gain of the system and more linear voltage ramp by the current source. This technique is especially used in the deep sub-micron technologies with the supply voltage below 1V, where headroom of a current source is low. Proposed comparator-based integrator is using comparator with about 27dB of gain which translates into 54dB of effective gain. Integrator was used to design the MASH sigma delta modulator which achieved SQNR of 86.0 dB at an OSR of 64.