Opamp gain compensation technique for continuous-time ΣΔ modulators

A new method that compensates for the low DC gain of nanometre operational amplifiers (opamps) used for high-speed continuous-time (CT) ΣΔ modulators is described. The proposed solution compensates for the integrator´s phase error which is a main limitation produced by the low opamp´s gain. The method uses a simple auxiliary gain stage and a resistor. Simulations of a second-order CT ΣΔ modulator utilising fast single-stage opamps with gain as low as 25 dB verify the effectiveness of the method.