Partial positive feedback for gain enhancement of low-power CMOS otas

Four circuit schemes that use partial positive feedback for gain enhancement in CMOS OTAs are examined. These circuit schemes are classified as type I and type II circuits. Type I circuits use a differential input pair with positive feedback and type II circuits use a active load with positive feedback. As the primary emphasis of these circuits is for micropower operation, the circuits have been examined in detail in the subthreshold region. A comparison of the primary characteristics of these circuits together with simulation results are presented. It is shown that partial positive feedback is a viable technique to increase the gain and the bandwidth of CMOS OTAs. Without any increase in power, a 20 dB increase in gain and a 5X improvement in bandwidth is feasible.