Active compensation of op-amp circuits

The performance of active RC circuits at high frequency is limited primarily by the finite gainbandwidthproducts (GBs) of op amps used. To avoid this effect, active circuits usually operate in a safe frequencyrange, well below the effective bandwidth, typically 0.01 times this value, even with some `passivecompensation¿. The main drawback of the passive compensation is that it can only be tailored to a given opamp and given operating environmental conditions. Recently, with the availability of low-cost dual and quadop amps which are enclosed in the same IC and have closely matched characteristics, `active compensation¿ has become attractive. Recent research treats only the active compensation of op-amp amplifiers. This paperpresents a generalised compensation technique to cover integrators and differentiators and higher-order compensationwith maximum circuit and tuning simplicity. It is found that these actively compensated circuitscan operate at frequencies as high as 0.25 times the effective bandwidth. An experimental study of the performance of the Tow-Thomas biquad bandpass filter, actively compensated by the proposed technique, isalso presented and it is found that the biquad can operate satisfactorily up to about 0.20 times the effectiveb and width without significant shift in its pole positions.