United States Patent Number: 6,222,418, April 24, 2001.
NOTE: At the time of publication, the author Vladimir Prodanov was not yet affiliated with Cal Poly.
A feed-forward compensated negative feedback circuit comprises an operational amplifier having an inverting and a non-inverting input and an output. A feedback element is connected between the output of the operational amplifier and its inverting input to form a negative feedback loop. The inverting input of the op-amp is driven with a first transconductance amplifier which produces an output current proportional to an input voltage. A feed-forward transconductance amplifier receives the input voltage and produces an inverted output current proportional to the input voltage. A feed-forward current is injected at the output of the operational amplifier. By providing at the output of the op-amp the current it would be required to carry over the feedback loop, a voltage differential at the op-amp inputs is avoided, thus eliminating parasitic current flows across the parasitic input capacitance and thereby improving the circuits overall performance. In a second embodiment of the invention, a unity-gain buffer is included in the feedback loop to produce a unidirectional path. To reduce the power requirements of the buffer, a feed-forward current is injected at a point between the feedback impedance element and the unity-gain feedback buffer such that the buffer does not need to source any current through the impedance element.
Electrical and Computer Engineering
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