Attenuator circuit employing bootstrapping

Abstract From the Canadian patent

When impedance elements such as FETs are used in attenuators, the elements have linear responses only when the signals attenuated are below certain signal levels. When signal conditions causing the element to operate non-linearly are detected, bootstrapping is applied to reduce the voltage across the element so that the element will operate linearly. The control signal at the gate of the element is then modified to compensate for the increase in effective impedance of the element caused by bootstrapping. The improved attenuators are especially useful in signal compressors and expanders.