Tunable high-pass filter characteristics of a special MOS transistor

An especially designed epitaxial, metal-oxide-semiconductor transistor has been employed in a novel mode of operation in which the inherent characteristics of the device provide a high-pass filter-type response with insertion gain in the pass band. The low-frequency cutoff property is due to a nonequilibrium phenomenon controlled by the minority carrier generation rate in the channel. The cutoff frequency of this filter is tunable with the drain bias voltage in an exponential manner over a wide range; secondary ionization plays a dominant role in this mode of operation. The experimental results obtained with the N-channel silicon devices are presented and discussed in terms of the physical model of the device.