CONTROLLABLE FILTER DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a controllable filter device equipped with a filter circuit network for filtering an input signal, and a transistor. SOLUTION: The transistor is constituted as a voltage follower having a controllable current source for providing a controllable DC transistor output current in an output circuit, and an output terminal of the voltage follower is connected to the filter circuit network so as to control the cut-off frequency of the filter device by a change in DC current fed by the current source. The filter circuit network may be a monopolar RC circuit network and the output of the voltage follower is connected to an additional capacitor (or resistance) of this electric network coupled to a connection point of an existing capacitor and a resistance. This filter device is controllable between cut-off frequencies of two values depending upon whether the additional capacitor (or resistance) is driven practically by the voltage follower, or controllable continuously over cut-off frequencies in a prescribed range depending upon the value of the current supplied by the current source. COPYRIGHT: (C)2007,JPO&INPIT