| 摘要 |
<p>PURPOSE:To execute fine adjustment automatically and to remove disturbance by finding out the minimum point of noise quantity by raising or lowering resonance frequencies of a filter and applying the voltage to a voltage dependent impedance element of the filter. CONSTITUTION:The comparison voltage 49 of an operational amplifier 48 is set as to make noises smaller than noises at which an output of the same operational amplifier 35 appears. A comparison voltage 53 of an operational amplifier 52 is adjusted and set to make noise smaller than noises at which an output of an operational amplifier 41 appears. Resistors 50, 54, 51 are resistors that synthesize outputs of the operational amplifiers 48, 52, and a voltage proportional to the quantity of noises is generated at both ends of the resistor 51, and a noise voltage variation detecting circuit 73 is formed. A noise sample and hold circuit 74 detects variation of noises and finds out the minimum point of noise. a bias circuit 72 changes the output, and a bias at the time of the minimum noise is given to a variable capacity diode 71. By this way, a filter 1 can be set automatically to the optimum resonance frequency.</p> |
