PURPOSE: To realize a low power equivalent resistor possible for pre-emphasis and de-emphasis operation by using a switched capacitor filter controlled by a voltage controlled oscillator as a signal transmission circuit.

CONSTITUTION: The switched capacitor filter consists of switches S1, S2, capacitors C1, C2 and an inverter 3 as shown in Fig. and becomes the low power equivalent variable resistor with high accuracy and large variable range by changing the oscillating frequency and waveform of the voltage controlled oscillator 2. The switched capacitor filter 52, when it is used for a tape recorder as shown in separate Fig., is switched into two systems at recording and reproduction by using a recording/reproduction switching signal R/P. Since the frequency of control signals , ' and the frequency of an AC bias signal are identical, no audible beat noise is generated at reproduction and emphasis is applied with low power.