| 摘要 |
PURPOSE:To prevent variance from taking place in a frequency characteristic of input voltage versus output signal even when a process parameter has a variance by applying respectively an input voltage to one input of a VCO and a constant voltage to the other in the VCO having the two input terminals. CONSTITUTION:The VCO30 outputs a signal having a frequency in response to a voltage applied to the input terminals IN1, IN2. Then the input voltage Vin is applied to the input terminal IN2 and the voltage Vc is applied to the input terminal IN1 respectively. On the other hand, a capacitor 36 is charged or discharged via switches 33, 34 operated alternately. Then a sample-and-hold circuit 37 holds a maximum value of a voltage Vd across a capacitor 37. The holding voltage Ve is compared with a reference voltage by an operational amplifier 31, resulting that the voltage Vc is controlled to a constant voltage. Thus, even when the process parameter is in variance, the variance in the frequency characteristic of input voltage versus output signal is avoided.
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