JPS6464403A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To suppress an oscillation amplitude without degrading an oscillation characteristic by using a voltage variable resistance body and a control voltage generating circuit for an oscillation circuit. CONSTITUTION:An oscillator by a C-MOS transistor(TR) to use a crystal oscillating element 101 is composed of a direct current returning resistance Rb, MOS TRs 103 and 105 for driving, a Pch depression MOSTR 104 as a drain resistance and a voltage generator 1 for the control of this drain resistance. A resistance value can be changed by changing the gate voltage of this TR 104. A generator 106 has a characteristic to increase an output voltage with accompanying the increasing of the amplitude of an input alternating current signal. Accordingly, the more an output voltage goes to be large, the more a drain resistance by the TR 104 goes to be large. Thus, when the oscillation amplitude grows up, an operating point is moved in a direction to decrease a dynamic range and a gain and the amplitude is suppressed. However, at an oscillation starting time, the operating point is in a position near a condition not to insert the drain resistance. Then, since the enough gain and dynamic range necessary for the oscillation are possessed, the oscillation characteristic is not degraded.