Thursday, September 25, 2014
Voltage Controlled Oscillator Circuit
A simple voltage controlled oscillator circuit which produces both triangular and square wave outputs is shown.
Then the output of the Schmitt trigger is high, the clamp transistor TR; is conducting and the input current passing through R2 is shunted to ground. The current passing through R 1 causes a falling ramp to be formed. When the Schmitt circuit changes state, its output switches TR; to the nonconducting state. The current flowing through R2 can be made twice that flowing through Fl; (R2 = R;/2) so that the rising part of the ramp has a similar slope to the negative part. The greater the value of the control voltage, the greater the frequency of oscillation. However, the voltage must exceed the constant input voltage (V,) or the circuit will fail to oscillate.
Then the output of the Schmitt trigger is high, the clamp transistor TR; is conducting and the input current passing through R2 is shunted to ground. The current passing through R 1 causes a falling ramp to be formed. When the Schmitt circuit changes state, its output switches TR; to the nonconducting state. The current flowing through R2 can be made twice that flowing through Fl; (R2 = R;/2) so that the rising part of the ramp has a similar slope to the negative part. The greater the value of the control voltage, the greater the frequency of oscillation. However, the voltage must exceed the constant input voltage (V,) or the circuit will fail to oscillate.
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