VCO Colpitts Oscillator

279

03:40:07

Does anyone know why changing the voltage at the base of the transistor changes the frequency?

published 4 years ago

sircube

4 years ago

Maybe some sort of Miller effect on the base-emitter junction?

jason9

4 years ago

@thebugger thought that too but Miller is ruled out here because it depends on the capacitance allowing signals to affect the base voltage, but that’s prevented here since the base is at a fixed voltage.

mlira

4 years ago

Is it not just that changing the voltage changes the resistance of the transistor, changing the rate the capacitor discharges at?

Issacsutt

4 years ago

Im pretty sure what’s happening is, with larger the base voltages, the more the transistor conducts and decreases the voltage drops across both capacitors which increases the frequency, and the same in reverse; with less base voltage the transistor conducts less, which increases the voltage drops and rise/fall times, decreasing the frequency.

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