RC phase shift oscillator

236

04:19:20

Shake your device to inject noise and start the oscillation. The inverting amplifier configuration is provided with a negative feedback network which shifts the phase by 180 degrees. The overall phase shift is thus 0 degree. The reference resistor is made 29 times larger than other resistors to make closed loop gain equal to 1. Both the points of Barkhausen Criteria are thus fulfilled to get the oscillation.

published 11 years ago

adreno

11 years ago

Really neat, nice design. Good rationale and description.

Bhawan

11 years ago

Thank u

yashgumaste

9 years ago

@Bhavan what will happen if we add one more resistor between 1kohm and 100nF capacitor

Bhawan

9 years ago

@yashgumaste. If another 1k resistor is added then the oscillation continuously get damped and finally reach to 0. Here, the resistor capacitor network provide 180 degree phase shift. The opamp is in invering configuration which provides another 180 degree phase shift. So, altogether there is 360 or 0 degree phase shift. This makes a positive feedback network which is a necessary condition for sustained oscillation. The values of resistor and capacitor are selected such that the network can form a 180 degree phase shift. So, in this particular circuit,if another resistor, as you mentioned, is used the resistor capacitor network won't provide a 180 degree phase shift. Therefore, oscillation gets decayed over time.

Bhawan

9 years ago

If your question is " How did you find out that the resistor capacitor network provides a 180 ° phase shift?" then you can comment me your email. I will provide you my hand written notes with circuit analysis and derivations of this circuit.

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