1. A phase-shift oscillator is a simple sine wave electronic oscillator that contains an inverting amplifier, and a feedback filter.

2. It 'shifts' the phase of the amplifier output by 180 degrees at the oscillation frequency.3. The filter produces a phase shift that increases with frequency. The most common

techniques to build filter is using three identical cascaded resistor-capacitor filters, which together produce a phase shift of zero at low frequencies, and 270 degrees at high frequencies.

4. At the oscillation frequency each filter produces a phase shift of 60 degrees and then combine all filter circuit produces total phase shift of 180 degrees.

1. Phase shift oscillator.

Figure : Phase Shift Oscillator.

from the circuit in figure we have three RC low-pass filter sections to develop a total phase

shift of 180°(60°x3).

From the circuit in result sheet without the op-amp and the feedback by using R=10k Ω

and C=0.01 μF , the gain obtained through the RC network is 8.23.

The RC network was connected to the op-amp and the feedback resistor RF=150 k Ω by

combinations of resistor as in result sheet, without making connection between V o and node X.

The peak value of waveforms obtained in node X was 0.5V and node Y was 0.5V ,where

waveforms at node Y is the input of the operational amplifier while waveforms at node X is the

output waveform. The gain obtained is 1

AV=V pof sinewaveat node Y

V pof sinewaveat node X¿ 0.5

0.5¿1

then sine wave input from node X was removed and a close-loop between V o and node X

was made, the waveform at node V o was recorded. The frequency of the output signal (V o) was

compared with the calculated in table below:

Table : The measured and calculated frequency values.

Measured Frequency Calculated Frequency

Hzf= 1

2πRC √6

The measured frequency was almost the same with the calculated frequency with a bit of

differences. This may due to the tolerance of resistors. The peak value of V o was 10V and

therefore the peak-peak value of V o was 20V.

Conclusion

The basic structure of the phase shift oscillator consists of a negative gain amplifier with

a three section RC ladder network in the feedback.

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