SINE WAVE GENERATION

Using Wien Bridge Oscillator – 741 Op amp

Sine Wave Generation

By Engr. Khurram Hashmi

Wien Bridge (Often used as AC

Bridge)

Feedback and Gain

741 Open loop gain : 200,000

Gain with feedback

Where β is feedback factor

Feedback may be Positive or Negative

Wien Bridge oscillator utilizes positive voltage

series feedback

Feedback Circuits

Oscillator Operation

When positive feedback is used in an amplifier

with closed loop gain |Af| >1 ,the amplifier acts

as an oscillator

No input signal is required to set an oscillator

circuit into oscillations.

When βA>1 the noise voltage present in the

circuit is amplified

The closer βA to 1. The purer the sinusoid

produced.

Oscillator Operation

Wien Bridge Oscillator

Frequency Feed back

Output Sinusoid

VCC

-VEE

Design formulae

Output Signal frequency

For simplification we take

and

Then

Feedback resistors ratio

Design Calculations

Choosing output frequency

and choosing

We get

3300pF standard values were used

R3=330 kΩ and R4= 67 kΩ such that

Designed circuit

Output Waveform

fo ≈ 1 kHz Amplitude ≈ 20 Vp-p