Wein Bridge Oscillator and Comparator

Topics: Wave, Phase, Feedback Pages: 4 (1453 words) Published: April 20, 2011

OBJECTIVE: - To design a Wein Bridge Oscillator which produces a periodic sine wave and give this output to a comparator circuit to compare it with reference signal.

THEORETICAL ANALYSIS: - We need to find out the resonant frequency at which the oscillations occur, the maximum, minimum and the average gain of the wein bridge oscillator circuit. For the comparator circuit we will find the upper and lower threshold limit. Resonant frequency = 1/ (2*pi*R*C) = 4.82 KHz.

Maximum Gain of Circuit = 1 + (R2/R3) = 3.51v
Minimum Gain of Circuit = 1 + [(R1*R2/R1+R2)/R3] = 2.92v
Average Gain of Circuit = (Maximum Gain+ Minimum Gain)/2 = 3.215v Where, R = 3.3k, C = 10nf, R1 = 39k, R2 = 11.8k and R3 = 4.7k Now for Comparator circuit,
Upper Threshold Voltage = [Vref*(R7+R8)/R8]-[Vn(R7/R8)] = 4.44v Lower threshold Voltage = [Vref*(R7+R8)/R8]-[Vp(R7/R8] = -4.99v Where, Vref = 0v, Vn = 12v, Vp = 13.5v, R7 = 3.7k and R8 = 10k Recalculating Value of R8 when Upper threshold voltage = 2.5v and Lower threshold Voltage is = -2.5v R8 = (Vn*R7)/Vth+ = 17.76k

R8 = (Vp*R7)/Vth- = 19.98k
Where, Vth+ = 2.5v and Vth- = -2.5v

SIMULATED WAVEFORMS: -The simulated waveform is shown on a graph with Time as its X-axis and Voltage as its Y-axis. The waveform in red is Wein Bridge Oscillator’s output waveform denoted by fout and the waveform in blue is Comparator’s waveform denoted by out. First waveform shows the frequency of oscillation produced by Wein Bridge, second shows both waveforms super-imposed on each other for proper analysis and third shows the gain. Cursor A and B are placed to find values of voltages and time at two different points. Note that the wave completes one cycle between cursor A and B. Cursor A gives 11.440m as time when amplitude is zero and cursor B gives11.649m. For frequency = 11.440-11.649 = 0.209 which is the time taken by sine wave to complete one cycle. Now, 1/0.209m ~ 4.77Khz which gives the...
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