how to calculate the amplitude for this sine circuit?

Thread Starter

danny2

Joined Oct 28, 2009
29
how to calculate the output at U3 op-amp?
let said my input is Vpeak=5.5V,frequency is 50Hz.
by the way,i cannot get a pure sinewave from the circuit.how to enchant to get a smooth sine waveform?
thank you.
 

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Audioguru

Joined Dec 20, 2007
11,248
The diodes block the input to the opamp. Remove them or explain why they are there.
The two 15V batteries, the two 50k resistors and the 200 ohm resistor also do not do anything and should be removed or explain why they are there.

It should be like this:
 

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Audioguru

Joined Dec 20, 2007
11,248
In my circuit the input impedance is 5k ohms and since it has a lot of negative feedback the output impedance is about 0.075 ohms at 1kHz.
 

Thread Starter

danny2

Joined Oct 28, 2009
29
The diodes block the input to the opamp. Remove them or explain why they are there.
The two 15V batteries, the two 50k resistors and the 200 ohm resistor also do not do anything and should be removed or explain why they are there.

It should be like this:
The non-linear V/I characteristic of the diodes is being used to progressively compress the peaks of the triangle wave so it approximates to a sine wave.
As the V10 triangular voltage increase,more current is shifted from D2 to D4 and from D3 to D1 until D2 and D3 cease conduction.Because the two 50k resistors ,the circuit is bipolar and functions similarly for positive and negative half cycle of the triangular wave(V10)


as for the 15V batteries and 200ohm resistor.i dont know it.ah,u give me a tough question.i found this circuit from this forum.couldnt remember where it is now.
 
Last edited:

Audioguru

Joined Dec 20, 2007
11,248
It is a pretty bad sine-wave but it is better than I thought it would be.
The top and bottom still look like a triangle point.
 

Audioguru

Joined Dec 20, 2007
11,248
ya,i also thought like that too,abit sharp on top and bottom.so you know how to improve it?
If you add more diodes and resistors then the triangle wave will have more breakpoints.
Look at the datasheet for the ICL8038 and XR2206 function grenerator ICs to see how many breakpoints they use.
The ICL8038 uses transistors instead of diodes and the XR2206 uses transistors in a differential amplifier circuit to convert the triange wave into a sine wave.
 

Audioguru

Joined Dec 20, 2007
11,248
You must plan and calculate the resistor values and input amplitude for low distortion.
Yours appear to be random.
Ask your teacher to explain how to do it.
 
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