Function Generator: Build a Sine, Ramp & Rect Wave

[abdo375]

I'm trying to build a function generator that will output a sine, ramp and rect wave and I need to change the amplitude and the frequency of the signal, as far as the first part goes, I've succeeded, but I can't seem to control the frequency and the amplitude of the signal independently.

 

[waht]

And you can't. You need to design an addition variable gain amplifier that will automatically compensate for an amplitude drop or gain. It's sometimes referred to as ALC, Automatic Level Control. That will level your amlitude through out your frequency range.

 

[berkeman]

I'm missing something. Where does the sine wave pop out?

 

[Averagesupernova]

Glad to see I'm not the only one who missed it Mike.

 

[abdo375]

I'm sorry should have made it more clear, it pops from the integrator circuit (the output of the third Op-Amp) and the rect wave from the differentiator circuit(last one).

 

[berkeman]

No, the integral of a triangle wave is not a sine wave. There is a different technique that is generally used for cheap tri --> sine conversion.

 

[abdo375]

The output of the Integrator: http://img369.imageshack.us/img369/5135/labprojectschematic112ka0.jpg"
cheap trick ?

 

[berkeman]

Hmmm. Well I don't get that. Does it make that sine-wave-looking waveform at only one frequency? Certainly a damped integration of a triangle wave is not a sine wave in general.

The cheap trick that I referred to is to use diodes and resistors to make an amplitude-dependent impedance that shapes the triangle into a sine. There used to be an IC with that inside it, but I forget the number.

 

[abdo375]

I see your point berkemen (I'm surprised I haven't before) , I'm going to look deeper into this.


too bad I can only use op-amps in the circuit, no IC's.

 

[berkeman]

I googled "triangle to sine conversion" and got lots of hits. Here's the first one:

http://www-personal.engin.umd.umich.edu/~fmeral/ELECTRONICS%20II/04%25c3-Opamp/02-%25c3FuncGenProject/Nonlinear%20Function%20Fitting.pdf