Hi, how to convert the output of a Voltage to Frequency converter (Square wave) into Triangular and Sine wave?

 

u can get a triangular wave by passing it through an integrator , to get sine wave u may need a tuned(high Q) amplifier or logrithmic wave shaping network(won't give perfect sinewave , also will have lot of harmonics)

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Gods own Country
Incredible !ndia

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"Give a man a fish, and he will eat for a day. Teach that man to fish, and he will eat for a lifetime."

 

You can get a "perfect" sine-wave by using a switched-capacitor Butterworth lowpass filter IC. Its oscillator can also be voltage-controlled so that its cutoff frequency tracks the frequency of the VCO.

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Uncle $crooge

 

"switched-capacitor Butterworth lowpass filter IC"...

How does it works actually? The output of the VFC (square wave) directly apply to the "Clock" input?

Attached Images

DI332Fig01.gif (1.8 KB, 31 views)

 

The clock frequency for the MAX7410 is 100 times its cutoff frequency. The output has a tiny amount of the clock frequency in it which is easily removed with a series resistor and a capacitor to ground from the output.

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Uncle $crooge

 

The problem with the integrator is that the amplitude of the output will proportional to 1/frequency. A fixed cutoff frequency filter will have amplitude problems also. As Audioguru said, a switched-capacitor filter is a good solution, but you have to run your V-F converter at 100X for the clock, and then divide by 100 for the signal. This may not be practical, depending on the desired signal frequency.
The easiest solution may be to build or buy a V-F converter thay includes a triangular wave as part of the oscillator.

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Ron

 

I found this circuit on the internet - is about converting Square to Triangular wave:

http://home.att.net/~theremin1/Circu.../converter.htm

Can i input the square wave of the VFC into this circuit to get the triangle wave (for wide range of frequencies)?

 

Assuming it works, you can use it with the limitations noted in this quote from the design article:
In other words, if the input to your V/F converter has high bandwidth (fast rise and/or fall times, or other high frequency components), the triangle wave amplitude will not be able to keep up with the rapid frequency changes.
What kind of V/F converter are you using? Maybe we can come up with a substitute that will generate a triangle wave as part of the oscillator.

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Ron

 

Thanks for the instant reply!

I'm using AD537 monolithic V-F converter. The frequency range: 0-150kHz.

http://www.analog.com/en/prod/0,2877,AD537,00.html

 

Fig. 28 in the app note you referenced shows how to get a triangle wave. You don't need an AD521 for the instrumentation amplifier (IA). You can use 3 op amps with GBW of 10MHz or more and make your own IA. Do a Google search for "instrumentation amplifier" if you don't know how to do it. You will need a negative supply to do this.
What are you using this for? If you don't need the high precision of the AD537, I could probably show you how to do it much less expensively.

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Ron

 

Programmable Frequency Generator - Range: 0-100kHz...

I'm using AD537 to generate the frequency. At the same time, I must able to display sine & triangular wave as well.

 

Do you know about function generators? That's what you are trying to make. Google max038, ICL8038, xr8038, xr2206, and "function generator". When posting a question, you should post more information than you think we will need in order to help you.

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Ron

 

Sorry for not giving sufficient information.

Ya! i know i'm doing sth like function generator. I'm using parallel port to control the frequency.

 

All the chips I mentioned seem to be voltage-controllable, and they have triangle and sine outputs. Can the AD537 do something that they can't?

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Ron

 

1. Why need Op-Amps with GBW 10MHz?
2. What do you mean by "You will need a negative supply to do this."?
3. How do I choose the resistor values for the IA design?

Please guide me.