Hi,
I have recently built a DDS signal generator that has a sine and square wave output and can go up to 10MHz. Sine is adjustable form 0 to 2.5 Vp-p and square wave is actually a TTL/CMOS type square wave (5V). Now I'm looking for a simple circuit to have a sawtooth output (converting one of those two signals in sawtooth type signal). Can anyone suggest any design.
Thanks in advance
Regards,
Nenad

 

Why don't you just do it in the software?

 

Why don't you just do it in the software?

Because the DA I'm using is AD9835 and it has a built in Cosine table and I'm using this mode to generate the wave

http://www.datasheetcatalog.org/datasheet/analogdevices/AD9835BRU.pdfhttp://www.datasheetcatalog.org/datasheet/analogdevices/AD9835BRU.pdf

 

You can use two current regulator diodes (back to back) as 1N5298, plus a capacitor to have your triangular wave out of your square or sine wave.

Or a single diode and capacitor for the sawtooth wave.

More info @ http://maxtechsales.com/Central_CLDs.htm#Triangle%20Wave%20Generator

Alberto

Thanks Alberto, I will try this to see if can go from 1Hz to 10MHz.
EDIT: I can't find this diodes in my country. Do you have another suggestion??

Thanks,
Nenad

 

You can use two current regulator diodes (back to back) as 1N5298, plus a capacitor to have your triangular wave out of your square or sine wave.

Or a single diode and capacitor for the sawtooth wave.

More info @ http://maxtechsales.com/Central_CLDs.htm#Triangle%20Wave%20Generator

Alberto

That won't work over a range of frequencies. The amplitude will be inversely proportional to frequency. AFAIK, the only way to convert a variable-frequency sine wave to a constant-amplitude triangle wave requires an automatic level control (ALC) loop. There would be a significant response time lag whenever the frequency is changed.
What you really need is a system with a separate COS lookup table, or a chip which has a selectable path from the phase accumulator directly to the DAC.

 

You can try on the web. Mauser; Digikey; Futerlec or RS components, just to name few.

Alberto

Where I live it is imposible to buy from them. Long story

That won't work over a range of frequencies. The amplitude will be inversely proportional to frequency. AFAIK, the only way to convert a variable-frequency sine wave to a constant-amplitude triangle wave requires an automatic level control (ALC) loop. There would be a significant response time lag whenever the frequency is changed.
What you really need is a system with a separate COS lookup table, or a chip which has a selectable path from the phase accumulator directly to the DAC.

So you are saying that there is no easy way. I thought to use a square wave and integrate it, but I'm not sure that will work. Any suggestions on that.
Thanks

 

You could have the output charge a capacitor quickly, and then use a constant current circuit to discharge the capacitor. However, you will need to adjust the constant current circuit for each frequency.

 

Where I live it is imposible to buy from them. Long story



So you are saying that there is no easy way. I thought to use a square wave and integrate it, but I'm not sure that will work. Any suggestions on that.
Thanks

The integrator time constant would have to change whenever you change the frequency.

 

Hi, there,
re your request for a sawtooth device.. they not that difficult to do, & oddly enough not so easy as it first appears...

I've not been a member on here for long, and came across loads of things relating to Square waves, sine, triangle, sawtooth... the help on here is outstanding.. but I learnt a awful lot by reading and reading the electronics over and over.. and if your heavily into complex wave forms and Generators. . then Go for this Book..

110 WAVEFORM Generator Projects for the Home Constructor.. by R.M.Marston...

The book is really outstanding.. he covers all the stuff that Ive read relating to signals generator.. specialised ones as well for instance he covers the Chip The XR-2206, IC.. and is available in the UK.. well thats where I got it from ..mind you I did not use that much..!!! never the less go for this book he really know sound waves equations inside out...

Yes it will be hard to grasp at first.. but well worth it.. Ive built from this & then modified the Generator circuits to suit my needs hmm takes time but one gets there..

Good luck..
PS: The book is by Newnes Technical Books..
so Im afraid you will proberly have to go on Ebay.. to look for it.. it was published in 1978!! many Moons ago lol
cheers all hope this helps

 

I'm looking for a simple circuit to have a sawtooth output

In your original post you talk about generating a sawtooth wvaform. Since then the thread has been about generating a triangle wave.
Not the same thing. A triangle wave is a modified form of square wave, and contains only odd harmonics. A sawtooth contains all harmonics.

See here:
http://www.csounds.com/ezine/spectra/ about half way down the page for the harmonic difference between the two.

If you're looking to generate a sawtooth, then you're not going to derive that from either a sine wave (no harmonics) or a square wave (odd harmonics only).