EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: david77 on May 11, 2012, 01:37:36 pm

Title: Low THD sinewave generator
Post by: david77 on May 11, 2012, 01:37:36 pm
Hi guys.

I'm in the first stages of a new project and the need for a low distortion sinewave generator has arisen.
So I'm looking at circuits and I'm not quite sure what to use.

What I want:
-------------------
- THD <1%
- Frequency: Switchable 333Hz, 1kHz, 3.15kHz, 6.3kHz, 10kHz, 15kHz, 20kHz
- Output voltage 1,55Vrms

So what would you suggest? A Wien-bridge? Using an XR2206?

David
Title: Re: Low THD sinewave generator
Post by: jimmc on May 11, 2012, 02:08:05 pm
XR2206 will struggle to meet 1% distortion, Wien bridge based oscillators can easily achieve it.
http://cds.linear.com/docs/Application%20Note/an43f.pdf (http://cds.linear.com/docs/Application%20Note/an43f.pdf) p 29
or if you want to go to extremes
http://cds.linear.com/docs/Application%20Note/AN132f.pdf (http://cds.linear.com/docs/Application%20Note/AN132f.pdf)

However if you want frequency stability better than around 1% look at DDS
http://www.analog.com/library/analogDialogue/archives/38-08/dds.pdf (http://www.analog.com/library/analogDialogue/archives/38-08/dds.pdf)

Jim
Title: Re: Low THD sinewave generator
Post by: T4P on May 11, 2012, 02:12:12 pm
Go for wien bridges for low THD and not too high frequencies...(I'm thinking high = >20MHz)
Title: Re: Low THD sinewave generator
Post by: david77 on May 11, 2012, 02:28:01 pm
I thought I might go the Vienna way ;).

Thanks for the literature, Jim Williams has been busy. Something to read in bed tonight.
I'm purely in the audio spectrum, nowhere near 20MHz, if I can achieve <1% THD and maybe 5% frequency and amplitude accuracy I'll be happy.
Title: Re: Low THD sinewave generator
Post by: T4P on May 11, 2012, 02:36:55 pm
Quote from: david77 on May 11, 2012, 02:28:01 pm
I thought I might go the Vienna way ;).

Thanks for the literature, Jim Williams has been busy. Something to read in bed tonight.
I'm purely in the audio spectrum, nowhere near 20MHz, if I can achieve <1% THD and maybe 5% frequency and amplitude accuracy I'll be happy.
Then that will make you a nice audio gen. Good luck!
Title: Re: Low THD sinewave generator
Post by: tekfan on May 11, 2012, 03:20:34 pm
I know I've posted this lonk in another thread but I am so impressed with this oscillator that I have to post it again:
http://sound.westhost.com/project22.htm (http://sound.westhost.com/project22.htm)

It's THD was below 0.02% when I measured it on a Hameg distortion analyzer. It wasn't even meant to measure such low distortion, so it is probably even lower than that.

This is a great little oscillator for audio work and measurments.
Title: Re: Low THD sinewave generator
Post by: david77 on May 11, 2012, 03:32:37 pm
Stupid me. Why didn't I look at Mr. Elliot's truly magnificent site? That's basically exactly what I had in mind, push-pull output and all.

Thanks tekfan.