Signal Generator

Thanks everyone that responded, it seems nothing is as clear cut as you first envisage!,  it does seem however that it is possible to build one using an Intel Atom @ 1.6Ghz or whatever giving a max output of approx 16Mhz...still a nice project for a rainy day, thanks also Kenny this is a case of..oh I have some PICs lets build something rather than me thinking "I could really do with a fast signal generator", as it happens I do need a signal generator, but dont need a terribly fast one for my audio work. Jorge...facinating, wasnt aware of that method!.

Hi John,

If this is for audio work, you should have said so. You are WWWAAAAYYYY over specing(?). Humans can hear frequencies from 20- 20000 Hz, so you could build a function generator that produces waveforms up to 100kHz and be golden.

A generator like that could be easily designed using an MCU(For example with a PIC see"Flying the PIC24" by Lucio di Jasio, Chp 9 if memory serves, he uses the PWM DAC method to output the audio stream from an MP3 file).

Kenny's idea is also brilliant and digital pots are very handy components.

Take your pick, but if you're going to do audio work I think the Atom idea is serious overkill. You mentioned you wanted a one chip solution, if memory serves the EXAR XR2206 chip can be used as a decent function generator. I have a kit from another manufacturer that will remain nameless, which used it. Maybe I built it poorly(very likely was in a rush to finish) but I wasn't too impressed by it, but maybe it works for you.

hth,

Jorge Garcia

I will be using it for other things as well as audio, otherwise like you say you dont need anything higher than 100KHz , but where would the fun be building just a 100KHz signal gen.

I must defend myself from (implicit) complaints of over engineering !

John asked in his original post about making a 0Hz to 100MHz bench signal generator using a fast processor and DACs - that isn't easy. (BTW -  as far as I know no one uses PWM to generate 100MHz sine waves and it is a very poor technique for high frequency low distortion sine wave generation.)

If the spec is reduced then of course other technologies might be appropriate.

For audio work there is a lot to be said for classic Wein bridge oscillators with thermistor or FET feedback control. (SImple, low cost, low distortion - downside is limited frequency range without switching).

You could make a not bad signal generator with one of the STM32F processors with the built in DAC because it supports DMA to the DAC. You wont be able to get much above 500kHz sample rate but it would be single chip (apart from the reconstruction filter).

Another approach would be to use an audio DAC (low noise, low distortion, built in reconstruction filter, low cost) with a processor with an I2S port but you won't get over 100kHz out of it. (and it won't be easy to sweep the frequency).

I use lots of different signal generators for different purposes - I don't think there is one design suitable for everything so perhaps you should concentrate on the one you need right now.

I must defend myself from (implicit) complaints of over engineering !

John asked in his original post about making a 0Hz to 100MHz bench signal generator using a fast processor and DACs - that isn't easy. (BTW -  as far as I know no one uses PWM to generate 100MHz sine waves and it is a very poor technique for high frequency low distortion sine wave generation.)

If the spec is reduced then of course other technologies might be appropriate.

For audio work there is a lot to be said for classic Wein bridge oscillators with thermistor or FET feedback control. (SImple, low cost, low distortion - downside is limited frequency range without switching).

You could make a not bad signal generator with one of the STM32F processors with the built in DAC because it supports DMA to the DAC. You wont be able to get much above 500kHz sample rate but it would be single chip (apart from the reconstruction filter).

Another approach would be to use an audio DAC (low noise, low distortion, built in reconstruction filter, low cost) with a processor with an I2S port but you won't get over 100kHz out of it. (and it won't be easy to sweep the frequency).

I use lots of different signal generators for different purposes - I don't think there is one design suitable for everything so perhaps you should concentrate on the one you need right now.