Question about a sine wave VCO

[goldsmith]

Hi dear All
Thank you for your time .
I'm looking for a sine wave VCO , which should be able to generate a sine wave with lowest drift with frequency of 10 HZ up to 150 KHZ .
( i know how to do it for a square wave , as well but for sine wave ..... ) ( is there any chip , available for this aim ? or perhaps any compact circuit ?)
Thanks in advance
Goldsmith

 

[betwixt]

Fairchilds ML2036 comes to mind but I'm not sure if it can reach 150KHz. It gives crystal stability and can be programmed in 1.5Hz steps.

I'm excluding anything controlled by RC networks because they wouldn't have low enough drift. You might be able to generate a good enough sine with PWM at those frequencies if you use a fast processor, I'm thinking in terms of PIC33F series or similar. Other than that, perhaps narrowing the range by mixing two higher frequencies might be worth considering, for example 10MHz with a synthesized 10.001 to 10.150 PLL.

Brian.

 

[goldsmith]

Hi dear Brian
Thanks so much for your reply . as i saw the datasheet of ML2036 it can give out put frequency from DC up to 50 KHZ ! If it could generate at least 100 KHZ , then it was a pretty good choice .
Isn't there any other integrated circuit like that , for handling this aim ?
Thank you again
Goldsmith

 

[betwixt]

None that I know of. Even 'overclocking' the ML2036 is unlikely to make it reach 150KHz.

It might be worth searching for a DDS device but I thnk you might find ones that work at 150KHz but not down as low as 10Hz.

Using PWM might work but you may have to accept some distortion at the highest frequencies. You could also try changing from a DAC at low frequiencies to DDS as the frequency increases but it would start to get complicated.

Brian.

 

[goldsmith]

Using PWM might work but you may have to accept some distortion at the highest frequencies. You could also try changing from a DAC at low frequiencies to DDS as the frequency increases but it would start to get complicated.

Thanks very much brian for your reply .
PWM method ? what do you mean by that ? is your mean that i try to compare a sine wave with a triangle wave ? but why this method ? or perhaps i've misunderstood your meaning ?
Can you tell me more about your exact meaning please ? ( more description )
Thanks a lot
Goldsmith

 

[D.A.(Tony)Stewart]

You can synthesize a sine wave with a parallel DAC from a square wave synth running at 2^N faster clock rate and using N bits to convert parallel output from a counter to a DAC to get a fixed output.
Similarily you can use a crude 8 bit johnson counter with 8 Sine weighted resistors for a 3 bit resolution or use binary counter with R,2R,4R,8R,16R etc. but a precision DAC is best.

 

[FvM]

I understand that the question is asking for an analog voltage controlled oscillator. Low drift means stable frequency without feedback, e.g. a PLL?

The last available analog sine function generator chip XR2206 has been discontinued by Exar a year ago, but it's still available at catalog disctributors and DIY stores. You get simple DDS chips for the XR2206 price, however. Also the XR2206 frequency range is only 1:2000, lower than the intended range.

The large range makes exact analog frequency control questionable, particularly if you are thinking of a linear VCO range.

If you mean digital frequency control, you would tell it, I presume.

 

[sequel]

take a look at the ICL8038 chip it comes in a handy package and can deliver the frequency that u are looking for....hope this helps

sequel...

 

[goldsmith]

You can synthesize a sine wave with a parallel DAC from a square wave synth running at 2^N faster clock rate and using N bits to convert parallel output from a counter to a DAC to get a fixed output.
Similarily you can use a crude 8 bit johnson counter with 8 Sine weighted resistors for a 3 bit resolution or use binary counter with R,2R,4R,8R,16R etc. but a precision DAC is best.

Hi dear Sunnyskyguy
Thanks for your reply .
MAy you tell me more about your idea , please ? it sounds pretty interesting !

Thanks and Regards

If you mean digital frequency control, you would tell it, I presume.

Hi dear FvM
Thanks for your reply .
of course an analog method is more suitable for me . but i'm interested to hear about digital methods of this aim too . may you tell me more about your latest suggestion , please ?

Best Regards

take a look at the ICL8038 chip it comes in a handy package and can deliver the frequency that u are looking for....hope this helps

sequel...

Hi dear Sequel
Thanks so much because of the nice chip ! it is really fine and i can going to use it right now .
Respect



However the ICL8038 can handle my aim and i'm going to use it . but i want know about the introduced methods , above too ( i want learn them too because i'm sure , in future i'll need them )
Regards and thanks to all
Goldsmith

 

[Tunelabguy]

Any truly voltage controlled oscillator that covers the range 10Hz to 150kHz is bound to be very sensitive to analog control voltage noise, and so the low drift that you seek will be nearly impossible. Digital methods are much more controllable. You said that analog control is more suitable for your present need. Why is that? Is it just that analog control is all you are comfortable with right now? Or does your current application inherently better suited to analog control? Finally, any analog control can be converted to digital control through the use of an A/D converter and a dedicated micro controller to read the A/D and generate the required digital control signals to the synthesizer.