How to interface a DAC to a VCXO?

[shell3]

I need a stable oscillator with digital tuning: 19.44 MHz +/- 100ppm. Since I am
not familiar with analog design: is it possible to use a digital to analog converter
and connect the DAC output to the Control Voltage pin of the VCXO. This way it
will be possible load a "digital" value in the DAC to tune the VCXO.
I did not find any app note on this subject, so I wonder....

Shell3
Thank you

 

[rfsystem]

Re: VCXO digital tuning

If you try to convert first into voltage domain and then use a varactor the tuning range of +-100ppm is not achiveable with integrated diodes like P+/NWELL. You have to use switch cap tuning. So the digital value control direct the switching.

 

[ddt694]

VCXO digital tuning

http://www.a-aengineering.com/QST_GPS.pdf

 

[rfsystem]

Re: VCXO digital tuning

The application in the above reference is using a VCXO for a 7.5e-9/V tuning gain. So hardly +-100ppm=+-100e-6. Please read the paper!

 

[ddt694]

VCXO digital tuning

hi, i think shell3's problem is how to interface a DAC to a VCXO but not how to design a VCXO.

 

[rfsystem]

Re: VCXO digital tuning

So it is a problem belonging to

Analog Circuit Design

I tought it is an integration problem.

 

[shell3]

Re: VCXO digital tuning

ddt694 paper is helping. I just need to add a Low Pass Filter bethween the the DAC and the VCXO.

I will switch new questions to Analog Circuit Design forum.

Thanks,