How can I control VCXO or the NCO?

Question

hi,
I am working on a HDTV receiver project. I did some PLL loop code in the FPGA to find the carrier frequency of the input signal. Then I want to use the control signal out of the FPGA to control the  VCXO. Can I do that? Is there a sample code for that? 
The other choice is use this control voltage to control the NCO on ADC.  Can I do that? Is there a sample code for that?
Guang CHEN
University of Illinois at Urbana Champaign
Message Edited by yakgg on 09-09-2007 01:11 PM

Answer 1

Hi
The module’s VCXO does not have a method of control from the FPGA.  The calibration data when running the module on internal calibration data is configured outside the access that is available when programming the FPGA.  The module’s PLL circuit is not accessible from the FPGA as well.
For configuring the NCO frequency on the fly, I believe it is technically possible, but not easy.  There is no example at this time nor has it been attempted as far as I know.  I say this as the control of the NCO frequency passes through the ni5640R Template Config ADC (FPGA).vi in the Configuration Timed Loop in the LV FPGA VI.  The hard part is adding all the logic and required factors that is implemented in the ni5640R ADC Configure NCO.vi that runs on the Host and creates the actual data input that is written to the FPGA and on to the ni5640R Template Config ADC (FPGA).vi.
Jerry