Frequency modulation on fpga

[Altera_Forum]

Hello, 

 does anybody knows how to design and implement a frequency modulator on fpga?  Some weeks ago, I implemented a sine wave generator and a frequency generator on base on a lookup table and now I want ot use this frequency generator to modulate the frequency of a carrier ( with a higher frequency) on fpga using vhdl. I have been told to use the princip of the VCO which generate a frequency base on the input voltage. my input voltage are the values of the frequency generator but I don´t know how to use those values to achieve the frequncy modulation. I red also about DDS/NCO but I just don t know how to use thier fonctioning princip to realize the frequency modulation in my case. if have a suggestion , please don t hesitate to respond.  thanks for your help. Dora

[Altera_Forum]

If I understand the question correctly, here's an idea to get the ball rolling. 

 Let's say you have an input clock which you use to increment a counter. Each time the counter reaches, say, 1000, you output the next sample of your waveform. This results in an output waveform at a constant centre frequency. Now if you use the value of your modulating input to add or subtract from the counter compare value, you will increase and decrease the interval between your output samples i.e. modulate the frequency. You could use a look up table to translate your input value to give the desired modulation range. For example by adjusting the compare value between 500 and 2000 you would get a modulation of 1 octave above and below the centre frequency.  This may not be suitable for your design but maybe it'll give you an idea.

[Altera_Forum]

hi sharkybaba, 

 this is exactly what I want. I thank you for your help.   Dora

[Altera_Forum]

--- Quote Start ---  Hello,  does anybody knows how to design and implement a frequency modulator on fpga?  Some weeks ago, I implemented a sine wave generator and a frequency generator on base on a lookup table and now I want ot use this frequency generator to modulate the frequency of a carrier ( with a higher frequency) on fpga using vhdl. I have been told to use the princip of the VCO which generate a frequency base on the input voltage. my input voltage are the values of the frequency generator but I don´t know how to use those values to achieve the frequncy modulation. I red also about DDS/NCO but I just don t know how to use thier fonctioning princip to realize the frequency modulation in my case. if have a suggestion , please don t hesitate to respond.  thanks for your help. Dora  --- Quote End ---    Hi Dora,  Due to i am a new learner of FPGA and i am now need to design a amplitude modulator project. May i know how do you design the sine wave generator on FPGA board.  Thank you.

[Altera_Forum]

You can use an NCO megacore to generate the sine wave and then route it to the DAC for the ouput. Look at the example design files as I am fairly sure they have an example there.