NCO DESIGN

[Patrick]

Hi everybody,

I would like to implement a NCO (Numerical Controlled Oscillator).

The output is a square wave. The reference clock is 352 MHz.
I want the output varies by step of 2,841ns around a 22MHz square signal.

What is the simplest way to implement it :

if rising_edge(clk_ref) then
count <= count + 1 + in;
end;

if (count>=16) then
output <= 1;
count <= 0;
else
output <= 0;
end;

 

[Charles M. Elias]

Hi everybody,

I would like to implement a NCO (Numerical Controlled Oscillator).

The output is a square wave. The reference clock is 352 MHz.
I want the output varies by step of 2,841ns around a 22MHz square signal.

What is the simplest way to implement it :

if rising_edge(clk_ref) then
count <= count + 1 + in;
end;

if (count>=16) then
output <= 1;
count <= 0;
else
output <= 0;
end;

I am no expert on NCOs, but here is a good website for the basic
theory of operation. It will not tell you the best way to implement a
VHDL design. I expect this depends on your target device. You can
also download a simulator if you wish.

Charles

http://www.geocities.com/CapeCanaveral/5611/dds.html