what is the maximum frequency can be reached in nco where the clock is 100mhz

[Yonis Rayyan]

hi
im younis and im designing a nco or as know direct digital synthesis i have 100mhz as clock can my nco give me a frequency of rang 88mhz to 120mhz
or the maximum frequency the nco can give is 50mhz ????

 

[Port Map]

DDS frequency can not be above fclk/2.
but if you have a 100MHz clock, then you can convert it to other frequencies by using DCM.

 

[Yonis Rayyan]

thx alot

but what is DCM ?

 

[Port Map]

DCM is a Digital Clock Manager. fro more information you can read its datasheet.

if you are using Xilinx tools, you can create a DCm and find it's datasheets in "Core Generator" SW.

can you explain more about your project?
I want to know where u want to use created frequency?
if it is possible for other parts to work with higher frequency clock?

 

[FvM]

If you set your NCO to 10 MHz output, it will also output 90 and 110 MHz spectral components by nature of the time discrete signal. If you understand frequency as pulse rate, it can't go above 50 MHz.

Firstly I would ask for the application. 88 to 120 MHz sounds somewhat like communication frequencies, a NCO would be most likely unsuitable for this kind of application that requires a spectrally pure signal.

 

[Yonis Rayyan]

im building a FM transmitter using vertix-pro 2 fpga board i thought i can make my nco generate that high frequency so i dont need a RF up converter and the created frequency i will use to modulate the baseband signal using digital mixer but i didnt start working in that maybe next week so if u have any information can help me i will be grateful to u

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If you set your NCO to 10 MHz output, it will also output 90 and 110 MHz spectral components by nature of the time discrete signal. If you understand frequency as pulse rate, it can't go above 50 MHz.

Firstly I would ask for the application. 88 to 120 MHz sounds somewhat like communication frequencies, a NCO would be most likely unsuitable for this kind of application that requires a spectrally pure signal.

can u explain more ?

 

[FvM]

can u explain more ?

I fear this ends up in retelling a time-discrete signal processing text book.

I restrict my answer to a brief result summary. To generate a clean carrier for a FM transmitter, you have basically two options:

- a synthesizer with analog VCO
- a time discrete signal generator (e.g. DAC based) that mixes the fixed frequency carrier with the baseband signal and filters the band of interest from the DAC output. To get rid of image frequency filters, it's preferably implemented as IQ (quadrature) modulator.

In addition all classical transmitter concepts from the "analog" age.

 

[Yonis Rayyan]

thank you u been really helpful