What is the relation between Fclk & MSPS in DAC design?

[airace]

dac clock fout

Hi all....I am designing a DAC for WLAN application...
I am not able to understand one thing about DACs....The speed is qouted as MSPS...and also a clock for the DAC is specified as Fclk in data-sheets..
..which is termed sampling frequency

Question: What is relation between Fclk & MSPS...i have seen one more term : update frequency....can any kind soul throw some light on this....

I am confused as to what is what...also sampling frequency for a DAC does not make sense (does it)

regards,

 

[dll_embed]

Re: Question on DAC

From what i know, they should comform to each other. 1MSPS corresponds to 1MHz of Fclk . It is also the update rate. The DAC i used is from AD.

regards

 

[Hughes]

Re: Question on DAC

The sampling frequency indicates how fast the output of the DAC updates. Usually the DAC's clock frequency is the same as the sampling frequency since most DACs take only one clock cycle for each conversion. If a conversion takes two clock cycles in some DAC, (e.g. a 16-bit DAC with 8-bit input data bus) then the Fclk should be double.

 

[airace]

Re: Question on DAC

that clears up some fog...thanx.....but there is one more thing
...the spec for SFDR for a specific DAC i am looking at says

SFDR,400 MSPS,Fout = 100 MHz........so then if update freq is same as MSPS, same as Fclk = sampling frequency.......what is Fout...

It is these so many terms which got me confused in the first place..

Thx

 

[Hughes]

Re: Question on DAC

Fout is, in my opinion, the frequency of the converted signal. According to Nyquist Theorem, the sampling frequency should be at least twice the signal frequency. So comes the difference between the sampling frequency Fclk, and Fout.

 

[jlm]

Re: Question on DAC

SFDR=sampling frequency data rate.

 

[airace]

Re: Question on DAC

hey SFDR is Spurious Frequency dynamic range...it is not what u hav indicated...

thx

 

[Hughes]

Re: Question on DAC

SFDR = Spurious-noise Free Dynamic Range

 

[nathan]

Re: Question on DAC

SFDR=Spurious Free Dynamic Range (i.e., the Dynamic Range also accounting for spurious signal)

Fout=100MHz I believe indicates that the above figure is measured with a signal sampled at that freq. In eneral SFDR changes for different sampling speed.

nathan

 

[airace]

Re: Question on DAC

yes SFDR is dependent on sampling frequency....it is basically the ratio of power of signal to highest harmonic due to reflections from/above nyquist band
and that is the reason i called 'F' - Frequency, but in literature.....what hughes and nathan have pointed out is found/correct......

 

[harkonnen]

Re: Question on DAC

SFDR is often specified for direct digital synthesis.

You generate a sine-signal with the DAC at a sampling rate higher than the signal you generate.
So, the generated sine-signal is for example 10MHz. So, your sampling-rate can be let's say 100MSPS (>2*10MHz: Nyquist)
SFDR is the power-difference between the 10MHz signal and the highest spur. That can for example be your aliasing spur at 100MHz.