How to connect the N-bit ADC to an (N+2)-bit DAC?

[nxing]

Testing ADC

Hello everyone,

I am designing a N-bit ADC and want to test it. In Allan's book, it states that I can put a (N+2)-bit ideal DAC after my ADC and then check the difference between the input and output. Can anybody tell me how to connect the N-bit ADC to an (N+2)-bit DAC? I mean where should I connect that two extra-bit?

Thanks

 

[Hughes]

Testing ADC

If the reference voltages are the same, you can connect two extra LSB's to VREF_LO of the DAC.

 

[nxing]

Re: Testing ADC

If that's the case, what's the meaning of that?

Thanks!

 

[Hughes]

Re: Testing ADC

Sorry, I had a mistake in the above input. The two least significant bits should be connected to Logic Low instead of VREF_LO.

 

[nxing]

Testing ADC

Then, why we need N+2 bit DAC instead of N bit? Can anybody explain it?

Thanks!

 

[flatulent]

Re: Testing ADC

The reason for N+2 is that it is linear to the N+2 bits and therefore to 1/4 bit at the N bit level. I have used the trick of designing in a N+1 bit ADC to a system and discarding the LSB. This made the data more linear than with an N bit DAC.

You can also capture the digital data from the ADC and do a FFT on it with N+2 bit or more arithmetic.

 

[braudelk]

Testing ADC

That is the requirement of accuracy

 

[braudelk]

Testing ADC

a better approach to test adc avoiding intergrating dac in the chip is to analysing the data from logic analyser directly. u can search a free program based on MATLAB in website,such as www.maxim.com.

 

[sadfish]

Testing ADC

After you add a DAC after the ADC, if there are some problem about the output, how do you know what's wrong?

 

[santhoshv78]

Re: Testing ADC

While giving the input to ADC, it should be synchronized with clock..How do u acheive this??

 

[kyrandia]

Re: Testing ADC

braudelk is right, you can never get a precise result by puting DAC after ADC. For ADC, we care SNDR, SFDR, INL, DNL ... . Visit Maxim, you will get a solution.

 

[watersky]

Testing ADC

what is kyrandia said is right. static parameter INL and DNL,and dynamic parameter ENOB are important. at the same time other parameters such as SNDR and SFDR and so on are attented by us.