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Design >> Mixed-Signal Design >> Why SFDR of my DAC is so bad...
https://designers-guide.org/forum/YaBB.pl?num=1316701665

Message started by Rocky.Lee on Sep 22^nd, 2011, 7:27am

Title: Why SFDR of my DAC is so bad...
Post by Rocky.Lee on Sep 22^nd, 2011, 7:27am

Hi,Everyone.
I've designed a 6-bit 1.2GHz DAC . And the SFDR test results make me very disappointed.
Results show as below(all results are tested in case of Fs=1.2GHz):
fo=10MHz SFDR=-39dBc
fo=101MHz SFDR=-31dBc
fo= 301MHz SFDR=-24dBc
fo=399MHz SFDR=-26dBc

Why my SFDR is so bad?
Need help...

Thanks.

Rocky.Lee

Title: Re: Why SFDR of my DAC is so bad...
Post by raja.cedt on Sep 22^nd, 2011, 8:48am

hello,
what kind of architecture, is current steering? how SFDR is faling with frequency? i think at very lower frequency it should be close enough to realistic value, but if your drivers (which drive diff pairs and other timing stuff) are not good it falls very fastly with frequency, i faced this once. So please give more info.

Thanks,

Title: Re: Why SFDR of my DAC is so bad...
Post by loose-electron on Sep 26^th, 2011, 6:27pm

As frequency goes up, several things start to become significant:

Switch timing.
Capacitive feedthrough of current steering switches.

Start there.

Get your timing to be phase aligned properly to high frequencies.

Minimize your switch size.

Minimize the size of the signals controlling your switches.

Consider compensaating the charge injection associated with the current steering switches.

Title: Re: Why SFDR of my DAC is so bad...
Post by ywguo on Oct 9^th, 2011, 5:40am

Rocky,

Is it lab test result? Could you please paste a few FFT plots?

Yawei