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Why SFDR of my DAC is so bad... (Read 2912 times)

Rocky.Lee New Member Offline Posts: 5 Nanjing,China	Why SFDR of my DAC is so bad... 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
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raja.cedt

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Posts: 1516
Germany

Re: Why SFDR of my DAC is so bad...
Reply #1 - 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,

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loose-electron

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San Diego California

Re: Why SFDR of my DAC is so bad...
Reply #2 - 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.

Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: Why SFDR of my DAC is so bad... Reply #3 - Oct 9^th, 2011, 5:40am Rocky, Is it lab test result? Could you please paste a few FFT plots? Yawei
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