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Biasing an array of current steering DACs

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big_fudge98

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Hi, I would like to bias an array of 128 current steering DAC's. I have made a current source as well. How would I bias 128 DAC's using this single current source? If I bias all 128 directly, would the added capacitance create startup issues?
 

wwfeldman

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i think you need to provide a fixed known current to each DAC individually
so that the behavior of one DAC does not effect the behavior of another DAC

more capacitance will likely increase start time
 

timof

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And even within one DAC, make sure that the voltage drop along the ground net, feeding the current sources, does ot create too large Vgs mismatch across current sources.
 

big_fudge98

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Yes. But can I directly mirror currents to 128 DAC's from the current source? Or should I do it in stages?
 

frankrose

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You can mirror the current with 128 branches. It won't be worse from mismatch and start-up viewpoints and actually the area will be smaller compared to cascaded NMOS/PMOS mirror stages.
If you want very fast and small DAC choose a segmented one.
 

big_fudge98

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Thanks.
What exactly is the 'segmented' one?
 

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