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Design >> Analog Design >> The VDD variation of DAC.
https://designers-guide.org/forum/YaBB.pl?num=1102315277

Message started by Question on Dec 5^th, 2004, 10:41pm

Title: The VDD variation of DAC.
Post by Question on Dec 5^th, 2004, 10:41pm

I design a DAC, using current steering architecture. The base current source cell likes the picture below.

The bias voltage come from bandgap circuit. it is steady. But the VDD will have 5% to 10% fluctuation becaues of the source out of the chip. So the output current will change a lot by different VDD voltage.

How can I slove this problem? Please give me some advice. It is emergency!!

Thank you very much.

Title: Re: The VDD variation of DAC.
Post by 101questions on Dec 6^th, 2004, 1:16pm

The bandgap output voltage should be referred to VDD. Then VDD ripple infuence would be somewhat reduced.

Title: Re: The VDD variation of DAC.
Post by sheldon on Dec 10^th, 2004, 5:58pm

Greetings,

You did not say much about the design of the bandgap.
Another approach when the bandgap is ground referenced
is to use :
1) a V-I converter to convert the bandgap voltage
reference voltage to a stable current, effectively an
n-channel current source.
2) Convert the single transistor current source into a
p-channel current mirror. A single diode connected
transistor can bias all the DAC current sources.

This will eliminate the sensistivity of the current source to
power supply voltage variations.