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.

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.