#### celebrevida

##### Member level 2

I need the following references:

0.75V

0.807V to 0.969V in 0.0108V steps (so 16 references in total)

I am considering these two options using poly resistors:

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1) From vss to vref0p75: 375k resistor (actually 10*37.5k in series)

From vref0p75 to vref0p807, a 28.5k resistor

From vref0p807 to vref0p969, (15*5.3756k resistors in series, each tap represents the 16 references)

From vref0p969 to vref1p5, 265.9k resistor (actually 10*26.59k in series)

(Total resistances=750k to limit Iload to ~2uA)

This gives me exactly the references I need to within 1mV.

But by using an assortment of different resistors, I wonder how well this works over process variation.

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2) From vss to vref1p5, use 128*5.847k resistors in series. Then choose the taps closest to what I need.

For the vref0p75, this works, I simply access the middle tap. But for the other 16, it doesn't exactly line up and I can be as much as 10mV off. However, by using 128 unit resistors, perhaps this might actually a better choice than (1) due to less process variation?

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What is the best choice for resistor ladder design to get closest to the voltage references I want over process variation?

And is there a third scheme that is better than either that I should consider?

Thanks!