On chip Reference voltage ckt for DAC

Hi All


I am designing a 3.3V DAC which requires a ref. voltage of 2.66 and 2.02 volts and these voltages must follow 3.3V power supply.

plz suggest me some architecture of level shifter to implement this ref. ckt.

Can you get the 3.3V supply out of a very good LDO linear regulator, so the supply doesn't vary at all, and so everything has a very solid 3.3V supply? Then, you can use very tightly-toleranced (even 1% may be alright) resistors to make some resistor dividers from the LDO output to get your reference voltages. I've done this, and it works quite well.

If you are *intentionally* varying the 3.3V supply, though, then this isn't a solution to linearly track the supply voltage...not sure why you would even begin to design a DAC with the intention of not having a steady supply voltage, though.

engrvip said:

Hi All


I am designing a 3.3V DAC which requires a ref. voltage of 2.66 and 2.02 volts and these voltages must follow 3.3V power supply.

plz suggest me some architecture of level shifter to implement this ref. ckt.

Click to expand...

If your voltages need to track the 3.3V supply linearly, then a "stiff" resistive voltage divider will work (as miles mentioned, using some tightly toleranced resistors... or that, in conjunction with a test-select resistor, to be chosen when the parts are installed on the PCB). To make it stiff, you need to have 100x or more current flowing through the divider than the DAC will draw. Example, if the DAC reference voltage input pin sinks 100uA of current, then you'd want your resistive divider to draw 100uA*100 = 10 mA. That way, 100uA / (10 mA+100uA) = ~1% variation.

Additionally, several vendors produce voltage reference ICs. Most are fixed, but some are adjustable. Maxim had the first results I found on google... **broken link removed**.

Thanks friends for ur suggestions....

But mine is a monolithic DAC and it is a part of an ASIC. It has to bias a sensor inside ASIC.

Sensor is biased 0.64v to 1.28v across it where + ve voltage is 3.3v from power supply and -ve voltage is given by DAC and varied insteps of 5mV from 2.02 to 2.66v.

And DAC reference voltage are to be generated internally from 3.3V power supply to the chip. Hence I want some kind of level shifter from 3.3v to 2.66and 2.02 volts to generate ref. voltages for my DAC.

This sounds like a resistor divider and a set of switches tapping
the points along it, under logic decode.

If you don't care much about settling time then you can use a
RDAC and op amp. Any active loop will add its settling tail to
the picture.

Yes Dick .........u r right it is a simple resistor divider 7-bit DAC with 128 resistors in a chain.

But my issue is about how to provide 2 ref. voltages 2.66 and 2.02 volts between which these resistors exist. ANd moreover I want these voltages to vary with power supply 3.3v so that the bias voltage across my sensor is not dirturbed with variation in supply.

Can u suggest me some level shifter which taps 3.3 from power supply and then gives these refernce voltages ???????