Author Topic: DAC minimum reference voltage? is it just a guide line? why????  (Read 2654 times)

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Offline SArepairmanTopic starter

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DAC minimum reference voltage? is it just a guide line? why????
« on: November 09, 2013, 04:06:02 pm »
Why do DAC chips have a minimum reference voltage?
I have a DAC that I like in mind but it says the minimum reference voltage is 1V. Why won't it work with say 100mV reference? Why do DACs have a minimum reference voltage requirement? My understanding of their operations (built a discrete DAC once) tells me that they should not have this requirement.
 

Offline qno

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Re: DAC minimum reference voltage? is it just a guide line? why????
« Reply #1 on: November 09, 2013, 05:15:00 pm »
Maybe look at  the noise figures.
Below a 1V reference the LSB is lower than the noise.
Why spend money I don't have on things I don't need to impress people I don't like?
 

Offline SArepairmanTopic starter

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Re: DAC minimum reference voltage? is it just a guide line? why????
« Reply #2 on: November 09, 2013, 05:35:26 pm »
if thats the case then I am fine.   :-+
A moving noise band is just fine with me.

I also read there might be gain errors if the minimum voltage is lower then the specification.

Is there anything else to watch out for?
« Last Edit: November 09, 2013, 05:37:56 pm by SArepairman »
 

Offline qno

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Re: DAC minimum reference voltage? is it just a guide line? why????
« Reply #3 on: November 09, 2013, 06:10:31 pm »
I guess not.
I one used a DAC as an attenuator.
Put an  biassed AC voltage on the reference and select the amplitude with the DAC.
It woked fine, only lower output levels sufferd S/N distortion.
Why spend money I don't have on things I don't need to impress people I don't like?
 

Offline madires

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Re: DAC minimum reference voltage? is it just a guide line? why????
« Reply #4 on: November 09, 2013, 10:21:27 pm »
Resolution and accuracy. Based on the design of the DAC it might not support such small steps.
 

Offline SArepairmanTopic starter

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Re: DAC minimum reference voltage? is it just a guide line? why????
« Reply #5 on: November 10, 2013, 01:43:00 am »
Resolution and accuracy. Based on the design of the DAC it might not support such small steps.

can you elaborate?
 

Offline SeanB

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Re: DAC minimum reference voltage? is it just a guide line? why????
« Reply #6 on: November 10, 2013, 08:49:05 am »
Some use the reference to drive transistors ( or FETs) switched inside the unit, and below the minimum level they do not turn fully on ( or off) enough to operate properly, giving rise to either a varying offset voltage and spurious outputs. To use a DAC with low voltage you need one with either a 4 quadrant reference input or one designed to be used as a variable attenuator.

Otherwise use a level above the minimum and divide the output down to the desired level using a buffer opamp and a resistive divider, or a fractional gain opamp circuit.
 


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