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# Regarding DAC output voltage mapping

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#### Maitry07

Hello,
I am planning to use DAC having the output range of 0 to 10 V with 14 bit resolution. ( if my DAC is having 2.5 V reference voltage)
so, my DAC output voltage will be =[ (2.5)/2^14-1 ]* digital data input

As my digital data input Hex value range is in between : 0x0033 to 0x0FE4 having the variation of 0x0033, 0x0034, 0x0035... and so on.
so, based on the hex values at the input of the DAC with having the reference voltage of 2.5 V and 14 bit resolution, the DAC output voltages will be
0.007906177 V, 0.007997726 V, 0.008090335 V,..... up to 0.620821168 V .

So, If I want to increase the ratio between 2 DAC output voltages and want to use the full range of DAC : 0-10 V , could you please provide guidance on type of signal conditioning to be used at the output of DAC?

Hi,

my DAC output voltage will be =[ (2.5)/2^14-1 ]* digital data input
Where does the "-1" come from? I don´t think it´s correct, but still a very tiny error.
(In doubt check datasheet)

0.007906177 V, 0.007997726 V, 0.008090335 V,..... up to 0.620821168 V .
Sadly your DAC is 14 bits, thus it has a resolution of about 4 decades. Giving values with a resolution in the nanovolts while talking about a DAC with a resolution in the 100uV (a factor of about 100000) does not match.
And your values are idealistic. On a real DAC you have offset error, gain error, nonlinearity and noise....
I recommend to keep the (unavoidable) errors in mind.

So, If I want to increase the ratio between 2 DAC output voltages and want to use the full range of DAC : 0-10 V , could you please provide guidance on type of signal conditioning to be used at the output of DAC?
If you want to use the full range of the DAC you have to input full range digitial data.
with giving up to 0x0FE4 you can never use full range DAC,

***

So I guess what you really want is to adjust the overall (not DAC) analog output range.
This could be done with an amplifier, usually made with an OPAMP.

Gain = analog_output_range / analog_input_range
Offset: how to add offset depends on the circuit.

Circuit: If you want to go this way, then I recommend a "4 resistor difference OPAMP circuit".
(also called a "differentail amplifier circuit").
Do internet search. You will find thousands of tutorials, videos, descriptions, calculation examples...

A good design does not start with a solution. It starts with application requirements and specifications.
Here mandatory: expected accuracy, precision, resolution. But also: available power supplies and other informtions. Maybe you need to use a dedicated microcontroller, a dedicated DAC, a dedicated voltage reference... All these informations have influence on the resulting (hardware) solution and the performance.

BUT:
I´d rather adjust the digital values (range and offset).
Mind: there is a data chain: digital value ---> DAC --> analog value --> filters --> amplifiers --> output.
When you "destroy" the performance in an early stage (DAC, range) you usually can never compensate for this in the following stages.
Realistically all following stages will "add new errors". Thus it´s better to cure the problem at it´s root.
Also: digital values are predictable, precise and stable, they don´t drift with time and temperature, but analog values will.

Klaus

Hello,

Thank you for your quick feedback.
Sorry for typo error in equation: What I am trying to say is that DAC output voltage for 14 bit resolution and 2.5 V ref. voltage = [2.5/16483] * digital input code

And my digital input is having this much of resolution and this range is fixed. so, the option I have to use proper amplifier that will increase the range.
Yes, I got your point, I need to take care for the signal conditioning chain for the analog output as it will add errors.

Hi,

= [2.5/16483] * digital input code
usually it is "16384" not 16383 and surely not 16483. Again: Did you check the datasheet?

Klaus

Missing information: I still don´t see why you don´t want to / can not change the digital values.

Hi,

I know many sites / hobbyists spread this (usually) wrong information.

Mind: You don´t need to believe in me, that´s O.K.
It´s me pointing on the reference, the manufacturer´s datasheet.

***

Your given link points to an 8 bit example. Many (old) 8 bit DACs use 5V as reference.
* so using the site`s formula the output on 0xFF would be 5.00V
* but indeed the output of a real DAC ideally is 4.98V

Klaus

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