reference voltage for adc

dear friends

how to create a fixed one volt reference for reference pin of adc.

thanks
amit

Depending on how accurate reference is needed, you emply precision voltage reference of, say, 1.25V, or similar, + voltage devider to exactly 1V and buffer-opamp. Example you can find here:
https://focus.ti.com/lit/ds/symlink/ref1112.pdf

hi Ianp, thanks for relying, one thing more can lm317 be used for this purpose......?

With best regards,
Amit

use only one potentiometer
One pin connected to VCC other to ground and the
variable knob pin connected to reference input.
use one voltmeter to measure the middle pin(variable pin) to ground to adjust to 1V


Bibin John
www.bibinjohn.tk

Any voltage regulator, including 317 and even +5Vcc, can be used for this purpose. But if you are after very high stability reference voltage you should consider appropriate source ..

Thanks everyone for replying. actually, i am having a voltage signal of 0.10 volt to 1.00 volts which i have to measure using adc at 8-bit accuracy, and microcontroller. i'm planning to use adc0831 for this purpose, can you guys tell me which one is better, amplyfying the signal to 0-5volt range using op-amps (with vref of adc at 5 volts) , or putting the vref of adc at 1.00 volts.
Thanks....
With best regards,
Amit

garg29 said:

hi Ianp, thanks for relying, one thing more can lm317 be used for this purpose......?

With best regards,
Amit

Click to expand...

lm317's minimum output voltage is 1.2 V
you should use voltage divider

Regards

you can use lm336. lm336 is a 3 pin device that works exactly like a zener diode with various brake voltages .in example there is lm336 Z2.5 & Z5,…. if you use a lm336 Z2.5 with a potentiometer like sample circuits in it’s data sheet from national semiconductor you will get a nice , low noisy and variable voltage reference between 0-2.5 volt.

Thanks everyone for replying. actually, i am having a voltage signal of 0.10 volt to 1.00 volts which i have to measure using adc at 8-bit accuracy, and microcontroller. i'm planning to use adc0831 for this purpose, can you guys tell me which one is better, amplyfying the signal to 0-5volt range using op-amps (with vref of adc at 5 volts) , or putting the vref of adc at 1.00 volts.
Thanks....
With best regards,
Amit

Better option is to amplify signal by the factor of 5. In this case you will be able to enjoy all 8-bit (256) resolution of your A/D converter.
To amplify this signal you will need an opamp that works well at the low-voltage level. You may consider here CA3130 ..

thanks for repyling ianp. but as you stated if i "put the vref of adc at 1.00 volts i won't get full 256 scale....i doubt for that....cause if once the vref is set to some value i think the adc should give full 255 reading on that value.....am i right or wrong somewhere...please correct me....Thanks

with best regards ,
Amit

For all types of ADC there is a minimal value of the Vref, with which one can get full resolution of the ADC. This is, particularly, due to switching noises of the MOS switches, used in ADC. Fith the lower reference the noise is the same, but the your signal is smaller, so the signal/noise ratio is smaller too.
That is why better to use non-inverting amplufier to amplify you signal to the maximal volage range of your ADC. The output of amplifier you can slightly shift in a positive direction to shift the signal zero for some tens of millivolts, to ensure, that the amplifier's offset voltage will be alwais positive, and the subtract the code, corresponding to 0 in amplifiers input from the ADC result.
To shift can be used very simple voltage divider, for example: 100 Ohm from the OpAmp output to the ADC input, and say 10k from the ADC input to the positive rail.

Varuzhan