# How to choose Reference for ADC

Hi everyone,

I'm wondering how to select a reference IC when I design ADC sometimes.
For expample, looking at AD7918, 10bit-ADC external referene and the gain error itself is 0.5LSB MAX.
Reference accuracy is said to be less than 1% according to the comment of datasheet.

Ive attached a file on this mail.Please refere to it.
But I'm wondering that the accuracy of reference is 1% sounds larger.
Because the resolution of 10bit is equivalent to 0.1% and the gain error of this device is only 0.5LSB(0.05%).
Please give me advice on the coneection between the gain error and the accuracy of reference voltage.
(In this case, reference noise and tempareture coefficient are not considered to make it simple)
And one more thing, I want to know how to estimate source current of ADC refinput to choose right reference IC.

Tarzan

Parents
• Hi Jakub,

First, you said the Gain error specification is not infuluenced by the reference variation and mesured by test specification.
So how much accurcy of Vref is used during the test?
And sencondly, in AD7918, if we use +/-1% refrence that datasheet mentions, can we acheve the DC statics peformance such as gain error:+/-0.5LSB ?
I think acutual gain error could be +/-10.5LSB if we use  +/-1% refrence ( vref initail error and ADC gain error from the fomula of Code=Vin*2^n/Vfef)

Is my perspective correct?
I'm not sure where this +/-1% refrence come from and what exactly happen if we use less accuracy of Vref (more than 1% accuracy).

Best regards,
Tarzan

• Hi Jakub,

First, you said the Gain error specification is not infuluenced by the reference variation and mesured by test specification.
So how much accurcy of Vref is used during the test?
And sencondly, in AD7918, if we use +/-1% refrence that datasheet mentions, can we acheve the DC statics peformance such as gain error:+/-0.5LSB ?
I think acutual gain error could be +/-10.5LSB if we use  +/-1% refrence ( vref initail error and ADC gain error from the fomula of Code=Vin*2^n/Vfef)

Is my perspective correct?
I'm not sure where this +/-1% refrence come from and what exactly happen if we use less accuracy of Vref (more than 1% accuracy).