Vref Question with Single Supply

Hello Gary1001 ,

Unfortunately having the Vref directly tied to ground at single supply operation will degrade its high CMR performance. 

Ideally from Figure 30 in the datasheet, Vref to ground is possible for single supply operation, as long as your input swing does not go to negative. If it does, this will clamp your output. 

If Vref is ground, this is simply added to your transfer function to the gain and differential inputs, however, still the device performance is not guaranteed beyond the datasheet spec on reference connection.

-L

Hi Lilipod,

Thank you for feedback.  Last question.  Is there a difference in CMR performance if I put Vref on 1vdc versus 2.048Vdc.  thanks!

Hi Gary1001 

Thank you for sharing your inquiries.

For the follow-up question regarding CMR performance vs Vref, the CMR parameter is mostly driven by how your offset voltage changes with respect to your CM input voltage, and for this device it has autocorrection architecture which corrects the offset errors, including those induced by any changes in the input or supply voltages.

However, since it is recommended not to use external buffer for the REF pin, we suggest using a precise voltage source to keep this line clean.

regards,

Once again, thanks for the quick response.  I think this is my final question.  If my input swings from 0.06 to 0.131Vdc and I want to maximize the range of my Vout (by adjusting Vref and Gain), is there any disadvantage to driving Vref with a 1vdc precision reference versus a 2.048vdc precision reference?  The Supply voltage to the opamp is 5Vdc.   Thanks!

Hi Gary1001 

There will be no disadvantage of increasing the reference level; but for it to work properly please refer to the product datasheet; specifically table 1 on page 3: https://www.analog.com/media/en/technical-documentation/data-sheets/AD8553.pdf

Then, it will be helpful in designing your circuit, if you can use one of our tool: “diamond plot tool” https://tools.analog.com/en/diamond/#difL=-0.1&difR=0.1&difSl=-0.1&gain=100&l=-8&pr=AD8422&r=8&sl=-8&tab=1&ty=1&vn=-15&vp=15&vr=0

Some of references in using the tool: https://www.analog.com/en/resources/app-notes/an-1401.html

Regards,

Thank you so much for the detailed information.