Issue with simple buffer design

[umesh49]

Hi,
I had implemented a buffer using op-amp OPA171AQDBVRQ1. This is simplest buffer with input at + and – is shorted the output.
It works good, except at few points it shows a jump of few millivolts. This small error even gets 3 times more at more than 100C ambient temperature.
Output was op-amp was not having any load/capacitor at output while doing the measurement using multimeter.
I am attaching here the output profile with input voltage.
Please let me know if any one came across such issue.
Thanks in advance for your help.

Regards,
Umesh

 

[Audioguru]

I think your input voltage has a problem at about +2.05V.

 

[crutschow]

What instrument are you using to measure the difference voltage?

 

[umesh49]

I am using high end multimeter which can measure up to 4 decimal digits. I verified the input voltage, it was coming from the DAC output and was having no issue.

 

[Audioguru]

Maybe your multimeter was changing ranges at around 2.0V which caused the sudden drop in its output voltage.
Maybe the DAC voltage source causes the problem at around 2.0V.

 

[kwkam]

it is pop noise. You need to choose a pop noise free buffer if you really care

 

[umesh49]

it is pop noise. You need to choose a pop noise free buffer if you really care

Hi Kwkam;
Thanks, this is something new I am hearing first time.
Is the POP noise is something which appears consistently at same input voltage? Where in the data sheet they define these characteristics.

Regards,
Umesh

 

[kwkam]

pop noise is random. Goto check the opamp pop noise in the web

 

[D.A.(Tony)Stewart]

THe noise you show is repetitive with X axis DAC output, so I wonder if there is any ground shift spike from the DAC inputs going from ...01111 to ...10000 . If so, this could be digital ground current getting into Analog ground reference for DAC.

I've seen this on ADC's before but not DACs.

 

[umesh49]

THe noise you show is repetitive with X axis DAC output, so I wonder if there is any ground shift spike from the DAC inputs going from ...01111 to ...10000 . If so, this could be digital ground current getting into Analog ground reference for DAC.

I've seen this on ADC's before but not DACs.

Hi,
Thanks for your reply. I had verified with ground and everything seems to be alright. It seems to be op-amp is doing something. I observed different magnitude of noise in different boards so it changes from part to part but noise happens around same input voltage always. I am thinking if it has something to do with the way op-amp works. bias point etc.

Regards,
Umesh