OPA316, level shift input signal, buffer output - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 13, 2016, 04:55:43 pm
content: 1. I have application where input signal voltage varies from +5V to -5V. Have to level shift the signal and fed it to microcontroller adc which is sampling at 1MSPS. Microcontroller adc range varies from 0V to 3.3VSelected OPA316 for this application. Attached find the circuit.2. Can I level shift the signal using single supply opamp(3.3V) volt from +-5V to 0-3.3Vdc3. I have calculated resistor values as in attached ckt. I dont have opamp right now, but if I simulate the resistor network without opamp, on applying +5V at vin, I got +3.3V at In+ & on applying -5V at Vin, I get 0V at In+.4. Is this ckt ok? What error margin I should take for voltage range?i think 1% resistor values will be ok.

author: Zero999
author_rank: Super Contributor
timestamp: September 13, 2016, 06:26:17 pm
content: All the op-amp does is buffer the signal. If the ADC has a high input impedance, then the op-amp can be omitted and it will still work perfectly.

author: Syntax_Error
author_rank: Regular Contributor
timestamp: September 14, 2016, 02:14:11 pm
content: https://www.google.com/?gws_rd=ssl#q=op+amps+for+everyone+pdfProvided without sarcasm or attitude. I include the search list instead of a link to the PDF in question because this provides additional tools and information. This PDF (Op Amps for Everyone) is simply written and very very useful for these type of conversion requirements.

author: rstofer
author_rank: Super Contributor
timestamp: September 14, 2016, 02:59:33 pm
content: Again, "Op Amps For Everyone" is a great reference. See section 4.3, pick the right case and follow the yellow brick road.I would get rid of the 10k resistor between the op amp and the ADC. MANY uC ADCs want to see a fairly low impedance source - like 2k (check the datasheet for your uC). The resistor serves no purpose and it can get in the way. If you want to protect the uC pin, try a 330 Ohm resistor instead.

author: Syntax_Error
author_rank: Regular Contributor
timestamp: September 14, 2016, 04:18:12 pm
content: Here's a few more.http://www.ti.com/lit/an/slyt104/slyt104.pdfhttp://www.ti.com/lit/an/sloa098/sloa098.pdfhttp://www.ti.com/lit/an/sloa097/sloa097.pdfAll seem relevant to your application.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 16, 2016, 05:59:32 am
content: Thanks

author: danadak
author_rank: Super Contributor
timestamp: September 16, 2016, 10:15:37 am
content: There are a number of ways of solving this, from something as simple as2 R's to developing a simple - supply for the OpAmp to expand its CMrange.https://www.dropbox.com/s/k1yn4m7heaixvmg/ADinput%20negative%20inputs.zip?dl=0Regards, Dana.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 17, 2016, 06:49:19 am
content: This ckt works. But it has one major consideration that source voltage should be able to both source & sink current.Let say I have a sensor which is not able to sink current like theromocouple. Suppose I have sensor with +-5V & it dont sink current.In that case what would be the ideal solution?