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10 years, 2 months ago.
level shift +-2 v signal to 0 - 3.3v to get it into ADC
Hey guys , I need to convert a 2 volts peak to peak signal into a 0 to 3.3v to get it into my ADC on LPC 11u24 . I have tried several designs but the problem is that all of the designs I found are based on single rail op amps . I only have dual supply op amps . Any suggestions ?
2 Answers
10 years, 2 months ago.
You could use one of the dual supply AD op amps in a non inverting configuration, bias the minus input of the op amp with a -2V reference voltage. This would then give you 0-4V out for your +/-2V in. To scale that you could reduce the gain of the op amp to less than unity but it may be a more stable design to just put a resistor divider to attenuate the input by 20% or so. That of course would alter the reference voltage or you could keep it at 2V and live with a .4V to 3.2V output range.
You may also want to take a look at the differential circuit on this page:
http://en.wikipedia.org/wiki/Operational_amplifier_applications
It is probably obvious but I will throw it out there anyway....you will need a +/- power supply for your op amp.
Please let me know how it all works out for you.
posted by 30 Jan 2014
10 years, 2 months ago.
Depending on the drive capabilities of the analog signal you provide, you could also use the audio input block mentioned at https://mbed.org/users/shintamainjp/notebook/simple-wave-recorder-player_en/ with an additional resistive attenuator at the analog input (attenuation : 4/3.3).
If necessary, you can leave out the LPF filter.
Are you sure your opamps are dual supply only as some dual supply types can also be used in single supply configurations?
Yes I am pretty sure about that . Or maybe I am missing something . I use AD711 , AD744
posted by 30 Jan 2014You are right, these are dual supply only. Following application note allows you to use them in a single supply setup but there are some limitations : http://www.analog.com/static/imported-files/application_notes/AN-581.pdf
posted by 30 Jan 2014
Since your mapping a larger range (4V) to a smaller range (3.3V) you don't need an opamp, three resistors will do. Since you shift towards positive voltages, just a positive auxiliary voltage will do.
posted by Ad van der Weiden 31 Jan 2014