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10 years, 10 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, 10 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, 10 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