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I have a signal that varies between 3 volts and 4 volts. Now I want to amplify that 1 volt difference to a range from 0 volt to 5 volts.

I tried to find a solution with an opamp or a transistor, but hopeless. What can do the trick in place of the question mark?

schematic

simulate this circuit – Schematic created using CircuitLab

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2 Answers 2

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look into this amplifier, by putting 3v on one of the input pins you can filter that out, you have the option to invert the signal to (depends on which pin you place the 3V)

enter image description here

http://en.wikipedia.org/wiki/Differential_amplifier#Other_differential_amplifiers

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You need a circuit called a difference amplifier.

http://en.wikipedia.org/wiki/Operational_amplifier_applications#Differential_amplifier_.28difference_amplifier.29

Connect your input to the noninverting input of the difference amplifier. Connect the inverting input to the positive supply. Then calculate the inverting gain so that you get the offset you want, and then figure out what resistor values you need to get that gain. Then figure out what resistor values you need to get the correct gain for the noninverting input. The equation you need is listed right on the linked page.

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