# Voltage range shifter from 0V to 3V to -/+1.5V

I'm trying design from scratch (discrete components and opamps) a circuit that could linearly translate from 0V to 3V range to -1.5V to +1.5V. Can someone provide suggestions and designs of how to do this?

edit: Ideally, the input and output relationship would look linear. Something like Vo = Vi - 1.5 The input voltage would be AC in the sense that it varies, such as a positively shifted sine wave.

• Can you clarify if this is an AC signal, or does it have a DC component? – Daniel Jun 20 '14 at 16:33
• Very similar to electronics.stackexchange.com/questions/115502/… – user36113 Jun 20 '14 at 16:35
• The terms AC and DC are often used completely wrongly. A DC voltage is stationary - it can never be varying between 0V and 3V. An AC voltage is a voltage that varies between two extremes. DC is often used, as in this case, to describe an AC voltage that has no negative values, and AC as any AC voltage where the voltage goes negative - more often it's even used to describe a sine wave with a 50% positive and 50% negative component. So I assume your signal is an AC signal which complex frequency components. – Majenko Jun 20 '14 at 16:47
• If all the voltages are DC, then what does it mean by saying, translates the voltage linearly? Please clarify. Or, if you trying for voltage level shifter, try using schmitt trigger or design a compartor using opamp. – AKR Jun 20 '14 at 16:56
• @Majenko, "DC" is also very often used to mean "varying only very slowly". I've never heard it used to mean "strictly positive". – The Photon Jun 20 '14 at 17:23

Conceptually if you put a 1.5 volt battery in series with the signal it would shift the signal down or up 1.5 volt. If on the other hand you used a precision shunt regulator (set to be regulating at 1.5 volts) and gave it some negative bias then this would also work: -

simulate this circuit – Schematic created using CircuitLab

The negative supply is just to bias the precision shunt regulator so that it is always "in regulation".

This is pretty similar to Andy's (already selected) idea, but implemented with an op-amp and TLV431 low-current reference. R3 biases the reference with 0.2 to 0.5mA. The TLV431 series impedance causes a small gain error of less than 50ppm. R1 and R2 establish the reference as about 1.5V (use the 'T' grade device and 1% or even 0.1% resistors if you want high accuracy (and calculate them more accurately than I did, including typical REF current).

simulate this circuit – Schematic created using CircuitLab

If your varying voltage has a known set of frequency components, or at least a known minimum frequency component, it is possible to construct a high-pass filter that filters out frequencies below that lowest frequency. That includes 0Hz, or the effective 1.5V DC offset to the signal. That could consist of, as the most basic, a capacitor (in series) and a resistor (in parallel).