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crutschow

Single Supply Non-Inverting Av=1 Op Amp Circuit With Positive Offset Adjustment

Circuit generates Av=+1 with simple positive offset value calculation

  1. crutschow
    Occasionally it is desired to have a single-supply non-inverting op amp circuit with some fixed, arbitrary positive offset.
    In general, this gives an interaction between the gain and offset voltages which makes it awkward to calculate the desired resistor values. And the calculations may generate non-standard resistor values.
    Here's a circuit that allows easy calculation of the offset with the offset voltage determined by standard resistor values and any offset resistor change doesn't affect the gain.
    The limitation is that the gain must be fixed at +1 for this simple relation to be valid.
    The LTspice simulation of the circuit is below.

    upload_2017-2-8_13-42-51.png

    The offset is determined by the value of R6 and R1 where R1=R2.
    The simulation shows offset values of 2V and 6V for R1=R2 values of 60kΩ and 20kΩ with a 0 to 4V ramp input.
    As can be seen, the offset value changes with the value of R1=R2, but the gain stays constant at Av=+1.

    If you want a more stable offset than provided by the supply voltage, replace V+ with a reference voltage at R2.

    Attached Files: