R1 and R2 divide down changes in potentiometer voltage by the ratio R2/(R1+R2). For a small error the potentiometer value would need to be small or Rf would need to be reduced by an equal amount.įor small offset voltage adjustments the adjustment of the potentiometer becomes difficult and most of the potentiometer range is not used.Īdding R1 and R2 overcomes both these problems. The equivalent resistance of Rf (equal to Rf/4) will add to Rf and cause gain errors. If R1 is a short circuit and R2 an open circuit the whole change in potentiometer voltage is applied to the end of Rf. To adjust a "ground" voltage that a resistor connects to, you can connect it to a potentiometer which is able to vary either side of ground. To compensate for an offset voltage by injecting a current you can apply an adjustable voltage from a potentiometer via a high-value resistor to an appropriate circuit node. That is, injecting a current causes it to flow in related circuitry and causes a voltage change, and adjusting voltage causes current flows to alter. This injects a small current into the node which causes an offset voltage.Ĭurrent injection effectively occurs at a high impedance point and voltage adjustment at a low impedance point, but both methods are functionally equivalent. Or a say 100 kohm resistor from the op-amp inverting input can be fed by a 10 kohm potentiometer connected to +/- 15 V. The ease of use of this method is improved by adding one two-resistor divider to the potentiometer voltage, as explained below. The methods described below can easily be applied to your circuit byĪdding a divider and potentiometer at the ground end of your R2. Or vary the voltage of a node which a circuit element connects to. The best method to use varies with the application circuit, but all eitherĪpply a variable current to a circuit node There are a range of methods which can be used to provide offset voltage compensation.