A very high gain voltage amplifier having a differential input, i.e. its output voltage is proportional to (and very much greater than) the voltage difference between its two inputs. Operational amplifiers usually have feedback circuits of resistors and/or capacitors connected between their output and inputs. These circuits make op-amps operate as voltage amplifiers with a gain precisely defined by the values of the resistors, or else enable them to perform mathematical operations, such as integration, or signal-conditioning functions, such as filtering. Operational amplifiers are generally employed in linear circuits, but with the addition of nonlinear components (e.g. diodes) other functions such as precision rectification and logarithmic amplification can be effected.