1. A multifunction amplifier comprising: a finite transconductance amplifier having a high input impedance and a desired output impedance, the desired output impedance being a function of an input resistor, a feedback resistor and a finite transconductance for the finite transconductance amplifier; and means for controlling the finite transconductance amplifier by turning on and off a current source supplying current bias for the finite transconductance amplifier such that when turned off the finite transconductance amplifier has an essentially infinite output impedance and when turned on has the desired output impedance.