Automatic adjustment of the output impedance of a balanced transconductor using a charged capacitor

This paper describes an automatic tuning method that can adjust the output impedance of a balanced transconductor to infinity. The method uses a charged capacitor connected across the output of a master transconductor with zero input voltage. As the voltage over this capacitor increases or decreases exponentially if the output impedance of the transconductor is negative or positive, a control loop setting this voltage to a fixed value also sets the output impedance of the transconductor to infinity