TABLE OF CONTENTS In [A1] it is proved how any linear, non reciprocal network can be represented starting from simple passive and active elements.
Passive elements needed for this representation are resistors and capacitors, while the active ones are two-terminal basic networks, introduced in this appendix.
The active components are named nullator and norator and are shown in figure A.1, with their main features.
The nullator is characterized by zero voltage and current, while in the norator the current flowing into a node is equal to the current coming out from the other node. Voltage and current magnitudes are not defined.
Starting from these networks and considering the theory developed by Tellegen [A2], in 1964, Carlin introduced an ideal amplifier which utilises nullators and norators, naming the obtained two-port network as nullor [A1]. In fact, as stated before, since any active network can be represented in terms of nullators and norators, the simplest component is their combination and the nullor can be considered as the natural ideal active block.
Nullor satisfies Tellegen's requirements for an ideal amplifier, which are zero input voltage and current, and arbitrary output voltage and current. As a consequence, the device has an infinite voltage gain and has become the starting point of every approach to amplifier theory. From nullor properties it comes that input and output impedance levels are not defined.
