Abstract:
Different models of nano-electronic quantum device Single Electron Transistor (SET)
are studied in this work, a modified macro model is proposed and at the end its
application in a communication circuit is presented. In the modified macro model it is
shown that an inherent problem in the earlier model like unwanted DC offset has been
successfully eliminated. I-V characteristics curve of the SET has been studied very
closely with the modified macro model. It is shown that how coulomb oscillation of
SET can be used to form variable transconductance region of operations. The variable
transconductance region of SET consists of a positive and a negative part and a new
phenomenon named ‘negative transconductance’ is observed which is very unique to
SET. It is also described how to bias a circuit to achieve that condition with the
operating principle described, a phase modulator circuit is proposed in this work
which utilizes negative transconductance. The circuit exploits the unique
characteristics of SET of having bi-polar transconductance for the proper operating
point. The biasing of the circuit is the one of the most critical parts since the region of
operation is very narrow. Different biasing conditions are also discussed for the SET
bases phase modulator circuit. Since almost every form of communication signal
handing systems always convert the original signal to a modulated signal for further
processing and increase gain of the transmitted signal, Phase modulator is one of the
most common of all elementary communication circuit configurations. The SET
based digital signal phase modulator circuit proposed in this work is the most
simplified for such circuits used so far. It is seen from the simulation data that SET
based digital signal phase modulator circuit performs very efficiently to convert
digital pulse to modulated signal.
