Noise Analysis of the Designed
COs
In this section, the noise analyses of the four COs designed and
simulated in this work have been done. Noise is defined as the random
fluctuations that affect currents and voltages and it actually sets the
lower limit of any signal without its quality being deteriorated. For
the conventional MOS based CO, noise analysis takes into account the
Thermal noise, Shot noise and Flicker noise. Thermal noise, also called
as Nyquist or Johnson noise, is associated with the random thermal
motion of charge carriers. Shot noise is caused by the random
fluctuations of the electric current due to electronic charge and the
Flicker noise, also called 1/f noise or pink noise, is present in both
the active and passive devices and becomes predominant at lower
frequencies. In the Stanford CNTFET model no noise source definition
exits. However, in various works noise models have been provided as an
extension to the Stanford CNTFET model; providing high flexibility to
choose the circuit simulators. In this work, an equivalent small signal
analysis model and the parameter extraction principle have been employed
for the noise analysis of the CNTFET based COs. The intrinsic and
extrinsic parameters have been extracted using s-parameter analysis and
then subsequently converted to Y and Z parameters. In CNTFETs, the noise
modeling can be done in both the saturation and triode regions
[26,30]. The various noise sources included in the analysis include
thermal noise, shot channel noise and the flicker noise. Figure 25 shows
the equivalent circuit of a CNTFET with added noise sources used in
analysis. The total noise is the root mean square value of the
individual noise contributions.