Figure 18: CPZ for (a) α=0.4 (b) α=0.45 (c) α=0.62 and (d) α=0.4
When these FOCs are placed in the oscillator circuitry, constant phase
zones are obtained in the phase response analysis too. The constant
phase behavior of the conventional MOS based CO, have been obtained for
three different orders, as shown in Figure 18. It can be seen that as
the order increases there is an increase in the constant phase spectrum.
The designed FOCs using passive RC ladder approximation technique
generates CPZ in a wide frequency range when placed in a CO circuitry.
This is another advantage of fractional order over integer based
circuits. Further, the power analysis has been done and it has been
observed that there is higher power consumption in fractional order
circuitry compared to the normal integer counterparts. For identical
circuit parameters, 19.5% increase in power is obtained for fractional
order CO circuit (11.82mW, α=0.62) compared to the conventional CO
(9.997 mW, α=0.62). Thus, though desired control and better phase
approximations are achieved, however, these ladder circuits being huge
cascade connection of resistors and capacitors tend to increase the
power consumption as well as the noise in the circuit too. Noise
analysis has been done in later in the paper.
CNTFET based integer order Colpitts
Oscillator
To remove the drawbacks of conventional MOSFET based fractional order
circuit we move towards a more optimum low power design approach using
CNTFETs. The CNTFET based circuits are known to offer lesser static
power dissipation due to lower IOFF and significantly
lesser dynamic power due to lower gate capacitance CGG.