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.