Design of the Frequency-Tunable CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 98

Table 6.9 Simulated 2-tone
output power and PAE at
− 35 dBc IMD3

3.7 GHz 5.2 GHz

2-tone

Conv. Tun. Conv. Tun.

Pout (dBm) 13 14 . 7 13 . 2 14 . 8

PA E ( % ) 6 . 7 8 . 8 8 . 9 11 . 5

However, if we do not look at the distortion and only compare the efficiency at
the same output power level, the conventional PA presents a slightly better PAE.
This difference in efficiency can be measured by the ratio between the PAE of the
tunable and that of the conventional PA shown in Figs. 6.19 and 6.21 . A PAE ratio
of 100% corresponds to equal efficiencies. The difference is large only at very low
output power levels and is very small elsewhere. Although, the consumption of the
control circuit is included in the PAE calculation, the small difference in efficiencies
can be explained by the fact that, due to the Q enhancement in the frequency-tunable
PA, the parasitic series resistance of the inductor is decreased and, consequently, the
power dissipated on it is lower.
These results indicate that the coupled-inductor technique can be used in a
frequency-tunable PA for dual-band operation at 3.7 and 5.2 GHz (TR = 34%).

6.5 Conclusion

This chapter presented the design of a frequency-tunable CMOS RF power ampli-
fier. It showed that a π -type output impedance matching network is suitable if only
the inductor in the series path is adjusted as frequency changes. The design of the
coupled inductors and the control circuit used to implement this variable inductance
was presented. The PA design was briefly discussed. Its design follows that of the
PA used with the dynamic supply in Chap. 3. Simulation results of the overall sys-
tem demonstrated that a better performance can be achieved when operating in two
different frequency bands if the frequency-tunable capability is implemented. In our
analysis, the 3.7 and 5.2 GHz frequency bands were considered.

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