In this work, we analyze the effects of an inter-stage capacitor located between the power stage input and the driver stage output on the overall efficiency of a RF CMOS power amplifier and on gate-drain reliability problems. To verify the analyzed effects, we designed a RF CMOS power amplifier with a center frequency of 1.85-GHz. Class-D amplifiers with a feedback resistor are used as driver stages, and a class-E amplifier is used as the power stage. A distributed active transformer is adapted for use in the output power combiner for high efficiency. The inter-stage capacitor between driver and the power stage is removed to enhance the switching operation of the power stage. By eliminating the inter-stage capacitor, the supply voltage of the driver stage can be decreased compared to that in a general amplifier. Accordingly, the power-added efficiency is improved and the gate-drain reliability problems are moderated compared to a general amplifier. The analyzed effect of the inter-stage capacitor is verified successfully using the measured results of the designed amplifiers.
2. Wang, S. and R.-X. Wang, "A tunable bandpass filter using Q-enhanced and semi-passive inductors at S-band in 0.18-μm CMOS," Progress In Electromagnetics Research B, Vol. 28, 55-73, 2011.
3. Wong, S.-K., C.-P. Ooi, W.-L. Pang, and K.-Y. Chan, "A high gain and high e±ciency CMOS driver amplifier for 3.5 GHz WiMAX applications," Journal of Electromagnetic Waves and Applications, Vol. 26, No. 4, 512-524, 2012.
4. Lee, C., J. Park, and C. Park, "X-band CMOS power amplifier using mode-locking method for sensor applications," Journal of Electromagnetic Waves and Applications, Vol. 26, No. 5-6, 604-633, 2012.
5. Seo, D., C. Lee, J. Park, and C. Park, "Power detection method using a virtual ground node for RF CMOS power amplifier applications," Journal of Electromagnetic Waves and Applications, Vol. 26, No. 17-18, 2341-2347, 2012.
6. Aoki, I., S. D. Kee, D. B. Rutledge, and A. Hajimiri, "Distributed active transformer --- A new power-combining and impedance-transformation technique," IEEE Trans. Microw. Theory and Tech., Vol. 50, No. 1, 316-331, Jan. 2002.
7. Aoki, I., S. D. Kee, D. B. Rutledge, and A. Hajimiri, "Fully integrated CMOS power amplifier design using the distributed active-transformer architecture," IEEE J. Solid-Stage Circuits, Vol. 37, No. 3, 371-383, Mar. 2002.
8. Park, C., Y. Kim, H. Kim, and S. Hong, "A 1.9-GHz CMOS power amplifier using three-port asymmetric transmission line transformer for a polar transmitter," IEEE Trans. Microw. Theory and Tech., Vol. 55, No. 2, 230-238, Feb. 2007.
9. Park, J., C. Lee, and C. Park, "A brief review: Stage-convertible power amplifier using differential line inductor," Wireless Engineering and Technology, Vol. 3, No. 4, 189-194, Oct. 2012.
10. Yang, J.-R., H.-C. Son, and Y.-J. Park, "A class E power amplifier with coupling coils for a wireless power transfer system," Progress In Electromagnetics Research C, Vol. 35, 13-22, 2013.
11. Kang, J., A. Hajimiri, and B. Kim, "A single-chip linear CMOS power amplifier for 2.4 GHz WLAN," IEEE International Solid-State Circuits Conference, 761-769, Feb. 2006.
12. Chowdhury, D., C. D. Hull, O. B. Degani, Y. Wang, and A. M. Niknejad, "A fully integrated dual-mode highly linear 2.4 GHz CMOS power amplifier for 4G WiMax applications," IEEE J. Solid-Stage Circuits, Vol. 44, No. 12, 3393-3402, Dec. 2009.
13. Afsahi, A., A. Behzad, and L. E. Larson, "A 65nm CMOS 2.4 GHz 31.5dBm power amplifier with a distributed LC power-combining network and improved linearization for WLAN applications," IEEE International Solid-State Circuits Conference, 452-453, Feb. 2010.
14. Chen, Y.-J. E., C.-Y. Liu, T.-N. Luo, and D. Heo, "A high-efficient CMOS RF power amplifier with automatic adaptive bias control," IEEE Microwave and Wireless Components Letters, Vol. 16, No. 11, 615-617, Nov. 2006.