Figure 2

Figure 2 Impedance design space.

This novel design concept provides more abundant optimal impedances solutions. The parameter α varies from 1 to √2, and the corresponding normalized real part of the fundamental optimal impedance (Z(1f,re)) varies from 1.28 to 1.81. Figure 2 shows optimal fundamental and harmonic impedances of the NSCMs when α = 11/10, 5/4 and √2. The quasi-continuous class F‐1 mode corresponds to Z(1f,re) = 1.28. The optimal impedances of the continuous class F mode are also shown in the Figure 2 (the red dot area where Z(1f,re) = 1.154). The design space between the quasi-class F‐1 continuous mode and the standard continuous class F mode is the space where high order current elements need to exist for positive current waveforms.

From Equations 5 and 6, the power at dc (Pdc), fundamental RF (PRF) and the DE η are computed:

Math 9

DE and output power normalized to the continuous class F mode are illustrated in Figure 3. The DE of the NSCMs ranges from 57.7 to 81.6 percent when α changes from 1 to √2. When α = √2, the DE of the quasi-continuous class F‐1 is 81.8 percent which is same as the DE of the typical continuous class F‐1 mode. Compared to the quasi-class F‐1 continuous mode, output power of the NSCMs declines by about 0 to 1.5 dB, but good performances is still achieved.

Figure 3

Figure 3 Theoretical normalized output power and drain efficiency.

From Figures 2 and 3, it is clear that the design space of the NSCMs covers a wider area where Z(1f,re)  is between 1.28 and 1.81 and α is between 1 and √2. This offers significantly more design freedom compared to traditional continuous modes. For example, if a DE above 70 percent is desired, an α parameter greater than 6/5 is chosen; for a DE above 60 percent, an α parameter greater than 1.04 is used.

BROADBAND HIGH EFFICIENCY PA DESIGN BASED IN NSCMs

A broadband (2.3 to 3.8 GHz) high efficiency PA employing a 10 W Cree (Wolfspeed) GaN HEMT device (CGH40010F) is designed to experimentally verify the design concept. From the last section, we know that when α > 6/5, a 70 percent DE can be sustained. An approximate CGH40010F large-signal package model from Chen et al.6 is employed together with an output matching network (OMN) to achieve optimal impedance matching.

Figure 4

Figure 4 PA matching network (a) and fabricated amplifier (b).

When exploiting the nonlinear device capacitance, it can dominate the third harmonic band response;5 so, in the OMN design, emphasis is placed on fundamental and second harmonic matching while keeping third harmonic impedances in the high efficiency region. Real frequency technology8 and stepped-impedance filter matching are the most common methods used in the matching network design. A stepped-impedance microstrip-line filter network is utilized in this work.

Figure 4a shows the final matching network with dimensions. A photo of the fabricated PA circuit implemented on a Rogers 4350B PCB with H = 20 mils is shown in Figure 4b. With the approximate package model of the device and the final OMN, we obtain the impedance trajectories normalized to Ropt at the package plane and current generator (I-gen) plane, as shown in Figure 5. It is clear that the impedances at the I-gen plane lie within the predicted region.

The de-embedded simulated intrinsic drain voltage and current, when the PA is biased at Vds = 28 V and Vgs = ‐2.8 V at 3.2 GHz, is shown in Figure 6. The half-sinusoidal voltage and quasi-half sinusoidal current waveforms corresponding approximately to the waveforms in Figure 1 are obtained.

Figure 5

Figure 5 Impedance trajectories of the output matching network at the package and I-gen planes.

Figure 6

Figure 6 Simulated 3.5 GHz voltage and current waveforms at the I-gen plane.

EXPERIMENTAL RESULTS

The PA is measured under the stimulus of a single-tone continuous waveform signal swept from 2.3 to 3.8 GHz in 0.1 GHz steps. The measured results, including output power, DE and power-added efficiency (PAE), are shown in Figure 7. Simulation results are given for comparison.

Figure 7

Figure 7 Measured and simulated drain efficiency, power-added efficiency, gain and output power of the broadband PA.

From the simulated results, we can see that the DE from 2.3 to 3.8 GHz is from 71 to 75.8 percent with a PAE of 65 to 74 percent, and the gain is from 10.2 to 12.6 dB over the entire bandwidth. The output power ranges from 40.2 to 42.6 dBm.

From the measured results, a DE of 69.5 to 77.9 percent with a PAE of 63.5 to 73.4 percent is achieved in the band of 2.3 to 3.8 GHz. Across the band, the measured gain and Pout are 9.8 to 12.3 dB and 40.4 to 42.9 dBm respectively. Measurement agrees well with simulation.

A performance comparison of this PA with other state-of-the-art continuous PAs is summarized in Table 1. The modified FE6 and ITRS PA FoM9 are used to evaluate PA performance and provide a complete comparison with previously published work. FE denotes the frequency-weighted average efficiency. The ITRS PA FoM includes both output power and gain in addition to the DE and frequency. Considering these measures, the NSCM provides excellent performance.

Table 1

CONCLUSION

Emerging from the classical continuous class F mode and SCMs, the NSCMs are obtained by shaping drain voltage and current waveforms simultaneously. These modes enable expansion of the real part of optimal impedances solutions, providing greater design flexibility for improved performance.

References

  1. S. C. Cripps, “RF Power Amplifiers for Wireless Communications, 2nd Edition,” Artech House, Norwood, Mass., 2006.
  2. S. C. Cripps, P. J. Tasker, A. L. Clarke, J. Lees and J. Benedikt, “On the Continuity of High Efficiency Modes in Linear RF Power Amplifiers,” IEEE Microwave and Wireless Components Letters, Vol. 19, No. 10, October 2009, pp. 665–667.
  3. V. Carrubba, A. L. Clarke, M. Akmal, J. Lees, J. Benedikt, P. J. Tasker and S. C. Cripps, “The Continuous Class F Mode Power Amplifier,” Proceedings of the 40th Europe Microwave Conference, September 2010, pp. 1674–1677.
  4. P. T. Wright, J. Lees, J. Benedikt, P. J. Tasker and S. Cripps, “A Methodology for Realizing High Efficiency Class J in a Linear and Broadband PA,” IEEE Transactions Microwave Theory and Techniques, Vol. 57, No. 12, December 2009, pp. 3196–3204.
  5. N. Tuffy, L. Guan, A. Zhu and T. J. Brazil, “A Simplified Broadband Design Methodology for Linearized High Efficiency Continuous Class F Power Amplifiers,” IEEE Transactions Microwave Theory and Techniques, Vol. 60, No. 6, June 2012, pp. 1952–1963.
  6. K. Chen and D. Peroulis, “Design of Broadband Highly Efficient Harmonic-Tuned Power Amplifier Using In-Band Continuous Class (-1)/F Mode-Transferring,” IEEE Transactions on Microwave Theory and Techniques, Vol. 60, No. 12, December 2012, pp. 4107–4116.
  7. J. Chen, S. He, F. You, R. Tong and R. Peng, “Design of Broadband High-Efficiency Power Amplifiers Based on a Series of Continuous Modes,” IEEE Microwave and Wireless Components Letters, Vol. 24, No. 9, September 2014, pp. 631–633.
  8. Z. Dai, S. He, F. You, J. Peng, P. Chen and L. Dong, “A New Distributed Parameter Broadband Matching Method for Power Amplifier via Real Frequency Technique,” IEEE Transactions on Microwave Theory and Techniques, Vol. 63, No. 2, February 2015, pp. 449–458.
  9. Y. Song, S. Lee, E. Cho, J. Lee and S. Nam,” A CMOS Class E Power Amplifier With Voltage Stress Relief and Enhanced Efficiency,” IEEE Transactions on Microwave Theory and Techniques, Vol. 58, No. 2, February 2010, pp. 310–317.