AN4001

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300 Watt Class E Amplifier Using MRF151A

Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. 13.56 MHz and 27.12MHz, laser and MRI applications tend to migrate towards 40 MHz, 80 MHz, and 128 MHz. Power levels span the gamut from a few watts to hundreds of kilowatts. 81.36 MHz with better than 82% efficiency. voltage waveforms in order to minimize power dissipation and maximize efficiency [1]. Figure 1. Class E Amplifier Block Diagram

Rev. 01262010 Visit www.macomtech.com for additional data sheets and product information. M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice. ADVANCED: Data Sheets contain information regarding a product M/A-COM Technology Solutions is considering for development. Performance is based on target specifications, simulated results, and/or prototype measurements. Commitment to develop is not guaranteed. PRELIMINARY: Data Sheets contain information regarding a product M/A-COM Technology Solutions has under development. Performance is based on engineering tests. Specifications are typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. DESIGN AND SIMULATION MRF 151A was chosen for this application beca use of its 50V operation capability as well as the low R DS-ON (~0.2ohm). Figure 2 shows the Level 1 SPICE model used in conjunction with Agilent’s ADS simulation software to optimize the Class E circuit. To ease computations equations 1.0, 4.0, and 5.0 were re-arranged to solve for C, R, L o, Co as a function of frequency f, output power P o, drain voltage V dd, and inductor Q. When these variables are set to 81.36MHz, 300 watt, 48V, and 5 respectively the calculated values are C = 92.4pF, R = 4.4ohm, Lo = 54nH and C o = 88.3pF. One issue that arises from t hese results is that the required shunt ca- pacitance C = 92.4pF is smaller than the output capacitan ce of MRF151A which, per the data sheet, is 220pF. This implies that a class E amplifier would not operate optimally. The maximum frequency of operation for opti- mal, class E performance, for a particular capacitance value is given by: For a C out = 220pF the maximum frequency for optimal performance is ~30MHz. Since the desired frequency of operation is 81.36 MHz, the ratio f/fmax is 2.7. According to [2], the obtainable efficiency for f/fmax,≈ 2.7 is approximately 82%, which is still an attractive number. The calculated component values were used as a starting point in the simulation and varied in order to maximize output power and minimize DC current. Another constraint used in this optimization was the instant aneous drain voltage which was capped at 125V, which is the breakdown voltage of MRF151A. Figure 3 shows the optimized circuit and Figures 4,5, and 6 show the resulting voltage and current waveforms on the transistor drain, voltage across the load resistor R, and DC cur- rent. On the input side, the gate is matched to 50 ohm using conjugate impedance values. ADS can be used to easily perform this task. A 25 ohm resistor has been added in shunt to improve the bandwidth and stability. The results suggest a power output of 319 watts and an efficiency of 84.1%. Also, the peak drain volt- age is 120.6 V. A sinusoidal signal has been used to drive the MRF151A circuit. It is possible to shape the drive signal in order to increase efficiency, however, that is beyond the scope of this paper. outRCf 0292.0 max = (6) R VP dd o 577.0≈ ddDpeak VV 56.3= RQ QX 67.0 110.1 81.01(1836.0 2 ++= Q Q RB (1) (2) (3) (4) (5) R VI dd dc 734.1=

Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. Figure 2. MRF151A SPICE Model

Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. Figure 3. Class E Amplifier Circuit in ADS Figure 4. Voltage and current waveforms on the drain of MRF151A

Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. Figure 5. AC voltage across the load resistor Figure 6. DC current drawn from the power supply. ponent values are L = 24 nH and C = 160 pF. and the lengths are 0.63” for 23nH and 0.97” for 24nH. to eliminate any contribution from the biasing network. 85 ºC the junction temperature would be only ~123 ºC. Figure 7. Lumped element quarter wave section Figure 8. Prototype of class E amplifier

Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. Table 1. Performance of Class E amplifier with MRF151A MOSFET Figure 9. Performance of Class E amplifier with MRF151A MOSFET harmonic levels can be improved further by including additional filter stages. reasonable prediction of the measured waveform.

Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. the drain circuit is about 30 A. ter than 82% efficiency and approximately 11dB gain. Figure 10. Drain voltage at Pout = 300 watt [1] H.Krauss, C. Bostian, F. Raab, Solid State Radio Engineering, John Wiley and Sons, 1980. [2] A. Grebennikov, N. O. Sokal, Switchmode RF Power Amplifiers, Elsevier, 2007. [3] G. Hiller, Designing With PIN Diodes, MACOM Application Note AG312.