High Efficiency GaN Class E Power Amplifier at 5.8GHz with Harmonic Control Network

High Efficiency GaN Class E Power Amplifier at

5.8GHz with Harmonic Control Network

Wenli Fu, Shiwei Dong, Chaoyue Yang, Ying Wang, Yazhou Dong

China Academy of Space Technology (Xi’an)

Xi’an, Shaanxi 710100, China

wlfu-193@https://www.360docs.net/doc/462462059.html,

AbstractüThis paper presents a 5.8GHz high efficiency class-E power amplifier (PA) using a 25-W GaN HEMT large signal model for wireless power transmission applications. The input and output harmonic control networks using ?/4 open-stub transmission lines is employed to obtain high output power and high efficiency. The simulation results show that the power-added efficiency (PAE) of 69% with a gain of 12.2dB and output power of 41.2dBm is achieved at 5.8GHz. The PAE over 63% and the output power over 40 dBm are maintained in 100 MHz bandwidth.

Keywords-class E power amplifier; GaN HEMT; power added efficiency (PAE)

I.I NTRODUCTION

The high-power amplifier plays critical role in wireless power transmission systems. In addition to achieving the desired power level, the overall DC-to-RF conversion efficiency is also very important because the efficiency enhancement means reduction of launch cost and energy consumption [1]. The class E concept is one of the most popular techniques for realizing high-efficiency power amplifiers. Compared to other switch-mode power amplifiers such as the class-D, -S, -F, and -F-1, the class-E PAs have the advantage of simple configuration with an output capacitor and a serial resonator, and the parasitic capacitance of the device always used as the output capacitance of the ideal class-E topology [2-6]. Regarding the semiconductor technology for the switching-mode device for a class E PA, silicon laterally diffused metal oxide semiconductor (Si LDMOS) devices have been the preferred choice at around 2 GHz [7]. Compared to LDMOS devices, the recent development of gallium nitride high electron mobility transistors (GaN HEMTs), which benefit from much higher f T, breakdown voltage and lower parasitic capacitances, makes them more suitable for the design of class E power amplifiers at high frequencies.

In this paper, a hybrid class-E PA operating at 5.8GHz for wireless power transmission is designed using a 25-W GaN HEMT large signal model. The input and output harmonic control networks with ?/4 open-stub transmission lines (TLINs) are used to suppress harmonic components.

II.B ASIC C ONCEPT OF THE C LASS E P A

Fig.1 shows the ideal circuit of class-E PA , which consists of a switching device, a parallel capacitor(C out), a series fundamentally tuned L0C0 resonant circuit, and a specific load impedance. The transistor is assumed as an ideal switch, the voltage across the switch is zero when the switch is turned ON, and the current through the switch is zero when it is turned OFF, the energy is stored in C out when the switch is the off-state, and the stored energy produces the current through

the load impedance. The parameters of the ideal class-E PA

can be expressed by[8]

out

R=0.5768

(1)

0.0292

f R

out

(2)

where V ds is the drain bias voltage, f0 is the operating

frequency, and P out is the output power of the PA. From (1)

and (2), it is seen that the lower the parasitic capacitance of the

device, the higher operating frequency at a fixed drain bias

voltage and a saturated output power.

Figure 1. Basic Class E amplifier schematic

III.THE P ROPOSED C LASS E P A

The proposed class-E PA was designed with Triquint

TGF2023-05 GaN HEMT die, which had a minimum drain

breakdown voltage of 80V and C ds of about 1.23pF at the

drain bias voltage of 28V from datasheets. Since C out

calculated using equation (2) is 0.7pF for the ideal class-E

operation at 5.8 GHz, smaller than the device source-to-drain

capacitance (C ds), thus C out in Fig.1 was replaced by C ds. Fig.2

shows the full schematic of the proposed class-E PA with

harmonic control network. The Rogers 5880 (?r=2.2,

h=0.254mm) has been used as the substrate. The input and

output harmonic control networks consist of three series

transmission lines (TL2?TL5 and TL7) and three ?/4 open-

stubs (TL3?TL6 and TL8) at the 2nd- and 3rd- harmonic

frequencies, as shown in Fig.2. For the input and output

fundamental matching networks (IMN and OMN), both L-

section matching circuit are employed. Fig.3 shows the

frequency response of the input and output networks. It can be

seen that the proposed harmonic control network can block

harmonic components effectively, the harmonic impedances

are nearly open compared to the fundamental impedance.

Fig. 4 shows characteristics of output power and power

added efficiency (PAE) according to gate and drain bias

voltage. The input power (P in) has been fixed at 29 dBm. It

Figure 2. Schematic of the proposed class-E PA

can be found that the output power increases with the increase of V gs and V ds , while PAE reaches maximum when V gs =-4.7V and V ds =28V. Therefore, the V gs of -4.7 V and V ds of 28 V are chosen as the optimum bias voltages, respectively.

Figure 3. Simulated frequency response of the input (left) and output (right)

networks

(a)

(b)

Figure 4. Output power and PAE according to (a) gate bias voltage (b) drain

bias voltage

Fig. 5 shows the simulated results of output power, power added efficiency, and power gain according to the input power level at the optimum bias voltages. The maximum PAE of 68.7% and P out of 41.2 dBm with power gain of 12.2dB is achieved at 5.8GHz.

Figure 5. Output power, PAE and power gain according to input power level

at 5.8GHz

Fig.6 shows the output power and PAE according to the operating frequency at the input power of 29 dBm. It can be found that high PAE and output power level were maintained over 63% and 40 dBm over the bandwidth of 100 MHz, respectively.

Figure 6. Output power and PAE according to operating frequency

The simulated time-domain waveforms of the drain voltage and current are shown in Fig.7. It can be seen that the waveforms differ from nominal class-E waveforms, this is mainly due to the conventional current waveform of the class-E PA cannot be retained because the capacitor cannot be charged or discharged fast enough to support the required voltage waveform [9]. Fig.8 shows the output spectrum of the PA from 1 GHz to 20 GHz for a fundamental output power of 41.2 dBm, harmonic suppression is better than -78 dBc at 2f 0 and more than -91 dBc at 3f 0.

Figure 7. imulated drain voltage (blue) and drain current (red) waveforms of

the class-E amplifier

Figure 8. Output spectrum of the designed class-E PA at an output power of

41.2 dBm.

In conclusion, table I shows the State-of-the-Art of PAE vs

output powers for C-band GaN HEMT amplifiers [10]-[13].

TABLE I.C OMPARISON O F C LASS-E G AN P AS

Freq P out PAE

[10] 5GHz 100W 31%

[11] 5.7GHz

34.5dBm 68.7%

[12] 4.8GHz 343W 53%

[13] 5.8GHz 7.3W 70.5%

This work 5.8GHz 41.2dBm 68.7%

IV.C ONCLUSION

We have proposed the high-efficiency hybrid class-E PA

at 5.8GHz using a 25-W GaN HEMT large signal model. The

input and output harmonic control networks using the ?/4

open-stub TLINs was used to suppress the harmonic

components and improve the efficiency. The results show that

2f0 suppression in excess of -78 dBc, and 3f0 suppression of

about -91 dBc at 41.2dBm of fundamental output power.

Moreover, high PAE of over 63% and high output power of

over 40 dBm were maintained in the bandwidth of 100 MHz.

The proposed class-E PA can deliver high efficiency for

wireless power transmission applications.

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