Soheil Dolatiary
email: soheildolatiary70@gmail.com

Farhad Razaghian
email: razaghian@azad.ac.ir

Design of Class-F Power Amplifier with Feedback and Compact Microstrip Resonant Cell

Keywords: Class-F Power Amplifier, Harmonic Control Circuit, Microstrip

Design of a class F power amplifier (PA) with microstrip feedback and compact microstrip resonant cell (CMRC) by using of the pHEMT ATF-34143 transistor is presented. To have suppress the third harmonic (7.2 GHz) a CMRC with miniaturized size and -50 dB suppression level is designed. On the other hand, a feedback with microstrip lines is used to increasing stability factor without changing the efficiency. Aim of this feedback is increasing stability factor (K) and to create unconditional stability of circuit. The drain voltage and fundamental frequency of the proposed PA is 1.5 V and 2.4GHz, respectively. The power added efficiency of the proposed class-F PA is equal to 61% with 10.2 dB of power gain under 10dBm input power.

Introduction

The use of wireless communication system has become a natural thing. Power amplifiers are used to radars and radio transmitters, in the last section before antennas. Due to the power amplifier (PA) has high energy consumption, improving of power amplifier efficiency is a challenging for designers [START_REF] Imani | Simultaneous presence of wind farm and V2G in security constrained unit commitment problem considering uncertainty of wind generation[END_REF]. High efficiency of the power amplifier can be obtained by using overdriven class-B, class-F, or class-E operation modes and their subclasses, depend on the technical requirements [START_REF] Grebennikov | RF and microwave power amplifier design[END_REF][START_REF] Rouholamini | Temperature of a photovoltaic module under the influence of different environmental conditions-experimental investigation[END_REF]. Class-F power amplifier with creating square drain voltage waveform and half-sinusoidal drain current waveform, can be obtain to high efficiency. High efficiency means reducing power consumption and longer lifetime for the battery [START_REF] Kazimierczuk | Drive-transformerless Class-D voltage-switching tuned power amplifier[END_REF][START_REF] Ketabdar | Numerical and Empirical Studies on the Hydraulic Conditions of 90 degree converged Bend with Intake[END_REF]. A method to increase power added efficiency (PAE) of class-F power amplifiers is presented in [START_REF] Chen | A 3.1-GHz class-F power amplifier with 82% power-added-efficiency[END_REF][START_REF] Montazeri | Static voltage stability analysis of IRAN south-east power system using extended CPF method[END_REF]. This method is a microstrip harmonic control circuit design by using parasitic effects of the transistor output. Although, this PA has a high PAE, but the drain voltage is 28 V. Harmonic control circuit (HCC) have the most important role in designing class-F power amplifier. In [START_REF] Chen | A class-F power amplifier with CMRC[END_REF][START_REF] Pourseif | Model Reference Adaptive Control for Robot Tracking Problem: Design & Performance Analysis[END_REF], a CMRC as HCC to class-F power amplifier design is presented. In [START_REF] Hayati | Design of a highly PAE class-F power amplifier using front coupled tapered compact microstrip resonant cell[END_REF][START_REF] Yousefpour | A dynamic approach for distribution system planning using particle swarm optimization[END_REF], front coupled tapered compact microstrip resonant cell (FCTCMRC) is used to a class-F PA design, which creates short circuit for second harmonic and open circuit for third harmonic. In [START_REF] Hayati | Class-F power amplifier with high power added efficiency using bowtie-shaped harmonic control circuit[END_REF][START_REF] Ketabdar | Experimental Survey of Energy Dissipation in Nappe Flow Regime in Stepped Spillway Equipped with Inclined Steps and Sill[END_REF], a bow-tie shaped CMRC as harmonic control circuit (BSHCC) is presented which has acceptable efficiency but the size of CMRC is relatively large. On the other hand, in [START_REF] Kazimierczuk | Drive-transformerless Class-D voltage-switching tuned power amplifier[END_REF][START_REF] Ketabdar | Numerical and Empirical Studies on the Hydraulic Conditions of 90 degree converged Bend with Intake[END_REF][START_REF] Chen | A 3.1-GHz class-F power amplifier with 82% power-added-efficiency[END_REF] using of CMRC instead of HCC may cause instability in the amplifier circuit. In this paper, a new method for the design of harmonic control circuit for power amplifier class-F with CMRC and microstrip feedback is proposed. An advantage of this CMRC is miniaturized size without affecting on matching circuit. In this design, pHEMT ATF-34143 transistor is used that obtained a power added efficiency of 61% and output power of 20.2 dBm under 10dBm input power.

Class -F power amplifier

Class-F power amplifier is one of the important switching mode power amplifiers, which can provides theoretically 100% drain efficiency. The PAE equation can be express as follow [START_REF] Rahmani | Novel Approach to Design of a Class-EJ Power Amplifier Using High Power Technology[END_REF]:

𝑃𝐴𝐸 % 𝑃𝑜𝑢𝑡 𝑃𝑖𝑛 𝑃𝑑𝑐 100 1 2 𝑃𝑑𝑐 𝑃𝑜𝑢𝑡 𝑃𝑖𝑛 𝑃𝑑𝑖𝑠𝑠 2
Hence, the power dissipation (Pdiss) can be calculated from:

𝑃𝑑𝑖𝑠𝑠 1 𝑇 𝑉 𝐼 𝑑𝑡 3 So, 𝑃𝐴𝐸 % 𝑃𝑜𝑢𝑡 𝑃𝑖𝑛 𝑃𝑜𝑢𝑡 𝑃𝑖𝑛 𝑃𝑑𝑖𝑠 100 4
According to (4) the PAE can be increase, by reduction the power dissipation. As shown in figure 1, class-F PAs reduces the power dissipation, by creating half-sinusoidal waveform for drain current and square waveform for drain voltage [START_REF] Rahmani | High Power Two-Stage Class-AB/J Power Amplifier with High Gain and Efficiency[END_REF].

CIRCUIT DESIGN

To achieve high PAE, a CMRC as shown in figure 2 (a) has been designed to suppress the third harmonic. In figure 3 (b), it can be observed that the proposed CMRC by suppressing third harmonic (7.2GHz) makes square voltage waveform in drain while the quarter wave length transmission line make half-sinusoidal current waveform. Figure 3 (c) shows the load voltage waveform, which included only fundamental harmonic and verified the output matching circuit has a good performance. But this amplifier with CMRC is unstable therefor, a feedback between output and input of circuit for stability is used. Microstrip lines and a resistance are used in feedback design. The demission of microstrip lines are optimized. The aims of feedback design are increase stability factor (k) and preservation power added efficiency (PAE). Figure 4

RESULTS

Figure 5 (a) shows efficiency and power added efficiency (PAE) of the proposed amplifier in range of output power. According to this figure maximum power added efficiency of 61% with output power of 20.2 dBm. Figure 5 (b) shows power gain and output power in range input power. Table 1 performance summary and comparison with other works.

CONCLUSION

This paper presents a class-F power amplifier with feedback and a CMRC as harmonic control circuit. The CMRC and the quarter wave length transmission lines creates zero impedance at the second harmonic and infinite impedance at the third harmonic. Moreover, to increase stability factor a feedback consists of transmission lines and a resistor is designed. Simulation results demonstrates PAE of 61% and output power of 20.2 dBm under 10 dBm input power. The proposed amplifier can be used in communication system.

Figure 1 .

 1 Figure 1. Voltage and current waveforms (a) without harmonic control, and (b) with harmonic control

Figure 2 (Figure 2 .Figure 3 .

 223 Figure 2. (a) The layout of the proposed CMRC and (b) its S-parameters responses

Figure 4 .

 4 Figure 4. (a) Stability factor (k) with and without feedback and (b) PAE with and without feedback

Figure 5 .

 5 Figure 5. (a) Power gain and output power versus input power, (b) Efficiency and PAE versus output power

  (a) shows the stability factor and PAE of the proposed PA without feedback and figure 4 (b) shows the stability factor and PAE of the proposed PA without feedback and preservation PAE

		1.10 1.10
	Stability Factor Stability Factor	0.95 1.00 1.05 0.95 1.00 1.05	With Feedback Without Feedback
		0.90 0.90
		2.0 2.0	2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9	3.0 3.0
			Frequency (GHz) Frequency (GHz)

Table 1 .

 1 Performance summary and comparison with other works Ref.

		Mode	Vdd(v)	f (GHz)	Gain	PAE%
					(dB)
	[2]	D	-	0.05-0.07		89.4
	[3]	F	28	3.1	15	82
	[4]	F	3	2.4	10	74
	[5]	F	3	1.1	14	86
	[6]	F	3.1	2.4	-	80
	This work	F	1.5	2.4	10.2	61