高频丙类功率放大器外文文献翻译.doc

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1、毕业设计（论文）外文文献翻译POWER AMPLIFIER2.0IntroductionThe main characteristics of an amplifier are Linearity, efficiency, output power, andsignal gain. In general, there is a trade off between these characteristics. For example,improving amplifiers linearity will degrade its efficiency. Therefore knowing the

2、importancedegree of each one of these characteristics is an essential step in designing an Amplifier. Thiscan be jugged based on the application. As an example high output power Amplifier is usedin the transmitter side of a transceiver, whereas high linear amplifier used in the receiver side.An ampl

3、ifier is said to be linear if it preserves the details of the signal waveform, thatis to say,Vo (t ) = A Vi (t )(2.1)where, Vi and Vo are the input and output signals respectively, and A is a constant gainrepresenting the amplifier gain. But if the relationship between Vi and Vo contains the higherp

4、ower of Vi, then the amplifier produces nonlinear distortion.The amplifiers efficiency is a measure of its ability to convert the dc power of thesupply into the signal power delivered to the load. The definition of the efficiency can berepresented in an equation form as=Signal power delivered to loa

5、dDC power Supplied to output circuit.(2.2)45For an ideal amplifier, the efficiency is one. Thus, the power delivered to the load is equal tothe power taken from the DC supply. In this case, no power would be consumed in theamplifier. In reality, this is not possible, especially in high frequency rea

6、lm of RF circuits. Inmany high frequency systems, the output stage and driver stage of an amplifier consumedpower in the amplification process.The gain of the amplifier (G) is equal to the magnitude of the output signal (Xo) overthe magnitude of the input signal (Xi) as shown in the equation.G =X oX

7、 i.(2.3)G can be voltage, current, or power gain depending on the application.The output power level plays an important role in evaluating the power amplifier. The poweroutput capability factor, PMAX, is the power output that would be produced with stresses of 1Volt and 1 Amp on the drain of the fie

8、ld effect transistor (FET). Multiplication of PMAX bythe drain voltage and current ratings of a real device produces the maximum output poweravailable from that device.The power output capability factor isPMAX =The Maximum Output PowerThe Peak Drain Voltage The Peak Drain Current.(2.4)2.1 Amplifier

9、ClassificationAmplifiers are classified according to their circuit configurations and methods ofoperation into different classes such as A, B, C, and F. These classes range from entirelylinear with low efficiency to entirely non-linear with high efficiency. The analysis presentedin this chapter assu

10、mes piecewise-linear operation of the active device. The majority of this6information is available in Solid State Radio Engineering by Krauss, Bostain, and Raab1980.The active device used in this research is the field effect transistor. The reason forchoosing this type of transistor is its superior

11、performance in the microwave rangeThe characteristics of the FET can be described by:iD = 0iD = g m (VGS - VT )cut-off region,active region, (2.5)iD =VDRonsaturation region.The regions of operation are defined by:cut-off region:active region :saturation region:VGS VT ,VGS VT and iD VD/Ron ,VGS VT an

12、d iD = VD/Ron .The term “saturation” is used here to denote the region where further increase in gate voltageproduces no increase in drain current, that is to say, iD is independent of VGS.2.2.1 Class AThe class-A amplifier has the highest linearity over the other classes. It operates in alinear por

13、tion of its characteristic; it is equivalent to a current source. As shown in figures.2.1and 2.2, the configurations of class-A, B, and C amplifiers can be either a pushpull or a singleended tuned version. Figure.2.3 shows the load-line and current waveform for the class-Aamplifier. To achieve high

14、linearity and gain, the amplifiers base and drain dc voltage shouldby chosen properly so that the amplifier operates in the linear region. The device, since it is on7(conducting) at all times, is constantly carrying current, which represents a continuous loss ofpower in the device.As shown in Fig.2.

15、3, the maximum ac output voltage Vom is slightly less than VDD andthe maximum ac output current Iom is equal to Idq. In the inductor-less system, the outputvoltage Vom will not be able to rise above the supply voltage, therefore, the swing will beconstrained to VDD/2 and not VDD. The drain voltage m

16、ust have a dc component equal to thatof the supply voltage and a fundamental-frequency component equal to that of the outputvoltage; henceVD ( ) = V DD + Vom sin .The dc power isPdc = VDD I dq ,the maximum output power is(2.6)(2.7) Po =1 2 V om I om 1 2 V DD I dq , （2.8）and the efficiency is = Po Pd

17、c 100 = 1 2 Vom Vom 100 50% （2.9）The difference between the dc power and output power is called power dissipation:Pd = Pdc - Po .(2.10)8Figure 2.1. Single-ended Power Amplifier (Class A, B, or C)9(a)(b)Figure 2.2.a. Complementary Pushpull Power Amplifier (Class A, B, or C)b.Transformer-coupled Pushp

18、ull Power Amplifier (Class A, B, or C)10300250200VGS5VGS4150Idq100500(Vdd,Idq)VGS3VGS2VGS105Vdd101520Vds (V)450400350300250200150100500Idd00.20.40.60.81Time (nsec)Figure 2.3. Load line and current waveform for the class-A poweramplifierId (mA)Id (mA)112.2.2 Class BThe class-B amplifier operates idea

19、lly at zero quiescent current, so that the dc poweris small. Therefore, its efficiency is higher than that of the class-A amplifier. The price paidfor the enhancement in the efficiency is in the linearity of the device.Figure 2.4 shows how the class-B amplifier operates. The output power for the sin

20、gle-ended class-B amplifier isthe dc drain current is ( 2.12)(2.11)the dc power (2.13)and the maximum efficiency when Vom = VDD isPo = 12 I om Vo .12300250200150VGS5VGS4VGS3VGS2100VGS150Idq005Vdd101520Vds (V)250200150100500Iom00.20.4 0.6Time (nsec)0.81Figure.2.4. Load line and current waveform for t

21、he class-B power amplifierId (mA)Id (mA)132.2.3 Class ABThe class-AB amplifier is a compromise between class A and class B in terms ofefficiency and linearity. The transistor is biased as close to pinch-off as possible, typicallyat 10 to 15 percent of Idss. In this case, the transistor will be on fo

22、r more than half a cycle,but less than a full cycle of the input signal.2.2.4 Class CThe previous classes, A, B, and AB are considered linear amplifier, where the outputsignals amplitude and phase are linearly related to the input signals amplitude and phase. Inthe application where linearity is not

23、 an issue, and efficiency is critical, non-linear amplifierclasses (C, D, E, or F) are used.Class-C amplifier is the one biased so that the output current is zero for more than onehalf of an input sinusoidal signal cycle. Figure 2.5 illustrates the operation of the class-Camplifier. A tuned circuit

24、or filter is a necessary part of the class-C amplifier.Classes-A, AB, B, and C amplifiers can be defined in terms of the conduction angle Yas follows: (2.15)14The conduction angle is (2 (2.16) The dc current is (2.17) Also, the output voltage (Vo) can be obtained in term of Y as (2.18)The output pow

25、er is (2.19the dc power isPdc = Vcc I dd ,and the maximum output voltage Vo isV OMAX = VDD .From the above equations the maximum efficiency is(2.20)(2.21) (2.22)Since the peak drain voltage and drain current areVDMAX = 2V DD ,andI DMAX = I dq + I ddrespectively, the power output capability factor is

26、 (2.25)(2.23)(2.24)Figure.2.6 shows the maximum efficiency versus the conduction angle. Although it is shownthat 100% efficiency is possible, it is impractical because the output power is zero, as shownin Fig.2.7.Although the preceding analysis was for the single-ended amplifier configuration, asimi

27、lar analysis can be done for the push-pull amplifier configuration. During the positive halfof the signal swing, one device will push the current to the load, and during the negative halfsignal swing, the other device will pull the current from the load. For example, in a class-Bpush-pull power ampl

28、ifier, every device is on for one half of the input cycle, which means thatthe conduction angle is equal to 180 degrees for each device. This is similar to two class-Bsingle-ended power amplifiers connected in a parallel line. From this observation, it ispossible to conclude that the efficiency of t

29、he push-pull power amplifier is the same as that ofthe single-ended power amplifier with the same conduction angle, and the output powercapability of the push-pull power amplifier is twice that of the single-ended power amplifier.And this result is due to using two FETs.16280240VGS5200VGS4160VGS3120

30、VGS280400VGS10510152015010050VddVds (V)0YIdd-5000.2 Idq0.40.60.811.2-100-150-200-250-300Time (nsec)Figure 2.5. Load line and current waveform for the class-C poweramplifierId (mA)Id (mA)171008060504020000.511.522.53Conduction AngleFigure 2.6. Efficiency vs. conduction angle0.140.120.10.080.060.040.0

31、2000.511.522.53Conduction AngleFigure 2.7. PMAX vs. conduction angleEfficiencyPMAX182.2.4 Class FThe class-F amplifier is one of the highest efficiency amplifiers. It uses harmonicresonators to achieve high efficiency, which resulted from a low dc voltage current product.In other words, the drain vo

32、ltage and current are shaped to minimize their overlap region.Figure.2.8 shows a class-F amplifier. The inductor L3 and capacitor C3 are used to implementa third harmonic resonator that makes it possible to have a third harmonic component in thecollector voltage. The output resonator is used to filt

33、er out the harmonic, keeping only thefundamental frequency at the output. The magnitude and the phase of the third harmoniccontrol the flatness of the collector voltage and the power of amplifier.The drain voltage is .(2.26)The setting Vom3 =Vom9produces maximum flatness for the drain voltage. And,

34、themaximum output occurs when the minimum point of Vd (q) is zero. Hence, (2.27)The dc current is (2.28)the dc power is (2.29)the fundamental current is (2.30)the maximum fundamental output power is (2.31)and, the maximum efficiency is (2.32) Figure 2.8. Single-ended power amplifier (class-F)212.2.5

35、 Other High-Efficiency ClassesThere are other high-efficiency amplifiers such as D, E, G, H, and S. These classesuse different techniques to reduce the average collector or drain power, which, in sequence,increase the efficiency. Classes D, E, and S use a switching technique, while classes G and Hus

36、e resonators and multiple power-supply voltage to reduce the collector current-voltageproduct. A detailed analysis of class-E amplifier will be presented in Chapter 5.Designers select the class type to be used based on the application requirements.Classes-A, AB, and B amplifiers have been used for l

37、inear applications such as amplitudemodulation (AM), single-sideband modulation (SSB), and quadrate amplitude modulation(QAM). Also it can be used in linear and wide band applications such as the multicarrierpower amplifier. Classes C, D, E, F, G, and H have satisfied the need for narrowband tunedam

38、plifiers of higher efficiency. Such applications include amplification of FM signals.2.3 Main Physical LimitationsThe descriptions of amplifiers in the previous sections have dealt with ideal devices.In reality, transistor amplifiers suffer from a number of limitations that influence amplifieroperat

39、ion and ultimately reduce their efficiency and output power.In practical FET, there are four fundamental effects that force the operation of FET todeviate from the ideal case: the drain source resistance, the maximum channel current If, theopen channel avalanche breakdown voltage, and the drain-source break down voltage Robert,1988. Figure 2.9 shows IDS-VDS characteristics of a typical MESFET (ATF-46100).Figure 2.9. IDS-VDS characteristics of