22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 1

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1 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 1

2 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 2

3 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 3

4 0 V in A v V out 0 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 4

5 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 5

6 TESTING EQUIPMENTS Analogue Multimeter Digital Multimeter Quartz Logic Oscilloscope 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 6

7 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 7

8 Amplified or enlarge or upgrade the voltage and current signal 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 8

9 1. In this set-up, the amplifier s output circuit is connected to the emitter and the collector. The input circuit connects to the emitter and the base. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 9

10 2. When no current flows through the input circuit, free electrons from the n-type material fill the available holes in the p-type material. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 10

11 3. This creates depletion zones (areas where current can t flow easily) at the boundaries between the n-type layer and the p-type layer. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 11

12 4. When current flows across the input circuit, it causes an extra voltage boost at the base electrode. This gets electrons moving again, shrinking the depletion zones. Electrical resistance drops, and the electrons can move from the emitter to the collector again. In this way, the voltage at the base electrode determines the overall resistance of the transistor and therefore the current in the output signal. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 12

13 HOW AN AMPLIFIER WORK 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 13

14 CLASSES OF AMPLIFIER Class A Amplifier Class B Amplifier Class C Amplifier 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 14

15 1. Class A Amplifier Use one or more transistors that conduct during both the positive and negative cycles of the signal. Class A amplifiers have current flowing through the transistor for the full cycle of the ac waveform. With class A bias, the base current is set so that collector current flows. Increasing or decreasing base current makes collector current to increase and decrease. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 15

16 Characteristic of Class A Amplifier The following condition should be satisfied to get a full cycle of the ac waveform: A DC bias point that has an appreciable DC current flowing even when there is no signal present. It also requires that an appreciable voltage be across the transistor from collector to emitter. Therefore the DC power supply is supplying an appreciable power even when there is no output signal being produced. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 16

17 Characteristic of Class A Amplifier It dissipates an appreciable power and therefore gets heated up. The power efficiency of class-a amplifiers is relatively low, typically under 12%. Theoretically an ideal capacitor coupled emitter follower could have efficiency up to 16%. An ideal form of an inductor coupled or transformer coupled class-a amplifier could have an efficiency of up to 50%, but a typical 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 17

18 Characteristic of Class A Amplifier lowest distortion but it is very inefficient and generates a lot of heat. Make a more efficient amplifier by employing a Double Ended or Push-Pull arrangement. Figure shows one type of output stage. This type of new arrangement involves pair of transistors, a NPN bipolar transistor and a PNP bipolar transistor. Ideally, these two transistors have equivalent properties - e.g. the same current gains. The circuit shown on the left now has two transistors which we can control using a pair of input voltages v1 and v2, and. We can therefore alter the currents I1 and I2 independently. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 18

19 Sample circuit of Class A Amplifier 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 19

20 2. Class B Amplifier Increases efficiency by using one transistor to conduct the positive portion of the waveform and another transistor to conduct the negative portion of the waveform. Distortions are well below human ear detecting ability. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 20

21 the base current is set to zero. No collector current flows and the transistor go into CUT OFF State. The collector current can only be made to increase from this point, not decrease, by increasing the bias. In other words, Class-B amplifiers have current flowing through the transistor for only half a cycle. There is no current flowing when there is no signal present. This means there is no power loss when no signal is being amplified, except a small amount in the bias circuit. Thus efficiency close to 80% can be achieved when signal gets amplified. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 21

22 Disadvantages Distortion in the waveform where it crosses zero. The transistor characteristic becomes nonlinear as it approaches cutoff. The transistor provides to little current as the voltage approaches zero. This causes what in known as crossover distortion. By changing the bias point so that there is a small current flow when the signal input is zero provides an overlap between the two transistors and one transistor starts to conduct before the other turns off. If the overlap is properly adjusted the extra current from the transistor that is just turning on will make up for the deficiency in the transistor that is turning off. When this offset bias is used the amplifier is known as a class-ab amplifier. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 22

23 3. CLASS C AMPLIFIER Collector current flows for less than one half cycle of the input signal. The class C operation is achieved by reverse biasing the emitter-base junction, which sets the dc operating point below cutoff and allows only the portion of the input signal that overcomes the reverse bias to cause collector current flow. Used as a radio-frequency amplifier in transmitters. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 23

24 Sample circuit of Class B Amplifier 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 24

25 The conclution, that two primary items determine the class of operation of an amplifier :- the amount of bias the amplitude of the input signal. With a given input signal and bias level, you can change the operation of an amplifier from class A to class B just by removing forward bias. Can be changed to class AB by increasing the input signal amplitude. If an input signal amplitude is increased to the point that the transistor goes into saturation and cutoff, it is then called an OVERDRIVEN amplifier. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 25

26 Blocks that failed in audio amplifier 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 26

27 Pre Audio Amplifier Amplified the small signal from an input unit. Coupling the input resistance. Limit the signal noise ratio 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 27

28 Sample of pre audio amplifier circuit 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 28

29 Tone Control Amplifier At the tone controls, pre-amp signal used to stabilize the pre-signal or a replacement will be dropped in the tone circuit. This construction consists of controls: Treble Bass Bahana (volume ) Balance 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 29

30 Treble - the audio controls or other high frequency words 'pitch' sound. The circuit made based on high frequency pass filter circuit. Bass - is a low frequency audio controls on the design of low-frequency pass filter circuit for adding a 'guttural'. Bahana - audio controls that rises or lowers the overall amplitude of the voltage. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 30

31 Driver /Pre Amplifier 2 Circuit constructed to ensure the pre-amplifier output signal from tone circuit not been losses. It also be used as a driver amplifier output power. As the driver input enforcement bias. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 31

32 TYPES OF POWER AMPLIFIER Single Ended Amplifier Push Pull Amplifier Complementary Symmetric Integrated circuit 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 32

33 Single Ended Amplifier The class A amplifier and coupled with the output transformer to make a suitable used of the speaker. The bias signal (dc voltage) is put by the driver or either of the transistor circuit or integrated circuit by using only one either NPN transistor or PNP 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 33

34 This is the simplest type of Class A power amplifier circuit. It uses a single-ended transistor for its output stage with the resistive load connected directly to the Collector terminal. When the transistor switches "ON" it sinks the output current through the Collector resulting in an inevitable voltage drop across the Emitter resistance thereby limiting the negative output capability. The efficiency of this type of circuit is very low (less than 30%) and delivers small power outputs for a large drain on the DC power supply. A Class A amplifier stage passes the same load current even when no input signal is applied so large heat sinks are needed for the output transistors. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 34

35 However, another simple way to increase the current handling capacity of the circuit while at the same time obtain a greater power gain is to replace the single output transistor with a Darlington Transistor. These types of devices are basically two transistors within a single package, one small "pilot" transistor and another larger "switching" transistor. The big advantage of these devices are that the input impedance is suitably large while the output impedance is relatively low, thereby reducing the power loss and therefore the heat within the switching device. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 35

36 Push-Pull Amplifier Class B or AB push-pull circuits are the most common form of design found in audio power amplifiers. Class AB is widely considered a good compromise for audio amplifiers, since much of the time the music is quiet enough that the signal stays in the "class A" region, where it is reproduced with good fidelity, and by definition if passing out of this region, is large enough that the distortion products typical of class B are relatively small. Class B and AB amplifiers are sometimes used for RF linear amplifiers as well. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 36

37 How a Push-Pull Amplifier work 1. During the positive cycle Q1 gets forward biased (on) and Q2 receive reverse bias (off). The current will flow through Q1 and the signal is amplified by it. positive peak output will be coupled by C1 to the speaker. 2. During the negative cycle Q1 gets reverse bias (off) and Q2 gets forward (on). The current will flow through Q2 and the signal is amplified by it. The negative peak output is coupled by C1 to the speaker. 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 37

38 Complimentary Symmetry Berfungsi dalam kelas B, untuk melengkapkan isyarat dari 180 ke 360, transistor keluaran disirikan samada menggunakan dua transistor yang berciri sama atau jenis berlawanan (compliment). 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 38

39 22/01/2011 disediakan oleh Rodzah Binti Hj Yahya 39