et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 1

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 2 chapter 2 transistors (BJT) 2.1 Transistor classification 2.2 Bipolar junction transistors (BJT) construction 2.3 Transistor action and operating 2.4 Quiescent Operating Point 2.5 Bipolar transistor characteristics 2.6 Transistor parameters 2.7 Current gain 2.8 Typical BJT characteristics and maximum ratings 2.9 Transistor operating configurations

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Transistor classification

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Bipolar junction transistors (BJT) construction Bipolar transistors generally comprise n-p-n or p-n-p junctions of either silicon (Si) or germanium (Ge) material. N: phosphorus or arsenic P: boron or gallium The junctions are, in fact, produced in a single slice of silicon by diffusing impurities through a photographically reduced mask. Silicon transistors are superior when compared with germanium transistors in the vast majority of applications

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 5 Figure 2.3 The symbols and simplified junction models for n-p-n and p-n-p transistors ◆ The symbols and simplified junction models for n-p-n and p-n-p transistors are shown in Figure 2.3. It is important to note that the base region is extremely narrow.

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 6 E – Emitter B – Base C - Collector Electronics-BTEC

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 7 ◆ In the n-p-n transistor, transistor action is accounted for as follows: ◆ the base-emitter junction is forward biased and the base-collector junction is reverse biased ◆ Around 99.5% of the electrons leaving the emitter will cross the Base collector junction and only 0.5% of the electrons will Recombine with holes in the narrow base region. Figure 2.4 Transistor action of n-p-n transistor 2.3 Transistor action

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 8

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 9 ◆ the base-emitter junction is forward biased and the base- collector junction is reverse biased Figure 2.5 Transistor action of p-n-p transistor

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 10 ◆ For an n-p-n transistor, the base-collector junction is reversed biased for majority carriers, but a small leakage current, I CBO, flows from the collector to the base due to thermally generated minority carriers (holes in the collector and electrons in the base), being present. The base-collector junction is forward biased to these minority carriers. ◆ With modern transistors, leakage current is usually very small (typically less than 100nA) and in most applications it can be ignored. ◆ The control of current from emitter to collector is largely independent of the collector-base voltage and almost wholly governed by the emitter-base voltage leakage current

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 11 ◆ In normal operation (i.e. for operation as a linear amplifier) the base-emitter junction of a transistor is forward biased and the collector-base junction is reverse biased. ◆ The current flowing in the emitter circuitis typically 100 times greater than that flowing in the base. Figure 2.7 bias and current flow bias and current flow

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide bias and current flow Leakage current ICBO

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide bias and current flow

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 14 ◆ Three basic circuit configurations are used for transistor amplifiers. ◆ These three circuit configurations depend upon which one of the three transistor connections is made common to both the input and the output. ◆ In the case of bipolar junction transistors, the configurations are known as common emitter, common collector (or emitter follower), and common base. Figure 2.8 Transistor operating configurations Transistor operating configurations

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide bipolar transistor characteristics ◆ The characteristics of a bipolar junction transistor are usually presented in the form of a set of graphs relating voltage and current present at the transistors terminals. Figure 2.9 measurement circuit of bipolar transistor characteristics

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 16 ◆ In this mode, the input current is applied to the base and the output current appears in the collector. Figure 2.10 Typical input characteristic

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 17 Figure 2.11 Output characteristics ◆ Each curve corresponds to a different value of base current. Note the ‘knee’ in the characteristic below V CE =2V. ◆ Also note that the curves are quite flat. ◆ For this reason (i.e. since the collector current does not change very much as the collector-emitter voltagechanges) we often refer to this as a constant current characteristic.

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 18 Figure 2.12 Transfer characteristic ◆ Here I C is plotted against I B for a small-signal general-purpose transistor. ◆ The slope of this curve (i.e. the ratio of I C to I B ) is the common-emitter current gain of the transistor.

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Bipolar transistor parameters ◆ In particular, the three characteristic graphs can be used to determine the following parameters for operation in common-emitter mode:

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Bipolar transistor parameters ◆ In particular, the three characteristic graphs can be used to determine the following parameters for operation in common-emitter mode:

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Bipolar transistor parameters ◆ In particular, the three characteristic graphs can be used to determine the following parameters for operation in common-emitter mode:

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Bipolar transistor parameters

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 23

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Current gain ◆ We use the symbol h FE to represent the static value of common-emitter current gain. ◆ Similarly, we use h fe to represent the dynamic value of common-emitter current gain. ◆ Note that h FE is found from corresponding static values while h fe is found by measuring the slope of the graph. ◆ Furthermore, most transistor parameters (particularly common-emitter current gain, h fe ) are liable to wide variation from one device to the next.

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Typical BJT characteristics and maximum ratings Table 2.2 Transistor characteristics and maximum ratings P TOT max is the maximum device power dissipation.

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide The junction field-effect transistor Figure 2.13 Conformation of N channel J.F.E.T

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide The junction field-effect transistor Figure 2.14 Symbol of JFET N channel JFETP channel JFET

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide The junction field-effect transistor Figure 2.15 Operation of N channel JFET

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Metal-oxide-semiconductor field-effect transistor Figure 2.16 depletion-type MOS FET depletion-type MOS FET N channelP channel Construction of N channel depletion-type MOS FET

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Metal-oxide-semiconductor field-effect transistor Figure 2.16 depletion-type MOS FET Enhancement-type MOS FET N channelP channel Construction of N channel enhancement-type MOS FET

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide Quiescent Operating Point

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 32

et Dignitas Guangdong Institute of Education ---BTEC electronic Amor Electronics chapter 2 transistors Slide - 33