Transistor common-emitter circuit

Eig. 11. (a) Common emitter circuit and (b) output characteristics for the n—p—n transistor, where is the operating (quiescent) point as determined by Rg. 

Characteristics of same pnp junction transistor as in Figs. 9.20 and 9.21, but in a common-emitter circuit. Adapted from Terman [5]. 

A totally different way of looking at transistor action is by using a common-emitter circuit (Fig. 9.19B) Now the input current is (a relatively small) iBr and the output is the relatively large) collector current zc this collector current is still controlled by the Ebers-Moll equation, but the current gain is now explicit ... 

The common-base circuit for an npn transistor (Fig. 9.19A) seems logical and simple, but its efficiency in amplification is not obvious and must be explained. The npn transistor in a common-emitter circuit (Fig. 9.19B) is a bit easier to understand as a current amplifier. There are four rules ... 

There are varieties of ways to use junction transistors in circuits as shown in the following examples. The common emitter circuit shown in Figure 22.4 is widely used for amplifier as well as switching applications. 

Eigure 11 shows a schematic and collector characteristics for a common emitter n—p—n transistor circuit. The load line crossing these characteristics shows the allowed operation of the transistor with a supply voltage, = 12 V a load resistor, 7 = 2 and a bias resistor, 7 g = 20 kQ. The load line corresponds to the equation = 7 7 -H. Plotting the load line on the collector characteristics defines BJT behavior 0.6 V is required... 

Common-base, common-emitter, and common-collector circuits for a bipolar npn transistor (A, B, C, respectively), and the equivalent grounded-grid, grounded-cathode, and grounded-plate circuits for vacuum-tube triodes (A corresponds to A, B to B, and C to C). Adapted from Terman [5]. 

A, B) Equivalent circuits for an npn transistor (C) In common-base configuration and (D) in common-emitter configuration. See Table 9.5 for numerical values. 

Fig.4. Data plot for a 20 nA current pulse. The pulse width was 16.5 fis. The circuit used for this data consisted of a single transistor in a common emitter configuration with a light emitting diode as the load element. This circuit was used instead of the operational amplifier circuit in Fig.l because it provides improved response at low current levels.

BASIC COMMON EMfiTER TRANSISTOR AMPLIFIER The basic common-emitter transistor amplifier circuit represents the electronics work done in the Active Area instrumentation lab. 

Transistors are always operated so that amplification is obtained for a signal whose voltage is small on the input side (relative to the bias on the emitter) and small on the output side (relative to the collector voltage). Therefore small-signal theory applies. The designer obviously wants all signals to be amplified linearly, that is, by a common factor this makes the circuit behave more reasonably. 

Figure 9.6. Differential amplifier performance with common-mode interference signals, (a) Upper trace 10-kHz sine wave with superimposed common-mode noise as amplified by conventional amplifier lower trace same signal amplified by differential amplifier, (b) Upper trace 10-kHz square wave with superimposed 60-Hz hum and broad-band noise as amplified by single-ended amplifier middle trace same signal as amplified by differential amplifier lower trace residual noise removed by filtering, (c) Circuit schematic for transistor differential amplifier with constant-current emitter stage, (d) Vacuum-tube differential amplifier in long-tailed pair configuration. (See Ferris, 1963.)...

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