Basic Electronic Devices and Circuits EE 111 Unit 4: BJT AMPLIFIERS Dr

Basic Electronic Devices and Circuits EE 111 Unit 4: BJT AMPLIFIERS Dr. Abdullah Almuhaisen Electrical Engineering Department College of Engineering Outline BJT AMPLIFIERS o amplifier operation o transistor models o operation of common-emitter amplifiers o operation of common-collector amplifiers o operation of common-base amplifiers o operation of multistage amplifiers Key Terms Quiz Tutorial 4 Homework 4 MicoProject: Application Activity: Audio Preamplifier for PA System Summary & References

EE 111 - Dr. A. Almuhaisen 2 Unit Objectives

. Describe amplifier operation . Discuss transistor ac models . Describe and analyze the operation of common-emitter amplifiers . Describe and analyze the operation of common-collector amplifiers . Describe and analyze the operation of common-base amplifiers . Describe and analyze the operation of multistage amplifiers

EE 111 - Dr. A. Almuhaisen 3 Introduction In this unit, we will learn: . How to use bipolar junction transistor (BJT) circuits as small-signal amplifiers. The term small-signal refers to the use of signals that take up a relatively small percentage of an amplifier’s operational range.

. How to reduce an amplifier to an equivalent dc and ac circuit for easier analysis, and we will learn about multistage amplifiers.

EE 111 - Dr. A. Almuhaisen 4 AMPLIFIER OPERATION

The biasing of a transistor is a dc operation. The purpose of biasing is to establish a Q-point about which variations in current and voltage can occur in response to an ac input signal. V AC Quantities • DC quantities were identified by nonitalic uppercase subscripts such as 퐼 , 퐼 , 푉 , and 푉 . 퐶 퐸 퐶 퐶퐸 rms avg • Vce AC quantities are indicated with lowercase V Vce ce subscripts such as 퐼푐, 퐼푒, 퐼푏, 푉푐, and 푉푐푒 (rms values V are assumed unless otherwise stated). CE Vce

• Instantaneous quantities are represented by both vce lowercase letters and subscripts such as 𝑖푐, 𝑖푒, 𝑖푏, and 푣푐e. • Resistance is also identified with a lower case 0 t subscript when analyzed from an ac standpoint 0 EE 111 - Dr. A. Almuhaisen 5 such as 푅푐 (ac collector resistance).

+VCC

Ic AMPLIFIER OPERATION Vb I CQ V BQ R1 RC The Linear Amplifier Vce C2

VCEQ Rs I A linear amplifier provides amplification of a signal C1 b IBQ without any distortion so that the output signal is Vs R R R an exact amplified replica of the input signal. 2 E L The voltage-divider biased transistor shows: o Sinusoidal ac source capacitively coupled to the base through 퐶1. o Load capacitively coupled to the collector through 퐶2. o The coupling capacitors block dc and thus prevent the internal source resistance, 푅푆, and the load resistance, 푅퐿, from changing the dc bias voltages at the base and collector. The capacitors ideally appear as shorts to the ac signal voltage. The sinusoidal source voltage: o causes the base voltage to vary sinusoidally above and below its dc bias level 푉퐵푄. o thus, producing a larger variation in collector current. . Notice that the voltage waveform is inverted between the input and output but has the same shape. EE 111 - Dr. A. Almuhaisen 6

AMPLIFIER OPERATION AC Load Line . As the sinusoidal base current increases, the collector current increases. Accordingly, the IC

collector voltage decreases. Q I B . Base current varies above and below its 푄-point 퐼푐(푠푎푡) I b value,퐼퐵푄.

. Accordingly, the collector current varies above Ic and below its 푄-point value,퐼퐶푄, in phase with the base current. ICQ Q ac load line . The sinusoidal collector-to-emitter voltage varies above and below its 푄-point value, 푉퐶퐸푄, 180°out of phase with the base voltage. . A transistor always produces a phase inversion 푉 between the base voltage and the collector 0 푐푒(푐푢푡표푓푓) VCE voltage. Vce . The ac load line differs from the dc load line

because the effective ac collector resistance is 푅퐿 VCEQ in parallel with 푅퐶 and is less than the dc collector resistance 푅퐶 alone.

EE 111 - Dr. A. Almuhaisen 7 Example 1

EE 111 - Dr. A. Almuhaisen 8 TRANSISTOR AC MODELS To visualize the operation of a transistor in an amplifier circuit, it is often useful to represent the device by a model circuit. A transistor model circuit uses various internal transistor parameters such as: o r parameters (based on resistance ) o h parameters r parameters r parameters transistor model r Parameters Description Generalized r parameters Simplified r parameters

훼푎푐 ac alpha (퐼푐/퐼푒)

훽푎푐 Ac beta (퐼푐/퐼푏)

푟′ ′ 25 푚푉 푒 푟푒 = ,ac emitter resistance 퐼퐸 ′ 푟푏 ac base resistance

′ 푟푐 ac collector resistance EE 111 - Dr. A. Almuhaisen 9 Example 2

EE 111 - Dr. A. Almuhaisen 10 TRANSISTOR AC MODELS

Comparison of the AC Beta 훽푎푐 to the DC Beta 훽퐷퐶 o As the curve is not linear the values of these two quantities can differ slightly. h Parameters A manufacturer’s datasheet typically specifies h (hybrid) parameters because they are relatively easy to measure. h Parameters Description Condition Relationships of h Parameters and r Parameters

ℎ𝑖 Input impedance Output 훼푎푐 = ℎ푓푏 a second subscript letter to (resistance) shorted 훽 = ℎ designate the common-emitter 푎푐 푓푒 (e), common-base (b), or ℎ Voltage feedback Input open 푟 푟′ = ℎ푟푒 common-collector (c) amplifier ratio 푒 ℎ표푒 configuration ℎ Forward current Output 푓 푟′ = ℎ푟푒+1 gain Shorted 푐 ℎ표푒 ′ ℎ ℎ표 Output admittance Input open 푟푒 1+ℎ 푟푏 = ℎ𝑖푒 − ℎ 푓푒 (conductance) 표푒 EE 111 - Dr. A. Almuhaisen 11 THE COMMON-EMITTER AMPLIFIER

Three amplifier configurations are the common-emitter, the common-base, and the common-collector. The common-emitter (CE) configuration has the emitter as the common terminal, or ground, to an ac signal. CE amplifiers exhibit high voltage gain and high current gain.

Common-emitter amplifier

• Voltage-divider bias • Coupling capacitors 퐶1 and 퐶3 • bypass capacitor, 퐶2

• Output signal, 푉표푢푡, is capacitively coupled from the collector to the load. • The amplified output is 180° out of phase with the input. • The emitter is common to both the input and output signals. There is no signal at the emitter because the bypass capacitor effectively shorts the emitter to ground at the signal frequency EE 111 - Dr. A. Almuhaisen 12 The Common-Emitter Amplifier

What is re' for the CE amplifier? Assume stiff voltage-divider bias.

VCC 27 kW +15 V VB  15 V = 4.26 V 68 kW  27 k W RC C3 R1 3.9 kW V = 4.26 V – 0.7 V = 3.56 V 68 kW E C 1 10 m F V 3.56 V E 1.0 m F RL IE    1.62 mA R 3.9 kW RE 2.2 kW 2 27 kW RE C2 2.2 kW 100 m F ' 25 mV 25 mV re    15.4 W IE 1.62 mA

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Thomas L. Floyd DC Analysis THE COMMON-EMITTER AMPLIFIER To analyze the Common-emitter amplifier, the dc bias values must first be determined. . DC equivalent circuit is developed by: o removing the coupling and bypass capacitors because they appear open as far as the dc bias is concerned. o This also removes the load resistor and signal source Theveninizing the bias circuit, results with:

EE 111 - Dr. A. Almuhaisen 14 THE COMMON-EMITTER AMPLIFIER AC Analysis AC equivalent circuit is developed by: 1. The capacitors 퐶1, 퐶2, and 퐶3 are replaced by effective shorts. . Reactance of these capacitance 푋퐶 is negligible at the signal frequency and can be considered to be 0 Ω. 2. The dc source is replaced by ground.

A dc voltage source has an internal resistance of near 0 Ω because it holds a constant voltage independent of the load (within limits); no ac voltage can be developed across it so it appears as an ac short. This is why a dc source is called an ac ground.

The amplifier is called a common-emitter amplifier because the bypass capacitor 퐶2 keeps the emitter at ac ground. Ground is the common point in the circuit.

EE 111 - Dr. A. Almuhaisen 15 THE COMMON-EMITTER AMPLIFIER

Input Resistance 푹풊풏(풕풐풕) The total input resistance is expressed as:

EE 111 - Dr. A. Almuhaisen 16 Example 3

Figure 6-13 Figure 6-8

EE 111 - Dr. A. Almuhaisen 17 THE COMMON-EMITTER AMPLIFIER

Voltage Gain The ac voltage gain

푽풐풖풕 푽풄 푰풆푹푪 푨풗 = = = ′ , where 퐼푐 ≅ 퐼푒 푽풊풏 푽풃 푰풆풓풆 푹푪 푨풗 = ′ 풓풆 Attenuation Attenuation is the reduction in signal voltage as it passes through a circuit and corresponds to a gain of less than 1.

푽풄 . Voltage gain 푨풗 = 푽풃 푉 푅 +푅 . Attenuation= 푠 = 푠 푖푛(푡표푡) 푉푏 푅푖푛(푡표푡) ′ 푉푐 . The overall voltage gain 퐴푣 = 푉푠 EE 111 - Dr. A. Almuhaisen 18 THE COMMON-EMITTER AMPLIFIER Effect of the Emitter Bypass Capacitor on Voltage Gain

The emitter bypass capacitor 푪ퟐ, provides an effective ac short. ′ The gain is maximum and equal to 푨풗= 푹푪 풓풆 . The reactance of the bypass capacitor must be very small compared to 푅퐸 at the operating frequency ퟏퟎ푿푪 ≤ 푹푬.

Voltage Gain Without the Bypass Capacitor

푹푪 The effect of 푅퐸 is to decrease the ac voltage gain 푨풗 = ′ 풓풆+푹푬 Effect of a Load on the Voltage Gain A load is the amount of current drawn from the output of an amplifier or other circuit through a load resistance.

푹풄 푅퐶푅퐿 the voltage gain is 푨풗 = ′ , where 푅푐 = 풓풆 푅퐶+푅퐿 EE 111 - Dr. A. Almuhaisen 19 When 푹풄 < 푹푪 , the voltage gain is reduced and if 푅퐿 ≫ 푅퐶 then 푹풄 ≅ 푹푪

Example 4

EE 111 - Dr. A. Almuhaisen 20 Example 5

EE 111 - Dr. A. Almuhaisen 21 The Common-Emitter Amplifier

Notice that the ac resistance of the collector circuit is RC||RL. What is the gain of the amplifier?

VCC +15 V

VRRRout cC P L Av    '' RC V r r C3 in e e R1 3.9 kW 68 kW C 3.9 kWWP 3.9 k 1 A 127 10 m F v 15.4 W 1.0 m F RL 3.9 kW R2 27 kW R C The gain will be a little lower if the E 2 2.2 kW 100 m F input loading effect is accounted for.

EE 111 - Dr. A. Almuhaisen 23 THE COMMON-EMITTER AMPLIFIER Stability of the Voltage Gain Stability is a measure of how well an amplifier maintains its design values over changes in temperature or for a transistor with a different 훽. ′ ′ The voltage gain (푨풗= 푹푪 풓풆) is unstable since it depends on 푟푒 which depends on 퐼퐸 and on temperature 푹푪 ′ With no bypass capacitor, the gain is 푨풗 = ′ and much less dependent on 푟푒 . 풓풆+푹푬 ′ ′ 푹푪 If 푅퐸 ≫ 푟푒 the gain is essentially independent of 풓풆 because 푨풗 ≅ . 푹푬 ′ Swamping 푟푒 to Stabilize the Voltage Gain ′ Swamping is a method used to minimize the effect of 풓풆 without reducing the voltage gain to its minimum value. This is a compromise with a reasonable gain with a reduced effect on the gain. 푹푪 푨풗 = ′ 풓풆 + 푹푬ퟏ ′ 푹푪 If 푹푬ퟏ ≫ 풓풆, then 푨풗 ≅ 푹푬ퟏ Input Resistance 푅 = 훽 풓′ + 푹 , this is an increase in the ac input resistance. 𝑖푛(푏푎푠푒) 푎푐 풆 푬ퟏ EE 111 - Dr. A. Almuhaisen 24 THE COMMON-EMITTER AMPLIFIER

Current Gain

The current gain is 훽푎푐 = 퐼푐 퐼푏 The overall current gain

퐼푐 퐴𝑖 = 퐼푠 푉푠 Where 퐼푠 = 푅푠+푅푖푛(푡표푡) Power Gain ′ The overall power gain is the product of the overall voltage gain 퐴푣 and the overall current gain 퐴𝑖. ′ 퐴푝 = 퐴푣퐴𝑖 ′ 푉푐 Where 퐴푣 = 푉푠

EE 111 - Dr. A. Almuhaisen 25 The Common-Emitter Amplifier

Greater gain stability can be achieved by adding a swamping resistor to the emitter circuit of the CE amplifier. The gain will be lower as a result. VCC +15 V

RC What is the gain with the addition C3 R1 3.9 kW 68 kW of the swamping resistor? (Ignore C 1 10 m F the small effect on re'.) 1.0 m F R VRRRout cC P L E1 R A    33 W L v V r'' R r R 3.9 kW in eE1 e E1 R 2

27 kW RE2 C2 3.9 kWWP 3.9 k 2.2 kW A 38.2 100 m F v 15.4 W  33 W

Multisim is a good way to check your calculation. For an input of

10 mVpp, the output is 378 mVpp as shown on the oscilloscope display for the swamped CE amplifier.

input

output

In addition to gain stability, swamping has the advantage of increasing the ac

input resistance of the amplifier. For this amplifier, Rin(tot) is given by Rin(tot) = R1||R2||bac(re' + RE1)

VCC +15 V

RC C3 R1 3.9 kW What is Rin(tot) for the amplifier if 68 kW C 1 10 m F bac = 200? 1.0 m F R Rin(tot) = R1||R2||bac(re' + RE1) E1 R 33 W L 3.9 kW = 68 kW||27 kW||200(15.4 W + 33 W) R 2 27 kW RE2 C2 = 6.45 kW 2.2 kW 100 m F

EE 111 - Dr. A. Almuhaisen 29 Example 8

EE 111 - Dr. A. Almuhaisen 30 The Common-Collector Amplifier

The common-collector (CC) amplifier is usually referred to as an emitter-follower (EF). . Collector is at ac ground . The voltage gain of a CC amplifier is approximately 1 . Advantages are its high input resistance and current gain. . There is no phase inversion Voltage Gain 퐼푒푅푒 푅푒 퐴푣 = ′ = ′ 퐼푒 푟푒 +푅푒 푟푒 +푅푒 ′ Usually, 푅푒 ≫ 푟푒 , thus 푨풗 ≅ ퟏ EE 111 - Dr. A. Almuhaisen 31 The Common-Collector Amplifier Input Resistance The emitter-follower is characterized by a high input resistance and thus can be used as a buffer to minimize loading effects when a circuit is driving a low-resistance load.

′ ′ 푉𝑖푛 푉푏 퐼푒 푟푒 + 푅푒 훽푎푐퐼푏 푟푒 + 푅푒 ′ 푅𝑖푛(푏푎푠푒) = = = ≅ ≅ 훽푎푐 푟푒 + 푅푒 퐼𝑖푛 퐼푏 퐼푏 퐼푏 ′ if 푅푒 ≫ 푟푒 , then 푅𝑖푛(푏푎푠푒) ≅ 훽푎푐푅푒

Total input resistance 푅𝑖푛(푡표푡) = 푅1 ∥ 푅2 ∥ 푅𝑖푛(푏푎푠푒)

Output Resistance 푹풔 푹풐풖풕 ≅ ∥ 푹푬 , 푅푠 is the source resistance. 휷풂풄 Output resistance is very low, thus EF useful for driving low-resistance loads.(derivation in the book)

Current Gain 푰풆 푨풊 = , where 퐼𝑖푛 = 푉𝑖푛 푅𝑖푛(푡표푡) 푰풊풏 Power Gain

푨풑 = 푨풗푨풊 ≅ 푨풊 , since 퐴푣 ≅ 1 EE 111 - Dr. A. Almuhaisen 32

Example 9

EE 111 - Dr. A. Almuhaisen 33 The Darlington Pair A Darlington pair is two transistors connected as shown. The two transistors act as one “super b” transistor. Darlington transistors are available in a single package. Notice there are two diode drops from base to emitter.

퐼푒2 = 훽푎푐1훽푎푐2퐼푏1

VCC 푅𝑖푛 = 훽푎푐1훽푎푐2푅퐸 VCC

R1 Thus, boosting the input RC C1 V resistance, and output current in Q1

Q2 C2 Vout R2 R E RL

CE Amplifier Darlington CC amplifier Load

VCC VCC

R1 RC C1 V in Q1

Q2 C2 Vout R2 R E RL

CE Amplifier Darlington CC amplifier Load EE 111 - Dr. A. Almuhaisen 35 The Sziklai Pair Another high b pair is the Sziklai pair (sometimes called a complementary Darlington), in which a pnp and npn transistor are connected as shown. This configuration has the advantage of only one diode drop between base and emitter.

+VCC

What is the relation between IE2 and IB1?

Vin βDC1

IB1 βDC2

The DC currents are: IC1 IE2 IC1 is bDC1 x IB1 and is equal to IB2 RE IE2 is approximately equal to bDC2 x IC1

Therefore, IE2 ≈ bDC1bDC2IB1

The common-base (CB) amplifier . The base is the common terminal and is at ac ground. . High voltage gain . Maximum current gain of 1. . Low input resistance . No phase inversion from emitter to collector CB amplifier used in applications such as when sources tend to have very low-resistance outputs.

EE 111 - Dr. A. Almuhaisen 37 THE COMMON-BASE AMPLIFIER

Voltage Gain 푉푐 퐼푐푅푐 퐼푒푅푐 푹풄 ′ 퐴푣 = = ′ ≅ ′ ≅ ′ (since usually 푅퐸 ≫ 푟푒 , where 푅푐 = 푅퐶 ∥ 푅퐿 ) 푉푒 퐼푒(푟푒∥푅퐸) 퐼푒(푟푒∥푅퐸) 풓풆

Input Resistance ′ 푉푖푛 푉푒 퐼푒 푟푒∥푅퐸 ′ ′ ′ 푅𝑖푛(푒푚𝑖푡푡푒푟) = = = = 푟푒 ∥ 푅퐸 ≅ 푟푒 , (since usually 푅퐸 ≫ 푟푒 ) 퐼푖푛 퐼푒 퐼푒

Output Resistance ′ 푅표푢푡 ≅ 푅퐶 , (since typically 푟푐 ≫ 푅퐶)

Current Gain 퐼표푢푡 퐼푐 퐴𝑖 = = ≅ 1 퐼𝑖푛 퐼푒

Power Gain 퐴푃 = 퐴푣퐴𝑖 ≅ 퐴푣 EE 111 - Dr. A. Almuhaisen 38 Example 11

EE 111 - Dr. A. Almuhaisen 39 MULTISTAGE AMPLIFIERS

To improve amplifier performance, stages are often cascaded where the output of one drives another. The overall voltage gain, of cascaded amplifiers is the product of the individual voltage gains. ′ 퐴푣 = 퐴푣1퐴푣2퐴푣3 … 퐴푣푛 (where n is the number of stages)

Amplifier voltage gain is often expressed in decibels (dB) as follows: 퐴푣(푑퐵) = 20 log 퐴푣

Overall voltage gain in dB is ′ 퐴푣(푑퐵) = 퐴푣1(푑퐵) + 퐴푣ퟐ(푑퐵) + ⋯ + 퐴풗풏(푑퐵)

EE 111 - Dr. A. Almuhaisen 40 Example 12

EE 111 - Dr. A. Almuhaisen 41 MULTISTAGE AMPLIFIERS Capacitively-Coupled Multistage Amplifier Both stages are identical common- emitter amplifiers with the output of the first stage capacitively coupled to the input of the second stage. Loading Effects Voltage gain of the first stage 푅푐1 퐴푣1 = ′ 푟푒 We must consider the loading effect of the second stage.

Looking at the AC equivalent of 1st Stage: 푅푐1 = 푅3 ∥ 푅5 ∥ 푅6 ∥ 푅𝑖푛(푏푎푠푒2) ′ 푅𝑖푛(푏푎푠푒2) = 훽푎푐푟푒 ′ 25 푚푉 (You can verify that 퐼퐸 = 1.05 mA, 푟푒 ≅ ′ 퐼퐸 ≅ 23.8 Ω, 푅𝑖푛(푏푎푠푒2) = 훽푎푐푟푒 = 3.57 KΩ) EE 111 - Dr. A. Almuhaisen 42

MULTISTAGE AMPLIFIERS

st 푅푐1 1.63 퐾Ω Thus, voltage gain of 1 Stage is: 퐴푣1 = ′ = = 68.5 푟푒 23.8 Ω Notice the 푅7 4.7 퐾Ω Voltage Gain of the Second Stage 퐴푣2 = ′ = = 197 difference 푟푒 23.8 Ω ′ Overall Voltage Gain 퐴푣 = 퐴푣1퐴푣2 = 68.5 197 = 13495 ′ 퐴푣(푑퐵) = 20 log 13495 = 82.6 푑퐵 DC Voltages in the Capacitively Coupled Multistage Amplifier Since 훽퐷퐶푅4 ≫ 푅2 and 훽퐷퐶푅8 ≫ 푅6, the dc base voltage for 푄1and 푄2 is 푅2 10 퐾Ω 푉퐵 ≅ 푉퐶퐶 = 10 푉 = 1.57 푉 푅1 + 푅2 57 퐾Ω The dc emitter and collector voltages are as follows: 푉퐸 = 푉퐵 − .07 푉 = 1.05 푉 푉퐸 1.05 푉 퐼퐸 = = = 1.05 푚퐴 푅4 1.0 퐾Ω 퐼퐶 ≅ 퐼퐸 = 1.05 푚퐴 푉퐶 = 푉퐶퐶 − 퐼퐶푅3 = 10 푉 − 1.05 푚퐴 4.7 퐾Ω = 5.07 푉

EE 111 - Dr. A. Almuhaisen 43 MULTISTAGE AMPLIFIERS

Direct-Coupled Multistage Amplifiers Notice that there are no coupling or bypass capacitors in this circuit.

Advantages of direct-coupled amplifiers o Can be used to amplify low frequencies all the way down to dc (0 Hz) without loss of voltage gain because there are no capacitive reactances in the circuit.

The disadvantage of direct-coupled amplifiers o Any small changes in the dc bias voltages from temperature effects or power-supply variation are amplified by the succeeding stages.

EE 111 - Dr. A. Almuhaisen 44 Selected Key Terms

r-parameter One of a set of BJT characteristic parameters that include aac, bac, re', rb', and rc'.

Common-emitter A BJT configuration in which the emitter is the common terminal to an ac signal.

ac ground A point in a circuit that appears as a ground to ac signals only.

Input resistance The resistance seen by an ac source connected to the amplifier input. Output resistance The ac resistance looking in at the amplifier output.

Common-collector A BJT configuration in which the emitter is the common terminal to an ac signal. Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Thomas L. Floyd

Quiz

1. The equation for finding the ac emitter resistance of a BJT is

' 25 mV a. re  IB

' 25 mV b. re  IE

' 0.7 V c. re  IB

' 0.7 V d. re  IE

2. For a CE amplifier, a swamping resistor will a. increase the input resistance b. increase the gain c. both of the above d. none of the above

3. In a CC amplifier, the power gain is approximately a. one b. equal to the voltage gain c. equal to the current gain d. none of the above

4. The amplifier shown is a a. differential amplifier

b. CE amplifier +VCC

RC c. CC amplifier C3 R1 C V d. CB amplifier 2 out R C L 1 Vin

R2 RE

5. An advantage to this amplifier is that it a. has high current gain

b. has high input resistance +VCC

RC c. is non-inverting C3 R1 C V d. all of the above 2 out R C L 1 Vin

R2 RE

6. Together, Q1 and Q2 form a a. Swamped amplifier

b. Differential pair VCC c. Sziklai pair R1 C1

d. none of the above Q1

Q2 C2 Vout R2 R E RL

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Thomas L. Floyd Summary - THE COMMON-EMITTER AMPLIFIER CIRCUIT WITH VOLTAGE- DC formulas AC formulas DIVIDER BIAS

• Input is at the base. Output is at the collector. • Phase inversion. • 퐶1and 퐶3 are coupling capacitors and 퐶2 is the emitter-bypass capacitor.

• Emitter is at ac ground due to EE 111 - Dr. A. Almuhaisen 52 the bypass capacitor. Summary - SWAMPED AMPLIFIER WITH RESISTIVE LOAD CIRCUIT WITH VOLTAGE- AC formulas DIVIDER BIAS

′ • Swamping stabilizes gain by minimizing the effect of 푟푒 • Swamping reduces the voltage gain from its unswamped value. • Swamping increases input resistance. • The load resistance reduces the voltage gain. The smaller the load resistance, the less the gain. EE 111 - Dr. A. Almuhaisen 53 Summary - THE COMMON-COLLECTOR AMPLIFIER CIRCUIT WITH VOLTAGE- DC formulas AC formulas DIVIDER BIAS

• Input is at the base. Output is at the emitter. • No phase inversion • Input resistance is high. Output resistance is low. • Maximum voltage gain is 1. • Collector is at ac ground. EE 111 - Dr. A. Almuhaisen 54 Summary – The COMMON-BASE AMPLIFIER CIRCUIT WITH VOLTAGE- DC formulas AC formulas DIVIDER BIAS

• Input is at the emitter. Output is at the collector. • No phase inversion. • Input resistance is low. Output resistance is high. • Maximum current gain is 1. EE 111 - Dr. A. Almuhaisen 55 • Base is at ac ground. Summary . The ac load line differs from the dc load line because the effective ac collector resistance is less than the dc collector resistance. . r parameters are easily identifiable and applicable with a transistor’s circuit operation. . A common-emitter amplifier has high voltage, current, and power gains, but a relatively low input resistance. . Swamping is a method of stabilizing the voltage gain. . A common-collector amplifier has high input resistance and high current gain, but its voltage gain is approximately 1. . A Darlington pair provides beta multiplication for increased input resistance. . A common-collector amplifier is known as an emitter-follower. . The common-base amplifier has a high voltage gain, but it has a very low input resistance and its current gain is approximately 1. EE 111 - Dr. A. Almuhaisen 56 Tutorial 1. Solving H/W 2. Supporting MicroProject

EE 111 - Dr. A. Almuhaisen 57 MicoProject Application Activity: Audio Preamplifier for PA System

Read Application Activity “Audio Preamplifier for PA System” from Floyd book. Submission report are at the End of Week 13, and presentations on week 14th .

Objectives: 1. Writing a technical report 2. Using MultiSim Software 3. Designing basic electronic circuits 4. Building a basic electronic circuit

5. Presenting your work using Power Point EE 111 - Dr. A. Almuhaisen 58

Home Work 4

EE 111 - Dr. A. Almuhaisen 59 Home Work 4

EE 111 - Dr. A. Almuhaisen 60 Home Work 4

EE 111 - Dr. A. Almuhaisen 61 Home Work 4

EE 111 - Dr. A. Almuhaisen 62 Home Work 4

EE 111 - Dr. A. Almuhaisen 63 Summary & References BJT AMPLIFIERS o amplifier operation o transistor models o operation of common-emitter amplifiers o operation of common-collector amplifiers o operation of common-base amplifiers o operation of multistage amplifiers Key Terms Quiz Tutorial 4 Homework 4 MicoProject: Application Activity: Audio Preamplifier for PA System References o Text Book: Thomas L. Floyd, "Electronic Devices (Conventional Current Version)" Prentice Hall, 9th Edition, 2011

EE 111 - Dr. A. Almuhaisen 64