Electronics1

Tubes, Transistors and Amplifiers

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CENT-112 Fundamentals of Electricity and Electronics

Interest In 1947, Bardeen & Brattain at Bell Laboratories created the first amplifier! Shockley (boss), came near to canceling the project. The three shared a Nobel Prize. Bardeen and Brattain continued in research (and Bardeen later won another Nobel). Shockley quit to start a semiconductor company in Palo Alto. It folded, but its staff went on to invent the integrated circuit (the "chip") & to found the Intel Corporation. 2

CENT-112 Fundamentals of Electricity and Electronics

Tetrode Tube (+) Plate

Control Grid: Controls amplification rate & electron flow with bias voltage. Shield: Screen gridincreases electron speed cathode to + plate.

(-) Shield

Heater: Heats gas to gas amplification state.

Control Grid (-) Cathode

Inert Gas: Mercury or Argon gas.

Inert Gas Heater 3

CENT-112 Fundamentals of Electricity and Electronics

Cathode Ray Tube (CRT)

3 Electron Beams (Red, Green, Blue)

(-) Cathode (+) Anode

Grids

Conductive Coating

Phosphor Coated Screen

The cathode is a heated filament (like light bulb filament) in a vacuum inside a glass tube. The ray is a stream of electrons that naturally pour off a heated cathode into the vacuum. The + anode attracts the electrons pouring off the cathode. In a TV's CRT, the stream of electrons is focused by a focusing anode into a tight beam and then accelerated by an accelerating anode. This tight, high-speed beam of electrons flies through the vacuum in the tube and hits the flat screen at the other end of the tube. This screen is coated with phosphor, which glows when struck by the beam.

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CENT-112 Fundamentals of Electricity and Electronics

Bipolar Transistors •History –Created in 1948 in the AT&T Bell Laboratories. –Scientists were performing doping experiments on semiconductor material (diodes) and developed a semiconductor device having three (3) PN junctions.

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CENT-112 Fundamentals of Electricity and Electronics

Bipolar Transistor Construction • NPN / PNP Block Diagrams Emitter N Base

P

N

Collector

Emitter

Collector P

N

P Base

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CENT-112 Fundamentals of Electricity and Electronics

Bipolar Transistor Theory • For any transistor to conduct, two things must occur.  The emitter - base PN junction must be forward biased.  The base - collector PN junction must be reverse biased. 7

CENT-112 Fundamentals of Electricity and Electronics

Bipolar Transistor Biasing (NPN)

FB

Emitter

-

N

RB

P

N

Base + 8

CENT-112 Fundamentals of Electricity and Electronics

Collector

+

Bipolar Transistor Biasing (PNP) FB RB

Emitter P

+

N

Collector P

Base + 9

CENT-112 Fundamentals of Electricity and Electronics

-

Bipolar Transistor Operation (PNP) •90% of the current carriers pass through the reverse biased base - collector PN junction and enter the collector of the transistor. •10% of the current carriers exit transistor through the base. •The opposite is true for a NPN transistor.

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CENT-112 Fundamentals of Electricity and Electronics

Amplifier Operation • The transistor below is biased such that there is a degree of forward bias on the base - emitter PN junction. • Any input received will change the magnitude of forward bias & the amount of current flow through the transistor.

+ 0

Input Signal 11

RB

RC

+VCC

+

Q1

0

Output Signal CENT-112 Fundamentals of Electricity and Electronics

Amplifier Electric Switch Operation •When the input signal is large enough, the transistor can be driven into saturation & cutoff which will make the transistor act as an electronic switch. •Saturation - The region of transistor operation where a further increase in the input signal causes no further increase in the output signal. •Cutoff - Region of transistor operation where the input signal is reduced to a point where minimum transistor biasing cannot be maintained => the transistor is no longer biased to conduct. (no current flows) 12

CENT-112 Fundamentals of Electricity and Electronics

Amplifier Electric Switch Operation –Transistor Q-point •Quiescent point : region of transistor operation where the biasing on the transistor causes operation / output with no input signal applied. –The biasing on the transistor determines the amount of time an output signal is developed.

–Transistor Characteristic Curve •This curve displays all values of IC and VCE for a given circuit. It is curve is based on the level of DC biasing that is provided to the transistor prior to the application of an input signal. 13

–The values of the circuit resistors, and VCC will determine the location of the Q-point. CENT-112 Fundamentals of Electricity and Electronics

Transistor Characteristic Curve 90 uA 80 uA 70 uA

IC

60 uA

Saturation

50 uA 40 uA 30 uA 20 uA 10 uA 0 uA

Cutoff

14

VCE

CENT-112 Fundamentals of Electricity and Electronics

IB Q-Point

Transistor Maintenance • When troubleshooting transistors, do the following: – Remove the transistor from the circuit, if possible. – Use a transistor tester, if available, or use a digital multimeter set for resistance on the diode scale. – Test each PN junction separately. ( A “front to back” ratio of at least 10:1 indicates a good transistor). 15

CENT-112 Fundamentals of Electricity and Electronics

Transistor Maintenance •This chart shows the readings for a good transistor. Test Lead Connection (+/ - ) Base- Emitter

NPN PNP Resistance Reading Resistance Reading (High / Low) (High / Low) LOW HI GH

Transistor Maintenance Chart

16

Emitter- Base

HI GH

LOW

Base - Collector

LOW

HI GH

Collector- Base

HI GH

LOW

Emitter- Collector

HI GH

HI GH

Collector- Emitter

HI GH

HI GH

CENT-112 Fundamentals of Electricity and Electronics

Questions Q1. What is the 7 step troubleshooting method? A1. Symptom recognition, symptom elaboration, list possible faulty functions, identify faulty function, identify faulty component, failure analysis, repair, retest. Q2. What was the most difficult problem you ever troubleshot? A2. Various 17

CENT-112 Fundamentals of Electricity and Electronics

Bipolar Transistor Amplifiers •Amplifier Classification –Amplifiers can be classified in three ways: •Type (Construction / Connection) –Common Emitter –Common Base –Common Collector

•Bias (Amount of time during each half-cycle output is developed). –Class A, Class B, Class AB, Class C

•Operation 18

–Amplifier –Electronic Switch CENT-112 Fundamentals of Electricity and Electronics

Common Emitter Schematic Output Signal Flow Path

+

RB

0

RC

+VCC

+

Q1

0

Input Signal

Output Signal

Input Signal Flow Path

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CENT-112 Fundamentals of Electricity and Electronics

Kirchoff Voltage Law • DC Kirchoff Voltage Law Equations and Paths +VCC

Base - Emitter Circuit RB

RC

IBRB + VBE - VCC = 0 Q1

20

Collector - Emitter Circuit ICRC + VCE - VCC = 0

CENT-112 Fundamentals of Electricity and Electronics

Common Emitter Operation + 0

Positive Going Signal

RC RB

Input Signal

Q1

Base becomes more (+) WRT Emitter ➨ FB ↑ ➨ IC ↑ ➨ VRC ↑ ➨ VC ↓ ➨ VOUT ↓ ( Less + )

Negative Going Signal Output Signal 21

+ 0

Base becomes less (+) WRT Emitter ➨ FB ↓ ➨ IC ↓ ➨ VRC ↓ ➨ VC ↑ ➨ VOUT ↑ ( More + ) CENT-112 Fundamentals of Electricity and Electronics

Common Base Schematic Q1

Input Signal Flow Path + 0

RE

RB CC

RC

+VCC

+ 0

Output Signal Flow Path 22

CENT-112 Fundamentals of Electricity and Electronics

Kirchoff Voltage Law • DC Kirchoff Voltage Law Equations and Paths Q1

RE

RB CC

23

RC

+VCC

Base - Emitter Circuit IBRB + VBE + IERE - VCC = 0 Collector - Emitter Circuit ICRC + VCE + IERE - VCC = 0

CENT-112 Fundamentals of Electricity and Electronics

Common Base Operation Q1

Positive Going Signal

RE

RB CC

+VCC

+ 0

Input 24 Signal

RC

0

Base becomes more (+) WRT Emitter ➨ FB ↓ ➨ IC ↓ ➨ VRC ↓ ➨ VC ↑ ➨ VOUT ↑ ( More + )

Negative Going Signal

Base becomes less (+) WRT Emitter ➨ FB ↑ ➨ IC ↑ ➨ VRC ↑ ➨ VC ↓ ➨ VOUT ↓ ( Less + )

Output Signal CENT-112 Fundamentals of Electricity and Electronics

Common Collector Schematic Output Signal Flow Path +VCC +

RB Q1

0

Input Signal

+

Input Signal Flow Path

25

RE

0

Output Signal

CENT-112 Fundamentals of Electricity and Electronics

Kirchoff Voltage Law • DC Kirchoff Voltage Law Equations and Paths +VCC Base - Emitter Circuit IBRB + VBE + IERE - VCC = 0

RB Q1

Collector - Emitter Circuit ICRC + VCE + IERE - VCC = 0

RE

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CENT-112 Fundamentals of Electricity and Electronics

Common Collector Operation +VCC

Positive Going Signal

Q1

Base becomes more (+) WRT Emitter ➨ FB ↑ ➨ IE ↑ ➨ VRE ↑ ➨ VE ↑ ➨ VOUT ↑ ( More + )

RB

RE

Negative Going Signal

+

+

0

0

27

Input Signal

Output Signal

Base becomes less (+) WRT Emitter ➨ FB ↓ ➨ IE ↓ ➨ VRE ↓ ➨ VE ↓ ➨ VOUT ↓ ( Less + )

CENT-112 Fundamentals of Electricity and Electronics

AZAZA VOPINI & House of BEC Common Common Common Common Common Common BB

EE

Av Av==Voltage VoltageGain Gain Zo Zo ==Output Output Impedance Impedance Ap Ap== Power Power gain gain Zin Zin==Input Input Impedance Impedance Ai Ai ==Current CurrentGain Gain 28

CENT-112 Fundamentals of Electricity and Electronics

CC

Transistor Bias Stabilization •Used to compensate for temperature effects which affects semiconductor operation. As temperature increases, free electrons gain energy and leave their lattice structures which causes current to increase.

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CENT-112 Fundamentals of Electricity and Electronics

Types of Bias Stabilization •Self Bias: A portion of the output is fed back to the input 180o out of phase. This negative feedback will reduce overall amplifier gain. •Fixed Bias: Uses resistor in parallel with Transistor emitterbase junction. •Combination Bias: This form of bias stabilization uses a combination of the emitter resistor form and a voltage divider. It is designed to compensate for both temperature effects as well as minor fluctuations in supply (bias) voltage. •Emitter Resister Bias: As temperature increases, current flow will increase. This will result in an increased voltage drop across the emitter resistor which opposes the potential on the emitter of the transistor. 30

CENT-112 Fundamentals of Electricity and Electronics

Self Bias Schematic +VCC

+

++o

o Initial Input

RC

Self Bias Feedback

+

RB Q1

= 31

+ o Resulting Input CENT-112 Fundamentals of Electricity and Electronics

o VOUT

Emitter Bias Schematic +VCC

DC Component AC Component

RC

+

+

Q1

o

-

o Initial Input 32

+

++

RB

RE

+

VOUT CE

-

CENT-112 Fundamentals of Electricity and Electronics

Combination Bias Schematic +VCC

DC Component AC Component

RC

+

+

o Initial Input

33

+

++

RB1

Q1

RB2

o

RE

+

VOUT CE

-

CENT-112 Fundamentals of Electricity and Electronics

Amplifier Frequency Response •The range or band of input signal frequencies over which an amplifier operates with a constant gain. •Amplifier types and frequency response ranges. •Audio Amplifier –15 Hz to 20 KHz

•Radio Frequency (RF) Amplifier –10 KHz to 100,000 MHz

•Video Amplifier (Wide Band Amplifier) –10 Hz to 6 MHz 34

CENT-112 Fundamentals of Electricity and Electronics

Class ‘A’ Amplifier Curve

90 uA 80 uA 70 uA

IC

60 uA

Saturation

50 uA 40 uA 30 uA 20 uA

Q-Point

10 uA 0 uA

Cutoff 35

VCE

CENT-112 Fundamentals of Electricity and Electronics

IB

Class ‘B’ Amplifier Curve

90 uA

IC

80 uA 70 uA 60 uA

Saturation

50 uA 40 uA 30 uA 20 uA

Q-Point

10 uA 0 uA

Cutoff 36

VCE

CENT-112 Fundamentals of Electricity and Electronics

IB

Class ‘AB’ Amplifier Curve Can be used for guitar distortion.

90 uA

IC

80 uA 70 uA 60 uA

Saturation

50 uA 40 uA 30 uA 20 uA

Q-Point

10 uA 0 uA

Cutoff 37

VCE

CENT-112 Fundamentals of Electricity and Electronics

IB

Class ‘C’ Amplifier Curve

90 uA

IC

80 uA

IB

70 uA 60 uA

Saturation

50 uA 40 uA 30 uA 20 uA 10 uA 0 uA

Cutoff 38

VCE

CENT-112 Fundamentals of Electricity and Electronics

Q-Point

Amplifier Coupling Methods •Direct: The output of the first stage is directly connected to the input of the second stage. Best Frequency Response No frequency sensitive components. •Impedance (LC) Coupling: Similar to RC coupling but an inductor is used in place of the resistor. Not normally used in Audio Amplifiers. •RC Coupling: Most common form of coupling used. Poor Frequency Response. •Transformer Coupling: Most expensive form coupling used. Mainly used as the last stage or power output stage of a string of amplifiers. 39

CENT-112 Fundamentals of Electricity and Electronics

Direct Coupling Schematic +VCC 2 RC2

+VCC 1 RC1

RB2 Q2

RB1 Q1

40

CENT-112 Fundamentals of Electricity and Electronics

RC Coupling Schematic +VCC 2 RC2

+VCC 1 RC1

RB1

CC

RB2 Q2

Q1

41

CENT-112 Fundamentals of Electricity and Electronics

Impedance Coupling Schematic +VCC 2 RC2

+VCC 1 RB2

RB1

CC Q1

42

CENT-112 Fundamentals of Electricity and Electronics

Q2

Transformer Coupling Schematic +V

CC 2

RC2

+VCC 1 RC1

RB2 Q2

RB1

T1 Q1

43

CENT-112 Fundamentals of Electricity and Electronics

Silicon Controlled Rectifiers •Silicon Controlled Rectifiers (SCR) –Construction •Block Diagram

Anode

Cathode P

44

Left Floating Region

N

P N Gate

CENT-112 Fundamentals of Electricity and Electronics

OPAMP Voltage Regulators

Vin

45

+

CENT-112 Fundamentals of Electricity and Electronics

Vout

SCR Schematic

Anode

Cathode

Gate

46

CENT-112 Fundamentals of Electricity and Electronics

SCR Bias •When the SCR is forward biased and a gate signal is applied, the lightly doped gate region’s holes will fill with the free electrons forced in from the cathode. FB

FB

Anode

+

Cathode P

N

P N

RB

+ 47

-

Gate

CENT-112 Fundamentals of Electricity and Electronics

SCR Operation •Acts as an electronic switch •Essentially a rectifier diode which has a controllable “Turn - on” point. Can be switched approximately 25,000 times per second. •Once the SCR conducts, the gate signal can be removed. The difference in potential across the anode & cathode of the SCR will maintain current flow. •When the voltage across the SCR drops to a level below the “Minimum Holding” value, the PN junctions will reform and current flow through the SCR will stop. 48

CENT-112 Fundamentals of Electricity and Electronics

SCR Phase Control •The term Phase Control refers to a process where varying the timing of the gate signal to an SCR will vary the length of time that the SCR conducts. –This will determine the amount of Voltage or Power delivered to a load.

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CENT-112 Fundamentals of Electricity and Electronics

Unijunction Transistors (UJT) •Construction: Originally called “Double-based Diodes.” –“P” Type material doped into the “N” type base material. –Placement of the Emitter into the Base determines the voltage level (%) at which the the UJT fires. •This % is called the “Intrinsic Standoff Ratio ( η ).” –Once constructed, the Intrinsic Standoff Ratio cannot be changed.

•The actual voltage value at which the UJT fires is determined by the amount of source voltage applied. 50

CENT-112 Fundamentals of Electricity and Electronics

UJT Block Diagram Base 2

Equivalent Circuit Base 2

Emitter

P

N

Emitter

Base 1

51

CENT-112 Fundamentals of Electricity and Electronics

Base 1

UJT Schematic Symbol Base 2 Emitter

Base 1

52

CENT-112 Fundamentals of Electricity and Electronics

UJT No Operation •When VE is less than or equal to the voltage base one to emitter requirement (VE-B1 ), the UJT will not fire. Base 2

++

Depletion Region Emitter

+

No Current Flow P

N

Base 1 53

-

CENT-112 Fundamentals of Electricity and Electronics

UJT Operation •When VE is more than the voltage base one to emitter requirement (VE-B1 ), the UJT will fire. Base 2

++ UJT Fires

Emitter VE > VE-B1

+

P

N

Base 1 54

CENT-112 Fundamentals of Electricity and Electronics

-

UJT Sawtooth Generator

R1

Q1 E

VOUT

C1

B2 B1 SW1

C1 Charge C1 Discharge

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CENT-112 Fundamentals of Electricity and Electronics

VBB

UJT Relaxation Oscillator VOUT VOUT

VOUT

+ 1

RB2

R1

+ 2 + 3

VOUT

Q1 VOUT

1

C1 RB1

C1 Charge C1 Discharge 56

CENT-112 Fundamentals of Electricity and Electronics

VOUT

VBB 2

SW1 3

UJT Relaxation Oscillator •The output of the Oscillator can be used for sweep generators, gating circuit for SCR’s, as well as timing pulses for counting and timing circuits.

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CENT-112 Fundamentals of Electricity and Electronics

Questions • Q3. What is the phase relationship between input and output voltage in a common emitter circuit? • A3. 180 degrees.

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CENT-112 Fundamentals of Electricity and Electronics

More Questions • Q4. What type of transistor bias uses both self and fixed bias? • A4. Combination bias. • Q5. What is the frequency response range of an RF amplifier? • A5. 10Khz – 100, 000 Mhz.

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CENT-112 Fundamentals of Electricity and Electronics

4 . Silicon Bilateral Switch (SBS) a . Construction

J1

A1

P

J2 N

A2 G 60

A1 CENT-112 Fundamentals of Electricity and Electronics

P

G

A2

b . Schematic Symbol

Anode 2

Anode 1

A2

A1

Gate 61

CENT-112 Fundamentals of Electricity and Electronics

c . Characteristic Curve

I (mA) Reverse Breakover Voltage

Breakback Voltage

V A2-A1

Holding Current (IHO )

62

Forward Breakover Voltage

CENT-112 Fundamentals of Electricity and Electronics

d . Characteristics 1 . More vigorous switching characteristic. ⇓V to almost zero. 2 . More temperature stable. 3 . More symmetrical wave form output. 4 . Popular in low voltage trigger control circuits.

e . Theory 1 . Lower breakover voltages than Diac. (+/- 8V is most popular). 2 . SBS has more pronounced “Negative Resistance” region. 3 . It’s decline in voltages is more drastic after it enters the conductive state. 63

CENT-112 Fundamentals of Electricity and Electronics

f . Operation 1 . As shown below, if a zener diode is placed in the gate circuit between “G” and “A1”, the forward breakover voltage (+VBO) can be altered to approximately that of the zener voltage (VZ). a . -VBO is unaffected. SBS A2

A1

G 64

CENT-112 Fundamentals of Electricity and Electronics

2 . Characteristic Curve

I (mA) Reverse Breakover Voltage

Breakback Voltage

V A2-A1

Holding Current (IHO )

65

Forward Breakover Voltage

CENT-112 Fundamentals of Electricity and Electronics

5 Silicon Unilateral Switch (SUS) a Construction

Anode

Cathode P

N

P

N

Gate

66

CENT-112 Fundamentals of Electricity and Electronics

b . Schematic Symbol

Anode

Cathode

Gate

67

CENT-112 Fundamentals of Electricity and Electronics

c Theory 1 Similar to the four (4) layer diode except the +VBO can be altered by using the gate terminal voltage.

d Operation

Reverse Breakdown Voltage

-V A-C

68

{

I

}

Much greater than Forward Breakover Voltage

Forward Breakover Voltage

CENT-112 Fundamentals of Electricity and Electronics

V A-C

6 . Varactor a . Construction

P

69

N

CENT-112 Fundamentals of Electricity and Electronics

b . Theory 1 . For testing purposes, a front to back ratio of 10:1 is considered normal. 2 . The size of the depletion region in a varactor diode is directly proportional to the amount of bias applied. a . As forward bias increases, capacitance (Depletion region) decreases. b . As reverse bias increases, capacitance (Depletion region) increases.

3 . In the capacitance equation below, it is shown that only the distance between plates can be changed. 70

Where: A = Plate Area k = Constant d = Distance between plates

C = Ak dCENT-112 Fundamentals of Electricity and Electronics

a . An increase in reverse bias increases the width of the gap (d) which reduces the capacitance of the PN junction and vice versa.

4 . Advantage: Allows DC voltage to be used to tune a circuit for simple remote control or automatic tuning function.

c . Operation 1 . used to replace old style variable capacitor tuning circuits. 2 . They are used in tuning circuits of more sophisticated communications equipment and in other circuits where variable capacitance is required. 71

CENT-112 Fundamentals of Electricity and Electronics

Depletion Region 20µ F P

N 3V

72

5ρ F

P

N 6V

CENT-112 Fundamentals of Electricity and Electronics

A . Special Purpose Amplifiers 1 . Differential Amplifier a . Schematic Diagram + VCC

RC (1) RB (1)

RC (2) VOUT

RB (2)

VIN (1)

VIN (2)

Q1

Q2

RE - VEE

73

CENT-112 Fundamentals of Electricity and Electronics

b . Operation + VCC

RC (1)

+

RB (1) VIN (1)

0

+

++

VOUT

RC (2)

-

RB (2)

++

+ Q1

+

+

0 VIN (2)

-Q

-

2

RE

+

- VEE

VOUT (+) / (-) ARE ASSIGNED BY WHICH VOLTMETER LEAD IS USED AS THE REFERENCE

74

CENT-112 Fundamentals of Electricity and Electronics

0

2 . Operational Amplifiers (OPAMPS) a .Block Diagram (Basic) + vCC

INVERTING INPUT

DIFFERENTIAL AMPLIFIER

NON-INVERTING INPUT

VOLTAGE AMPLIFIER

OUTPPUT AMPLIFIER

OUTPUT

+ - vEE

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CENT-112 Fundamentals of Electricity and Electronics

b . Ideal OPAMP Characteristics 1 . Infinite (∝) Input Impedance a Draws little or no current from source. 2 . Zero Output Impedance 3 . Infinite (∝) Gain 4 . Infinite (∝) Frequency Response a Constant gain over any range of input signal frequencies.

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CENT-112 Fundamentals of Electricity and Electronics

c . Types of OPAMPS 1 . Linear (Output is Proportional to Input) a . Inverting RF

+

+ + 0

77

+

VIN R1

VOUT 0

-

CENT-112 Fundamentals of Electricity and Electronics

b . Non - Inverting

RF

+

+ R1

+ 0

78

VIN

+

VOUT 0

-

CENT-112 Fundamentals of Electricity and Electronics

c . Summing

VIN 1 VIN 2 VIN 3 VIN 4

R1

+ 0

+ 0

+ 0

+ 0

VIN 1

+ R2

VIN 2

RF

R3 VIN 3

+

R4

+

VIN 4 R5

79

0

VOUT

-

CENT-112 Fundamentals of Electricity and Electronics

d . Difference

VIN 1 VIN 2 VIN 3 VIN 4 VIN 5

80

R1

+ 0

+

VIN 1

R2 RF

VIN 2

0

+ VIN 3

R4

0

+ 0

+

R3

0

+

+

VIN 4

R5 VIN 5

+

0

VOUT

-

CENT-112 Fundamentals of Electricity and Electronics

2 . Non - Linear (Output is not Proportional to Input) a . Comparator

VREF ATTACHED TO EITHER + OR - TERMINALS (EXAMPLE SHOWS OUTPUT WITH VREF CONNECTED TO THE NON-INVERTING TERMINAL.)

+ VIN

VREF

(WAVEFORM WOULD BE INVERTED IF VREF WAS ATTACHED TO THE INVERTING TERMINAL)

+

0

+ VOUT

0

81

+

VIN

VREF

VOUT

-

CENT-112 Fundamentals of Electricity and Electronics

b . Differentiator

RF

+ 0

82

+

+

C1

+

VIN R1

VOUT 0

-

CENT-112 Fundamentals of Electricity and Electronics

c . Integrator

C1

+

+ + 0

83

+

VIN R1

VOUT 0

-

CENT-112 Fundamentals of Electricity and Electronics