Ppt of Analog

CENT-112 Fundamentals of Electricity and Electronics1

Tubes, Transistors and Amplifiers


InterestIn 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.


(+) Plate

(-) Shield

Control Grid

(-) Cathode

Heater

Inert Gas

Tetrode TubeControl Grid: Controls amplification rate & electron flow with bias voltage.

Shield: Screen grid- increases electron speed cathode to + plate.

Heater: Heats gas to gas amplification state.

Inert Gas: Mercury or Argon gas.


Cathode Ray Tube (CRT)

(+) Anode(-) Cathode

3 Electron Beams (Red, Green, Blue)

GridsPhosphor

CoatedScreen

ConductiveCoating

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.


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.


• NPN / PNP Block Diagrams

Bipolar Transistor Construction

Emitter

Emitter

N P N

P N P

Collector

Base

Base

Collector


• 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.

Bipolar Transistor Theory


+ N P NEmitter

Base +

-

FB RB

Bipolar Transistor Biasing (NPN)

Collector


P N PEmitter Collector

Base

+

-

-

FB RB

Bipolar Transistor Biasing (PNP)


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.


• 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.

Amplifier Operation

RB

RC

Q1

+

0

+VCC

Input Signal

+

0

Output Signal


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)


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.

–The values of the circuit resistors, and VCC will determine the location of the Q-point.


Transistor Characteristic Curve

IC

VCE

Q-Point

IB

0 uA

10 uA

20 uA

30 uA

40 uA

50 uA

60 uA

70 uA80 uA90 uA

Saturation

Cutoff


• 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).

Transistor Maintenance


Transistor Maintenance Chart

•This chart shows the readings for a good transistor.Test Lead

Connection( + / - )

NPNResistance Reading

(High / Low)

PNPResistance Reading

(High / Low)Base - Emitter LOW HIGH

Emitter - Base HIGH LOW

Base - Collector LOW HIGH

Collector - Base HIGH LOW

Emitter - Collector HIGH HIGH

Collector - Emitter HIGH HIGH

Transistor Maintenance


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


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–Amplifier

–Electronic Switch


Common Emitter Schematic

RB

RC

Q1

+

0

+VCC

Input Signal

+

0

Output Signal

Output Signal Flow Path

Input Signal Flow Path


• DC Kirchoff Voltage Law Equations and Paths

Kirchoff Voltage Law

RB

RC

Q1

+VCC

Base - Emitter Circuit

ICRC + VCE - VCC = 0

IBRB + VBE - VCC = 0

Collector - Emitter Circuit


Common Emitter Operation

Positive Going Signal

Negative Going Signal

Output Signal

Input Signal

+

+

0

0 Base becomes more (+) WRT Emitter FB IC VRC

VC VOUT ( Less + )

Base becomes less (+) WRT Emitter FB IC VRC

VC

VOUT ( More + )

RC

RB

Q1


Common Base Schematic

+

0

+

0+VCC

RBRCRE

Q1

CC






+VCC

RBRCRE

Q1

CC

Base - Emitter CircuitIBRB + VBE + IERE - VCC = 0

Collector - Emitter CircuitICRC + VCE + IERE - VCC = 0


Common Base Operation



+VCC

RBRCRE

Q1

CC

Base becomes more (+) WRT Emitter FB IC VRC

VC

VOUT ( More + )

Base becomes less (+) WRT Emitter FB IC VRC

VC VOUT ( Less + )Input

Signal

0Output Signal

+

0


Common Collector Schematic

RB

RE

Q1

+

0

+VCC

Input Signal +

0

Output Signal






RB

RE

Q1

+VCC

Base - Emitter CircuitIBRB + VBE + IERE - VCC = 0

Collector - Emitter CircuitICRC + VCE + IERE - VCC = 0


Common Collector Operation



RB

RE

Q1

+VCC

Base becomes more (+) WRT Emitter FB IE VRE

VE

VOUT ( More + )

Base becomes less (+) WRT Emitter FB IE VRE

VE VOUT ( Less + )Input

Signal

0 0

+ +

Output Signal


AZAZA VOPINI & House of BEC

Av = Voltage Gain

Zo = Output Impedance

Ap = Power gain

Zin = Input Impedance

Ai = Current Gain

Av = Voltage Gain

Zo = Output Impedance

Ap = Power gain

Zin = Input Impedance

Ai = Current Gain

Common Common Common

B E C

Common Common Common

B E C


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.


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 emitter-base 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.


Self Bias Schematic

RB

RC

Q1

+VCC

+

=

Initial Input

Self Bias Feedback

Resulting Input

+

+

+

+

o o

o

o

VOUT


Emitter Bias Schematic

RB

RC

Q1

+VCC

+

o

VOUT

RE

++

+

+

-

-Initial Input

+

o

CE

DC Component

AC Component


Combination Bias Schematic

RB1

RC

Q1

+VCC

+

o

VOUT

RE

++

+

+

-

-Initial Input

+

o

CE

DC Component

AC Component

RB2


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


Class ‘A’ Amplifier Curve

IC

VCE

IB

0 uA

10 uA

20 uA

30 uA

40 uA

50 uA

60 uA

70 uA80 uA90 uA

Saturation

Cutoff

Q-Point


Class ‘B’ Amplifier Curve

IC

VCE

IB

0 uA

10 uA

20 uA

30 uA

40 uA

50 uA

60 uA

70 uA

80 uA

90 uA

Saturation

Cutoff

Q-Point


Class ‘AB’ Amplifier Curve

IC

VCE

IB

0 uA

10 uA

20 uA

30 uA

40 uA

50 uA

60 uA

70 uA

80 uA

90 uA

Saturation

Cutoff

Q-Point

Can be used for guitar distortion.


Class ‘C’ Amplifier Curve

IC

VCE

IB

0 uA

10 uA

20 uA

30 uA

40 uA

50 uA

60 uA

70 uA

80 uA

90 uA

Saturation

CutoffQ-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.


Direct Coupling Schematic

RB1

RC1

Q1

+VCC1

RB2

RC2

Q2

+VCC2


RC Coupling Schematic

RB1

RC1

Q1

+VCC1

RB2

RC2

Q2

CC

+VCC2


Impedance Coupling Schematic

RB1

Q1

+VCC1

RB2

RC2

Q2

CC

+VCC2


Transformer Coupling Schematic

RB1

RC1

Q1

+VCC1

RB2

RC2

Q2

+VCC2

T1


Silicon Controlled Rectifiers

•Silicon Controlled Rectifiers (SCR)

–Construction

•Block Diagram

Anode Cathode

Gate

P PN N

Left Floating Region


OPAMP Voltage Regulators

Vin Vout

-+


SCR Schematic

Anode Cathode

Gate


SCR Bias

Anode

Gate

P PN NCathode

-

FB FB

RB

+

+

•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.


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.


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.


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 ( ).”–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.


UJT Block Diagram

Emitter

Base 2

Base 1

P N Emitter

Base 2

Base 1

Equivalent Circuit


UJT Schematic Symbol

Emitter

Base 2

Base 1


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.

Emitter

Base 1

Base 2

P N

++

-

+

No Current Flow

Depletion Region


UJT Operation

Emitter

Base 1

Base 2

P N

++

-

+

UJT Fires

VE > VE-B1

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


UJT Sawtooth Generator

R1

C1

Q1

E

B1

B2

VBB

SW1VOUT

C1 Discharge

C1 Charge


UJT Relaxation Oscillator

R1

C1

Q1

VBB

SW1

VOUT1

C1 Discharge

C1 Charge

RB2

RB1

VOUT2

VOUT3

VOUT2

VOUT3

+

+

+

VOUT1


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.


Questions• Q3. What is the phase relationship between

input and output voltage in a common emitter circuit?

• A3. 180 degrees.


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.


4 . Silicon Bilateral Switch (SBS)a . Construction

A2A1

G

P PN

J1 J2

A2A1

G


b . Schematic Symbol

Anode 2 Anode 1

A2 A1

Gate


c . Characteristic Curve

V A2-A1

I (mA)

Holding Current (IHO)

Reverse Breakover Voltage

Forward Breakover Voltage

Breakback Voltage


d . Characteristics1 . 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 . Theory1 . 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.


f . Operation1 . 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


2 . Characteristic Curve

V A2-A1

I (mA)

Holding Current (IHO)

Reverse Breakover Voltage


Breakback Voltage


5 Silicon Unilateral Switch (SUS)a Construction

P PN NAnode Cathode

Gate


b . Schematic Symbol

Anode Cathode

Gate


c Theory1 Similar to the four (4) layer diode except the +VBO can

be altered by using the gate terminal voltage.

d Operation

V A-C-V A-C

I


Reverse Breakdown Voltage

{ }Much greater than Forward Breakover Voltage


6 . Varactora . Construction

P N


b . Theory1 . 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.

C = Akd

Where: A = Plate Areak = Constantd = Distance between plates


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 . Operation1 . 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.


3V 6V

20F 5F

P N P N

Depletion Region


A. Special Purpose Amplifiers1 . Differential Amplifier

a . Schematic Diagram

+ VCC

- VEE

RE

RB (1)

RC (1)RC (2)

RB (2)

Q1 Q2

VOUT

VIN (1) VIN (2)


b . Operation

+ VCC

- VEE

RE

RB (1)

RC (1)RC (2)

RB (2)

Q1 Q2

VOUT

VIN (1) VIN (2)

+ -

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

+

0

+

0++ ++

+ +

- -

+

0

VOUT


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

DIFFERENTIAL AMPLIFIER

VOLTAGE AMPLIFIER

OUTPPUT AMPLIFIER

NON-INVERTING INPUT

INVERTING INPUT

+

-

+ vCC

- vEE

OUTPUT


b . Ideal OPAMP Characteristics1 . Infinite () Input Impedance

a Draws little or no current from source.2 . Zero Output Impedance3 . Infinite () Gain4 . Infinite () Frequency Response

a Constant gain over any range of input signal frequencies.


c . Types of OPAMPS1 . Linear (Output is Proportional to Input)

a . Inverting

+

-VOUT

VIN

RF

R1

+

0

+

0

+

-


b . Non - Inverting

+

-VOUT

VIN

RF

R1 +

0

+

0

+

-


c . Summing

+

-VOUT

VIN1

RF

R5

+0

+

0+

-

VIN4

+0

VIN3

+0

VIN2

+0

VIN1

VIN2

VIN3

VIN4

R1

R2

R3

R4


d . Difference

+

-VOUT

VIN1

RF

+0

+

0+

-

VIN4

+0

VIN3

+0

VIN2

+0

VIN1

VIN2

VIN3

VIN4

R1

R2

R3

R4

VIN5 0+ R5

VIN5


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

a . Comparator

+

-VOUT

VIN

+

0

+

0

+

--

VREF

VREF ATTACHED TO EITHER + OR - TERMINALS

(EXAMPLE SHOWS OUTPUT WITH VREF CONNECTED TO THE NON-INVERTING TERMINAL.)

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

VIN VREF

VOUT


b . Differentiator

+

-VOUT

VIN

RF

R1

+

0

+

0

+

-

C1


c . Integrator

+

-VOUT

VIN

R1

+

0

+

0

+

-

C1

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