Electron Devices A broader perspective

Electron Devices A broader perspective
Dr. N.Shanmugasundaram Professor & Head, ECE Department Sri Eshwar College of Engineering Coimbatore

Overview of Presentation
Semiconductor Theory PN Junction Diode BJT FET (JFET & MOSFET) Rectifiers and Power Supplies Special Function Devices 19-Feb-19 Dr.NSS / SECE

Semiconductor Basics Stable atom has 8 electrons in outermost orbit
Insulator has 8 electrons Semiconductor has exactly 4 electrons (eg. Si, Ge) Metal has less than 4 electrons 19-Feb-19 Dr.NSS / SECE

Energy Levels in Semiconductor
The more distant the electron from the nucleus, the higher the energy state. Energy level of electrons at Outermost orbit is VALENCE BAND. Energy needed in Electrons for conduction is CONDUCTION BAND. 19-Feb-19 Dr.NSS / SECE

Intrinsic Semiconductor
No Impurities (pure semiconductor) No Charge carriers at 0º K (−273.15° Celsius) Only few carriers at room temperature N = P Not suitable for Electron Devices 19-Feb-19 Dr.NSS / SECE

Semiconductor Theory Extrinsic Semiconductor P Type:
Trivalent Impurity (eg. Boron) Holes – Charge carriers N Type: Pentavalent Impurity (eg. P) Electrons – Charge carriers 19-Feb-19 Dr.NSS / SECE

Semiconductor Theory Comparison of Metals, Semiconductors & Insulators
Forbidden Energy gap, VB, CB Comparison of Intrinsic & Extrinsic semiconductor Comparison of P-type and N-type Semiconductors 19-Feb-19 Dr.NSS / SECE

Semiconductor Theory 19-Feb-19 Dr.NSS / SECE

PN Junction Diode 19-Feb-19 Dr.NSS / SECE

PN Junction Diode Effect of temperature 19-Feb-19 Dr.NSS / SECE

Avalanche in the snowy mountain..
Avalanche Breakdown Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche. Electron avalanche Avalanche in the snowy mountain.. 19-Feb-19 Dr.NSS / SECE

FIGURE - Zener diode symbol.
Zener Diode:- is a silicon pn junction device that differ from rectifier diodes because it is designed for operation in the reverse- breakdown region. - if Zener diode is forward-biased, it operates the same as a rectifier diode. Function: to provide a stable reference voltage for use in power supplies, voltmeter & other instruments, voltage regulators. FIGURE - Zener diode symbol. 19-Feb-19 Dr.NSS / SECE

FIGURE - General diode V-I characteristic.
Zener breakdown: - occurs in a Zener diode at low reverse voltages. - Zener diode is heavily doped to reduce the breakdown voltage This causes a very thin depletion region. 19-Feb-19 Dr.NSS / SECE

PN Junction Diode Forward & Reverse Biasing Depletion region
Reverse saturation current (Is) Equation for Forward current (If) Barrier potential / Knee voltage (Si & Ge) Breakdown voltage (PIV) Static and Dynamic resistance Parameters (If, PIV, Pd..) Applications Zener Diode & its Characteristics 19-Feb-19 Dr.NSS / SECE

BJT – Bipolar Junction Transistor
Model of First Transistor 19-Feb-19 Dr.NSS / SECE

BJT is a 3-Terminal device. BJT is a CURRENT CONTROLLED device.
Terminals are EMITTER, BASE, COLLECTOR. Main application of BJT: SWITCH and AMPLIFIER. Can be operated in 3 regions: CUT-OFF, ACTIVE and SATURATION. 3 BJT configurations are CB, CE and CC. Commonly used configuration: CE Biasing methods: Base resistor, Collector Feedback, Potential divider. 19-Feb-19 Dr.NSS / SECE

19-Feb-19 Dr.NSS / SECE

Two Types of BJT: NPN & PNP
IE = IC + IB 19-Feb-19 Dr.NSS / SECE

Common Base Configuration
Common Emitter Configuration Common Collector Configuration 19-Feb-19 Dr.NSS / SECE

Three types of Biasing are: Fixed Bias (Simple, but not stable)
Biasing is a process through which collector current IC is kept constant withstanding the variations in β, Temperature. Three types of Biasing are: Fixed Bias (Simple, but not stable) Collector Feedback Bias Voltage Divider Bias (Stable and Best) 19-Feb-19 Dr.NSS / SECE

Fixed Biasing (Simple)

Collector Resistor (Voltage Feedback) Biasing

Voltage Divider Biasing (Stable)

IC = Collector current IB = Base current IE = Emitter current

Simulation of transistor as an amplifier

INPUT/OUTPUT PHASE RELATIONSHIP
Transistor Configuration Comparison AMPLIFIER TYPE COMMON BASE COMMON EMITTER COMMON COLLECTOR INPUT/OUTPUT PHASE RELATIONSHIP 0° 180° VOLTAGE GAIN HIGH MEDIUM LOW CURRENT GAIN a = IC / IE b = IC / IB γ = IE / IB POWER GAIN INPUT RESISTANCE OUTPUT RESISTANCE APPLICATION NOT USED AMPLIFICATION IMPEDANCE MATCHING 19-Feb-19 Dr.NSS / SECE

Transistor Terminal Identification

Transistor Testing 1. Curve Tracer - Provides a graph of the characteristic curves. 2. DMM - Some DMM’s will measure DC or HFE. 3. Ohmmeter 19-Feb-19 Dr.NSS / SECE

BJT – h parameters 19-Feb-19 Dr.NSS / SECE

BJT – h parameters hie hre hfe hoe input impedance (Ω)
reverse voltage ratio (dimensionless) hfe forward current transfer ratio (dimensionless) hoe output admittance (Siemen) 19-Feb-19 Dr.NSS / SECE

BJT – as a Switch 19-Feb-19 Dr.NSS / SECE

BJT Application Biasing Regions of Operation Classes of Operation
Frequency Response h-Parameters Important relationships of a transistor 19-Feb-19 Dr.NSS / SECE

FET 19-Feb-19 Dr.NSS / SECE

FIELD EFFECT TRANSISTOR (FET)
FET is a UNI-POLAR transistor. FET is a VOLTAGE CONTROLLED device. 3-terminals of FET: SOURCE, GATE, DRAIN. Main application of FET: SWITCH and AMPLIFIER. Can be operated in 3 regions: CUT-OFF, ACTIVE and SATURATION. Biasing methods: Base resistor, Collector Feedback, Potential divider. Advantage of FET over BJT: FET requires virtually no input (bias signal) current and gives an extremely high input resistance. High noise immunity and thermal stability 19-Feb-19 Dr.NSS / SECE

Field Effect Transistor (FET) Bipolar Junction Transistor (BJT)
Field Effect Transistor (FET) Bipolar Junction Transistor (BJT) 1 LOW VOLTAGE GAIN HIGH VOLTAGE GAIN 2 HIGH CURRENT GAIN LOW CURRENT GAIN 3 VERY INPUT IMPEDANCE LOW INPUT IMPEDANCE 4 HIGH OUTPUT IMPEDANCE LOW OUTPUT IMPEDANCE 5 LOW NOISE GENERATION MEDIUM NOISE GENERATION 6 FAST SWITCHING TIME MEDIUM SWITCHING TIME 7 EASILY DAMAGED BY STATIC ROBUST 8 SOME REQUIRE AN INPUT TO TURN IT "OFF" REQUIRES ZERO INPUT TO TURN IT "OFF" 9 VOLTAGE CONTROLLED DEVICE CURRENT CONTROLLED DEVICE 10 MORE EXPENSIVE THAN BIPOLAR CHEAP 11 DIFFICULT TO BIAS EASY TO BIAS 19-Feb-19 Dr.NSS / SECE

BJT: FET: 19-Feb-19 Dr.NSS / SECE

MOSFET 19-Feb-19 Dr.NSS / SECE

Features Characteristics (Transfer, Drain) Biasing Regions of Operation Frequency Response Important Parameter - gm Important relationships of a transistor 19-Feb-19 Dr.NSS / SECE

Rectifier and Power Supplies

Rectifier Rectification is the process of
converting an AC signal into a DC signal. 19-Feb-19 Dr.NSS / SECE

Rectifier Half wave Rectifier: One diode is used
Rectifies only half of the wave Efficiency: 40.6% (max) 19-Feb-19 Dr.NSS / SECE

Rectifier Full wave Rectifier: Two diodes are used
Rectifies both positive and negative half cycle of the wave Efficiency: 81.2% (max) 19-Feb-19 Dr.NSS / SECE

Rectifier Bridge Rectifier: Four diodes are used
Rectifies both positive and negative half cycle of the wave Need NO center tap in the transformer Efficiency: 81.2% 19-Feb-19 Dr.NSS / SECE

Rectifier Bridge Rectifier with C Filter: 19-Feb-19 Dr.NSS / SECE

Rectifier Different Filters: 19-Feb-19 Dr.NSS / SECE

Special Purpose Devices

FIGURE - Zener diode symbol.
Zener Diode:- is a silicon pn junction device that differ from rectifier diodes because it is designed for operation in the reverse- breakdown region. - if Zener diode is forward-biased, it operates the same as a rectifier diode. Function: to provide a stable reference voltage for use in power supplies, voltmeter & other instruments, voltage regulators. FIGURE - Zener diode symbol. 19-Feb-19 Dr.NSS / SECE

FIGURE - General diode V-I characteristic.
Zener breakdown:- occurs in a Zener diode at low reverse voltages. - Zener diode is heavily doped to reduce the breakdown voltage This causes a very thin depletion region. 19-Feb-19 Dr.NSS / SECE

FIGURE - Tunnel diode symbols.
A tunnel diode or Esaki diode is a type of semiconductor diode which is capable of very fast operation, well into the microwave frequency region, by using quantum mechanical effects. FIGURE - Tunnel diode symbols. 19-Feb-19 Dr.NSS / SECE

Forward bias operation
Under normal forward bias operation, as voltage begins to increase, electrons at first tunnel through the very narrow p–n junction barrier because filled electron states in the conduction band on the n-side become aligned with empty valence band hole states on the p-side of the pn junction. As voltage increases further these states become more misaligned and the current drops – this is called negative resistance because current decreases with increasing voltage. As voltage increases yet further, the diode begins to operate as a normal diode, where electrons travel by conduction across the p–n junction, and no longer by tunneling through the p–n junction barrier. Thus, the most important operating region for a tunnel diode is the negative resistance region. 19-Feb-19 Dr.NSS / SECE

FIGURE - Tunnel diode characteristic curve.

FIGURE - Parallel resonant circuit.

FIGURE - Basic tunnel diode oscillator.

3. VARACTOR DIODE The reverse-biased varactor diode acts as a variable capacitor. 19-Feb-19 Dr.NSS / SECE

FIGURE - The reverse-biased varactor diode acts as a variable capacitor.

FIGURE - Varactor diode capacitance varies with reverse voltage.

FIGURE 6 - A Resonant band-pass filter using a varactor diode for adjusting the resonant frequency over a specified range. 19-Feb-19 Dr.NSS / SECE

FIGURE - Symbol for an LED. When forward-biased, it emits light.

FIGURE - Electroluminescence in a forward-biased LED.

FIGURE - Basic operation of an LED.

FIGURE - Examples of typical spectral output curves for LEDs.

FIGURE - Typical LEDs. 19-Feb-19 Dr.NSS / SECE

FIGURE - The 7-segment LED display.

5. LASER DIODE A Laser diode, also known as an injection laser or diode laser, is a semiconductor device that produces coherent radiation (in which the waves are all at the same frequency and phase) in the visible or infrared (IR) spectrum when current passes through it. Laser diodes are used in optical fiber systems, compact disc (CD) players, laser printers, remote-control devices, and intrusion detection systems. 19-Feb-19 Dr.NSS / SECE

Figure: Structure of DH LASER Diode

FIGURE - Basic laser diode construction and operation.

6. PHOTODIODE FIGURE - Photodiode. 19-Feb-19 Dr.NSS / SECE

FIGURE - Typical photodiode characteristics.

FIGURE - Operation of a photodiode.

7. PIN DIODE FIGURE - PIN diode. 19-Feb-19 Dr.NSS / SECE

but it makes the PIN diode suitable for attenuators, fast switches,
A PiN diode is a diode with a wide, lightly doped 'near' intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor regions. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts. The wide intrinsic region is in contrast to an ordinary PN diode. The wide intrinsic region makes the PIN diode an inferior rectifier (the normal function of a diode), but it makes the PIN diode suitable for attenuators, fast switches, photo detectors, and high voltage power electronics applications. 19-Feb-19 Dr.NSS / SECE

FIGURE - PIN diode characteristics.

FIGURE - Diode symbols. 19-Feb-19 Dr.NSS / SECE

8. SILICON CONTROLLED RECTIFIER

Two Transistor model of SCR

The switching action of gate takes place only when
(i) SCR is forward biased i.e. anode is positive with respect to cathode. (ii) Suitable positive voltage is applied between the gate and the cathode. Once the SCR has been switched on, it has no control on the amount of current flowing through it. The current through the SCR is entirely controlled by the external impedance connected in the circuit and the applied voltage. The forward current through the SCR can be reduced by reducing the applied voltage or by increasing the circuit impedance. A minimum forward current must be maintained to keep the SCR in conducting state. This is called the holding current rating of SCR. If the current through the SCR is reduced below the level of holding current, the device returns to off-state or blocking state. Note: The gate can only trigger or switch ON the SCR, it cannot switch OFF. 19-Feb-19 Dr.NSS / SECE

Terminology Firing Angle
The angle (in the input AC) at which the gate is triggered is known as 'firing angle'. Holding Current It is the minimum anode current (with gate being open) required to keep the SCR in ON condition. Break Over voltage It is the minimum forward voltage with gate being open, at which an SCR starts conducting heavily (i.e., the SCR is turned ON) . 19-Feb-19 Dr.NSS / SECE

9. UNIPOLAR JUNCTION TRANSISTOR
A unijunction transistor (UJT) is an electronic semiconductor device that has only one junction. The UJT has three terminals: an emitter (E) and two bases (B1 and B2). The base is formed by lightly doped n-type bar of silicon. Two ohmic contacts B1 and B2 are attached at its ends. The emitter is of p-type and it is heavily doped. 19-Feb-19 Dr.NSS / SECE

Intrinsic Standoff Ratio

Unijunction transistor: (a) emitter characteristic curve, (b) model for VP .

Application of UJT – RELAXATION OSCILLATOR

REVIEW: A unijunction transistor consists of two bases (B1, B2) attached to a resistive bar of silicon, and an emitter in the center. The E-B1 junction has negative resistance properties; it can switch between high and low resistance. The intrinsic standoff ratio is η= RB1 /(RB1 + RB2), for a unijunction transistor. The trigger voltage is determined by η. Unijunction transistors and programmable unijunction transistors are applied to oscillators, timing circuits, and Thyristor triggering. 19-Feb-19 Dr.NSS / SECE

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