Podcast
Questions and Answers
Which of the following components is considered a two-port network?
Which of the following components is considered a two-port network?
- Transistor (correct)
- Capacitor
- Inductor
- Resistor
A diode is an example of a linear one-port network.
A diode is an example of a linear one-port network.
False (B)
What characteristic of MOSFETs makes them preferred over BJTs in many applications?
What characteristic of MOSFETs makes them preferred over BJTs in many applications?
higher switching speed, greater efficiency, and lower power loss
MOSFETs are commonly used in CMOS circuits for building ______.
MOSFETs are commonly used in CMOS circuits for building ______.
Match the following transistor types with their conduction characteristics:
Match the following transistor types with their conduction characteristics:
What is the primary application of MOSFETs in power electronics?
What is the primary application of MOSFETs in power electronics?
The threshold voltage of a MOSFET is the voltage required to switch it off.
The threshold voltage of a MOSFET is the voltage required to switch it off.
Briefly describe the function of the 'inversion layer' in a MOSFET.
Briefly describe the function of the 'inversion layer' in a MOSFET.
In an n-channel enhancement-mode MOSFET, a ______ voltage must be applied from gate to source to induce a channel.
In an n-channel enhancement-mode MOSFET, a ______ voltage must be applied from gate to source to induce a channel.
Match the MOSFET type with its typical operating state:
Match the MOSFET type with its typical operating state:
In which region of operation does a MOSFET act like a closed switch, allowing saturated current flow?
In which region of operation does a MOSFET act like a closed switch, allowing saturated current flow?
In the cut-off region, a MOSFET behaves like an open switch with no current flow.
In the cut-off region, a MOSFET behaves like an open switch with no current flow.
Explain how the channel's mobile negative charge density is controlled in a MOSFET.
Explain how the channel's mobile negative charge density is controlled in a MOSFET.
The saturation region of a MOSFET is achieved once $V_{DS}$ exceeds the ______ voltage.
The saturation region of a MOSFET is achieved once $V_{DS}$ exceeds the ______ voltage.
Match the characteristics of Enhancement and Depletion type MOSFETs:
Match the characteristics of Enhancement and Depletion type MOSFETs:
Which factor primarily influences the drain current in a MOSFET?
Which factor primarily influences the drain current in a MOSFET?
Applying a voltage to the gate is unnecesary for an enhancement-mode MOSFET to conduct.
Applying a voltage to the gate is unnecesary for an enhancement-mode MOSFET to conduct.
Define threshold voltage in a MOSFET.
Define threshold voltage in a MOSFET.
The region where the drain current of a MOSFET attains a constant value is called the ______.
The region where the drain current of a MOSFET attains a constant value is called the ______.
Match the formulas to the regions that they are applicable in. $V_{GS}$ is Gate-Source voltage, $V_{TH}$ is Threshold Voltage, $V_{DS}$ is Drain-Source voltage, and $V_{DS(sat)}$ is Drain-Source saturation voltage.
Match the formulas to the regions that they are applicable in. $V_{GS}$ is Gate-Source voltage, $V_{TH}$ is Threshold Voltage, $V_{DS}$ is Drain-Source voltage, and $V_{DS(sat)}$ is Drain-Source saturation voltage.
In the current-voltage characteristic equation for a MOSFET, what does the term $C_{ox}$ represent?
In the current-voltage characteristic equation for a MOSFET, what does the term $C_{ox}$ represent?
The input impedance of MOSFET is low.
The input impedance of MOSFET is low.
In MOSFET design, what is the significance of the ratio W/L?
In MOSFET design, what is the significance of the ratio W/L?
In MOSFET I-V relation, ___ is the transconductance paramenter.
In MOSFET I-V relation, ___ is the transconductance paramenter.
Match the components of a MOSFET to what this can be thought of as:
Match the components of a MOSFET to what this can be thought of as:
MOSFET is a --- terminal device.
MOSFET is a --- terminal device.
Transistors are one-port network devices.
Transistors are one-port network devices.
What type of application is high, what is the transistor?
What type of application is high, what is the transistor?
Generally, MOSFETs use high ___ applicaitons.
Generally, MOSFETs use high ___ applicaitons.
Match MOSFETs to their common applications.
Match MOSFETs to their common applications.
Flashcards
One-Port Component
One-Port Component
Electrical network with current entering/leaving through one terminal.
Two-Port Component
Two-Port Component
A device with current entering/leaving through two ports.
MOSFET
MOSFET
Semiconductor device with three terminals: Gate, Drain, Source.
Enhancement-type MOSFET
Enhancement-type MOSFET
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Threshold Voltage
Threshold Voltage
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Saturation Region
Saturation Region
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Cut-Off Region
Cut-Off Region
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Ohmic/Linear Region
Ohmic/Linear Region
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Current-Voltage Characteristic Equation
Current-Voltage Characteristic Equation
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N-Channel Enhancement Mode
N-Channel Enhancement Mode
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Study Notes
- Module covers Non-Linear Two Port Devices
Basic Concepts
- Transistors are non-linear two port devices
- Transistor types are compared
MOSFET Operation and Response
- Device structure and operation outlined
- Depletion MOSFET vs. Enhancement MOSFET are covered
- MOSFET Characteristics explained
MOSFET Models
- Analysis of MOSFET Circuits is performed
- Focus on MOSFET Based Amplifier Circuits
- Includes Small Signal Model
- Includes High Frequency Model
One-Port and Two-Port Components
- A two terminal electrical network in which current enters through one terminal and leaves through another terminal is a one-port component.
- Resistors, Inductors, and Capacitors are examples of linear one-port networks.
- Diodes are an example of nonlinear one-port networks.
- A two port electrical network in which current enters through one port and leaves through another port is a two-port component.
- Transistors, Transformers, Op-Amps, Amplifiers, and Transmission lines (power or communication) are examples of two-port networks.
Examples of Two-Port Circuits
- Transformers as Two-port Circuit
- Transistors as Two-port Circuit
- Op-Amps as Two-port Circuit
- Amplifiers as Two-port Circuit
- Transmission Lines as Two-port Circuit
Diodes vs. Transistors
- Illustrates basic functionality of a diode
- Outlines the configuration of a BJT transistor
- Depicts the configuration of a FET transistor
Transistor Types
- BJT
- NPN
- PNP
- Field effect transistor
- Junction FET
- Depletion Mode
- N-Channel
- P-Channel
- Depletion Mode
- Metal Oxide Semiconductor FET
- Depletion Mode
- N-Channel
- P-Channel
- Enhancement Mode
- N-Channel
- P-Channel
- Depletion Mode
- Junction FET
MOSFET vs BJT vs IGBT
- MOSFET: Metal Oxide Semiconductor Field Effect Transistor
- BJT: Bipolar Junction Transistor
- IGBT: Insulated Gate Bipolar Transistor
Comparison of Transistors (BJT, MOSFET, IGBT)
| Characteristic | BJT | MOSFET | IGBT |
|---|---|---|---|
| Conduction | Bipolar (both electrons & holes) | Unipolar (only electrons or holes) | Bipolar (electron + hole) |
| Voltage Rating | High (<1kV) | High (<1kV) | Very High (>1kV) |
| Current Rating | High (<500A) | High (>500A) | High (>500A) |
| Control | Current controlled | Voltage controlled | Voltage controlled |
| Input Drive | Current ratio (10-20 times) | Voltage VGS (3-10V) | Voltage VGE (4-8V) |
| Switching Speed | Slow (μς) | Very fast (ns) | Moderate |
| Switching Losses | High | Low | Moderate |
| Efficiency | Low | High | Moderate |
| Size on Chip | More | Less | Less |
| Cost | Low | Medium | High |
| Noise Generation | Medium | Low | Low |
| Input Impedance | Low | High | High |
| Output Impedance | Low | Medium | Low |
| Application | Low-frequency amplifiers, power supplies | High-frequency applications, but limits high-power applications | High-power applications with moderate switching speeds |
Benefits and Applications of MOSFETs
- Preferred over BJTs offering higher switching speed, greater efficiency, and lower power loss.
- Used for switching and amplifying signals in electronic circuits/devices.
- Applications:
- Switching: Fast and low-power switches in digital circuits.
- Amplification: Used in audio and RF amplifiers, particularly for high frequency amplifiers.
- Logic Circuits: Used in CMOS for building logic gates and high density VLSI circuits.
- Power Electronics: Used in power supply regulation circuits and converters like SMPS and DC Buck/Boost converters.
- Microprocessors & Memory: Core of CPUs, GPUs, and memory chips.
- Signal Processing: Used in ADCs and DACs.
- RF & Communication: Used in high-frequency circuits.
- Protection: Used as electronic relays for over-voltage protection.
- Motor Control (Motor Drive): Controls DC motors in robotics and automation.
- Automotive: Used in EVs, ignition, and control systems.
MOSFETs
- MOSFET is a metal oxide semiconductor field effect transistor
- Three terminal device (gate, source, drain)
- Voltage between gate and source controls the current through the drain
NMOS
- N-channel enhancement-mode MOSFET cross-section
- P-type substrate is used, with two heavily doped n-type regions
- A thin, electrically insulating, oxide layer is grown over the substrate surface between the two n-type regions.
- Layers of metallization or poly-silicon allow connection to external conductors.
- Applying sufficient positive voltage from gate to source induces an n-type channel in the p-type body.
- The voltage to form a conducting channel is the threshold voltage.
- Additional positive gate-source voltage increases mobile negative charge density.
- Current typically flows from the drain to the source in n-channel FET applications.
- The channel's mobile negative charge density is controlled by an electric field from the gate to source voltage.
- The gate and channel act as plates, with the oxide as an insulating dielectric, working as a parallel plate capacitor.
Operation of MOSFET
- n-channel Enhancement-type MOSFET is highlighted: Vgs < Vthreshold shows 'capacitor like operation"
- p-channel Enhancement-type MOSFET is highlighted: Vgs = 0V shows Implanted p-channel
Important Terminology
- Threshold Voltage: Minimum voltage to switch on the MOSFET.
- Saturation Region: Area where the drain current maintains a constant value
- Channel & Inversion layer:
- Electric field near gate attracts electrons near oxide and creates the channel.
- Electron accumulation near the oxide forms an inversion layer.
- Electron density near the oxide determines channel current; a larger gate-source voltage means a larger electron density at the gate.
Enhancement Mode vs. Depletion Mode
- Depletion Type MOSFET: A gate voltage must be applied to deplete the channel region in order to turn off the transistor
- Enhancement Type MOSFET: Conduction between source and drain regions is enhanced by applying a gate voltage
- Enhancement Type (normally OFF device): a voltage must be applied to the gate to ON the MOSFET
- Depletion Type (normally ON device): a voltage must be applied to the gate to OFF the MOSFET
Why N-Channel Enhancement Mode is Preferred?
| MOSFET Type | VGS <<< 0 | VGS = 0 | VGS >> 0 |
|---|---|---|---|
| N-channel Enhancement | OFF | OFF | ON |
| N-channel Depletion | OFF | ON | ON |
| P-channel Enhancement | ON | OFF | OFF |
| P-channel Depletion | ON | ON | OFF |
MOSFET Characteristics
- Output Characteristics/Current-Voltage Characteristics/Drain Characteristics: the plot drawn between output voltage (VDS) and output current (ID)
- When VGS < VTH, ID = 0
- When VGS > VTH, if a potential difference is created between drain and source (VDS), current (ID) flows through the output if a potential difference is created between drain and source (VDS)
- For small VDS, drain current increases linearly
- For larger VDS, drain current gets saturated
- Three operating regions:
- Cut-Off Region: MOSFET is OFF with no current flow, behaving like an open switch.
- VGS < VTH, ID = 0; VDS = VDD
- Ohmic or Linear Region: Current ID increases with VDS.
- VGS > VTH, VDS < VDS(sat), MOSFETs are used as resistors.
- Saturation Region: Current IDs is constant despite increases in VDS, occurring once VDS exceeds the pinch-off voltage.
- VGS > VTH, VDS > VDS (sat), The device acts like a closed switch.
- Cut-Off Region: MOSFET is OFF with no current flow, behaving like an open switch.
Current-Voltage Characteristic Equation
- ID = (1/2) * μnCox * (W/L) * (VGS - VTN)^2
- K, is MOSFET transconduction parameter in (AV-2), which is the function of electric and geometric parameters
- constant for a given fabrication technology.
- Cox is oxide capacitance per unit area
- µn is the mobility of electrons in the inversion layer
- Ratio of channel width (W) to channel length (L) - W/L is variable in the design of MOSFETs
- VGS is the input (Gate-Source) voltage
- VDs is the output (Drain-Source) voltage
- VTN (or VTH) is the threshold voltage.
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