These slides are about MOSFET digital Switching

1. MOSFET
DIGITALSWITCHING
Presented to:
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Presented by:
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2. Jens Martensson
In this topic, we’ll discuss about:
• What is MOSFET?
• Construction of MOSFET
• Working of MOSFET
• CMOS (p-MOS & n-MOS)
• Function as NAND Gate.
• Function as NOR Gate.
• Comparison of MOSFET & BJT.
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3. Jens Martensson
What is MOSFET?
• A metal–oxide–semiconductor field effect transistor.
• It is used for switching or amplifying signals.
• The ability to control voltage.
• MOSFET’s are now even more common than BJT in digital and
analog circuits.
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MOSFET Structure

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p-region
n-region
Source Drain
Gate
Body
Construction of
MOSFET
1. Source & Body Internally connected
2. Connected to Ground & equal to 0V.

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Holes
Electrons
𝑣𝐺𝑆
Working of MOSFET

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Holes
Electrons
𝑣𝐺𝑆
Electric Field
𝑣𝐷𝑆
𝐼𝐷
Working of MOSFET

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C-MOS (p-MOS & n-MOS)
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Circuit p-MOS working
• It combines n-MOS and p-MOS in a series.
• Consume a little DC power.
• One of the channel is always “off”, as MOSFET’s are used in
series.
• When the MOSFETs are switching, there is current for a very short
time because both transistors are on during this very short
transition from one state to the other.
• Also known as inverter in digital electronics.

8. Jens Martensson
Function as NAND Gate
• Two additional MOSFETs.
• Q2 is connected in parallel with Q1
• Q3 is connected in series with Q4.
• When both inputs, VA and VB = 0, Q1 and Q2 are “on” while Q4
and Q3 are “off”, making Vout VDD.
• When both inputs = VDD, Q1 and Q2 are “off” while Q4 and Q3 are
“on”, making Vout 0.
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Table (NAND Gate operation)
Circuit

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Function as NOR Gate
• Two additional MOSFETs
• Q1 is connected in parallel with Q2
• Q3 is connected in series with Q4.
• When both inputs, VA and VB = 0, Q1 and Q2 are “on” while Q3 and
Q4 are “off”, making Vout VDD.
• When both inputs = VDD, Q1 and Q2 are “off” while Q3 and Q4 are
“on”, making Vout 0.
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Table (NOR Gate operation)
Circuit

10. Jens Martensson
Comparison of MOSFET & BJT
MOSFET
• Voltage controlled.
• Positive temperature coefficient.
• Turn-off faster than BJT.
• Low power-loss.
BJT
• Only power transistor before MOSFET.
• Requires base current to turn on, relatively slow-
off characteristics.
• Negative temperature coefficient.
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Uses of MOSFET
Power MOSFETs are used for:
• Motor control.
• AC-to-AC conversion.
• DC-to-DC conversion.
• Load switching.

11. Thank You