Electronics Spring 2020 Ran Yang http://physics.wm.edu/~ran/ Lecture v
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E lectron ics
S p r i n g 2 0 2 0 R a n Ya n g
http://physics.wm.edu/~ran/
L e c t u r e v
What are we doing
every week?
Design
• Pre-lab Homework
• Lecture
Simulation
• Pre-lab Homework
• Lecture
Build in real world
• Lab
Trouble Shooting
• Lab
• Simulation
Midterm Exam
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• We do have class on 3/2 Monday
• We do have lab 6 on 3/3, 3/4 and 3/5
• The exam will happen in the first 50 minutes of the lab 6
• Talk to me if you have accommodation pleaseTime
• Lab 1 to Lab 5 homework/lab , Textbook Chapter 1 to 7, and Chapter 14
• As long as you understand your design homework and your lab procedure you are good to go
• Circuit design, Circuit analysis & troubleshooting and physics/mathContents
• Closed book & closed notes
• A pencil, an eraser and a ruler
• A scientific calculator with its battery full
• If you use a scientific calculator on your phone, the phone must be set to airplane mode
• I do not provide a formula sheet
Rules
Trans i s to r
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• The bottom region is called the emitter
• the middle region is the base
• the top region is the collector
A transistor has three doped regions
• the base region is much thinner as compared to the collector and emitter regions.
• npn device
• Recall that the majority carriers are free electrons in n-type material and holes in p-type material.
an actual transistor
• the emitter is heavily doped.
• the base is lightly doped.
• The doping level of the collector is intermediate
• The collector is physically the largest of the three regions
Doping
Trans i s to r
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• Some of the free electrons in the n region will diffuse across the junction and recombine with the holes in the p region.
• Visualize the free electrons in each n region crossing the junction and recombining with holes.
• For each of these depletion layers, the barrier potential is approximately 0.7 V at 25°C
Depletion layer
B iased Trans i s to r
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• When the subscripts are the same, the voltage represents a source (𝑉𝐵𝐵 𝑎𝑛𝑑 𝑉𝐶𝐶).
• When the subscripts are different, the voltage is between the two points (𝑉𝐵𝐸 , 𝑉𝐶𝐸).
Double Subscripts
• Single subscripts are used for node voltages, that is, voltages between the sub-scripted point and ground
• 𝑉𝐶𝐸 = 𝑉𝐶 − 𝑉𝐸• 𝑉𝐶𝐵 = 𝑉𝐶 − 𝑉𝐵• 𝑉𝐵𝐸 = 𝑉𝐵 − 𝑉𝐸
Signal subscripts
Trans i s to r cu r ren t s
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• When the subscripts are the same, the voltage represents a source (𝑉𝐵𝐵 𝑎𝑛𝑑 𝑉𝐶𝐶).
• When the subscripts are different, the voltage is between the two points (𝑉𝐵𝐸 , 𝑉𝐶𝐸 ).
Double Subscripts
• Single subscripts are used for node voltages, that is, voltages between the sub-scripted point and ground
•𝑉𝐶𝐸 = 𝑉𝐶 − 𝑉𝐸•𝑉𝐶𝐵 = 𝑉𝐶 − 𝑉𝐵•𝑉𝐵𝐸 = 𝑉𝐵 − 𝑉𝐸
Signal subscripts
Current
Beta
B iased Trans i s to r Cur ren t
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• When the subscripts are the same, the voltage represents a source (𝑉𝐵𝐵 𝑎𝑛𝑑 𝑉𝐶𝐶).
• When the subscripts are different, the voltage is between the two points (𝑉𝐵𝐸 , 𝑉𝐶𝐸).
Double Subscripts
• Single subscripts are used for node voltages, that is, voltages between the sub-scripted point and ground
• 𝑉𝐶𝐸 = 𝑉𝐶 − 𝑉𝐸• 𝑉𝐶𝐵 = 𝑉𝐶 − 𝑉𝐵• 𝑉𝐵𝐸 = 𝑉𝐵 − 𝑉𝐸
Signal subscripts
• 𝑉𝐸 =
𝐼𝐵 =
Trans i s to r Operat ion
Ran Yang || [email protected]
• the voltage represents a source (𝑉𝐵𝐵 𝑎𝑛𝑑 𝑉𝐶𝐶).
• the voltage is between the two points (𝑉𝐵𝐸 , 𝑉𝐶𝐸).
Double Subscripts
• Single subscripts are used for node voltages, that is, voltages between the sub-scripted point and ground
• 𝑉𝐶𝐸 = 𝑉𝐶 − 𝑉𝐸• 𝑉𝐶𝐵 = 𝑉𝐶 − 𝑉𝐵• 𝑉𝐵𝐸 = 𝑉𝐵 − 𝑉𝐸
Signal subscripts
𝐼𝐵 =𝑉𝐵𝐵 − 𝑉𝐵𝐸
𝑅𝐵
𝑉𝐶𝐸 = 𝑉𝐶𝐶 − 𝐼𝐶𝑅𝐶
• the region in the middle where VCE is between 1 and 40 V.
• the emitter diode is forward biased, and the collector diode is reverse biased.
• the collector is gathering almost all the electrons that the emitter has sent into the base. This is why changes in collector voltage have no effect on the collector current. This region is called the active region.
• the collector current is constant in this region.
Active Region - Normal operation
• The transistor should never operate in this region
• because it will be destroyed
Breakdown Region
• the early rising part of the curve, where VCE is between 0 V and a few tenths of a volt.
• the collector diode has insufficient positive voltage to collect all the free electrons injected into the base.
• In this region, the base current IB is larger than normal and the current gain 𝛽 is smaller than normal
Saturation Region
Trans i s to r Operat ion
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Active Region - Normal operation
Breakdown Region
Saturation Region
• Notice that the base current is zero, but there still is a small collector current.
• On a curve tracer, this current is usually so small that you cannot see it. We have exaggerated the bottom curve by drawing it larger than usual.
• This bottom curve is called the cutoff region of the transistor, and the small collector current is called the collector cutoff current.
Cutoff Region
Trans i s to r Operat ion Reg ions
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• Amplifier
• the active region is called the linear region because changes in the input signal produce proportional changes in the output signal.
Active Region
• Never
Breakdown Region
• Digital switching
Saturation Region / Cutoff Region
VDB des ign gu ide l i ne
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Operation point Q at the middle of the load line
W h a t h a ve we l e a r n e d
t o d ay ?
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What’s a transistor
Transistor biasing
Emitter biasing
LED driver – current source
VDB
VDB design tips
What t o s t udy fo r n ex t week ?R e a d C h a p t e r 8 a n d 9
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Review Lab 1 to Lab 5
Basic BJT AmplifiersSmall-Signal operation
Analyzing an Amplifier
Voltage gainThe loading effect of input impedance
CC amplifier Output impedance
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