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‫הרצאה ‪4 #‬‬
‫מעגלים משולבי דיודה ‪ -‬תכונות ויישומים‬
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‫מקורות‪:‬‬
‫‪Sedra/smith: sec 3.6 P172-176‬‬
‫‪Opto-electric diodes – data sheets‬‬
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Zener diodes
Zener diodes designed specifically for operation in
reverse breakdown.
• They can handle large currents, hence they are
physically larger.
Point on I-V curve where breakdown
occurs called Zener knee (-VZK, -IZK)
Figure 4-1
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Reverse-Breakdown Region – Modeling
Vz=Vzo+rzIz
Figure 4-2
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Zener Example
Zener Diode is characterized by:
- VZ0 = 5.5V
- rz=40Ω incremental resistance
calculate the output voltage VO.
Figure 4-3
Solution
1) Replace Zener with model
2) Perform circuit analysis by
solving for I in the network
3) Compute Vo
Figure 4-4
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Example - 2
The 6.8-V zener diode in circuit Figure 4-5 (a) is specified to have
VZ = 6.8 V at IZ = 5mA, rZ =20, and IZK= 0.2mA.
The supply voltage V+ is nominally 10V, but can vary by +/- 1 V.
Figure 4-5
 (a)Find VO with no load and V+ at its nominal value.
 (b)Find the change in VO resulting from +/- 1V change in V+.
 (c)Find the change in VO resulting from connecting a load RL =
2 k.
 (d)Find the value of VO when RL = 0.5k.
 (e)What is the minimum value of RL for which the diode still
operates in the breakdown region?
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Photodiodes
Figure 4-6: Large Area SI Detector packaged in a T05 Can
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Rise Time: 20ns (Measured With 50 Load & 12V Bias)
Active Area: 13mm2 (3.6 X 3.6mm)
NEP W/Hz: 1.2 (10-14) Wv-Hz
Dark Current: 20nA
Spectral Range: 350-1100nm
Figure 4-7
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Figure 4-8: Spectral Responsivity of Si Photodiode
Si, Ge,GaAs and its compounds, e.g. InxGa1-xAs Indium Gallium
Arsenide, are the materials used in the field of opto-electronics.
Diodes that can convert photons to electrons, ie light to current, are
called photodiodes
The PV photodiodes uses the pn junction to separate the electron
and hole carriers generated by the light
The PC photodiodes is basically a resistor whose carrier
concentrations are increased when light particles (photons) are
absorbed in the material.
The increase in carriers results in increased conductance and
current flow
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Light Emitting Diodes (LED):
An LED is a special PN junction which emits
monochromatic light when operated in a forward biased
direction
Figure 4-9
LED’s forward voltage drop is about 1.1 to 1.5 Volts.
Shorter wavelength diodes have the largest voltage drops.
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bandgap energy Eg of the LED:
Eg=hc/λ = 1240eV-nm/ λ
Where:
h = Plank's Constant = 4.13 x 10-15 eV•s
c = speed of light = 2.998 x 108 m/s
λ = wavelength in nm
Material
Gallium Phosphide
Aluminum Arsenide
Gallium Arsenide
Indium Phosphide
Aluminum-Gallium
Arsenide
Indium-Gallium-ArsenidePhosphide
Formula
GaP
AIAs
GaAs
InP
Energy Gap
2.24 eV
2.09 eV
1.42 eV
1.33 eV
Wavelength
550 nm
590 nm
870 nm
930 nm
AIGaAs
1.42-1.61 eV
770-870 nm
InGaAsP
0.74-1.13 eV
1100-1670 nm
LEDs spontaneous emission based on direct band-to-band
transitions, or through impurity states
Figure 4-10
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LIGHT EMITTER PERFORMANCE CHARACTERISTICS
Peak Wavelength: This is the wavelength at which the
source emits the most power.
Spectral Width: light is emitted in a range of wavelengths
centered at the peak wavelength.
Emission Pattern.
Speed: Rise or fall time
Emission Power:
Figure 4-11: Optical Output vs. Current in a LED
Linearity represents the degree to which the optical output
is directly proportional to the electrical current input.
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