Transcript JFET DC Biasing - Brookdale Community College

JFET Biasing
ENGI 242/ELEC 222
JFET Fixed Bias
VGG + IGRG + VGS = 0
Since IG = 0
VGS = - VGG
RG is present to limit current
in case VGG is connected
with wrong polarity
This would forward bias the
gate-source junction causing
high currents, which would
destroy the transistor
Since GS is
reverse biased, IG
= 0 and VRG = 0
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DC Analysis for JFET Fixed Bias Network
VGS 

ID = IDSS  1 
VP 

2
VGS = - VGG
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JFET Fixed Bias Plotting Shockley’s Equation
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JFET Fixed Bias Graphical Solution
VGS 

ID = IDSS  1 
V
P


2
Since VGS = - VGG
VGG 

ID = IDSS  1 
V
P


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2
JFET Fixed Bias
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Graphical Solution for JFET Fixed Bias
VGS 

ID = IDSS  1 
VP 

2
VGG 

ID = IDSS  1 
VP 

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JFET Self Bias Configuration
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JFET Self Bias DC Equivalent Circuit
IG = 0
VRG = 0
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Transconductance Curve
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JFET Self Bias Load Line
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JFET Self Bias
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JFET Self Bias Transconductance Curve
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Graphical Solution of JFET Self Bias
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JFET Self Bias Effect on Variation of RS
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Self Bias
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JFET Voltage Divider Bias
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JFET Voltage Divider Bias DC Analysis
Input
 R2 
VG = VDD 

R
1
+
R
2


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Output
-VG + VGS + IDRS = 0
VGS = VG - IDRS
ENGI 242/ELEC 222
VDS = VDD - ID (RD + RS)
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JFET Voltage Divider Bias Load Line
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The Effect of RS on Q-point
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JFET Voltage Divider Bias
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JFET Voltage Divider Bias Q-point
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Voltage Divider Bias
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MOSFET Biasing
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D-MOSFET Self Bias
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Determining the Q-point for D-MOSFET Self Bias
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N Channel D-MOSFET Voltage Divider Bias
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Q Point of D-MOSFET Voltage Divider Bias
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Effect on Change in Q Point with Variation of RS
With an N Channel
D-MOSFET,
VGS may be positive
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D-MOSFET Fixed Bias
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E-MOSFET Feedback Bias
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DC Equivalent For the E-MOSFET Feedback Bias
IG = 0
VGS = VDS
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Transfer Curve for the E-MOSFET Feedback Bias
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Determining the Q-point for E-MOSFET Feedback Bias
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Q-point for the E-MOSFET Fixed Bias
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EMOS Feedback Bias Example
VGSTH = 4V
VGSon = 7.5V
IDon = 5mA
VDD = 22V
k=
IDon
(VGSon - VGSTH)2
ID = k(VGS - VGSTH)2
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EMOS Feedback Example
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Voltage Divider Bias for an N E-MOSFET
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Q-point for E-MOSFET Voltage Divider Bias
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