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JFET Biasing
ELEC 121
January 2004 ELEC 121 2
JFET Fixed Bias
RG is present to limit current in case VGG is connected with wrong polarityThis 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
GS
GG G G
GG
GS
G
V + I R + V = 0
Sin
V = -
ce I =
V
0
January 2004 ELEC 121 3
DC Analysis for JFET Fixed Bias Network
2GS
D DSSP
VI = I 1 -
V
GS GGV = - V
January 2004 ELEC 121 4
JFET Fixed Bias Plotting Shockley’s Equation
January 2004 ELEC 121 5
JFET Fixed Bias Graphical Solution
GS GG
2GS
D DSSP
2GG
D DSSP
Since V = - V
V I = I 1 -
V
V I = I 1 -
V
January 2004 ELEC 121 6
JFET Fixed Bias
January 2004 ELEC 121 7
Graphical Solution for JFET Fixed Bias
2GS
D DSSP
2GG
D DSSP
V I = I 1 -
V
V I = I 1 -
V
January 2004 ELEC 121 8
JFET Self Bias Configuration
January 2004 ELEC 121 9
JFET Self Bias DC Equivalent Circuit
VRG = 0
IG = 0
January 2004 ELEC 121 10
Transconductance Curve
January 2004 ELEC 121 11
JFET Self Bias Load Line
January 2004 ELEC 121 12
JFET Self Bias
January 2004 ELEC 121 13
JFET Self Bias Transconductance Curve
January 2004 ELEC 121 14
Graphical Solution of JFET Self Bias
January 2004 ELEC 121 15
JFET Self Bias Effect on Variation of RS
January 2004 ELEC 121 16
Self Bias
January 2004 ELEC 121 17
JFET Voltage Divider Bias
January 2004 ELEC 121 18
JFET Voltage Divider Bias DC Analysis
Input Output
2G DD
1 2
R V = V
R + R DS DD D D SV = V - I (R + R )G D G GS D S
GS G D S
-V + I R + V + I R = 0
V = V - I R
January 2004 ELEC 121 19
JFET Voltage Divider Bias Load Line
January 2004 ELEC 121 20
The Effect of RS on Q-point
January 2004 ELEC 121 21
JFET Voltage Divider Bias
January 2004 ELEC 121 22
JFET Voltage Divider Bias Q-point
January 2004 ELEC 121 23
Voltage Divider Bias
January 2004 ELEC 121 24
JFET Self Bias with Dual Supply
January 2004 ELEC 121 25
Determination of Q-point for Self Bias with Dual Supply
January 2004 ELEC 121 26
Common Gate JFET Self Bias
January 2004 ELEC 121 27
Common Gate JFET Self Bias DC Bias Circuit
January 2004 ELEC 121 28
Common Gate JFET Self Bias
