Electronic Devices
Final Term
Lecture - 07
Reference book:
Electronic Devices and Circuit Theory
(Chapter-7)
Robert L. Boylestad and L. Nashelsky , (11th Edition)
Faculty of Engineering
American International University-Bangladesh
SELF-BIAS EXAMPLE Contd.
• Plot the transfer curve using IDSS and VP using shorthand method:
VGS ID
0 IDSS
0.3VP IDSS/2
0.5VP IDSS/4
VP 0mA
Faculty of Engineering
American International University-Bangladesh
SELF-BIAS EXAMPLE Contd.
• Superimpose the load line on top of the transfer curve:
Faculty of Engineering
American International University-Bangladesh
JFET: VOLTAGE-DIVIDER BIAS
• The source VDD was separated into two equivalent sources to permit a further
separation of the input and output regions of the network.
• Since IG = 0A, Kirchoff’s current law requires that IR1= IR2 and the series equivalent
circuit appearing to the left of the figure can be used to find the level of VG.
Faculty of Engineering
American International University-Bangladesh
VOLTAGE-DIVIDER BIAS
• VG can be found using the voltage divider rule:
RV
VG 2 DD
R1 R2
• Using Kirchoff’s Law on the input loop:
VD VDD I D RD VDS VDD I D ( RD RS )
VS I D RS VGS VG I D RS
• Rearranging and using ID =IS:
VDD
I R1 I R 2
R1 R2
• Again the Q point needs to be established by plotting
a line that intersects the transfer curve.
Faculty of Engineering
American International University-Bangladesh
VOLTAGE-DIVIDER BIAS
• Graphical Approach ( to find VGSQ and IDQ):
• Plot a line for:
» VGS = VG when ID = 0A
» VGS = 0V when ID = VG/RS.
• Plot the transfer curve using IDSS and VP using shorthand method.
• The Q-point is located at the intersection.
VGS ID
0 IDSS
0.3VP IDSS/2 VGS VG I D RS
0.5VP IDSS/4
VP 0mA
Faculty of Engineering
American International University-Bangladesh
EFFECT OF INCREASING VALUES OF RS
Faculty of Engineering
American International University-Bangladesh
JFET: VOLTAGE-DIVIDER BIAS EXAMPLE
• Determine IDQ, VGSQ, VD, VS, VDS and VDG.
R2VDD
VG VGS VG I D RS
R1 R2
VDS VDD I D ( RD RS )
VGSQ 1.8V I DQ 2.4mA
VD 10.24V VS 3.6V
VDS 6.64V VDG 8.24V
Faculty of Engineering
American International University-Bangladesh
VOLTAGE-DIVIDER BIAS EXAMPLE Contd.
• Graphical Approach ( to find VGSQ and IDQ):
• Plot a line for:
» VGS = VG when ID = 0A
» VGS = 0V when ID = VG/RS.
• Plot the transfer curve using IDSS and VP
using shorthand method.
• Identify the Q-point.
VS I D RS
R2VDD
VG
R1 R2
VDS VDD I D ( RD RS )
VGS VG I D RS VDS VD VS
VD VDD I D RD VDG VD VG
Faculty of Engineering
American International University-Bangladesh
D-MOSFET SELF-BIAS
• D-MOSFET bias circuits are similar to
JFETs.
• The only difference is that D-MOSFETs can
operate with positive values of VGS and with
ID values that exceed IDSS.
IG 0A ID IS
VGS 2
ID IDSS(1 )
VP
Faculty of Engineering
American International University-Bangladesh
D-MOSFET SELF-BIAS
• Graphical Approach (to find VGSQ and IDQ):
• Plot the transfer curve using IDSS and VP using
shorthand method.
• Plot ID vs VGS using VGS = -IDRS.
• Take a positive value of VGS and find the ID value
using
VGS 2
ID IDSS(1 )
VP
• The Q-point is located at the intersection.
Faculty of Engineering
American International University-Bangladesh
D-MOSFET SELF-BIAS EXAMPLE
• Determine the IDQ, VGSQ and VD.
• Graphical Approach (to find VGSQ and IDQ):
• Plot the transfer curve using IDSS and VP
using shorthand method.
• Take a positive value of VGS and find the ID
value using
VGS 2
ID IDSS(1 )
VP
• Plot ID vs VGS using VGS = -IDRS.
• Identify the intersection Q-point.
Faculty of Engineering
American International University-Bangladesh
D-MOSFET SELF-BIAS EXAMPLE
VD VDD I D RD VGS 2
ID IDSS(1 )
VP
VGSQ = -4.3 V
IDQ = 1.7 mA
VGS
ID
VD = 9.46 V RS
Faculty of Engineering
American International University-Bangladesh
D-MOSFET VOLTAGE-DIVIDER BIAS
• D-MOSFET bias circuits are similar to JFETs.
IG 0A ID IS
VGS 2
ID IDSS(1 )
VP
Faculty of Engineering
American International University-Bangladesh
D-MOSFET VOLTAGE-DIVIDER BIAS
• Graphical Approach (to find VGSQ and IDQ):
• Plot the transfer curve using IDSS and VP using
shorthand method.
• Take a positive value of VGS and find the ID
value using
VGS 2
ID IDSS(1 )
VP
• Plot ID vs VGS using VGS = VG - IDRS.
• The Q-point is located at the intersection.
Faculty of Engineering
American International University-Bangladesh
End of Lecture-7
Faculty of Engineering
American International University-Bangladesh
