Upload
nayeli-rosemond
View
265
Download
9
Tags:
Embed Size (px)
Citation preview
1
JFET
Bollen
2
AGENDA
Bollen
JFETOverviewJFET vs BJTPhysical structureWorkingInput parametersDC formulaOutput parametersTransconductanceAc parametersSimulatioin parameters micro cap
JFETFixed biasSelf biasVoltage divider biasMOSTFETComponentDCac
3
J-FET
Bollen
FET =
Field
Effect
Transistor
N-channel
or
P-channel
4
J-FET, OVERVIEW
Bollen
5
JFET vs BJT
Bollen
6
J-FET vs BJT
Bollen
7
Physical structure
Bollen
There is one PN junction from gate to channel used in REVERSE
8
JFET working
Bollen
9
JFET working
Bollen
10
JFET input parameters
Bollen
Vp and Idss
In data sheet
p =
pinch-off
dss =
drain source shorted or saturated
= maximum current
11
JFET DC formula
Bollen
2
1 gsds dss
p
UI I
U
ID
0–VGS
10 mA
8.0
6.0
4.0
2.0
(mA)
1 2 3 4
10dssI mA
4pU Volt
Solve with abc formula
12
JFET Output parameters
Bollen Uds < Up = ohmic region, Uds > Up = saturated region
13
JFET
Bollen
JFET
is not often used in the ohmic (triode) region
If so it is used as an variable resistor
14
JFET output
Bollen
15
JFET output
Bollen
16
JFET transconductance
Bollen
17
JFET transconductance
Bollen
18
JFET ac parameters
Bollen
2
1
p
gsdssds U
UII
V
mA
U
Ig
gs
dsm
dss
ds
p
dssm I
I
U
Ig
2
3,33mg mS or mmho or m
19
JFET simulation parameters micro cap
Bollen
pto VV
2p
dss
U
Ibeta
VTO Threshold voltage
BETA Transconductance parameter
20
JFET fixed bias
Bollen
Steady Ugs,
no variation possible,
so we make the same effect with resistors. U = I . R
Now we can vary around the bias point
21
JFET self bias
Bollen
Ug = 0 volt, NO gate current
Ugs = Ug – Us = 0 – Ids.Rs
Rin = 1 Meg Ohm
2
1
p
gsdssds U
UII
22
JFET self bias
Bollen
Varying Rs
= varying the Q-point
= operating point
23
JFET voltage divider bias
Bollen
Ug 0 volt
Ugs = Ug – Us
= Vg – Ids.Rs,
bias is made at
GATE and SOURCE
24
MOSFET
Bollen
Metal
Oxide
Silicium
Field
Effect
Transistor
25
MOSFET
Bollen
2
2p
ds gs TH
K WI V V
L
gs
th
W with m
L length m
V gate source voltage
V treshold voltage
2tan /
ds
p
I FET drain current mA
K transconduc ce parameter mA V
26
MOSFET
Bollen
2
2p
ds gs TH
K WI V V
L
27
MOSFET dc
Bollen
2
2p
ds gs TH
K WI V V
L
28
MOSFET ac
Bollen
m p gs TH
Wg K V V
L