EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1...
Transcript of EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1...
![Page 1: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/1.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 1
EDC UNIT IV- Transistor and FET Characteristics
LessonLesson--19: 19: JFET Characteristics JFET Characteristics Quantitative Discussion Quantitative Discussion
![Page 2: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/2.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 2
1. Revision1. Revision
![Page 3: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/3.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 3
Output CharacteristicsOutput Characteristics
![Page 4: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/4.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 4
Output characteristics of an n-channel JFET with the gate short-circuited to the source VGS = 0
![Page 5: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/5.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 5
Quantitative DiscussionQuantitative Discussion
![Page 6: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/6.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 6
Output characteristics of an nOutput characteristics of an n--channel JFET channel JFET with the gate shortwith the gate short--circuited to the sourcecircuited to the source
The initial rise in ID is related to the buildup of the depletion layer as VDS increases.
The curve approaches the level of the limiting current IDSS when ID begins to be pinched off.
The physical meaning of this term leads to one definition of pinch-off voltage, VP , which is the value of VDS at which the maximum IDSS flows.
![Page 7: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/7.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 7
![Page 8: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/8.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 8
Increasing VDS increases the widths of depletion layers, which penetrate more into channel and hence result in more channel narrowing toward the drain.
The resistance of the n-channel, RABtherefore increases with VDS.
The drain current: IDS = VDS/RAB
![Page 9: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/9.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 9
![Page 10: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/10.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 10
JFET Transfer CharacteristicsJFET Transfer Characteristics
![Page 11: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/11.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 11
There is a convenient relationship between IDSand VGS.
Beyond pinch-off
Where IDSS is drain current when VGS= 0 and VGS(off) is defined as –VP, that is gate-source voltage that just pinches off the channel.
The pinch off voltage VP here is a +ve quantity because it was introduced through VDS(sat).
VGS(off) however is negative, -VP.
2
)(
1
offGS
GSDSSDS V
VII
![Page 12: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/12.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 12
Transconductance drain current as a Transconductance drain current as a function of Voltage between gatefunction of Voltage between gate--sourcesource
• Conductance is reciprocal of resistance• D.C. Transconductance Gm = ID ÷
VGS
![Page 13: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/13.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 13
The transconductance curveThe transconductance curve The process for plotting
transconductance curve for a given JFET:
Plot a point that corresponds to value of VGS(off).
Plot a point that corresponds to value of IDSS.
Select 3 or more values of VGSbetween 0 V and VGS(off). For value of VGS, determine the corresponding value of ID from equation for ID
Plot the point from (3) and connect all the plotted point with a smooth curve.
![Page 14: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/14.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 14
![Page 15: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/15.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 15
JFET Biasing CircuitsJFET Biasing Circuits
![Page 16: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/16.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 16
![Page 17: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/17.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 17
Example:Example: Plot the dc bias line for the voltagePlot the dc bias line for the voltage--drivers biasing drivers biasing circuitcircuit
![Page 18: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/18.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 18
SummarySummary
![Page 19: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/19.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 19
We learnt We learnt
The resistance of the n-channel, RABincreases with VDS.
The drain current: IDS = VDS/RAB
![Page 20: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/20.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 20
We learntWe learnt
• Transconductance Gm = ID ÷ VGS• Quantitative Relation
2
)(
1
offGS
GSDSSDS V
VII
![Page 21: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/21.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 21
We learnt• When VGS = 0, ID changes nearly
linearly till pinch-off voltage. After pinch-off voltage the drain-source current remains constant at IDSS.
• When VGS is –ve (for n-JFET) at certain value of VGS, ID does not increase and is 0, transconductance = 0
![Page 22: EDC UNIT IV- Transistor and FET Characteristics Devices... · 2008 EDC Lesson 19- " , Raj Kamal, 1 EDC UNIT IV- Transistor and FET Characteristics Lesson-19: JFET Characteristics](https://reader030.fdocuments.us/reader030/viewer/2022013107/5aef975c7f8b9a572b8e5a46/html5/thumbnails/22.jpg)
2008 EDC Lesson 19- " , Raj Kamal, 22
End of Lesson 19End of Lesson 19