finals-JFET Flashcards
is a 3 terminal semiconductor device in which current conducted by one type of carrier i.e. by electron or hole.
JFET
4 main Parts of JFET Device
1) Source
2) Drain
3) Gate
4) Channel
terminal which majority carriers enter into the channel is called ________ terminal __
Source, S
terminal which majority carriers leave from the channel is called ________ terminal __
Drain, D
There are two internally connected heavily-doped impurity regions to create two P-N junctions. These impurity regions are called the _______ terminal __
Gate, G
The region between the source and drain, sandwiched between the two gates is called the ________
Channel
in JFET, n-type region between the p regions offers a _________________
resistance to current flow
in JFET, the resistance varies with the voltage applied to ___________
gate terminal VG
FET has 3 terminals:
Basic Operation of JFET
Gate (G), Drain (D) and Source (S)
in n-channel FET, ____ and ____ are connected to n-channel and ____ is connected to the p-type material
Basic Operation of JFET
Drain and Source, Gate
The voltage applied at gate terminal controls the current flow between the other two terminals;
Basic Operation of JFET
Source and Drain
it can be thought of as a resistance connected between Source and Drain, which is a function of the gate voltage VG
Basic Operation of JFET
FET
varies in different types of FETs
Basic Operation of JFET
mechanism of gate control
in operation of JFET, a reverse voltage is applied to the:
Basic Operation of JFET
Gate and Forward voltage between Drain and Source
2 Basic Operation of JFET:
1) VG=0V and VDS=0V
2) VG=0V and VDS is +ve
There occurs a ________ at the p-n junction as the electrons from n-channel combine with holes from p-gate
Basic Operation of JFET
depletion region
since no voltages are applied, the depletion regions are of:
Basic Operation of JFET
equal thickness and symmetrical
is zero as VD is 0V wrt source
Basic Operation of JFET
Drain current ID
VG=0V and VDS is increased from 0 to a more:
Basic Operation of JFET
positive voltage
the depletion region between p-gate and n-channel ____ as more electrons from n-channel combine with holes from p-gate
Basic Operation of JFET
increases
increasing the depletion region;
Basic Operation of JFET
1) decreases - size of n-channel which;
2) increases - resistance of the n-channel
Though the resistance of the channel increases with increasing VDS, the ____ doesn’t decrease, rather it increases because drain voltage wet source increases
Basic Operation of JFET
current ID
being larger at the drain end than at the source end
Basic Operation of JFET
wedge shaped depletion regions
it is the curve between drain current (ID) and drain-source voltage (VDS) for different gate-source voltage (VGS)
JFET
IV Characteristic Curve
after pinch off voltage the drain current become constant, this constant level is known as ___________
JFET
Saturation Level
The region behind the pinch off voltage where the drain current increase rapidly is known as ____________
JFET
Ohmic Region
it is the region, when the drain-source voltage (VDS) is high enough to cause the JFET’s resistive channel to breakdown and pass uncontrolled maximum current
Breakdown Region
The gate-source voltage, when the drain current become zero is called cut-off voltage. Denoted as VGS(off)
Cutoff Region
a linear region, JFET behaves like an ordinary resistor
REGIONS OF JFET ACTION
Ohmic Region
the Saturation Region, JFET operates as a constant current device. The JFET is used as an amplifier in this region
REGIONS OF JFET ACTION
Pinch Off Region
If VDS is increased beyond its avalanche breakdown voltage. Id increases to an excessive value.
REGIONS OF JFET ACTION
Breakdown Region
Two depletion regions touch each other, channel width is zero, ID is zero.
VGS (off) = -Vp
REGIONS OF JFET ACTION
Cut Off Region
3 JFET Modes of Operation
1) Common Source (CS) Configuration
2) Common Gate (CG) Configuration
3) Common Drain (CD) Configuration
- Most common modes of operation
- High input impedance
- High voltage gain
- Used in audio frequency amplifier
- Output signal 180o “out-of-phase” with the input
JFET Modes of Operation
Common Source (CS) Configuration
- Input terminal: Source
- Output terminal: Drain
- Low input impedance
- High output impedance
- Used in high frequency and in impedance matching circuits
- Output signal 0 degrees “In-phase” with the input
JFET Modes of Operation
Common Gate (CG) Configuration
- Input terminal: Gate
- Output terminal: Source
- High input impedance
- Low output impedance
- Near-unity voltage gain
- Used in buffer amplifiers, also called source follower
- Output signal 0 degrees “In-phase” with the input
Common Drain (CD) Configuration
3 Biasing Circuits used for JFET
1) Fixed Bias Circuit
2) Self Bias Circuit
3) Potential Divider Bias Circuit
