FET Flashcards
What defines the operating conditions of a current-controlled device?
A current defines the operating conditions
In contrast, a voltage-controlled device is defined by a specific voltage.
What is a unique feature of the JFET regarding its operation?
It can be used as a voltage-controlled resistor
This is due to the sensitivity of the drain-to-source impedance to the gate-to-source voltage.
What is the maximum current for any JFET labeled as?
I DSS
It occurs when VGS = 0 V.
At what condition does the minimum current for a JFET occur?
At pinch-off defined by VGS = VP
VP is the pinch-off voltage.
What type of relationship exists between the drain current and the gate-to-source voltage of a JFET?
A nonlinear relationship defined by Shockley’s equation
The sensitivity of ID to changes in VGS increases as the current level approaches IDSS.
What do the transfer characteristics (ID versus VGS) represent?
Characteristics of the device itself
They are not sensitive to the network in which the JFET is employed.
What is the value of ID when VGS = VP/2?
ID = IDSS/4
At ID = IDSS/2, VGS = 0.3 V.
How are maximum operating conditions determined for a JFET?
By the product of the drain-to-source voltage and the drain current
What are the two types of MOSFETs?
- Depletion
- Enhancement
How does the transfer characteristic of a depletion-type MOSFET compare to a JFET?
It has the same transfer characteristics for drain currents up to IDSS
Beyond IDSS, the characteristics of a depletion-type MOSFET continue, while those of a JFET end.
What direction does the arrow in the symbol of n-channel JFETs or MOSFETs point?
Into the center of the symbol
For p-channel devices, the arrow points out of the center.
What defines the transfer characteristics of an enhancement-type MOSFET?
A nonlinear equation controlled by the gate-to-source voltage, threshold voltage, and a constant k
The constant k is approximately 0.3 milli A/V^2.
What happens to the plot of ID versus VGS for an enhancement-type MOSFET?
It rises exponentially with increasing values of VGS
What precautions should be taken when handling MOSFETs?
Handle with additional care due to static electricity
Do not remove any shorting mechanism between the leads until the device is installed.
What is a CMOS device?
A complementary MOSFET device employing a combination of p-channel and n-channel MOSFET
It has high input impedance, fast switching speeds, and low operating power levels.
What is one effective use of the complementary arrangement (CMOS)?
As an inverter
What input voltage turns the nMOS (N-CHANNEL ENHANCEMENT MOSFET) on?
5 V
An input of 0 V leaves it off.
What input voltage turns the pMOS (P-CHANNEL MOSFET) on?
-5 V
VGS = 0 V leaves it off.
What is the operation of a CMOS Circuit when Vi = 0 V?
Q1 = off, Q2 = on, Vo = 5 V
What is the operation of a CMOS Circuit when Vi = 5 V?
Q1 = on, Q2 = off, Vo = 0 V
What is a BiFET circuit?
A combination of BJT and JFET with JFET transistors at the inputs and bipolar transistors for current source
What does the current mirror in a BiFET circuit ensure?
Each JFET is operated at the same bias current
What advantage does the BiMOS unit provide over the BiFET?
Higher input impedance due to the use of MOSFET transistors
What type of circuit can be built using complementary MOSFET transistors?
Differential amplifier circuit
