Electronic devices: 2 marks

1. Define the term hybrid parameters. A transistor can be treated as a two part network. The terminal behavior of any

two part network can be specified by the terminal voltages V1 & V2 at parts 1 & 2 respectively and current i1 and i2, entering parts 1 & 2, respectively, as shown in figure.

Of these four variables V1, V2, i1 and i2, two can be selected as independent variables and the remaining two can be expressed in terms of these independent variables. In Hybrid parameters the input current i1 and output Voltage V2 are takes as independent variables, the input voltage V1 and output current i2 can be written as

V1 = h11 i1 + h12 V2

i2 = h21 i1 + h22 V2

The four hybrid parameters h11, h12, h21 and h22 are defined as follows.

h11 = [V1 / i1] with V2 = 0

= Input Impedance with output part short circuited.

h22 = [i2 / V2] with i1 = 0

= Output admittance with input part open circuited.

h12 = [V1 / V2] with i1 = 0

= reverse voltage transfer ratio with input part open circuited.

h21 = [i2 / i1] with V2 = 0

= Forward current gain with output part short circuited.

2. Draw the hybrid PI model for CE configuration.The hybrid-pi model is a popular circuit model used for analyzing the small

signal behavior of bipolar junction and field effect transistors. Sometimes it is also called "Giacoletto model" because it was introduced by L.J. Giacoletto.

3. In which regions the transistor is used as a switch.Transistor will act as a switch only in Cut-off & Saturation regions. Since

in the cutoff region the transistor will become completely OFF & in the saturation region there is maximum current flow (i.e.) completely ON. Hence the transistor will behave like a switch (ON & OFF) in these regions.

4. What is the use of heat sink?In electronic systems, a heat sink is a passive heat exchanger that cools a device

by dissipating heat into the surrounding medium. In computers, heat sinks are used to cool central processing units or graphics processors. Heat sinks are used with high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light emitting diodes (LEDs), where the heat dissipation ability of the basic device is insufficient to moderate its temperature.

5. Define the term field effect transistor.The FET is a device in which the flow of current through the conducting region is

controlled by an electric field. Hence the name Field Effect Transistor (FET). As current conduction is only by majority carriers, FET is said to be a unipolar device. Based on the

construction, the FET can be classified into two types: Junction FET (JFET) & Metal Oxide Semiconductor FET (MOSFET).

6. Compare FET and Transistor.FET BJT (Transistor)

1. FET is a unipolar device 1.BJT is a Bipolar device2. FET consumes less power 2. It consumes large power compared

to FET3. FET function as voltage regulators as applied voltage on gate control the output characteristics

3. BJT function as regulators of currents as small current is regulating a large current.

4. FET have a positive temperature coefficient, stopping thermal runaway.

4. the Bipolar transistor is liable for thermal runaway due to a negative temperature co-efficient.

5. BJTs are used where high gain & fast response are required.

5. FETs have los-medium gain.

7. Define drain resistance

Drain resistance(rd), is the reciprocal of the slope of the drain characteristics and

is defined by,

rd = (∆VDS/∆ID),VGS held constant.

It is the ratio of a small change in drain voltage to the corresponding small change in the drain current at a constant gate voltage. It has the unit of resistance in ohms.

8. Define mutual conductanceFor an amplifying device, such as a transistor or an electron tube, the ratio of the

change in output current to the change in input current. For example, in a tube, it is the ratio of the change in plate current to the change in grid voltage, with the plate voltage held constant. 

9. What is the difference in gate construction between FET and MOSFET? In MOSFET, gate terminal connected to the substrate through a sio2 insulator

layer. Whereas in JFET, gate terminal will be directly connected to the substrate.

10. Define threshold voltage.Threshold voltage is defined as the minimum voltage that required to make the

transistor ON. The threshold voltage, commonly abbreviated as Vth or VGS (th), of a field-effect transistor(FET) is the minimum gate-to-source voltage differential that is needed to create a conducting path between the source and drain terminals.

11. What is the difference between construction of power MOSFET and MOSFET?A power MOSFET is a specific type of metal oxide semiconductor field-

effect transistor (MOSFET) designed to handle significant power levels. The design of power MOSFETs was made possible by the evolution of CMOS technology,

developed for manufacturing integrated circuits in the late 1970s. The power MOSFET shares its operating principle with its low-power counterpart, the lateral MOSFET.

The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of transistor used for amplifying or switching electronic signals.

Although the MOSFET is a four-terminal device with source (S), gate (G), drain (D), and body (B) terminals,[1] the body (or substrate) of the MOSFET is often connected to the source terminal, making it a three-terminal device like other field-effect transistors.

12. Define intrinsic standoff ratio.It is the ratio of RB1 to the sum of RB1 and RB2. It can be expressed as η = RB1/(RB1+RB2)  or η = RB1/RBBO. The typical range of intrinsic standoff ratio is from 0.4 to 0.8.