# UNIT III  Switching characteristics of Devices

1.Define rise time for transistor.

Ans: It is the time required for the collector current (output) to rise from 10% to 90% of the IC(sat)(maximum current).

2.Define storage time for transistor.

Ans: It is the time interval between the instant at input IB=0and the instant when output IC has fallen to 90% of its max value.

3.Define fall time for transistor.

Ans: The time required for output (IC) to fall from 90%  to 10% of maximum value(IC(sat))  is termed as fall time.

4.Define delay time for transistor.

Ans: This is the time interval between the application of base current (input) and commencement of collector current(Output) is called delay time.

Or

It is the time required for the output current(IC ­)  to rise from 0 to 10% of the steady state output( IC(sat)).

5. Draw the piece wise linear characteristics of diode.

6.What is the principle of sampling gate.

Ans: It is transmission circuit which allows an input signal to pass through it during a selected time interval and blocks its passage outside of this time interval. The interval of time selected by gate signal. It is generally a rectangular pulse. It uses either series switch or parallel switch.

7.What is sampling  gate.

Ans: It is transmission circuit which allows an input signal to pass through it during a selected time interval and blocks its passage outside of this time interval.

8.What are the different types of sampling gates.

Ans: There two types sampling gates

1. Unidirectional sampling gates

2. Bi-directional sampling gates

We can design by using diode or transistor.

9.What is the difference between uni-directional and bi-directional sampling gate.

Ans: . Unidirectional sampling gate transmits signal of only one polarity. Where as Bi-directional sampling gate can transmit signal of both polarities

10.What are the temperature dependent parameters of transistor.

Ans: Forward current gain (hfe ), Reverse saturation current
(Ic0) and Cut in voltage (VBE).

11. What are the other names of sampling gates.

Ans: Sampling gates can also called as time selection gates, linear gate and transmission gate.

12.What is the difference between sampling gate and logic gate.

Ans: The output of sampling gate is same as input for selected time interval where as logic gate is pulse or voltage level which produced depends on Boolean algebra.

13.Explain how diode works as switch.

Ans:Diode in forward bias acts as closed switch and diode in reverse bias acts as open switch.

14.Explain how transistor works as switch.

Ans: Transistor in saturation region acts as closed switch and transistor in cutoff region acts as open switch.

• Updated
Feb 08, 2016
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