Analog Electronics II Week 4 Chp 2 (Dc Biasing) Cont'

8/14/2019 Analog Electronics II Week 4 Chp 2 (Dc Biasing) Cont'

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Mohd Shawal JadinMohd Shawal Jadin

ANALOG ELECTRONICS II

FET DC BIASING- Review & ContinueFET DC BIASING- Review & Continue


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ANALOG ELECTRONICS II - BEE2233 FKEE UMP

Learning Objectives

1

2

Describe various configuration of FET biasing1

Analyze various configuration of FET biasing.2

Upon completion of the chapter the student

should be able to:


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Group Discussion

Form a group of 5-6Write : your group and

members nameAnswer all questions in 7minutes for eachquestion

10 marks per question +

bonusANALOG ELECTRONICS II - BEE2233 FKEE UMP


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Find:

VGSQ, IDQ

VG

VD

VDS

VS

IG

Example 1


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Calculate the value of VDS

Example 2


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What is the new

value of RD

when there is 7

V across VDS?

Example 3


7/22ANALOG ELECTRONICS II - BEE2233 FKEE UMP

Given the valuesof VDQ and IDQ for

this circuit,

determine therequired values

of RD

and RS

.

Example 4


8/22ANALOG ELECTRONICS II - BEE2233 FKEE UMP

Determine thequiescent values

of ID and VGS.

Example 5


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o age- v er asCalculations


Using Kirchhoff's Law:

Rearranging and using ID

=IS:

Again the Q point needsto be established by

plotting a line that

intersects the transfer

curve.


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Voltage-Divider Q-point


1. Plot the line: By plotting two points: VGS

= VG, I

D=0 and V

GS= 0, I

D= V

G/R

S

2. Plot the transfer curve by plotting IDSS, VP and calculated values of ID.3. Where the line intersects the transfer curve is the Q point for the circuit.


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o age- v er asCalculations


Using the value of ID at the Q-point, solve forthe other variables in the Voltage-Divider

Bias circuit:


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Test yourself..

Find IDQ and VGSQ


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Exercise..

Determine Q-point for JFET


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Exercise..For what value of R

Dis the

voltage across VDS zero?


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Depletion-Type MOSFETs


Depletion-typeMOSFET bias circuits

are similar to JFETs.

The only difference is

that the depletion-Type MOSFETs can

operate with positive

values of VGS

and

with ID

values that

exceed IDSS

.


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The dc analysisSame as the FET calculations

Plotting the transfer characteristics of the device Plotting the at a point that VGS exceeds the 0V or more

positive values Plotting point when VGS=0VandID=0A The intersection between Shockley characteristics and

linear characteristics defined the Q-point of the MOSFET

The problem is that how long does thetransfer characteristics have to be draw? We have to analyze the input loop parameter relationship. As RS become smaller, the linear characteristics will be in

narrow slope therefore needs to consider the extend oftransfer characteristics for example of voltage dividerMOSFET,

The bigger values of VP the more positive values we shoulddraw for the transfer characteristics

SDGGS

RSGSG

RIVV

VVV

=

= 0

A l i th MOSFET i it f


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Analyzing the MOSFET circuit forDC analysis

How to analyze dcanalysis for theshown network?

It is a . Typenetwork Find VG or VGS Draw the linear

characteristics Draw the transfer

characteristics Obtain VGSQ and IDQ

from the graph

intersection


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Plot line for VGS = VG, ID = 0 and ID =VG/RS, VGS = 0.

Plot the transfer curve by plottingIDSS, VP and calculated values of ID.

5. Where the line intersects the transfer

curve is the Q-point.

Use the ID at the Q-point to solve for

the other variables in the voltage-divider bias circuit. These are the

same calculations as used by a JFET

circuit.


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When RS changethe linear characteristics will change..

Plot line for VGS = VG, ID = 0

and ID = VG/RS, VGS = 0 Plot the transfer curve by

plotting IDSS, VP and

calculated values of ID.

Where the line intersects thetransfer curve is the Q-

point.

Use the ID at the Q-point to

solve for the other variablesin the voltage-divider bias

circuit. These are the same

calculations as used by a

JFET circuit.


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Mohd Shawal JadinMohd Shawal Jadin

Analog Electronics II Week 4 Chp 2 (Dc Biasing) Cont'

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