2. BJT
Common Emitter & Collector Curve
Presentation Topic:-
Zeeshan Rafique (16201519-026)
Muhammad Abbas (16201519-001)
Muhammad Umar (16201519-099)
Zaid Khalid (16201519-106)
Developed By: Zeeshan Rafiq
3. COMMON EMITTER
• It is called common-emitter configuration since :
- emitter is common or reference to both input and output
terminals.
- emitter is usually the terminal closest to or at ground
potential.
• Almost amplifier design is using connection of CE due to
the high gain for current and voltage.
• Two set of characteristics are necessary to describe the
behavior for CE ;input (base terminal) and output
(collector terminal) parameters.
• This circuit has two loops. The Left Loop is the base
loop & the right loop is the collector loop.
• Note: The current relation are still applicable
IE=IC+IB & IC= b IB
Developed By: Zeeshan Rafiq
4. Input
characteristics:- Input takes the form of a forward biased pn
junction.
Input characteristics are therefore similar to those
of a semiconductor diode.
Output
Characteristics:-
Input characteristics Graph
The magnitude of IB in micro ampere and not as horizontal as IE in
common-base circuit.
The output set relates an output current IC to an output voltage VCE for
various level of input current IB.
There are three portions as shown in Next Slides:-
Developed By: Zeeshan Rafiq
5. COMMON EMITTER
• Active Region:
The active region, located at upper-right quadrant,
has the greatest linearity.()
The curve for IB are nearly straight and equally
spaced.
In active Region, B-E junction is forward Biased..
• Cutoff Region
The region below IB =0UA is defined as cutoff region.
• Saturation Region
The small portion near the ordinate, is the
saturation region, which should be avoided for linear
amplification
In the dc mode, the level of IC and IB at the operation
point are related by: Normally B ranges from 40 to
400
Active Region
Saturationregion
Collector output Graph
Developed By: Zeeshan Rafiq
6. Common Emitter Configuration (Base
Biases)
• In the base loop, the VBB source biased the emitter
diode with RB as a current limiting resistance.
• By changing VBB or RB ,we can change the base
current. So base current will change the collector
current.
• It means that small current(BASE) will produce large
current (Collector).
• In the collector loop, a source voltage VCC reverse
biases the collector diode through RC .
Double scripts notation is used with transistor circuit.
When the subscript is same, represent a
source(VCC)(VBB)
Single scripts are used for node voltages, that is,
voltages between the subscript point and
ground(reference).
In CE (BaseBiase) Connection, dc current gain beta exist
which can be change overall output.
By applying simple KVL, we can find Output VoltagesAt input side:
IB =
VBB - VBE
RB
Now at Output
side:
VCE=VCC-ICRC & .’. IC=BIB
Developed By: Zeeshan Rafiq
7. Current Gain Beta dependency:-
• Itself transistor
• Collector Current
• Temperature
Due to Beta dependency in Base Bias we avoid some
case to use in it amplifier circuit.
So we use another configuration.
Developed By: Zeeshan Rafiq
8. Common Emitter Configuration (Emitter Bias)
• Digital circuits are the type of circuits used in
computers. In this area, Base bias and circuits derived
from base bias are useful.
• But when it comes to amplifiers, we need circuits whose
Q points are immune to changes in current gain.
• As you can see, the resistor moved from base circuit to
the emitter circuit. That one make change all over the
world. Q point have greater less effect due to current
gain
• BASIC IDEA
• Base supply voltage directly applied to base and trouble
shooter will read VBB BW Base and Ground.
• Now emitter is above the ground and has a voltage given
by:
VE=VBB-VBE IE=( VBB-VBE
) R
E
• Now we Find Collector Voltage By KVL at output
sideVCE=VCC-IC(RC+RE)
IE=~ IC
IC=( VBB-VBE )
R
E
We can draw from this formula a load line Developed By: Zeeshan Rafiq
9. Minor effect of Current Gain factor
• This current gain has minor effect on the collector current. Under
applying all operating conditions, the three currents are related by:
• IE=IC+IB
Which can be rearranged as:
IE=IC+(IC+IC/Bdc )
Developed By: Zeeshan Rafiq
10. COLLECTOR CURVE
This set of curves is also called a family of curves.
• When VCE is zero, the collector diode is not
reverse bias. This is why, graph shows a collector
current of zero when VCE is zero.
• When VCE is increasing from Zero, the collector
current rises sharply.
• When VCE is few tenths of a volts, the collector
current becomes almost constant and equal to
1mA.
Developed By: Zeeshan Rafiq
