The document discusses transistors and BJT amplifiers. It provides information on different types of transistors including BJT and FET. It then focuses on BJT, explaining that BJTs are of two types - NPN and PNP. It discusses common emitter amplifiers, noting that they have medium voltage gain but high power gain. It also discusses the input and output characteristics of BJTs and common emitter amplifiers.

3. Transistor And Its Types
1. BJT
2. FET

4. 1) BJT is a type of transistor.
2) BJTs are of two types namely NPN & PNP.
3) BJTs will consume more power in the on-state.It
cannot switch with less than a 0.3v voltage drop.
4) BJTs are preferred for low -current applications.
5) BJTs is liable for thermal runway (over heating) due to
a negative temperature co-efficient.
6) BJTs are used where we need high & fast response.
7) BJTs have a higher cutoff frequency & a higher
maximum current than FETs.
8) Current moves between E,B,C.
1) Transistor is a semi-conducting device which amplifies &
switches input signal.
2) Transistors are broadly divided into three types : BJTs,FETs
& IGBTs.
3) Transistor’s will consume more power in the on-state &
preferred in wide line or load variations.
4) Transistor’s preferred in low- current & low -voltage
applications.
5) Transistor have a positive temperature co-efficient &
stopping thermal runway & sometime liable for thermal
runway due to a negative temperature co-efficient.
6) Transistor have low medium gain & sometime high gain.
7) Transistors are preferred in high frequency applications.
8) Current moves between E,B,C for BJTs & source & drain
for FETs.

8. BJT AMPLIFIER
BJT Class B Amplifier
Class B Amplifier operation has zero DC bias as the
transistors are biased at the cut-off, so each transistor
only conducts when the input signal is greater than
the Base-emitter voltage. Therefore, at zero input
there is zero output and no power is being consumed.

9. We have already discussed BJT as a transistor, now we’re going to discuss
BJT as an amplifier .
So, let’s see.
• What is an amplifier?
• An amplifier is an electronic device that increases
the voltage, current, or power of a signal. Amplifiers
are used in wireless communications and
broadcasting, and in audio equipment of all kinds.
They can be categorized as either weak-signal
amplifiers or power amplifiers.
Characteristics of Common Emitter Amplifier
The voltage gain of a common emitter amplifier is medium.
The power gain is high in the common emitter amplifier.
There is a phase relationship of 180 degrees in input and
output.
In the common emitter amplifier, the input and output
resistors are medium.
The characteristics graph between the bias and the gain is
shown below.

10. • Input Impedance of an Amplifier
The Input Impedance of an amplifier defines its input characteristics with
regards to current and voltage looking into an amplifiers input terminals Input
Impedance, ZIN or Input Resistance as it is often called, is an important
parameter in the design of a transistor amplifier and as such allows amplifiers
to be characterized according to their effective input and output impedances
as well as their power and current ratings.
• Output Impedance of an Amplifier
The Output Impedance of an amplifier can be thought of as
being the impedance (or resistance) that the load sees “looking
back” into the amplifier when the input is zero. Working on the
same principle as we did for the input impedance, the
generalised formula for the output impedance can be given
as: ZOUT = VCE/IC.

11. What is the output characteristics of BJT?
The output characteristics of BJT can be divided into
three areas – cut-off, saturation and active region. In
the cut-off region both collector-base and emitter-
base pn-junctions are reverse-biased – transistor is
off.
What is the input characteristics of BJT?
Input is between the base and emitter. The output is
between the collector and emitter. Input
characteristics are the variation of base current (IB)
with the base-emitter voltage (VBE).

12. The common emitter amplifiers are used in the low-frequency voltage
amplifiers.
These amplifiers are used typically in the RF circuits.
In general, the amplifiers are used in the Low noise amplifiers.
The common emitter circuit is popular because it’s well-suited for voltage
amplification, especially at low frequencies.
Common-emitter amplifiers are also used in radio frequency transceiver
circuits.
Common emitter configuration commonly used in low-noise amplifiers.

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