Transistor amplifiers come in various forms and are powered by AC signals. This variant is the only method of presenting the common emitter amplifier circuit to operate between two peak values since it can be switched between positive and negative values. The biasing amplifier is a crucial amplifier design procedure that determines the precise working point of a transistor amplifier that is prepared to accept signals, hence minimizing output signal distortion.
What are Bipolar Junction Transistors?
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| Bipolar Transistor Construction Image used courtesy of electronic-tutorial |
Bipolar Transistor Configurations
Since the bipolar transistor has three terminals, it can be
connected to an electronic circuit in essentially three different ways, with
one terminal serving as the common terminal for both the input and output
signals. Since the transistor's static properties change depending on the
circuit configuration, each connection technique reacts differently to its
input signal.
- The common base configuration lacks current gain but provides voltage gain.
- Both current and voltage gain are present in the common emitter configuration.
- The common collector configuration lacks voltage gain but offers current gain.
What is an Amplifier?
An electronic circuit called an amplifier is used to boost
the voltage, current, or power of a weak input signal. Amplification is the
process by which a weak signal is made stronger. The most crucial restriction
throughout the amplification process is that the signal's magnitude should only
rise; the original signal's form should remain unchanged. A key element in this
case is the transistor (BJT, FET). The first step when using a transistor as an
amplifier is to decide on the best configuration for the device. To obtain the
appropriate Q-point, the transistor should then be biased. Gain is obtained by
applying the signal to the amplifier's input.
What is a Common Emitter Amplifier?
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| Common Emitter Amplifier Circuit Image used courtesy of electronic-tutorial |
Common Emitter Amplifier Configuration
Three different transistor configurations are employed in
electronic circuit design: common emitter, common base, and common collector.
Because of its primary characteristics, the most widely used is the common
emitter. In this type of amplifier, the base terminal receives the signal,
while the circuit's collector terminal receives the output. However, as the
name implies, the emitter circuit's primary characteristic is the same for both
the input and the output. The majority of electronic circuit designs make
extensive use of the common emitter transistor layout. Although this
arrangement is equally suitable for PNP and NPN transistors, NPN transistors
are utilized more often because of their extensive application. The BJT's
emitter is shared by the input and output signals in a common emitter amplifier
configuration, as seen below. For a PNP transistor, the setup is the same, but
the bias will be reversed in comparison to an NPN transistor.
Working Principle of Common Emitter Amplifier
The forward bias across the emitter-base junction rises
throughout the upper half cycle when a signal is applied across it. As a
result, the collector current rises as more electrons go through the base from
the emitter to the collector. More voltage drops across the collector load
resistor RC as the collector current increases. The forward bias voltage across
the emitter-base junction is reduced during the negative half cycle. The
collector current in the entire collector resistor Rc reduces as the collector-base
voltage drops. As a result, the collector resistor is across the amplified load
resistor. The circuit for the common emitter amplifier is displayed above. It
is evident from the CE circuit's voltage waveforms that the input
and output waveforms have a 180-degree phase shift.
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| Common Emitter Circuit Image used courtesy of elprocus |
The common emitter amplifier circuit is depicted in the circuit diagram below. It uses voltage divider biasing to provide the base bias voltage as needed. A potential divider with two resistors connected so that the midway is used to supply base bias voltage is part of the voltage divider biasing. The common emitter amplifier has various electronic components, including The RL resistor, also known as the load resistance, is used at the output; the R1 resistor is used for the forward bias, and the R2 resistor is used for the development of bias. The purpose of the RE resistor is thermal stability.
The C1 capacitor, also referred to as the coupling capacitor, is utilized to isolate the AC signals from the DC biasing voltage. The figure displays the properties of a common emitter amplifier transistor in terms of bias versus gain. Since R1 and bias are inversely proportional, an increase in the R2 resistor results in a rise in the forward bias. A tiny base current flows when the alternating current is applied to the transistor's base in the common emitter amplifier circuit.
Thus, with the aid of the RC resistance, a
significant quantity of current flows through the collector. Because the value
is so large and ranges from 4 to 10 kohm, the voltage close to the resistance
RC will fluctuate. Common emitter transistors function as amplifier circuits
because of the enormous amount of current that is present in the collector
circuit, which amplifies the weak signal.
Advantages
- The common emitter amplifier is an inverting amplifier with a low input impedance.
- This amplifier has a high output impedance.
- When paired with medium voltage and current gain, this amplifier exhibits the highest power gain.
- The common emitter amplifier has a large current gain.
Disadvantages
- The common emitter amplifier does not react at high frequencies.
- This amplifier's voltage gain is erratic.
- These amplifiers have a very high output resistance.
- There is significant thermal instability with these amplifiers.
- Increased output resistance
Applications
- Low-frequency voltage amplifiers employ common emitter amplifiers.
- RF circuits are the usual application for these amplifiers.
- Generally speaking, low-noise amplifiers use the amplifiers.
- Because it works well for voltage amplification, particularly at low frequencies, the common emitter circuit is often used.
- Circuits for radio frequency transceivers also use common-emitter amplifiers.
- Low-noise amplifiers frequently use a common emitter arrangement.
Conclusion
This kind of bipolar transistor design has a much lower voltage gain than the conventional base configuration, but it has a higher input impedance, current, and power gain. An inverting amplifier circuit is the common emitter arrangement. This indicates that there is a 180-degree phase shift between the output signal and the input voltage signal. Transistors are used as analog signal amplifiers because of their analog current control capabilities. It significantly affects electronic technologies.
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