Common emitter amplifier schematic symbol
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There are different types of transistor amplifiers operated by using an AC signal input. This is interchanged between the positive value and negative value, hence this is the one way of presenting the common emitter amplifier circuit to function between two peak values. This process is known as the biasing amplifier and it is an important amplifier design to establish the exact operating point of a transistor amplifier which is ready to receive the signals hence it can reduce any distortion to the output signal.
In this article, we will discuss common emitter amplifier analysis. The Amplifier is an electronic circuit that is used to increase the strength of a weak input signal in terms of voltage, current, or power. The process of increasing the strength of a weak signal is known as Amplification. One most important constraint during the amplification is that only the magnitude of the signal should increase and there should be no changes in the original signal shape.
When a transistor is used as an amplifier, the first step is to choose an appropriate configuration, in which the device is to be used. Then, the transistor should be biased to get the desired Q-point. The signal is applied to the amplifier input and output gain is achieved. The common emitter amplifier is a three basic single-stage bipolar junction transistor and is used as a voltage amplifier. The input of this amplifier is taken from the base terminal, the output is collected from the collector terminal and the emitter terminal is common for both the terminals.
The basic symbol of the common emitter amplifier is shown below. In electronic circuit design, there are three kinds of transistor configurations are used like common emitter, common base, and common collector, In that, the most frequently used one is common emitter due to its main attributes.
This kind of amplifier includes the signal which is given to the base terminal then the output is received from the collector terminal of the circuit. But, as the name suggests, the main attribute of the emitter circuit is familiar for both the input as well as output. The configuration of a common emitter transistor is widely used in most electronic circuit designs. This configuration is evenly appropriate to both the transistors like PNP and NPN transistors but NPN transistors are most frequently used due to the widespread use of these transistors.
The arrangement is the same for a PNP transistor , but bias will be opposite w. When a signal is applied across the emitter-base junction, the forward bias across this junction increases during the upper half cycle.
This leads to an increase in the flow of electrons from the emitter to a collector through the base, hence increases the collector current. The increasing collector current makes more voltage drops across the collector load resistor RC. The negative half cycle decreases the forward bias voltage across the emitter-base junction. The decreasing collector-base voltage decreases the collector current in the whole collector resistor Rc.
Thus, the amplified load resistor appears across the collector resistor. The common emitter amplifier circuit is shown above. From the voltage waveforms for the CE circuit shown in Fig. The below circuit diagram shows the working of the common emitter amplifier circuit and it consists of voltage divider biasing, used to supply the base bias voltage as per the necessity. The voltage divider biasing has a potential divider with two resistors are connected in a way that the midpoint is used for supplying base bias voltage.
There are different types of electronic components in the common emitter amplifier which are R1 resistor is used for the forward bias, the R2 resistor is used for the development of bias, the RL resistor is used at the output it is called the load resistance. The RE resistor is used for thermal stability.
The C1 capacitor is used to separate the AC signals from the DC biasing voltage and the capacitor is known as the coupling capacitor. The alternating current is applied to the base of the transistor of the common emitter amplifier circuit then there is a flow of small base current. Hence there is a large amount of current flow through the collector with the help of the RC resistance. The voltage near the resistance RC will change because the value is very high and the values are from 4 to 10kohm.
Hence there is a huge amount of current present in the collector circuit which amplified from the weak signal, therefore common emitter transistors work as an amplifier circuit. The current gain of the common emitter amplifier is defined as the ratio of change in collector current to the change in base current.
The voltage gain is defined as the product of the current gain and the ratio of the output resistance of the collector to the input resistance of the base circuits. The following equations show the mathematical expression of the voltage gain and the current gain. The resistances R1, R2, and RE used to form the voltage biasing and stabilization circuit. The biasing circuit needs to establish a proper operating Q-point otherwise, a part of the negative half cycle of the signal may be cut-off in the output.
The capacitor C1 is used to couple the signal to the base terminal of the BJT. If it is not there, the signal source resistance, Rs will come across R2, and hence, it will change the bias. C1 allows only the AC signal to flow but isolates the signal source from R2. If it is not used, then the amplified AC signal following through RE will cause a voltage drop across it, thereby dropping the output voltage.
The coupling capacitor C2 couples one stage of amplification to the next stage. This technique used to isolate the DC bias settings of the two coupled circuits.
The first step in AC analysis of Common Emitter amplifier circuit is to draw the AC equivalent circuit by reducing all DC sources to zero and shorting all the capacitors. The below figure shows the AC equivalent circuit. The next step in the AC analysis is to draw an h-parameter circuit by replacing the transistor in the AC equivalent circuit with its h-parameter model.
The below figure shows the h-parameter equivalent circuit for the CE circuit. The voltage gain of a CE amplifier varies with signal frequency. It is because the reactance of the capacitors in the circuit changes with signal frequency and hence affects the output voltage.
The curve drawn between voltage gain and the signal frequency of an amplifier is known as frequency response. The below figure shows the frequency response of a typical CE amplifier. Moreover, CE cannot shunt the RE effectively because of its large reactance at low frequencies. These two factors cause a drops off of voltage gain at low frequencies. This increases the loading effect of the amplifier stage and serves to reduce the voltage gain. Moreover, at high frequencies, the capacitive reactance of base-emitters junction is low which increases the base current.
Due to these two reasons, the voltage gain drops off at a high frequency. The effect of the coupling capacitor C2 in this frequency range is such as to maintain a constant voltage gain. Thus, as the frequency increases in this range, the reactance of CC decreases, which tends to increase the gain.
However, at the same time, lower reactance means higher almost cancel each other, resulting in a uniform fair at mid-frequency. So from this, we can decide the voltage gain for any sinusoidal input in a given range of frequency. The frequency response of a logarithmic presentation is the Bode diagram. Most of the audio amplifiers have a flat frequency response that ranges from 20 Hz — 20 kHz.
For an audio amplifier, the frequency range is known as Bandwidth. These frequency points are also known as decibel points. So the BW can be defined as. This reduction within gain is known commonly as the roll-off section of the frequency response curve. So, the order of the circuit is multiplied with these values. After that, we can properly say that the frequency point is also the frequency at which the gain of the system has reduced to 0. The circuit diagram of the common emitter transistor amplifier has a common configuration and it is a standard format of transistor circuit whereas voltage gain is desired.
The common emitter amplifier is also converted as an inverting amplifier. The different types of configurations in transistor amplifiers are common base and the common collector transistor and the figure are shown in the following circuits. The characteristics graph between the bias and the gain is shown below.
The Vcc supply voltage will determine the utmost Ic collector current once the transistor is activated. So a small change within the base current will make a huge change within the collector current. So one transistor may include a Beta value whereas another may include of Beta value, however, both the transistors are NPN BC transistors because Beta is a feature of the structure of the transistor but not of its function.
The emitter current Ie is nothing but the voltage across the emitter resistor. In any electronic circuit design, impedance levels are one of the main attributes that need to consider. The impedance or resistance level comes from the truth that the output is used from the collector terminal because there is a reverse-biased junction. The single-stage common emitter amplifier is shown below and different circuit elements with their functions are described below.
This capacitor will allow simply AC signal to supply. The connection of the emitter bypass capacitor can be done in parallel to RE to give a low reactance lane toward the amplified AC signal. Once a weak input AC signal is given toward the base terminal of the transistor, then a small amount of base current will supply, because of this transistor act, high AC.
Thus, a feeble signal is applied toward the base terminal which appears in the amplified form within the collector circuit. Its characteristics can be drawn on both the axis like a frequency on X-axis whereas voltage gain is on Y-axis.
The graph of frequency response can be attained which is shown in the characteristics. So we can observe that the gain of this amplifier can be decreased at very high and low frequencies, however, it stays stable over an extensive range of mid-frequency area. The fL or low cut off frequency can be defined as when the frequency is below 1.
The range of frequency can be decided at which the amplifier gain is double the gain of mid-frequency. The CE amplifier is one of the main configurations of a transistor amplifier. Suppose, the learner has some knowledge on the theory of transistor amplifier like the use of AC equivalent circuits. To determine the output impedance, these measurements can be used. Design the circuit accordingly and check all the above calculations. Utilize DC coupling as well as dual-trace on the oscilloscope.
Evaluate the outcomes using your Pre-lab computations. This article discusses the working of the common emitter amplifier circuit.
Common emitter amplifier
Electrical Academia. Amplifier Definition: An amplifier is an electronic device that uses a small input signal voltage or current to control a larger output signal. This principle works best when the output load, or impedance , of the circuit, is greater than the input load. Examine Figure 1.
Common emitter configuration of BJT
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. According to the Wikipedia page for common emitter amplifiers, the addition of an emitter resistor decreased the gain of the circuit. Why then does the resistor reduce the gain? Please note I am very new to transistor circuits, and to electronics in general. When cut off, the collector current is zero. When saturated, the base current is high, and VCE is small. These are the two modes when using a transistor as a switch.
Common emitter amplifier
The Application Activity in this section involves a preamplifier circuit for a public address system. The complete system includes the preamplifier, a power amplifier, and a dc power supply. You will focus on the preamplifier in this section and then on the power amplifier in Section 7. The things you learned about biasing a transistor in Section 5 are now applied in this section where bipolar junction transistor BJT circuits are used as small-signal amplifiers.
Common emitter
MediaSpace Videos. A BJT can be wired into a circuit in many different ways. One way to use it as an amplifier or switch is to connect it in the common emitter configuration. In the common emitter configuration, the input port of the BJT is the connection from base to emitter. In the common emitter configuration, the output port of the BJT is the connection from collector to emitter. But instead of treating circuit analysis as a math problem, let us develop intuition about these models.
Common emitter
The common emitter circuit is probably the most widely used transistor configuration. The emitter electrode is common to both input and output circuits. The common emitter amplifier has a typical input impedance of 1kilo ohms and a typical output impedance of 10 kilo-ohms. This results in a remarkable overall performance. The common emitter amplifier circuit comprises of a voltage divider bias and coupling capacitor C B and C C at the input and output and a bypass capacitor C E which is connected from the emitter to the ground. The capacitor C B couples the input signal to the input port of the amplifier.
Transistor Common Emitter Amplifier
In electronics , a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor BJT amplifier topologies, typically used as a voltage amplifier. In this circuit the base terminal of the transistor serves as the input, the collector is the output, and the emitter is common to both for example, it may be tied to ground reference or a power supply rail , hence its name. The analogous field-effect transistor circuit is the common-source amplifier , and the analogous tube circuit is the common-cathode amplifier.
Common Emitter Amplifier Circuit Working & Its Characteristics
RELATED VIDEO: Design And Build A Common Emitter AmplifierTransistor Circuit Design Tutorial Includes: Transistor circuit design Circuit configurations Common emitter Common emitter circuit design Emitter follower Common base See also: Transistor circuit types The common emitter transistor amplifier circuit is one of the mainstay circuits for use within electronic circuit design offering many advantages. The common emitter circuit configuration is used in many areas of electronic circuit design: as an audio amplifier, as a basic switch for logic circuits, as a general analogue amplifier and in many other applications. The common emitter circuit configuration provides voltage gain combined with a moderate current gain, as well as a medium input and a medium output impedance. As such the common emitter configuration is a good all round circuit for use in many applications. It is also worth noting at this stage that the common emitter transistor amplifier inverts the signal at the input.
This voltage phase shift can be explained as follows:. The ac emitter resistance of a transistor is a dynamic value like zener impedance that is used only in ac calculations. For a small-signal amplifier, the value of. The process used to determine the value of is demonstrated in Example 9. The ac current gain of a transistor is different than its dc current gain.
What I'm struggling with is to understand intuitively what all those resistance are making. Everytime I think about it, everything seems too intricate and coupled. What I'm asking is an intuitive explanation of how to solve this circuit, but it is maybe a bad question for StackExchange, I'm not sure. One way to visualize this fact is that the emitter "follows" the base.
If I were you, I would have gone the other way.
As a specialist, I can help. Together we can come to the right answer.