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When it comes to amplifier configurations, the common-emitter configuration is one of the most popular. This type of amplifier is found in a variety of applications, from audio amplifiers to power amplifiers. In this blog post, we will take a look at the common-emitter configuration and discuss some of its key features.
What is a Common Emitter Configuration?
The common emitter configuration is one of the three basic single-stage amplifier topologies. It is so named because the emitter terminal of the transistor serves as the circuit node common to both input and output signals. The other two basic configurations are common base and common collector. Of these, the common-emitter topology offers several distinct advantages:
Common emitters have higher current gain than either common collectors or common bases.
Common emitters offer superior voltage gain to common collectors and vice versa.
Common emitters are easier to impedance match to a load than either common collectors or common bases.
Key Features of Common Emitter Configuration
There are several key features of the common-emitter configuration that make it so popular:
The gain of a common emitter amplifier is determined by the transistor’s beta (β). The higher the beta, the higher the gain. Common emitters have high input impedance and low output impedance. This makes them ideal for use as voltage amplifiers. Common emitters are typically used in amplification stages where a large voltage gain is required. One of the main disadvantages of common emitter amplifiers is that they are subject to parasitic effects such as capacitive coupling and feedback. These effects can reduce the overall performance of the amplifier. Another disadvantage is that common emitters tend to be less stable than other amplifier topologies.
Common Emitter Configuration Examples
Now that we’ve discussed some key features of the common-emitter configuration, let’s take a look at a few examples.
One of the most popular applications for common emitters is audio amplification. Audio amplifiers are typically used to amplify low-level signals, such as those from a microphone or music player. Common emitters are also used in power amplifiers. Power amplifiers are used to amplify high-power signals, such as those from a radio transmitter. Another common application for common emitters is voltage amplification. Voltage amplifiers are used to amplify low-voltage signals, such as those from a sensor or thermocouple.
As you can see, the common-emitter configuration has a wide range of applications. Whether you’re looking for an amplifier for audio, power, or voltage amplification, the common emitter is a great option.
Common Emitter Transistor
The transistor is the key active component in a common-emitter amplifier circuit. Two types of transistors can be used in this type of amplifier: Bipolar Junction Transistors (BJTs) and Field effect transistors (FETs). BJTs are the most popular type of transistor for use in common-emitter amplifiers. This is because they have a high current gain (β). FETs can also be used in common-emitter amplifiers, but their performance is not as good as BJTs.
There are two types of BJT transistors: NPN and PNP. NPN transistors are the most commonly used type in amplifier circuits. PNP transistors can also be used, but they are less common.
The transistor in a common-emitter amplifier circuit is biassed using a voltage divider circuit. This type of biassing arrangement is known as self-biassing. The voltage divider bias circuit consists of two resistors: a base resistor (Rb) and an emitter resistor (Re). The base resistor is connected between the transistor’s base terminal and the positive power supply voltage. The emitter resistor is connected between the transistor’s emitter terminal and the ground.
The two resistors in the voltage divider circuit are chosen so that they provide the correct amount of bias current to the transistor. The bias current is the current that flows through the transistor’s base-emitter junction. The amount of bias current required depends on the transistor’s beta value.
The voltage divider circuit also provides a DC path for the AC signal to ground. This is known as a bypass capacitor (Cb). The bypass capacitor is connected between the transistor’s base terminal and the ground.
The value of the bypass capacitor is chosen so that it has a low impedance at the transistor’s operating frequency. This allows the AC signal to bypass the resistor divider circuit and flow directly to ground.
Conclusion
Overall, the common-emitter configuration is a versatile and widely used amplifier circuit. By understanding the basics of how it works, you can use it to build amplifiers for a variety of applications. With a little practice, you’ll be able to design and build your common-emitter amplifiers with ease.
