The common emitter amplifier is one of the most widely used configurations in transistor amplifiers. It offers a high current gain, medium input impedance, and medium output impedance, making it suitable for a wide range of applications. In this article, we will delve into the world of common emitter amplifiers and provide a step-by-step guide on how to design one.
Understanding the Common Emitter Amplifier Configuration
The common emitter amplifier configuration is a type of bipolar junction transistor (BJT) amplifier. In this configuration, the emitter is common to both the input and output circuits. The base serves as the input terminal, while the collector serves as the output terminal. The common emitter amplifier is known for its ability to provide a high current gain, making it suitable for applications where a high output current is required.
Advantages of the Common Emitter Amplifier
The common emitter amplifier offers several advantages, including:
- High current gain: The common emitter amplifier is capable of providing a high current gain, making it suitable for applications where a high output current is required.
- Medium input impedance: The common emitter amplifier has a medium input impedance, making it suitable for applications where a medium input impedance is required.
- Medium output impedance: The common emitter amplifier has a medium output impedance, making it suitable for applications where a medium output impedance is required.
Disadvantages of the Common Emitter Amplifier
While the common emitter amplifier offers several advantages, it also has some disadvantages, including:
- Low input resistance: The common emitter amplifier has a low input resistance, making it susceptible to input loading effects.
- High output resistance: The common emitter amplifier has a high output resistance, making it susceptible to output loading effects.
Designing a Common Emitter Amplifier
Designing a common emitter amplifier involves several steps, including:
Step 1: Determine the Operating Point
The first step in designing a common emitter amplifier is to determine the operating point. The operating point is the point at which the transistor operates, and it is determined by the intersection of the load line and the transistor’s characteristic curve. To determine the operating point, we need to know the transistor’s characteristic curve and the load line.
Determining the Transistor’s Characteristic Curve
The transistor’s characteristic curve is a graph that shows the relationship between the collector current and the collector-emitter voltage. The characteristic curve is typically provided by the transistor’s manufacturer and can be found in the transistor’s datasheet.
Determining the Load Line
The load line is a graph that shows the relationship between the collector current and the collector-emitter voltage. The load line is determined by the load resistor and the power supply voltage.
Step 2: Choose the Transistor
Once we have determined the operating point, we can choose the transistor. The transistor should be chosen based on its characteristic curve and the operating point. The transistor should be able to operate at the desired operating point and provide the required current gain.
Step 3: Choose the Load Resistor
The load resistor is used to determine the load line. The load resistor should be chosen based on the desired load line and the operating point. The load resistor should be able to provide the required load impedance and ensure that the transistor operates at the desired operating point.
Step 4: Choose the Biasing Resistors
The biasing resistors are used to establish the operating point. The biasing resistors should be chosen based on the desired operating point and the transistor’s characteristic curve. The biasing resistors should be able to provide the required bias voltage and ensure that the transistor operates at the desired operating point.
Calculating the Component Values
Once we have chosen the transistor, load resistor, and biasing resistors, we can calculate the component values. The component values can be calculated using the following formulas:
- Load resistor: RL = (VCC – VCE) / IC
- Biasing resistors: RB1 = (VCC – VBE) / IB, RB2 = (VCC – VBE) / (IB + IC)
Where:
- RL is the load resistor
- VCC is the power supply voltage
- VCE is the collector-emitter voltage
- IC is the collector current
- RB1 and RB2 are the biasing resistors
- VBE is the base-emitter voltage
- IB is the base current
Example Design
Let’s design a common emitter amplifier using the steps outlined above.
- Determine the operating point: Let’s assume that we want to operate the transistor at a collector current of 10 mA and a collector-emitter voltage of 10 V.
- Choose the transistor: Let’s choose a transistor with a characteristic curve that allows it to operate at the desired operating point. Let’s assume that we choose a transistor with a current gain of 100.
- Choose the load resistor: Let’s choose a load resistor that provides a load impedance of 1 kΩ. Using the formula above, we can calculate the load resistor value: RL = (VCC – VCE) / IC = (20 – 10) / 10 mA = 1 kΩ.
- Choose the biasing resistors: Let’s choose biasing resistors that provide a bias voltage of 0.7 V. Using the formulas above, we can calculate the biasing resistor values: RB1 = (VCC – VBE) / IB = (20 – 0.7) / 0.1 mA = 193 kΩ, RB2 = (VCC – VBE) / (IB + IC) = (20 – 0.7) / (0.1 mA + 10 mA) = 1.9 kΩ.
| Component | Value |
|---|---|
| Load Resistor (RL) | 1 kΩ |
| Biasing Resistor (RB1) | 193 kΩ |
| Biasing Resistor (RB2) | 1.9 kΩ |
Conclusion
Designing a common emitter amplifier involves several steps, including determining the operating point, choosing the transistor, choosing the load resistor, and choosing the biasing resistors. By following these steps and using the formulas outlined above, we can design a common emitter amplifier that meets our requirements. Remember to always check the transistor’s datasheet and characteristic curve to ensure that it can operate at the desired operating point.
What is a Common Emitter Amplifier?
A common emitter amplifier is a type of bipolar junction transistor (BJT) amplifier that uses the emitter as a common terminal for both the input and output circuits. This configuration is widely used in electronic circuits due to its high current gain, moderate voltage gain, and high input impedance.
The common emitter amplifier is commonly used in audio amplifiers, radio frequency amplifiers, and other applications where a high gain is required. It is also used as a building block for more complex amplifiers, such as the Darlington amplifier and the cascode amplifier. The common emitter amplifier is a versatile circuit that can be used in a wide range of applications.
What are the Key Components of a Common Emitter Amplifier?
The key components of a common emitter amplifier include the transistor, the input resistor, the output resistor, and the power supply. The transistor is the heart of the amplifier, and it is responsible for amplifying the input signal. The input resistor is used to set the input impedance of the amplifier, while the output resistor is used to set the output impedance.
The power supply is used to provide the necessary voltage and current to the amplifier. Other components, such as capacitors and inductors, may also be used to filter the input and output signals, and to provide additional gain. The choice of components will depend on the specific application and the desired performance of the amplifier.
How Does a Common Emitter Amplifier Work?
A common emitter amplifier works by using the transistor to amplify the input signal. The input signal is applied to the base of the transistor, and the output signal is taken from the collector. The emitter is common to both the input and output circuits, and it is used as a reference point for the amplifier.
When the input signal is applied to the base of the transistor, it causes a small change in the current flowing through the transistor. This change in current is amplified by the transistor, resulting in a larger change in the current flowing through the collector. The output signal is then taken from the collector, and it is a amplified version of the input signal.
What are the Advantages of a Common Emitter Amplifier?
The common emitter amplifier has several advantages, including high current gain, moderate voltage gain, and high input impedance. It is also a relatively simple circuit to build and maintain, and it is widely used in many applications.
Another advantage of the common emitter amplifier is its ability to provide a high degree of isolation between the input and output circuits. This makes it useful in applications where the input and output signals need to be isolated from each other. Additionally, the common emitter amplifier can be used with a wide range of transistors, making it a versatile circuit.
What are the Disadvantages of a Common Emitter Amplifier?
The common emitter amplifier has several disadvantages, including a relatively low voltage gain and a high output impedance. It also requires a relatively high power supply voltage, which can be a disadvantage in some applications.
Another disadvantage of the common emitter amplifier is its sensitivity to temperature changes. The transistor’s current gain and voltage gain can be affected by changes in temperature, which can cause the amplifier’s performance to degrade. Additionally, the common emitter amplifier can be prone to oscillation, which can cause the amplifier to become unstable.
How Do I Design a Common Emitter Amplifier?
To design a common emitter amplifier, you will need to determine the required gain, input impedance, and output impedance. You will also need to choose a suitable transistor and other components, such as resistors and capacitors.
The design process typically involves calculating the required values for the input and output resistors, as well as the power supply voltage and current. You will also need to consider factors such as temperature stability and noise reduction. There are many online resources and design tools available to help with the design process.
What are Some Common Applications of a Common Emitter Amplifier?
The common emitter amplifier is widely used in many applications, including audio amplifiers, radio frequency amplifiers, and other electronic circuits. It is also used in medical devices, such as electrocardiogram (ECG) amplifiers, and in industrial control systems.
The common emitter amplifier is also used in many consumer electronics devices, such as televisions and radios. It is a versatile circuit that can be used in a wide range of applications, and it is widely used in many industries. Its high gain and moderate voltage gain make it a popular choice for many applications.