Common collector configuration

Definition

The common collector configuration, also known as an emitter follower, is a three-terminal electronic circuit that uses a bipolar junction transistor (BJT) where the collector terminal is common to both the input and output. This setup provides high input impedance, low output impedance, and voltage gain close to unity, making it particularly useful for buffering applications. It connects the output to the emitter, which helps in providing current amplification without significant voltage change.

5 Must Know Facts For Your Next Test

1. In a common collector configuration, the output voltage follows the input voltage closely, which results in a voltage gain of approximately one.
2. This configuration has very high input impedance, making it suitable for connecting to high-impedance sources without loading them down.
3. The common collector acts as a buffer stage; it allows for current amplification while maintaining a low output voltage swing.
4. Because the collector is common to both input and output, this setup minimizes distortion in signals and provides better linearity compared to other configurations.
5. The emitter follower can drive low-impedance loads effectively, which is essential in many signal processing applications.

Review Questions

• How does the common collector configuration impact input and output impedances in a circuit?
  • The common collector configuration significantly influences input and output impedances by offering high input impedance and low output impedance. This makes it ideal for connecting high-impedance sources to lower-impedance loads without compromising signal integrity. The high input impedance ensures that minimal current is drawn from the input source, while the low output impedance allows for efficient power transfer to connected devices.
• Discuss how the common collector configuration achieves its near-unity voltage gain and what implications this has for its use in electronic circuits.
  • The common collector configuration achieves near-unity voltage gain by directly connecting the output at the emitter to the input at the base. This means that any small changes in the base-emitter voltage result in similar changes at the emitter, maintaining a consistent voltage level. The implication of this behavior makes it an excellent choice for buffering applications where voltage levels need to be preserved while still providing current amplification.
• Evaluate the advantages and disadvantages of using a common collector configuration in a practical electronic application.
  • Using a common collector configuration offers several advantages such as high input impedance, low output impedance, and simple integration into circuits as a buffer stage. However, it also has disadvantages including limited voltage gain and potential challenges when driving very low-impedance loads. Balancing these factors is critical when designing circuits to ensure optimal performance while addressing specific application requirements.

Related terms

Bipolar Junction Transistor (BJT): A type of transistor that uses both electron and hole charge carriers, consisting of three regions: emitter, base, and collector.

Voltage Gain: The ratio of output voltage to input voltage in a circuit, indicating how much a circuit amplifies the voltage signal.

Input and Output Impedance: Input impedance is the resistance seen by the input source, while output impedance is the resistance presented by the output to the load; both affect how circuits interact with one another.