Explain the concept of emitter-follower configuration in transistor amplifiers.
1 Answer
The emitter-follower configuration, also known as the common collector configuration, is a common type of transistor amplifier used to boost the current and decrease the output impedance of a signal source. It is widely employed in various electronic applications due to its unique characteristics and benefits.
In the emitter-follower configuration, a bipolar junction transistor (BJT) is used with its emitter terminal connected directly to the ground (common) potential. The input signal is applied to the base terminal, and the amplified output is taken from the emitter terminal. The collector terminal is typically connected to a DC biasing voltage through a resistor.
Here's how the emitter-follower configuration works:
Signal input: The input signal is connected to the base terminal of the transistor. The base-emitter junction of the BJT acts as a diode, allowing the base current to flow according to the input signal. This causes a corresponding variation in the collector current, as the transistor amplifies the input signal.
Amplification: The transistor's inherent gain (hfe) amplifies the input signal at the base-emitter junction. The amplified signal appears across the emitter resistor (RE), which is in series with the emitter. The emitter current (IE) is approximately equal to the collector current (IC), making the emitter current the amplified version of the input signal.
Voltage gain: The voltage gain of the emitter-follower configuration is slightly less than unity, i.e., less than 1. This means that the output voltage follows the input voltage but with a gain slightly less than 1. The main advantage of the emitter-follower is its high input impedance and low output impedance.
Impedance characteristics: The emitter-follower configuration offers a very high input impedance, as the base-emitter junction appears as a forward-biased diode, which does not draw much current from the input source. This high input impedance allows the amplifier to avoid loading effects on the input source, making it an ideal buffer between low impedance sources and high impedance loads.
Low output impedance: The emitter-follower has a low output impedance due to the presence of the emitter resistor (RE). This allows the circuit to drive low impedance loads effectively, which is useful when interfacing with other circuits or devices.
Voltage level shifting: The emitter-follower can also serve as a level shifter because its output voltage is approximately equal to the input voltage plus the base-emitter voltage drop (VBE) of the transistor. This can be useful when you need to shift the DC bias level of a signal.
Overall, the emitter-follower configuration is commonly used as a voltage buffer and impedance matching stage in various electronic circuits to ensure signal integrity, prevent signal degradation, and provide better current delivery capabilities.
In the emitter-follower configuration, a bipolar junction transistor (BJT) is used with its emitter terminal connected directly to the ground (common) potential. The input signal is applied to the base terminal, and the amplified output is taken from the emitter terminal. The collector terminal is typically connected to a DC biasing voltage through a resistor.
Here's how the emitter-follower configuration works:
Signal input: The input signal is connected to the base terminal of the transistor. The base-emitter junction of the BJT acts as a diode, allowing the base current to flow according to the input signal. This causes a corresponding variation in the collector current, as the transistor amplifies the input signal.
Amplification: The transistor's inherent gain (hfe) amplifies the input signal at the base-emitter junction. The amplified signal appears across the emitter resistor (RE), which is in series with the emitter. The emitter current (IE) is approximately equal to the collector current (IC), making the emitter current the amplified version of the input signal.
Voltage gain: The voltage gain of the emitter-follower configuration is slightly less than unity, i.e., less than 1. This means that the output voltage follows the input voltage but with a gain slightly less than 1. The main advantage of the emitter-follower is its high input impedance and low output impedance.
Impedance characteristics: The emitter-follower configuration offers a very high input impedance, as the base-emitter junction appears as a forward-biased diode, which does not draw much current from the input source. This high input impedance allows the amplifier to avoid loading effects on the input source, making it an ideal buffer between low impedance sources and high impedance loads.
Low output impedance: The emitter-follower has a low output impedance due to the presence of the emitter resistor (RE). This allows the circuit to drive low impedance loads effectively, which is useful when interfacing with other circuits or devices.
Voltage level shifting: The emitter-follower can also serve as a level shifter because its output voltage is approximately equal to the input voltage plus the base-emitter voltage drop (VBE) of the transistor. This can be useful when you need to shift the DC bias level of a signal.
Overall, the emitter-follower configuration is commonly used as a voltage buffer and impedance matching stage in various electronic circuits to ensure signal integrity, prevent signal degradation, and provide better current delivery capabilities.