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, hence its name. An analogous circuit called the common source is constructed using field-effect transistors Common-emitter amplifiers generally have a very high gain which can vary widely from one transistor to the next, as it is a strong function of both temperature and bias current, making the actual gain unpredictable. Stability is another problem associated with such high gain circuits, due to any unintentional positive feedback that may be present. Other problems associated with the circuit are the low input dynamic range imposed by the small-signal limit and the high distortion resulting if this is exceeded. One common way of alleviating these issues is with the use of negative feedback, particularly with emitter degeneration. Emitter degeneration typically refers to the addition of a small resistor (or any impedance) between the emitter of the transistor and ground. The effect of this is to reduce the overall transconductance Gm = gm of the circuit by a factor of gmRE + 1, making the voltage gain depend more on the ratio of the resistors than the transistor's characteristics: The distortion and stability characteristics of the circuit are thus improved, but at the expense of a reduction in gain. Common-emitter circuits are used to amplify weak voltage signals, such as the faint radio signals detected by an antenna. When used in radio frequency circuits, it is common to replace the load resistor with a tuned circuit. This is done to limit the bandwidth to a narrow band centered around the intended operating frequency. More importantly it also allows the circuit to operate at higher frequencies as the tuned circuit can be used to resonate any inter-electrode and stray capacitances, which normally limit the frequency response. Common emitters are also commonly used as low noise amplifiers. At low frequencies and using a simplified Hybrid-Pi model, the following small signal characteristics can be derived. If the emitter degeneration resistor is not present, RE = 0 Ω. According to these formulas and in agreement with the previous discussion, when RE is increased the input resistance is increased and the gain is reduced. {| ! ! Definition ! Expression ! Current gain ! Voltage gain ! Input resistance ! Output resistance |} The bandwidth of the common emitter amplifier tends to be low, due to high capacitance resulting from the Miller effect. The base-collector capacitance is effectively multiplied by the factor 1 − Av, thus increasing the total input capacitance and lowering the overall bandwidth. The discussion of bandwidth parallels that in the article on the common source amplifier. A fix for this bandwidth problem is the cascode amplifier. == ==
The gain of a common-emitter amplifier is collector resistor divided by emitter resistor, or hFe, whichever is less. Since hFe depends on temperature, designing the amplifier to be dependent on resistance ratio makes it more stable. As such, the emitter resistance serves to stabilize the amplifier.
emitter follwer
The signal gain of a CE BJT amplifier is hFe or collector resistance divided by emitter resistance, whichever is less.
Applied input signal at the base of the amplifier appears across the emitter resistor (RE) due to inter electrode capacitance so it should be bypassed the emitter resistor (RE) through the bypass capacitor (CB). unbypassed signal will be amplified (common emitter amplifier) and reverse back from the emitter to the collector through the base, amplified signal from the emitter to the collector (common emitter amplifier) is 1800 out of phase to the amplified signal from the base to the collector (common base amplifier), so reduced the gain.
The question does not quite make sense. It sounds like you are asking why does changing the emitter resistor in a class C common collector amplifier not affect the output voltage? If so, the answer is that the common collector is an emitter follower, meaning that the emitter will follow the base, less the base-emitter junction voltage, within the limits of hFe. The resistor is simply there to ensure output biasing when the base voltage goes low.
With a common emitter amplifier it's the emitter that is usually grounded.
A: REFERS TO A common emitter amplifier
The gain of a common-emitter amplifier is collector resistor divided by emitter resistor, or hFe, whichever is less. Since hFe depends on temperature, designing the amplifier to be dependent on resistance ratio makes it more stable. As such, the emitter resistance serves to stabilize the amplifier.
I think you mean a common emitter amplifier, which is an amplifier of voltage. Emitter-follower or common collector amplifiers are used to match impedances, or to amplify power or current. The emitter-follower is a type of common emitter circuit that has a resistor between the emitter and ground. The output signal is taken from the point between the emitter and its resistor.
what is the other name of common emitter amplifier
Itamplifiesthe gain
Common Emitter - Class A Amplifier.
emitter follwer
bbc
b'cose the gain of the amplifier is high ..
In the common emitter amplifier, an increase of base-emitter current causes a larger increase of collector emitter current. This means that, as the base voltage increases, the collector voltage decreases. This is a 180 degree phase shift.
common emitter