A: The ratio of emitter/collector resistance is the gain. by adding a capacitor on the emitter the AC parameters will shift as a function of frequency
The capacitor is called a bypass capacitor , it provides a low impedence path for AC emitter current to groun.
If a bypass capacitor is used the voltage drop across emitter resistance is reduced which in turn increases the gain.....
A capacitor has lower resistance (impedance) as frequency increases. Adding an emitter capacitor effectively lowers the emitter resistance as frequency increases. Since gain in a typical common emitter amplifier is collector resitance divided by emitter resistance, this decrease in emitter resistance will increase gain as frequency increases.
A common-emitter (CE) transistor amplifier circuit typically includes a NPN transistor, a biasing resistor network, an input coupling capacitor, and an output coupling capacitor. The input signal is fed into the base of the transistor through the coupling capacitor, while the collector is connected to a power supply through a load resistor. The emitter is usually grounded or connected to a resistor. This configuration allows for voltage amplification, where the output is taken from the collector.
Without a bypass capacitor it is just equal to Rc
The emitter bypass capacitor, in a typical common emitter configuration, increases gain as a function of frequency, making a high pass filter. Removing the capacitor will remove the gain component due to frequency, and the amplifier will degrade to its DC characteristics.
comparerission between CB,CC&CE
The emitter bypass capacitor in a common emitter amplifier will have less resistance as the frequency increases. Since gain in this configuration is collector resistance divided by emitter resistance (within limits of hFe), the gain will thus increase for higher frequencies, making this into a high pass filter.
the amplification factor is a function of β. Higher β causes a higher amplification.
The common base configuration is not suitable for current amplification primarily because it has a low input impedance and high output impedance, which limits its ability to deliver significant current gain. This configuration typically provides voltage gain but does not amplify current effectively, making it less ideal for applications requiring substantial current amplification. Additionally, the input signal must be applied to the emitter, which can make it less convenient for many circuit designs compared to common emitter or common collector configurations.
No the base emitter circuit is not the same as a common base circuit. The three BJT circuits all have the base emitter circuit. Wheter each terminal is common to both inputs and outputs of the circuit determines the type of transistor configuration.Henry Lee Everson PE;229-560-9769
An emitter resistor in a common emitter circuit will cause the stage to experience the effects of degenerative feedback if it is unbypassed. The degenerative feedback reduces gain. This is probably the primary effect in the described circuit.