The voltage gain of a common emitter transitor amplifier is (inverted) collector resistor divided by emitter resistor, unless this would exceed hfe or the transistor is operating in non-linear mode.
The current gain of a common emitter is equal to beta or hfe using the hybrid-pie approximation.
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A bipolar transistor can be used in different configurations in linear electronic design. Most well known is the common emitter CE configuration with a base current as input signal resulting in a collector signal multiplied by the current gain factor. The second configuration is known as the emitter follower or common collector configuration. Here the input signal is in the form of a voltage between the base and the common connection. The output signal is found in the form of a voltage at the emitter with a relative low output impedance. The voltage swing at the input is almost as large at the output where the input impedance equals the product of the current gain factor and the emitter resistance. The third configuration is known as common base CB. Here the input current at the emitter almost equals the output current at the collector. The current gain is nearly equal to 1.
The base is excited by a very low current. That turns the transistor on so that a higher amount of current flow comes out.
The emitter resistor in a common emitter configuration provides negative feedback to the transistor, reducing both its voltage gain and distortion.
Kirchoff's current law states that the current in every point in a series circuit is the same. In the case of a transistor in common emitter configuration, you can take advantage of that fact and state that the collector current is equal to the emitter current. The truth is somewhat different, because the gain of the transistor is not infinity, so the base current must be added to the emitter current. With a reasonably high gain, however, you can ignore the base current. Consider that the emitter voltage is related to the base voltage by the forward drop of the base-emitter junction, about 0.7 volts, and the collector and emitter currents are the same. Now look at the collector and emitter resistors. If the currents are the same, and the voltage across the emitter resistor is known, then you know the voltage across the collector resistor as well. This is an application of both Kirchoff's and Ohm's laws. The gain, then, of this amplifer is collector resistance divided by emitter resistance. It is an inverting amplier in this configuration. In some configurations, the emitter resistor is zero ohms. This does not mean the gain is infinity - it now means that the gain is limited by the gain of the transistor, which it is anyway - the emitter resistor is used to stabilize the gain and reduce dependency on individual transistor gains, which do vary.
Reason: The common Emitter mode has voltage and current gain better than the other two configurations(CB and CC). i.e it has a current gain greater than that of CC mode and greater voltage gain than that of CB mode.
output current is emitter current i.e.,Ie
output current is zero
A bipolar transistor can be used in different configurations in linear electronic design. Most well known is the common emitter CE configuration with a base current as input signal resulting in a collector signal multiplied by the current gain factor. The second configuration is known as the emitter follower or common collector configuration. Here the input signal is in the form of a voltage between the base and the common connection. The output signal is found in the form of a voltage at the emitter with a relative low output impedance. The voltage swing at the input is almost as large at the output where the input impedance equals the product of the current gain factor and the emitter resistance. The third configuration is known as common base CB. Here the input current at the emitter almost equals the output current at the collector. The current gain is nearly equal to 1.
comparerission between CB,CC&CE
the common emitter configuration is most widely used in amplifer circuits because of its high voltage,current & power gain.the common emitter configuration is most widely used in amplifer circuits because of its high voltage,current & power gain.
The base is excited by a very low current. That turns the transistor on so that a higher amount of current flow comes out.
Common Emitter Configuration has maximum impedance.
The emitter resistor in a common emitter configuration provides negative feedback to the transistor, reducing both its voltage gain and distortion.
The Common Collector configuration amplifies current, by having the emitter voltage follow the base voltage, with an offset of the forward conduction voltage of about 0.7 volts, with a current gain of beta. (hFe)
Kirchoff's current law states that the current in every point in a series circuit is the same. In the case of a transistor in common emitter configuration, you can take advantage of that fact and state that the collector current is equal to the emitter current. The truth is somewhat different, because the gain of the transistor is not infinity, so the base current must be added to the emitter current. With a reasonably high gain, however, you can ignore the base current. Consider that the emitter voltage is related to the base voltage by the forward drop of the base-emitter junction, about 0.7 volts, and the collector and emitter currents are the same. Now look at the collector and emitter resistors. If the currents are the same, and the voltage across the emitter resistor is known, then you know the voltage across the collector resistor as well. This is an application of both Kirchoff's and Ohm's laws. The gain, then, of this amplifer is collector resistance divided by emitter resistance. It is an inverting amplier in this configuration. In some configurations, the emitter resistor is zero ohms. This does not mean the gain is infinity - it now means that the gain is limited by the gain of the transistor, which it is anyway - the emitter resistor is used to stabilize the gain and reduce dependency on individual transistor gains, which do vary.
because in ce configuration value of input voltage requried to make the transistor on is very less value of the output voltage or output current
In a common emitter amplifier, the base-emitter current causes a corresponding collector-emitter current, in the ratio of hFe (beta gain) or collector resistance over emitter resistance, which ever is less. Since this ratio is usually greater than one, the differential collector current is greater than the differential base current. This results in amplification of the base signal. As you increase the base-emitter current, the collector-emitter current also increases. This results in the collector being pulled towards the emitter, with the result that the differential collector voltage decreases. This results in inversion of the base signal.