bias
The signal gain of a CE BJT amplifier is hFe or collector resistance divided by emitter resistance, whichever is less.
A: REFERS TO A common emitter amplifier
what is the other name of common emitter amplifier
It depends on where the capacitor is located. If it is across the emitter resistor, then the gain of the CE amplifier will be higher at higher frequencies.Remember that gain in the CE amplifier is collector resistance divided by emitter resistance, or hFe, whichever is lower. Placing a capacitor across the emitter resistor will serve to make the effective resistance smaller at higher frequencies, resulting in increased gain, up to the limit of hFe.If this is not the intended location of the capacitor, then please restate the question and provide the capacitor location.
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.
Gain in a CE configuration of a BJT is collector resistance divided by emitter resistance, subject to the limit of hFe. The emitter bypass capacitor will have lower impedance at high frequency, so the gain will be higher at higher frequency, making this a high-pass amplifier.
Disadvantages of CE amplifier:1. It has a high output resistance.2. It responds poorly to high frequencies.3. It has high thermal instabilities.4. It's voltage gain is very unstable.
It can be used as a feedback and to ground unwanted signals and frequencies
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 (for example, it may be tied to ground reference or a power supply rail), hence its name.
In a ce amplifier, an increase of base voltage causes the collector current to rise. This causes an increased voltage drop through the collector load resistor, so the collector voltage drops. With a cc amplifier the increase in current causes more voltage across the emitter load resistor, therefore the emitter voltage rises.
Biasing in a single stage common-emitter amplifier means to place the base-emitter current at a point where the collector-emitter current is in the middle of the transistor's linear range.First, you pick the target range and output impedance of the amplifier, picking the collector and emitter resistors. The gain of the stage is collector resistance divided by emitter resistance, limited by available hFe. You want to try to pick a resistor pair that will place the collector voltage in the center of the desired range, while keeping the desired operating current where you want it.Then, you pick the base resistor divider pair such that the base voltage is the forward bias drop of the base-emitter above (NPN) or below (PNP) the emitter voltage. You find that emitter voltage by considering the collector voltage, along with the operating current and the collector and emitter resistors. (Its straightforward Ohm's law, considering that the collector-emitter forms the third resistor in the divider chain.) You have to consider hFe in this calculation, as well as realizing that the two base resistors will form the input impedance of the stage. (Well, actually, base-emitter current is included in the input impedance calculation, but that is usually a small contribution if the hFe is high enough.)Then you need to consider the power dissipation in the stage, and make sure that the transistor can handle that, and that hFe will not drift unacceptably under temperature. (Stable designs are such that the hFe is far greater than the ratio of collector resistance over emitter resistance, so that your limits are based on ratio, and not on hFe. Problematic designs are when the desired gain is greater than hFe, such as when the emitter resistance is zero - this makes gain equal to hFe, and introduces the possibility of thermal runaway.)
Gain of ce-cb cascode is nearly equal to the gain of ce amplifier, because in a ce-cb cascode, the gain of the ce stage is equal to 1, and the gain of the cb stage is nearly equal to an isolated ce amplifier. Hence, gain of both are nearly equal. On the other hand, Bandwidth of ce-cb cascode is much higher than the bandwidth of ce amplifier because the cb stage in the cascode configration is not subjected to any Miller effect, thereby improving the high frequency response. The absence of Miller effect is due to the fact that the base of the cb stage is grounded thus, shielding the collector signal from being fed back into the emitter input. To be more clear, the gain of CE stage in cascode is nearly 1, which reduces the miller effect on the cb stage greatly.