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What are charactersitics of two stage common emitter amplifiers?
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∙ 12y ago
less current flowing through them
Wiki User
∙ 12y ago
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What is an AF amplifier?
AF means audio frequency. Audio Amplifiers can be subgrouped as voltage amplifiers (or pre-amplifiers) and power amplifiers. The voltage amplifier will raise the level of level of the output of a microphone from say 1 mV to 500mV or 1V. The power amplifier will be the interface between this and the load, which is a speaker. The resistance of the speaker is often 4 ohm or 8 ohm. You cannot have a speaker with 1k as resistance! As such to get say 8W output, an amplifier providing 8V will have to pump 1 amp into an 8 ohm speaker. Thus power amplifiers will have to drive a lot of current into the load. Voltage amplifiers cannot do this. A power amplifier sometimes just has unity voltage gain, but has ability to drive a lot of current into the load. Typical power amplifiers are operated in class B, where for 50% of the signal swing, one transistor provides current, and for the other 50%, the other transistor in a class B provides current into load. Class B amplifiers have cross over distortion, But this can be overcome by pre-biasing, or making the stage operate as class AB. The power amplifiers can also be used to power low resistance loads such as a step up transformer.
What happens when the emitter bypass capacitor is shorted?
Then gain becomes equal to hFe and thermal runaway becomes a problem. Further, the reduction of gain as frequency decreases is eliminated, so the stage's operation as a high pass filter is compromised.
What is stagger tuned amplifier?
Stagger Tuned Amplifiers are used to improve the overall frequency response of tuned Amplifiers. Stagger tuned Amplifiers are usually designed so that the overall response exhibits maximal flatness around the centre frequency.It needs a number of tuned circuit operating in union. The overall frequency response of a Stagger tuned amplifier is obtained by adding the induvidual response together. Since the resonant Frequencies of different tuned circuits are displaced or staggered, they are referred as STAGGER TUNED AMPLIFIER.The main advantage of stagger tuned amplifier is INCREASED BANDWIDTH. Its Drawback is Reduced Selectivity and critical tuning of many tank circuits. They are used in RF amplifier stage in Radio Receivers.
Working of RC coupled amplifier?
In a two stage RC coupled amplifier, the two transistors are identical and a common power supply is used. The input is provided to the first stage of the amplifier where it is amplified and this output is used as input for the second stage. This is amplied once again by the other transistor in the second stage and the final output is obtained. There will be a 180 degree phase shift after the first stage amplification which is nullified by the 180 degree phase shift of the second stage amplification.Thus, we obtain an output which is an amplified signal of the input and is in phase with the input signal.
What are the applications of RC coupled amplifier?
They are widely used as voltage amplifiers (ie. In the initial stages of public address systems) because of their excellent audio-fidelity over a wide range of frequency. However because of poor impedance matching this type of coupling transistor circuits is rarely employed in final stages
Why output voltage in common base amplifier is in phase to input voltage?
The output of a common emitter stage is inverted, it is not out of phase.
What is effect of an unbypassed resistor on the common emitter amplifier circuit?
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.
Why use a npn transistor in a common emitter bjt single stage amplifier circuit?
You can use an npn or a pnp bjt in a common emitter amplifier circuit. The decision of which one to use is based on whether you want the collector and base to be more positive (npn) or more negative (pnp) than the emitter.
Why the single stage common emitter transistor amplifier is famous and widely used in most of the application?
because of low cost and gain is high well amplified
What is the difference between single stage and multi stage amplifiers?
single stage amplifier contain only one stage transistor amplifier but multi stage contain more than one amplifier stage
What is meant by biasing in a single stage ce amplifier?
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.)
What is the Frequency response of common emitter amplifier?
The voltage gain is a measure of the amplified output available at the collector terminal divided by the voltage measured on the base. This if you have 10 mV applied to the base and voltage of 1 volt at the collector the voltage gain is 100ANSWERThe maximum voltage gain of a common emitter amplifier is dependant on the transistor itself. Some have only a very small voltage gain such as in Radio Frequency Power transistors. These are almost all used as common emitter circuits for bipolar transistors or common source for FETs.. On the other hand some darlington transistors can have common emitter gains of hundreds of thousands. If the stage has an unbypassed emitter resistor, the voltage gain is equal to Rload/RE, (Rload is the parallel value of the resistance from collector to the supply and the resistance of the load).If the emitter resistance is bypassed, the value of resistance to be used for RE is the internal Re which is equal to 25mV/Ie
What is advantage and disadvantages of multistage amplifier?
A multistage amplifier is composed of several single stage amplifiers.
How emitter bypass resistor stabilizes the amplifier against temperature?
In the common emitter (Class A) amplifier design of a BJT, gain is collector resistance divided by emitter resistance, or hFe, whichever is less. If the emitter resistance is zero, then gain is hFe. In this configuration, gain is unstable, because hFe is temperature dependent. In fact, under certain circumstances, a BJT can experience thermal runaway. The emitter resistor (along with the collector resistor) places a limit on the expected gain of the stage. If, for example, you design with a ratio of 10, then you expect a gain of 10. If hFe is 25-100, gain is still 10.
What is the explanation for the working CE BJT amplifier?
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.
What risk might be incurred by connecting the mixing desk to a different mains supply to that of the guitar amplifiers on stage?
AN EXPLOSION OF fun
What is common emitter amplifier with degeneration?
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. == ==
