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Why must input impedance be high?
The high impedance ensures that it draws very little current. It is the amplifier’s task to convert a low energy, voltage-driven signal into a higher-voltage output signal. Low impedance circuits can be dangerous because of the high current draw that they produce. Op amps avoid this by having very high input impedance.
What is the input impedance of common collector amplifier?
A common-collector (CC) amplifier typically has a high input impedance (typically in the hundred kΩ range) and a very low output impedance (on the order of 1Ω or 10Ω). This makes the common- collector amplifier excellent for “driving” small loads.
What is meant by high input impedance?
In electronics, high impedance means that a point in a circuit (a node) allows a relatively small amount of current through, per unit of applied voltage at that point. In audio systems, a high-impedance input may be required for use with devices such as crystal microphones or other devices with high internal impedance.
What is the most important characteristic of a common collector amplifier?
The common-collector amplifier has quite large current gain, larger than any other transistor amplifier configuration….Common Collector Transistor Amplifier Characteristics.
| Parameter | Characteristics |
|---|---|
| Power gain | Medium |
| Input or output phase relationship | Zero degree |
| Input resistance | High |
| Output resistance | Low |
How big is the input resistance of a common collector amplifier?
This equation shows that the common-collector amplifier has a large input resistance, due to the product (β+1) R E. In many texts, R source +r ∏ is neglected, because it is a lot smaller than (β+1) R E. How small? R source can be around 10 kΩ, while r ∏, is around 1 kΩ.
Why is input impedance higher in common base than common emitter?
This behavior is absent in the common emitter, because the input interacts with the base current, not the collector emitter current. In the common emitter, we even get feedback-driven impedance raising action if we add an unbypassed emitter resistor.
Which is the equation for input and output resistance?
which is the equation shown in most articles or textbooks. The output resistance depends mainly on the source resistance R source, the transistor input resistance r ∏, and it is small, since these two resistor values are divided by a large number, β+1.