An Explanation of Transistor as an Amplifier

Amplifiers are circuits that are meant to increase a signal’s strength. The applied input might be voltage or current signals depending on the application. For example, amplification is used in radio transmissions, long-distance communication, and other applications. In addition, amplifiers are employed in several other applications, including telecommunications, audio and video equipment, controllers, etc. 

In terms of gains and uniformity, a transistor should be efficient. In addition, it must have a large bandwidth. When these properties are present in a transistor, it may be employed in various applications, including audio amplifiers. But, first, let us find out how to calculate AC current gain, voltage gain, and power gain.

Transistor as an Amplifier:

There are two sorts of transistors: switch and amplifier. We’ll look at how transistors are used as amplifiers in this section. The transistor will be on at saturation, and it will also be ultimately off at cutoff. Therefore, when we want a transistor to operate as an amplifier, we must make it work in the active area between saturation and cutoff.

As in the three combinations/configurations below, a transistor could be seen as an amplifier.

CB or Common Base Configuration: Here, the transistor base is connected to the ground, resulting in a relatively low output impedance with little amplification. This arrangement will have a meagre gain.

CC or Common Collector Configuration: In this design, the collector is linked to the ground, the output resistance is low for a high power density, and the gain is superior when matched to the CB configuration.

CE or Common Emitter Configuration: The emitter will be linked to the ground in this setup, and the input impedance shall become high, the output resistance shall be medium, and the gain shall become high.

The transistor will function as an amplifier by increasing the intensity of a weak signal. There will be three terminals on the transistor: base, collector, and emitter. The transistor’s emitter and base will be forward biassed, but the collector base area is reverse biassed. Forward bias occurs when the P-region of the transistors gets linked to the positive electrode of the supply, and the N-terminal covers the hostile network. In contrast, reverse bias occurs when the P-region of the transistors gets attracted to the supply’s negative terminal.

Advantages & Applications:

Every transistor acting as an amplifier offers various benefits for electronics and communication. They are:

• The use of transistors as amplifiers for signal enhancement can be used in FM signal transmission.
• Since the received signal at the outcome is of great strength, it may be employed in long-distance communication.
• In wireless communication, amplifiers play an essential function.
• Such transistor amplifiers are used in the amplification of radio transmissions.
• These sorts of amplifiers are also used in optical fibre communication.
• The transistor amplifier’s primary function is that of an audio amplifier, and it is employed in many of our day-to-day activities.

How to Calculate AC Current Gain, Voltage Gain & Power Gain

AC Current Gain:

The proportion of the variation in the collector current to the variation in the emitter current at fixed collector-base voltage is known as AC current gain (aac).

aac or = Δic / Δie

aac or must be slightly less than one.

Voltage Gain:

The proportion of output voltage change to the varying input voltage is known as voltage gain. AV is the abbreviation for it. Thus,

Av = Δic × R0 / Δie × Ri

But  aac or = Δic / Δie, which is AC current gain.

Av = (R0 / Ri)

AV is relatively high, even though it is a little less than 1, because R0>> Ri.

Power Gain:

The output power variation to the variation in input power is known as power gain. 

Power Gain = Voltage Gain × AC Current Gain

Power Gain = α 2 (R0 / Ri)

Conclusion:

Every transistor acting as an amplifier offers various benefits with regard to electronics and communication. The proportion of the variation in the collector current to the variation in the emitter current at fixed collector-base voltage is known as AC current gain (aac). The formula is aac or = Δic / Δie. The proportion of output voltage change to the varying input voltage is known as voltage gain. Av = (R0 / Ri) is voltage gain. AV is the abbreviation for it. The proportion of output power variation to the variation in input power is known as power gain (α 2 (R0 / Ri)).