The term ‘amplify’ stands for ‘make it stronger’. The strength of the signal is usually measured in terms of ‘amplitude’. Thus, an amplifier is a device which aids to strengthen a weak signal. An amplifier can be termed ideal if it has good fidelity, lousy efficiency and uses feedback property. There are different classes of amplifiers. They are class A, class AB and class C. There are also some special classes like G, H, D and T usually called as Digital amps. Let’s have a brief overview about them.
Class A amplifier uses one or more transistors that conduct electricity during both the cycles of the signal. These amplifiers have low distortion, but they are inefficient because they generate lot of heat. In order to overcome this problem class B amplifiers are used. They use one transistor to conduct electricity during positive cycles of the waveform and another transistor to conduct electricity during the negative cycles of the same. Most of the audio amplifiers used today are class B. Class B amplifiers used today works efficiently in such a way that it’s distortions cannot be detected by human ear.
The above two amplifier concepts were merged and Class A/B was created by making one transistor to conduct electricity when another is also conducting but, this created its own distortion. This caused an overlap between two signals called as ‘gumming’. This means that the signal would become larger when both the devices conduct. Another class of amplifier is Class D amplifiers and it is also referred as ‘Digital amplifiers’. In this case, either the transistors are switched on or off to represent positive and negative cycles. This may cause distortion since, both the transistors cannot be switched on or off at the same time. This sort of amplifiers are used in subwoofers.
Class T amplifiers are more refined switching amplifiers. It implies the concept of signal processing which automatically eliminates switching distortion. A normal power supply requires three times the output to drive an amplifier to maximize its RMS rating. To understand how an amplifier works you need to understand the basic types of amplification. They are Voltage amplifier, current amplifier and power amplifier. Of these the first two are basic types and the third one is the derived type. Voltage amplifier is the one that boosts the voltage of a signal. Current amplifier is one that strengthens the current of a signal. Power amplifier is a combination of these two which works accordingly. The following are the basic factors.
The first criteria is feedback in which the output is taken as input but 180 degrees out of phase. The second one is fidelity in which the output must be an exact replica of the input which may be amplified. The third one is efficiency in which for every watt of output you need to use at least two watts of DC power supply.
The quality of an Op Amps can be characterized by a number of specifications. The first one is the gain of the amplifier. This is determined as the ratio of the input to the output and is usually measured in decibels. The next one is bandwidth which may be defined as the difference between the lower and upper half power points. So, it is usually called as – 3 db bandwidth.
Efficiency is the next factor. This is measured as how much power of the input is usefully applied to amplifier output. The efficiency of the amplifier limits the amount of the output that is usefully available. Linearity is the other factor which determines the quality of the amplifier. An ideal amplifier should be 100% linear but in real they are linear only up to certain limits.
Noise factor is the measure of how much noise is produced in the amplification process. Noise is an unavoidable and undesirable factor of the device. Noise factor is measured in terms ratio of input signal to the output signal. Slew rate is the maximum rate of change of output variable measured in terms of volts per second. Rise time of an amplifier is the time taken by the output to change from 10% to 90% of its final stage when driven by a single stage of input.
Then, regarding the kinds of amplifiers it is of various types. They are power amplifiers, vacuum tube amplifiers, transistor amplifiers, Op Amps, fully differential amplifier, video amplifier, oscilloscope vertical amplifier, distributed amplifier, microwave amplifier and so on. Each varies from other based on its own characteristics and specifications.