Power Amplifiers
Generally, an amplifier is any device that uses a small amount of energy to control a larger amount of energy. In popular use, the term today usually refers to an electronic amplifier, often as in audio applications. more...
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The relationship of the input to the output of an amplifier — usually expressed as a function of the input frequency — is called the transfer function of the amplifier, and the magnitude of the transfer function is termed the gain.
General characteristics of amplifiers
Most amplifiers can be characterized by a number of parameters.
Gain
How much an amplifier increases the signal level is called the gain. This is usually measured in decibels (dB). Mathematically speaking, the gain is equal to the output level divided by the input level (for power gain in decibels gain is computed by the relation G(dB)=10log(Pout/Pin)(Electrical)).
Output dynamic range
Output dynamic range is the range, usually given in dB, between the smallest and largest useful output levels. Since the lowest useful level is limited by output noise, this is quoted as the amplifier dynamic range.
Bandwidth and rise time
The bandwidth (BW) of an amplifier is usually defined as the difference between the lower and upper half power points. This is therefore also known as the −3 dB BW. Bandwidths for other response tolerances are sometimes quoted (−1 dB, −6 dB etc.).
As an example, a good audio amplifier will have a −3 dB BW from around twenty hertz to about twenty kilohertz (the range of normal human hearing).
The rise time of an amplifier is the time taken for the output to change from 10% to 90% of its final level when driven by a step input. For a Gaussian response system (or a simple RC roll off), the rise time is approximated by:
Tr * BW = 0.35, where Tr is in seconds and BW is in Hz.
Settling time and aberrations
Time taken for output to settle to within a certain percentage of the final value (say 0.1%). This is usually specified for oscilloscope vertical amplifiers and high accuracy measurement systems.
Slew rate
Slew rate is the maximum rate of change of output variable, usually quoted in volts per second (or microsecond).
Noise
This is a measure of how much noise is introduced in the amplification process. Noise is an undesirable but inevitable product of the electronic devices and components. It is measured in either decibels or the peak output voltage produced by the amplifier when no signal is applied.
Read more at Wikipedia.org
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