In electronics, the figures of merit of an amplifier are numerical measures that characterize its properties and performance.
The gain of an amplifier is the ratio of output to input power or amplitude, and is usually measured in decibels.
The gain of a good quality full-range audio amplifier will be essentially flat between 20 Hz to about 20 kHz (the range of normal human hearing).
Professional touring amplifiers often have input and/or output filtering to sharply limit frequency response beyond 20 Hz-20 kHz; too much of the amplifier's potential output power would otherwise be wasted on infrasonic and ultrasonic frequencies, and the danger of AM radio interference would increase.
Class A amplifiers are very inefficient, in the range of 10–20% with a max efficiency of 25% for direct coupling of the output.
RCA manufactured an AM broadcast transmitter employing a single class-C low-mu triode with an RF efficiency in the 90% range.
The reason for this is that the loss of efficiency produces heat as a by-product of the energy lost during the conversion of power.
In RF linear Power Amplifiers, such as cellular base stations and broadcast transmitters, special design techniques can be used to improve efficiency.
Doherty designs, which use a second output stage as a "peak" amplifier, can lift efficiency from the typical 15% up to 30-35% in a narrow bandwidth.
Sometimes this non linearity is deliberately designed in to reduce the audible unpleasantness of hard clipping under overload.
Linearization is an emergent field, and there are many techniques, such as feed forward, predistortion, postdistortion, in order to avoid the undesired effects of the non-linearities.
[3] In many switched mode amplifiers, dynamic range is limited by the minimum output step size.
Many amplifiers are ultimately slew rate limited (typically by the impedance of a drive current having to overcome capacitive effects at some point in the circuit), which sometimes limits the full power bandwidth to frequencies well below the amplifier's small-signal frequency response.
In response to a step input, the overshoot is the amount the output exceeds its final, steady-state value.