Amplifiers are used to provide a number of functions:
- Increase or attenuate magnitude of a physical quantity.
- Transform signals from one physical variable to another (e.g. charge to voltage).
- Remove DC biases.
- Provide impedance matching.
Care should be taken to ensure:
- Satisfactory frequency response.
- Satisfactory 'slew rate' i.e. response to maximum rate of rise of a signal.
- Voltage amplifier
- Charge amplifier
- Differential amplifier
- Class A: An amplifier so designed that the bias is set on the linear portion of the characteristic curve and in which the input signal amplitude is confined to the linear operating region.
- Class AB1: An amplifier with slightly higher bias than the Class A and with a larger input signal having amplitudes reaching (but not exceeding) the cutoff and positive regions of grid-signal swing.
- Class AB2: An amplifier with higher bias than the Class AB1 and with grid signal excursions extending into the cutoff and positive tube characteristic regions.
- Class B: An amplifier with bias at or near the tube cutoff point. Positive alternations of the input signal cause current flow.
- Class C: An amplifier biased beyond the cutoff point so current flows for only a portion of the positive alternations of the input signal.
The growth of the radiation field in the laser resonator cavity. As the light wave bounces back and forth between the cavity mirrors, it is amplified by stimulated emission on each pass through the active medium.