Editing Preamplifier (section)

==Description==
An ideal preamp will be linear (have a constant [[Gain (electronics)|gain]] through its operating range) and have high [[input impedance]] (requiring only a minimal amount of current to sense the input signal) and low [[output impedance]] (when current is drawn from the output there is minimal change in the output voltage).  It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the [[signal-to-noise ratio]] (SNR). The noise performance of a preamplifier is critical. According to [[Friis formulas for noise|Friis's formula]], when the gain of the preamplifier is high, the SNR of the final signal is determined by the SNR of the input signal and the [[noise figure]] of the preamplifier.

Three basic types of preamplifiers are available:
* current-sensitive preamplifier
* [[parasitic capacitance|parasitic-capacitance]] preamplifier
* [[charge amplifier|charge-sensitive preamplifier]].