The pre AMP amplifier is circuit or electronic device placed between signal source and amplifier. It is designed to receive the weak voltage signal from the signal source. The preamplifier amplifies the useful signal as well as the noise. The low-noise preamplifier is preamplifier that minimizes the noise factor of the circuit. For weak signal detection instruments or devices, pre AMP amplifier
is one of the main components to introduce noise.
The noise factor of whole detection system mainly depends on the noise factor of pre-AMP amplifier
. The minimum signal that instrument can detect also depends on the noise of preamplifier.
Pre-AMP amplifier is usually connected directly to the sensor used to detect signal. Only when the best source resistance is equal to the signal source output resistance, noise factor of the circuit will be minimized.
1. Improve SNR of the system (improves the SNR because preamplifier close to the probe, short transmission lines, distributed capacitance Cs decreases)
2. Reduce relative external influence (signal is enlarged initially by preamplifier)
3. The reasonable layout, easy to adjust and use (preamplifier is not adjustable, and the main amplifier adjust zoom multiples, forming constantly)
4. Realize impedance transformation and matching (preamplifier design for high input impedance and low output impedance) 
The Classification of Pre AMP Amplifier Voltage sensitive preamplifier (Voltage amplifier)
Charge sensitive preamplifier (current integrator with capacitance negative feedback) with stable output gain, low noise and good performance
Current sensitive preamplifier (current preamplifier, parallel feedback current amplifier)
It can get timely information and response fast. It can be transmitted over long distances. The rising time and width of output pulse are narrow, and it is suitable for high count rate measurement.