Field Effect Transistor (FET) Preamplifier in EDS Systems
- Practical Electron Microscopy and Database -
- An Online Book -  

This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.


The schematic in Figure 3811a illustrates the components of an entire EDS system.

Schematic illustration of the components of an entire EDS system

Figure 3811a. Schematic illustration of the components of an entire EDS system.

Overall, each absorbed X-ray photon generates a charge cloud that is composed of a number of electron-and-hole pairs, and the charge carriers are moved due to high voltage and are collected in the detector. The charge-sensitive preamplifier (PA) converts the charge pairs into a voltage pulse. The pulse is amplified and shaped in a spectroscopic amplifier (SPA).  In this SPA process, one needs to optimize some constants such as gain, shaping time, pole zero, and base-line. The maximum of the intensified pulse is detected or stretched by peak-detector or peak-stretcher (PS). Finally, each pulse is individually measured with an analog-digital converter (ADC).

The main functions of the LN2 device in EDS systems in EMs are to reduce thermal e-h pair, prevent the Li atoms from diffusing, reduce noise in the FET (Field Effect Transistor) preamplifier, and optimize the energy-resolution. Figure 3811b shows the schematic illustration of an EDS detector with a FET preamplifier.

Schematic illustration of EDS detector

Figure 3811b. Schematic illustration of EDS detector.



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