Analog-to-Digital (A/D) Donverter
- 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.



Figure 4221a shows an example of SEM systems. In all EMs (electron microscopes), detected information signal is amplified by a secondary electron detecting/amplifying system and then A/D-converted by an A/D converter.

Example of computer-controlled EMs: SEM system

Figure 4221a. Example of computer-controlled EMs: SEM system.

The schematic in Figure 4221b illustrates the components of an entire EDS system.

Schematic illustration of the components of an entire EDS system

Figure 4221b. 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).



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