ADC stands for Analog to Digital Converter, and as the name suggests it's used for converting analog signals (world is analog) into bits, to allow digital processing.
The main parameters that characterize an ADC are the resolution (in bits) and the speed of conversion. That is also the main tradeoff between fast ADCs, made for real time control of quick signals, and precision ADCs, used for accurate conversions like audio applications. In general faster and higher resolution ADCs are higher power than slower and lower resolution ones.
Types of ADCs include
- Flash: Damn Fast™, but use a lot of chip real estate, therefore only low resolution
- Successive Approximation
- Dual-Slope and Multi-Slope
Walt Kester - The Data Conversion Handbook (ebook)