What is an ADC and what key specifications should you consider?

ADC (Analog-to-Digital Converter) converts continuous analog signals to discrete digital values. Key specifications: Resolution (bits) determines the number of discrete levels (2^n); 10-bit = 1024 levels, 12-bit = 4096 levels. Sampling rate (samples per second) must be >2x signal frequency (Nyquist). Reference voltage sets the input range; Vref = 3.3V with 12-bit gives 0.8mV resolution. DNL/INL (Differential/Integral Non-Linearity) measure accuracy. SNR and ENOB (Effective Number of Bits) indicate quality. Input types: single-ended or differential. Conversion time affects throughput. Common architectures: SAR (successive approximation), Sigma-Delta (high resolution), Flash (high speed), Pipeline.