ADC Resolution (LSB)

Formula

Description

The least significant bit (LSB) of an ADC represents the smallest voltage change it can detect, determined by dividing the full-scale reference voltage by the number of quantization levels (2^N). A 12-bit ADC with a 3.3V reference has an LSB of 3.3/4096 = 0.806 mV. This sets the theoretical resolution limit; actual performance is often limited by noise, which makes several LSBs of the reading uncertain. The effective number of bits (ENOB) is always less than the stated resolution due to noise, INL, DNL, and other error sources.

Variables

• LSB — Least significant bit voltage (V)
• Vref — ADC reference voltage (V)
• N — ADC resolution in bits

Practical Notes

Common ADC resolutions: 8-bit (256 levels, ~20mV LSB at 5V), 10-bit (1024 levels, ~3.2mV at 3.3V), 12-bit (4096 levels, ~0.8mV at 3.3V), 16-bit (65536 levels, ~50µV at 3.3V), 24-bit (16M levels, used for precision measurement). Noise-free resolution is typically 2-4 bits less than the stated resolution. Oversampling by 4x gains 1 extra bit of effective resolution.