ADC Theoretical SNR

Formula

Description

The theoretical maximum signal-to-noise ratio of an ideal N-bit ADC is determined by quantization noise alone. Each additional bit adds 6.02 dB of dynamic range (since each bit doubles the number of levels, and 20×log₁₀(2) = 6.02). The 1.76 dB term accounts for the relationship between the full-scale sinusoidal signal power and the uniformly distributed quantization noise. In practice, ADCs never achieve this theoretical limit due to thermal noise, clock jitter, nonlinearities, and other analog imperfections. The SINAD (signal-to-noise-and-distortion) specification measures the actual performance.

Variables

• SNR — Maximum signal-to-noise ratio (dB)
• N — ADC resolution in bits

Practical Notes

Theoretical SNR by resolution: 8-bit = 49.9 dB, 10-bit = 61.9 dB, 12-bit = 74.0 dB, 16-bit = 98.1 dB, 24-bit = 146.2 dB. Real-world ENOB = (SINAD - 1.76) / 6.02. A 12-bit ADC with SINAD of 68 dB has ENOB of 11 bits. High-resolution sigma-delta ADCs (24-bit) typically achieve 19-21 ENOB.