ADC SNR and ENOB calculator
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KEY POINTS
The ideal SNR of an N-bit ADC is 6.02N + 1.76 dB, and the effective number of bits is ENOB = (SINAD − 1.76) / 6.02. Thermal noise, jitter and nonlinearity leave real ADCs one to three bits below their nominal resolution. Jitter-limited SNR is −20·log₁₀(2π·fin·tj), so 70 dB on a 1 GHz signal requires jitter of about 50 fs.
Estimate SNR and ENOB from design values
ENOB from measured SINAD
SINAD is often measured below full scale, so the shortfall (1 dB at −1 dBFS) is added back to give ENOB referred to full scale.
SNR ceiling set by input frequency and jitter (jitter 1 ps)
Resolution, ideal SNR and LSB
| Resolution | Ideal SNR | Codes | 1 LSB (Vref = 3.3 V) |
|---|---|---|---|
| 8 bit | 49.92 dB | 256 | 12,890 µV |
| 10 bit | 61.96 dB | 1,024 | 3,223 µV |
| 12 bit | 74.00 dB | 4,096 | 805.7 µV |
| 14 bit | 86.04 dB | 16,384 | 201.4 µV |
| 16 bit | 98.08 dB | 65,536 | 50.35 µV |
| 18 bit | 110.12 dB | 262,144 | 12.59 µV |
| 20 bit | 122.16 dB | 1,048,576 | 3.147 µV |
| 24 bit | 146.24 dB | 16,777,216 | 0.1967 µV |
Why ENOB is lower than the resolution
Even an ideal N-bit ADC leaves quantization error from rounding the analog value to 2^N steps, giving an SNR of 6.02N + 1.76 dB for a full-scale sine wave. Real ADCs add thermal noise, clock jitter and comparator offset and nonlinearity (distortion), so the effective number of bits (ENOB) derived from measured SINAD is typically one to three bits below the nominal resolution.
The higher the signal frequency, the larger the voltage error caused by timing error at the sampling instant (jitter). Achieving 70 dB SNR on a 1 GHz signal requires jitter of about 50 fs. In high-speed ADCs for wireless communications and test instruments, the clock source matters as much as the resolution.
FAQ
Where does 6.02N + 1.76 dB come from?
It is the ratio of a full-scale sine wave's power to the quantization noise power of an ideal N-bit converter. Each extra bit adds about 6 dB.
How does oversampling improve SNR?
Spreading quantization noise over a wider bandwidth and filtering to the signal band improves SNR by 10·log₁₀(OSR), about 3 dB per doubling.
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Last updated: October 23, 2026