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ADC SNR Calculator

Enter the effective number of bits to get the ideal SNR.

Result

64.97 dB

How it is calculated

The tool evaluates SNR(dB) = 6.02 × ENOB + 1.76. ENOB is the effective number of bits, a plain number that may include decimals, since real converters seldom reach their nominal bit count. The 6.02 is the dB gain per bit (about 20·log102) and 1.76 dB comes from assuming a full-scale sine input and quantisation noise only. The result is the best-case SNR in dB for that many effective bits, rounded to 2 decimals. ENOB must not be negative. The tool runs one way, from bits to dB; to get ENOB from a measured SNR, rearrange to ENOB = (SNR − 1.76) ÷ 6.02. Zero bits returns 1.76 dB because the constant is part of the formula.

Worked example

A datasheet specifies an effective resolution of 10.5 bits for a nominal 12-bit ADC. Step 1: 6.02 × 10.5 = 63.21. Step 2: add 1.76 to get 64.97 dB. For comparison, an ideal 12-bit converter gives 6.02 × 12 + 1.76 = 74.00 dB, so the loss of 1.5 effective bits costs about 9 dB of signal-to-noise ratio.

Try this example →

Common mistakes

  • Typing the nominal bit count (for example 12) when the datasheet gives a lower ENOB. The tool then shows the ideal 74.00 dB, which a real converter will not reach.
  • Treating the output as a measured SNR. It is the theoretical best case from quantisation noise only; thermal noise, jitter and distortion in the real circuit make the actual value lower.
  • Comparing it with SINAD or SFDR figures as if they were the same quantity. The formula gives the ideal SNR for a full-scale sine wave, not distortion-inclusive values.
  • Applying it to a signal well below full scale. The 1.76 dB constant assumes a full-scale input, so a smaller signal has a lower SNR than the tool shows.

About this calculator

The ideal signal-to-noise ratio of an analog-to-digital converter is set entirely by its resolution, expressed through the classic formula SNR = 6.02 × ENOB + 1.76 dB, where ENOB is the effective number of bits. The 6.02 dB-per-bit factor comes from the fact that each additional bit halves the quantization step size, and the 1.76 dB constant falls out of assuming a full-scale sine-wave input and uniformly distributed quantization error.

Electronics and DSP engineers use this relationship to predict the theoretical best-case SNR a given ADC bit-depth can deliver. You enter the effective number of bits and the calculator returns the SNR in dB. To go the other way and back-calculate a real-world ADC's effective number of bits from the SNR on a datasheet, rearrange the formula by hand: ENOB = (SNR − 1.76) / 6.02 — a standard step when comparing ADC parts or validating audio and instrumentation designs against the manufacturer's specs.

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