ADC Resolution, ENOB and Aliasing Calculator
Step size, ideal signal-to-noise ratio, effective number of bits, quantisation noise and the alias frequency of a signal sampled by an analogue-to-digital converter.
Results
The dashed line marks the value you entered.
What this tool does
An N-bit converter divides its input range into 2ᴺ steps, and rounding to the nearest one adds a noise of LSB ÷ √12, which for a full-scale sine gives the well-known SNR = 6.02 N + 1.76 dB. Real converters fall short of it: the datasheet SINAD is turned back into effective bits with ENOB = (SINAD − 1.76) ÷ 6.02, which is why a '12-bit' part is often a 10.5-bit one at high frequency. A signal above half the sampling rate does not disappear but folds back to a lower frequency, so an anti-aliasing filter has to come before the converter.
Formula
LSB = V_FS ÷ 2ᴺ · SNR = 6.02 N + 1.76 dB · ENOB = (SINAD − 1.76) ÷ 6.02 · q_rms = LSB ÷ √12 · alias = |f − f_s × round(f ÷ f_s)|
Variables
| Symbol | Meaning | Unit |
|---|---|---|
nb | Converter resolution | bit |
vfs | Full-scale input range | V |
sinad | Measured SINAD (from the datasheet) | dB |
fin | Input signal frequency | kHz |
fs | Sampling rate | kHz |
LSB | Size of one step (1 LSB) | mV |
SNR | Ideal signal-to-noise ratio | dB |
EN | Effective number of bits (ENOB) | bit |
QN | Quantisation noise (rms) | µV |
CO | Number of output codes | — |
NY | Nyquist frequency | kHz |
AL | Frequency the signal appears at after sampling | kHz |
AS | Is the signal aliased? | — |
Worked example
- Converter resolution12 bit
- Full-scale input range3.3 V
- Measured SINAD (from the datasheet)68 dB
- Input signal frequency130 kHz
- Sampling rate100 kHz
- Size of one step (1 LSB)0.8057 mV
- Ideal signal-to-noise ratio74.01 dB
- Effective number of bits (ENOB)11.00 bit
- Quantisation noise (rms)232.58 µV
- Number of output codes4096
- Nyquist frequency50.00 kHz
- Frequency the signal appears at after sampling30.00 kHz
- Is the signal aliased?Yes — it folds back to the frequency shown
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.