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ADC Quantization Noise Calculator

Calculate ADC quantization noise, SQNR, ENOB, and noise spectral density. Analyze dynamic range for analog-to-digital converter design. Free, instant results.

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Formula

SQNR=20log⁡10(2)⋅N+10log⁡10 ⁣(32) dB,LSB=Vref2NSQNR = 20\log_{10}(2)\cdot N + 10\log_{10}\!\left(\tfrac{3}{2}\right) \text{ dB}, \quad LSB = \frac{V_{ref}}{2^N}
N— ADC resolution (bits)
SQNR— Signal-to-quantization-noise ratio (dB)
LSB— Least significant bit voltage (V)
V_ref— ADC reference voltage (V)

How It Works

The Quantization Noise Calculator computes signal-to-quantization-noise ratio (SQNR) and LSB voltage for analog-to-digital converters — essential for ADC selection, data acquisition system design, and audio/video codec development. DSP engineers, embedded systems designers, and instrumentation specialists use this to match ADC resolution to application requirements. Per Kester "Data Conversion Handbook" (Analog Devices), quantization noise arises from rounding continuous amplitude to discrete levels. The exact SQNR formula is 20*log10(2)*N + 10*log10(1.5) = 6.0206*N + 1.761 dB, where N = bit resolution. A 16-bit ADC achieves 98.09 dB SQNR — sufficient for CD-quality audio per AES17 standard. Each additional bit improves SQNR by exactly 6.02 dB and doubles amplitude resolution. For a 5V reference, 12-bit ADC has 1.22 mV LSB while 24-bit achieves 298 nV LSB — enabling microvolt-level precision in scientific instrumentation.

Worked Example

Select ADC resolution for a 100 mV full-scale sensor with 10 uV noise floor requiring 80 dB dynamic range. Step 1: Required SQNR >= 80 dB + 6 dB margin = 86 dB. Step 2: Solve for N: 6.02*N + 1.76 >= 86, so N >= 14.0 bits. Step 3: Select 16-bit ADC (98.09 dB SQNR) for 12 dB margin. Step 4: LSB = 100mV / 65536 = 1.53 uV — well below sensor noise floor. Step 5: Verify: quantization noise = 100mV / (sqrt(12) * 65536) = 0.44 uV RMS, sensor-noise-limited as intended. Per Analog Devices MT-001, the ADC contributes < 5% of total system noise.

Practical Tips

  • ✓Per IEEE 1241-2010, select ADC with SQNR 10-20 dB above signal dynamic range for noise-limited operation
  • ✓Use dithering (adding 0.5-1 LSB noise) to decorrelate quantization noise and eliminate idle tones per Kester
  • ✓For audio applications, 16-bit provides 96 dB dynamic range meeting AES17-2015 professional audio standard
  • ✓24-bit ADCs achieve 144 dB theoretical SQNR but thermal noise limits practical ENOB to 18-20 bits

Common Mistakes

  • ✗Using approximate SQNR formula 6N+1.76 instead of exact 6.0206N+1.761 — causes 0.3 dB error at 16 bits per IEEE 1241
  • ✗Assuming higher sampling rate improves quantization noise — oversampling helps only with noise shaping per Schreier "Understanding Delta-Sigma Data Converters"
  • ✗Neglecting ADC reference voltage tolerance — 0.1% Vref error adds 0.1% gain error to all conversions

Frequently Asked Questions

Error from rounding analog amplitude to nearest digital level. Uniformly distributed over ±0.5 LSB, RMS value = LSB/sqrt(12) = 0.289*LSB. For 12-bit ADC with 4.096V reference, LSB = 1 mV and quantization noise = 289 uV RMS. Per Widrow & Kollar, this appears as white noise when dithered properly.
Each additional bit halves quantization noise voltage and improves SQNR by 6.02 dB. 8-bit: 50.1 dB SQNR. 12-bit: 74.0 dB. 16-bit: 98.1 dB. 24-bit: 146.2 dB. Per Kester, practical thermal noise limits 24-bit ADCs to ~120 dB actual SNR (20-bit ENOB).

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