Anti-Aliasing Filter Order Calculator

Compute the required analog anti-aliasing filter order to suppress aliasing below a target SNR for a given sample rate and signal bandwidth.

Calculator Electronics Updated Apr 23, 2026
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How to Use
  1. Enter sample rate, signal bandwidth (passband), and required aliasing rejection.
  2. Tool computes required Butterworth/Chebyshev filter order for fs/2 stopband attenuation.
Input
Hz (kHz, MHz OK)
Hz
dB
Presets
Filter Response
Butterworth N
—
Chebyshev 1dB
—
Guard Band
—
Stop fs/2
—

Show Work

Enter values.

Formulas

Nyquist limit
f_stop = fs / 2
Above this aliases.
Butterworth N
N = log(10^(A/10) − 1) / (2·log(f_stop/f_pass))
Round up.
12-bit ADC
Need ~74 dB
Matches ENOB.
16-bit ADC
Need ~96 dB
Matches ENOB.
Oversampling bonus
Guard ∝ fs/(2·fp)
Higher fs = easier filter.
Digital decimator
Sigma-delta ADCs
Analog order drops to 1-2.

History of Anti-Alias Filtering

Claude Shannon and Harry Nyquist formalized the sampling theorem in the 1920s-40s: any signal above fs/2 aliases into the baseband unless filtered. Early digital audio and telemetry systems relied on steep 7th-10th order analog filters before ADC. Modern sigma-delta converters (pioneered in the 1970s at Bell Labs) use heavy oversampling plus digital decimation to shift most alias rejection into the digital domain - reducing analog filter order to 1st or 2nd even for 24-bit audio performance.

About This Calculator

Enter sample rate, passband frequency, and required alias rejection in dB (typical = ADC ENOB × 6 dB/bit). The tool computes required filter orders for Butterworth (maximally flat passband) and Chebyshev (sharper transition, ripple).

For oversampling ADCs (sigma-delta, SAR with 4-8× oversampling), reduce analog filter order by 2-3 — the ADC\'s digital decimator handles the rest. Everything runs client-side.

Frequently Asked Questions

Why anti-alias?

Signals above fs/2 fold back into the usable passband as aliases. Anti-alias filter attenuates them before the ADC. Target rejection: 10·log₂(2^ENOB) dB for the ADC\'s effective bits (e.g., 12-bit needs ~72 dB).

Guard band?

Ratio (fs/2)/f_pass defines the filter transition region. Wider guard band = easier filter, fewer poles. Oversampling (fs > 2·f_signal) trades ADC sample-rate for simpler analog filter.

Digital half?

Modern ADCs with integrated digital decimation filters do most of the alias rejection digitally, leaving the analog filter only to reject out-of-band signals beyond the decimation filter\'s stopband. Reduces analog filter order dramatically.

Common Use Cases

Audio 44.1 kHz ADC

20 kHz passband, 22.05 kHz stop, 96 dB SNR: 5-6 order Chebyshev.

Oversampling ADC

1 MSPS ADC for 10 kHz signal: 50× guard band → 2nd-order Butterworth works.

Scope Front-End

1 GS/s, 500 MHz BW: 2-3 order Gaussian-response low-pass for smooth step response.

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