analyze_error_envelope_spectrum#

Overview#

analyze_error_envelope_spectrum analyzes the envelope spectrum of ADC errors to detect amplitude modulation (AM) patterns. This reveals signal-dependent errors that modulate with the input amplitude.

By default the input is treated as an ADC output signal: the function fits and subtracts a sine internally, then analyzes the envelope of that residual. When you already have a residual/error waveform, pass input_kind="error" to skip the sine fit. That residual-input mode matches MATLAB errevspec.

Syntax#

from adctoolbox import analyze_error_envelope_spectrum

# Basic usage
result = analyze_error_envelope_spectrum(signal, fs=100e6, create_plot=True)

# MATLAB errevspec-style usage with a precomputed residual
result = analyze_error_envelope_spectrum(error, fs=100e6, input_kind="error")

Parameters#

  • signal (array_like) — Input ADC signal, or a residual/error waveform when input_kind="error"

  • fs (float) — Sampling frequency in Hz

  • frequency (float, optional) — Normalized input frequency for signal-input sine fitting

  • input_kind ("signal" or "error", default="signal") — Whether to fit/subtract a sine internally or analyze the input directly as residual

  • create_plot (bool, default=True) — Display envelope spectrum

  • ax (matplotlib axis, optional) — Axis for plotting

Returns#

Dictionary containing:

  • spectrum metric keys such as enob, sndr_dbc, sfdr_dbc, snr_dbc, thd_dbc, sig_pwr_dbfs, and noise_floor_dbfs

  • error_signal — Error signal used for envelope extraction

  • envelope — Extracted envelope

  • input_kind — Input contract used for the analysis

Interpretation#

Envelope Spectrum

Likely Cause

DC component only

Signal-independent error (no AM)

Peak at 2×Fin

Memory effect, residue amplifier gain error

Peak at Fin

Asymmetric nonlinearity

Multiple peaks

Complex memory effects

Use Cases#

  • Detect memory effects in pipelined/SAR ADCs

  • Identify signal-dependent settling errors

  • Reveal gain errors in residue amplifiers

See Also#

References#

  1. M. Mishali et al., "Automatic Testing of Pipelined ADCs," Proc. IEEE Int. Test Conf., 2007