adctoolbox-user-guide

name

adctoolbox-user-guide

description

Router skill for using ADCToolbox from Python. Trigger when a task involves: computing or plotting spectra (SNDR, SFDR, ENOB, THD) from ADC output, fitting a sine to measured aout, calibrating SAR weights (weight_sine / weight_sine_lite), generating synthetic ADC stimulus/output, or validating aout/dout buffer shapes. For deeper debug (dashboards, phase-plane, bit-level, error decomposition, static nonlinearity, ramp INL/DNL, cap-to-weight), open references/advanced-debug.md. NOT for analog topology selection, transistor sizing, Spectre simulation, or layout/parasitic review — those belong to the analog-agents skills (analog-design, analog-verify, analog-audit). NOT for editing ADCToolbox source code — use adctoolbox-contributor-guide instead.

ADCToolbox Usage Guide

Router, not a full manual. Keep the basic tier resident; open references/*.md only when you need more.

1. When to use (and not to use)

Use for:

• Writing, fixing, or reviewing Python that calls ADCToolbox APIs
• Picking the right spectrum / calibration helper
• Getting from a raw dout / aout buffer to SNDR / SFDR / ENOB
• Generating synthetic ADC stimulus for a testbench
• Forward-modeling an ADC architecture in Python — for SAR, use adctoolbox.models.sar_convert / sar_reconstruct / sar_ideal_weights / sar_apply_cap_mismatch (binary or sub-radix-2, with optional unit-cap mismatch + sampling noise + comparator noise; vectorized). Convention: vin is interpreted relative to quant_range=(v_min, v_max), default (0, 1). SAR weights are still explicit and normalized by sum(bit_weights) + 1 LSB (for example [8, 4, 2, 1] / 16, or redundant [8, 4, 4, 2, 1] / 20). For differential SAR, pass VIP - VIN with a differential quant_range such as (-VDD, VDD). Keep analog CDAC weights and digital reconstruction weights explicit; they match unless modeling mismatch or calibration.

Do NOT use for:

• Analog topology / transistor design → analog-design, analog-explore
• Spectre simulation, pre/post-layout audit → analog-verify, analog-audit
• Editing ADCToolbox's own source → adctoolbox-contributor-guide

2. Critical conventions (read first — these are the common bug sources)

Names

• bits is the per-sample binary decision matrix shape (N_samples, N_bits), values in {0, 1} — used by every digital-calibration / bit-level helper.
• aout is the analog output (1D float array) — used by spectrum and error-analysis helpers.
• ADC integer codes are not bits; convert separately if your data is packed as integers.

Frequency units

• fs, Fin, plotting frequencies: Hz.
• fit_sine_4param(...)["frequency"]: normalized Fin/Fs (range 0–0.5), not Hz.
• calibrate_weight_sine, calibrate_weight_sine_lite, analyze_enob_sweep, generate_dout_dashboard: freq parameter is normalized Fin/Fs.
• generate_aout_dashboard: freq is in Hz (it normalizes internally).
• analyze_spectrum does NOT take Fin — it auto-detects the fundamental from the FFT.

Return shapes

Most analysis functions return dict. Notable exceptions and dict-key gotchas:

Function	Return
analyze_spectrum, analyze_spectrum_polar, analyze_spectrum_virtuoso	dict — keys: enob, sndr_dbc, sfdr_dbc, snr_dbc, thd_dbc, sig_pwr_dbfs, noise_floor_dbfs, nsd_dbfs_hz, harmonics_dbc
quick_sndr	dict — minimal: only sndr_dbc, enob. No SFDR/THD/HD/NSD breakdown.
compute_spectrum	dict — top-level keys metrics (same as above) and plot_data (freq, power_spectrum_db_plot, complex_spectrum, fundamental_bin, …)
fit_sine_4param	dict — frequency (normalized), amplitude, phase, dc_offset, rmse, fitted_signal, residuals
find_coherent_frequency	tuple (fin_actual_hz, best_bin)
calibrate_weight_sine	dict — weight, offset, calibrated_signal, ideal, error, refined_frequency
calibrate_weight_sine_lite	ndarray (weights only)
analyze_bit_activity	ndarray (% of 1's per bit, length = N_bits)
analyze_overflow	tuple of 4 ndarrays (range_min, range_max, ovf_pct_zero, ovf_pct_one)
analyze_enob_sweep	tuple (enob_sweep, n_bits_vec)
analyze_weight_radix	dict — radix, wgtsca, effres (weight-list resolution estimate)
fit_static_nonlin	tuple (k2, k3, fitted_sine, fitted_transfer)
convert_cap_to_weight	tuple (weights, c_total)

analyze_weight_radix(weights)["effres"] is computed from significant absolute weights as log2(sum(abs_w_sig) / min(abs_w_sig) + 1). It estimates the theoretical span of the supplied SAR/DAC weight list; it is not a missing-code, DNL/INL, or SAR-reachability check.

calibrate_weight_sine(...) returns solver-unit-sine scaled waveform fields by default (scale_convention == "solver_unit_sine"). Use scale_calibration_output(...) before interpreting calibrated sig_pwr_dbfs, noise_floor_dbfs, or nsd_dbfs_hz against a known ADC/code full-scale.

When docs conflict, trust the current __init__.py exports + the tests/integration/test_user_guide_skill_examples.py smoke tests.

3. Basic workflow — spectrum

from adctoolbox import (
    analyze_spectrum, analyze_spectrum_polar,
    find_coherent_frequency, fit_sine_4param,
)
from adctoolbox.fundamentals import validate_aout_data

validate_aout_data(aout)
metrics = analyze_spectrum(aout, fs=fs, create_plot=False)
print(metrics["sndr_dbc"], metrics["sfdr_dbc"], metrics["enob"])

For subplot layouts, pass the target Matplotlib axes directly. Do this before falling back to custom FFT plotting:

fig, axes = plt.subplots(3, 1)
for ax, trace in zip(axes, traces):
    metrics = analyze_spectrum(trace, fs=fs, create_plot=True, ax=ax)

Side-bin defaults differ by entry point. analyze_spectrum and compute_spectrum use waveform-based auto detection when side_bin=None. quick_sndr keeps side_bin=None as the coherent-main-lobe fast path; pass side_bin="auto" when you want its SNDR/ENOB-only path to match the analyzer's auto side-bin selection for a dominant non-coherent single tone. Auto detection adds an ideal-tone FFT pass, so keep explicit/coherent side bins in hot optimization loops when the capture setup allows it.

To set up a coherent capture upstream (where you control the stimulus frequency), snap Fin to an FFT bin first:

fin_hz, k_bin = find_coherent_frequency(fs, fin_target_hz, n_fft=len(aout))
# now drive the test with fin_hz

Pick the variant by output:

• analyze_spectrum — magnitude spectrum + SNDR/SFDR/ENOB/THD metrics dict (default — annotated white-bg plot, Hann window)
• analyze_spectrum_virtuoso — same metrics, but Cadence Virtuoso / ADE-Explorer dark-theme stem plot. Defaults to rectangular window (one stem = one bin, no main-lobe smearing).
• analyze_spectrum_polar — phase-aware (I/Q or mixer contexts); same keys
• quick_sndr — lean SNDR + ENOB only. Use in optimization loops, parameter sweeps, spec gates. No plot, no SFDR/THD/HD/NSD breakdown. Returns just {sndr_dbc, enob}. Its default side_bin=None is the coherent fast path; side_bin="auto" is available when non-coherent single-tone accuracy matters more than speed.
• compute_spectrum (from adctoolbox.spectrum) — both metrics and plot-ready data (access via result["plot_data"]["freq"] etc.)
• find_coherent_frequency — pre-step at signal generation time, not analysis
• fit_sine_4param — pre-step for nonlinearity work; remember its "frequency" key is normalized Fin/Fs

For the lean path:

from adctoolbox import quick_sndr
m = quick_sndr(aout, fs=fs)
print(m["sndr_dbc"], m["enob"])
# For a dominant non-coherent single tone, opt into analyzer-style side-bin
# detection. This is slower than the coherent default.
m_auto = quick_sndr(aout, fs=fs, side_bin="auto")
# Override the window when the upstream stimulus is coherent and
# you want a clean rectangular FFT instead of Hann:
m = quick_sndr(aout, fs=fs, win_type='rectangular')

4. Basic workflow — digital calibration

from adctoolbox import calibrate_weight_sine, scale_calibration_output
from adctoolbox.calibration import calibrate_weight_sine_lite
from adctoolbox.fundamentals import validate_dout_data

validate_dout_data(bits)            # bits: (N_samples, N_bits) in {0, 1}

freq_norm = fin_hz / fs             # normalized — not Hz
result = calibrate_weight_sine(bits, freq=freq_norm)
weights = result["weight"]
calibrated = result["calibrated_signal"]

# Map solver-unit-sine calibration output back to an ADC/code convention
# before interpreting dBFS, noise floor, or NSD.
# Use the same nominal ADC/code weights that define the desired full scale.
result_adc = scale_calibration_output(result, target_weights=nominal_weights)
calibrated_adc = result_adc["calibrated_signal"]

weights_fast = calibrate_weight_sine_lite(bits, freq_norm)   # ndarray, no dict

calibrate_weight_sine returns a dict with weight, offset, calibrated_signal, ideal, error, refined_frequency. The _lite variant returns just the weights ndarray and is positional (no freq= kw). calibrated_signal is in solver-unit-sine scale unless explicitly rescaled. Ratio metrics are scale-invariant; sig_pwr_dbfs, noise_floor_dbfs, and nsd_dbfs_hz are not. max_scale_range=None is self-referenced, so calibrated dBFS can look tidy while still having no physical ADC full-scale meaning. Supply an explicit range when interpreting calibrated spectra against an ADC/code full-scale. If freq is omitted, calibrate_weight_sine estimates the tone frequency and then fine-searches it against the calibration residual. If the coherent training frequency is already known, pass freq=k/N to keep that exact frequency fixed; use force_search=True only when you deliberately want to refine a provided frequency.

5. Import rules (compressed)

Kind	Use
Anything re-exported by adctoolbox.__init__	from adctoolbox import X
Submodule-only public tool (siggen, toolset, aout, calibration, fundamentals, spectrum)	from adctoolbox.<submodule> import X

If a flat import fails, check the submodule's __init__.py before concluding the tool is gone. Common submodule-only names: ADC_Signal_Generator (siggen), compute_spectrum (spectrum), calibrate_weight_sine_lite (calibration), validate_aout_data / validate_dout_data / convert_cap_to_weight (fundamentals), analyze_phase_plane / analyze_error_phase_plane (aout), generate_aout_dashboard / generate_dout_dashboard (toolset).

6. Going further

• Dashboards, phase-plane, bit-level, error decomposition, static nonlinearity, ramp INL/DNL, cap-to-weight → references/advanced-debug.md
• Function signatures / return keys → references/api-quickref.md
• Ready-to-adapt example files → references/example-map.md

Highly Recommended Baseline: For the simplest end-to-end analysis

• plot template, adapt 02_spectrum/exp_s03_analyze_spectrum_savefig.py (see references/example-map.md for the path). The packaged CLI adctoolbox-get-examples [dest] dumps the full example tree.

Every code block in this file (and in references/advanced-debug.md) is exercised by python/tests/integration/test_user_guide_skill_examples.py — if a future edit breaks one, that test fails.