File imdmeas_core.h¶

FileList > imdmeas > imdmeas_core.h

IMDMeasure — two-tone intermodulation (IMD2/IMD3) and intercept. More...

#include "clib_common.h"
#include "jm_perf.h"
#include "measure/measure_core.h"
#include "psd/psd_core.h"
#include <complex.h>

Classes¶

Type	Name
struct	imdmeas_state_t IMDMeasure state: owned window, FFT plan and one-sided power scratch.

Public Functions¶

Type	Name
imd_meas_t	imdmeas_analyze (imdmeas_state_t * state, const float * x, size_t n_in) Two-tone IMD/TOI of a real capture (finds the two strongest tones).
imdmeas_state_t *	imdmeas_create (size_t n, double fs, double full_scale, size_t bits, double dynamic_range_db) Create an IMDMeasure analyser (auto Kaiser window).
void	imdmeas_destroy (imdmeas_state_t * state) Destroy an IMDMeasure analyser.
void	imdmeas_reset (imdmeas_state_t * state) Reset (no-op: each analyze() call is independent).
size_t	imdmeas_spectrum_dbfs (imdmeas_state_t * state, const float * x, size_t x_len, float * out) DC-centred dBFS magnitude spectrum of a capture (length nfft). The same averaged PSD the metrics use, for an analyzer-display backdrop.
size_t	imdmeas_spectrum_dbfs_max_out (imdmeas_state_t * state) Capacity (== nfft) of the spectrum_dbfs output buffer.

Detailed Description¶

Drive two equal-amplitude tones f1<f2; the analyser finds them as the two strongest lobes, integrates each fundamental and the intermodulation products (2f1-f2, 2f2-f1 for IMD3; f2-f1 for IMD2) over their window main lobes (folded into the analysed band), and reports the third/second-order intercepts.

Lifecycle: create -> [analyze]* -> destroy

Public Functions Documentation¶

function imdmeas_analyze¶

Two-tone IMD/TOI of a real capture (finds the two strongest tones).

imd_meas_t imdmeas_analyze (
    imdmeas_state_t * state,
    const float * x,
    size_t n_in
)

Returns:

the IMD metric record (by value; zeroed if no two tones are found).

>>> from doppler.measure import IMDMeasure
>>> import numpy as np
>>> t = np.arange(4096)
>>> # two equal tones at 200 & 250 cycles + 3rd-order products 40 dB down
>>> x = (np.cos(2*np.pi*200*t/4096) + np.cos(2*np.pi*250*t/4096)
...      + 0.01*np.cos(2*np.pi*150*t/4096)
...      + 0.01*np.cos(2*np.pi*300*t/4096)).astype(np.float32)
>>> r = IMDMeasure(n=4096, fs=1.0).analyze(x)
>>> round(r.f1, 4), round(r.f2, 4), round(r.imd3_dbc, 0)
(0.0488, 0.061, -40.0)

function imdmeas_create¶

Create an IMDMeasure analyser (auto Kaiser window).

imdmeas_state_t * imdmeas_create (
    size_t n,
    double fs,
    double full_scale,
    size_t bits,
    double dynamic_range_db
)

The window is always Kaiser; its shape is auto-selected so the sidelobes sit below the requested dynamic range (see measure_resolve_dr()), keeping the resolution bandwidth as fine as n allows.

Parameters:

n Capture/frame length (>= 2).
fs Sample rate (Hz, > 0).
full_scale Amplitude that equals 0 dBFS (> 0). Ignored if bits > 0.
bits ADC depth: bits>0 sets the 0-dBFS reference to 2^(bits-1) and, unless overridden, the dynamic-range target.
dynamic_range_db Explicit sidelobe/dynamic-range target (dB); used when > 0, else derived from bits.

Returns:

Heap state, or NULL on bad args / allocation failure.

function imdmeas_destroy¶

Destroy an IMDMeasure analyser.

void imdmeas_destroy (
    imdmeas_state_t * state
)

Parameters:

state May be NULL.

function imdmeas_reset¶

Reset (no-op: each analyze() call is independent).

void imdmeas_reset (
    imdmeas_state_t * state
)

function imdmeas_spectrum_dbfs¶

DC-centred dBFS magnitude spectrum of a capture (length nfft). The same averaged PSD the metrics use, for an analyzer-display backdrop.

size_t imdmeas_spectrum_dbfs (
    imdmeas_state_t * state,
    const float * x,
    size_t x_len,
    float * out
)

function imdmeas_spectrum_dbfs_max_out¶

Capacity (== nfft) of the spectrum_dbfs output buffer.

size_t imdmeas_spectrum_dbfs_max_out (
    imdmeas_state_t * state
)

The documentation for this class was generated from the following file native/inc/imdmeas/imdmeas_core.h