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Fix some math to account for leaky bins #76

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Merged
fronzbot merged 1 commit into from
Sep 3, 2024
Merged

Fix some math to account for leaky bins #76

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42 changes: 30 additions & 12 deletions adc_eval/spectrum.py
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,8 @@ def enob(sndr, places=1):
def sndr_sfdr(spectrum, freq, fs, nfft, leak, full_scale=0):
"""Get SNDR and SFDR."""
# Zero the DC bin
spectrum[0] = 0
for i in range(0, leak + 1):
spectrum[i] = 0
bin_sig = np.argmax(spectrum)
psig = sum(spectrum[i] for i in range(bin_sig - leak, bin_sig + leak + 1))
spectrum_n = spectrum
Expand Down Expand Up @@ -79,7 +80,7 @@ def sndr_sfdr(spectrum, freq, fs, nfft, leak, full_scale=0):
return stats


def find_harmonics(spectrum, freq, nfft, bin_sig, psig, harms=5, leak=20):
def find_harmonics(spectrum, freq, nfft, bin_sig, psig, harms=5, leak=20, fscale=1e6):
"""Get the harmonic contents of the data."""
harm_stats = {"harm": {}}
harm_index = 2
Expand Down Expand Up @@ -109,7 +110,7 @@ def find_harmonics(spectrum, freq, nfft, bin_sig, psig, harms=5, leak=20):

harm_stats["harm"][harm_index]["bin"] = bin_harm_max
harm_stats["harm"][harm_index]["power"] = pwr_max
harm_stats["harm"][harm_index]["freq"] = round(freq[bin_harm] / 1e6, 1)
harm_stats["harm"][harm_index]["freq"] = round(freq[bin_harm] / fscale, 1)
harm_stats["harm"][harm_index]["dBc"] = dBW(pwr_max / psig)
harm_stats["harm"][harm_index]["dB"] = dBW(pwr_max)

Expand Down Expand Up @@ -151,6 +152,7 @@ def plot_spectrum(
window="rectangular",
no_plot=False,
yaxis="power",
fscale="MHz",
):
"""Plot Power Spectrum for input signal."""
wsize = data.size
Expand All @@ -159,10 +161,21 @@ def plot_spectrum(
"hanning": np.hanning(wsize),
}

fscalar = {
"Hz": 1,
"kHz": 1e3,
"MHz": 1e6,
"GHz": 1e9,
}

if window not in windows:
print(f"WARNING: {window} not implemented. Defaulting to 'rectangular'.")
window = "rectangular"

if fscale not in fscalar:
print(f"WARNING: {fscale} not implemented. Defaulting to 'MHz'.")
fscale = "MHz"

wscale = {
"rectangular": 1.0,
"hanning": 1.633,
Expand All @@ -179,6 +192,8 @@ def plot_spectrum(

pwr_dB = 10 * np.log10(pwr) - scalar

xscale = fscalar[fscale]

sndr_stats = sndr_sfdr(pwr, freq, fs, nfft, leak=leak, full_scale=full_scale)
harm_stats = find_harmonics(
pwr,
Expand All @@ -188,19 +203,20 @@ def plot_spectrum(
sndr_stats["sig"]["power"],
harms=harmonics,
leak=leak,
fscale=xscale,
)

stats = {**sndr_stats, **harm_stats}

if not no_plot:
plt_str = get_plot_string(stats, full_scale, fs, nfft, window)
plt_str = get_plot_string(stats, full_scale, fs, nfft, window, xscale, fscale)

fig, ax = plt.subplots(figsize=(15, 8))
ax.plot(freq / 1e6, pwr_dB)
ax.plot(freq / xscale, pwr_dB)
ax.set_ylabel(f"Power Spectrum ({yunits})", fontsize=18)
ax.set_xlabel("Frequency (MHz)", fontsize=16)
ax.set_xlabel(f"Frequency ({fscale})", fontsize=16)
ax.set_title("Output Power Spectrum", fontsize=16)
ax.set_xlim([0, fs / 2e6])
ax.set_xlim([0, fs / (2 * xscale)])
ax.set_ylim([1.1 * min(pwr_dB), 0])
ax.annotate(
plt_str,
Expand Down Expand Up @@ -241,7 +257,7 @@ def plot_spectrum(
return (pwr, stats)


def get_plot_string(stats, full_scale, fs, nfft, window):
def get_plot_string(stats, full_scale, fs, nfft, window, xscale=1e6, fscale="MHz"):
"""Generate plot string from stats dict."""

plt_str = "==== FFT ====\n"
Expand All @@ -252,22 +268,22 @@ def get_plot_string(stats, full_scale, fs, nfft, window):
plt_str += "==== Signal ====\n"
plt_str += f"FullScale = {full_scale} dB\n"
plt_str += f"Psig = {stats['sig']['dBFS']} dBFS ({stats['sig']['dB']} dB)\n"
plt_str += f"fsig = {round(stats['sig']['freq']/1e6, 2)} MHz\n"
plt_str += f"fsamp = {round(fs/1e6, 2)} MHz\n"
plt_str += f"fsig = {round(stats['sig']['freq']/xscale, 2)} {fscale}\n"
plt_str += f"fsamp = {round(fs/xscale, 2)} {fscale}\n"
plt_str += "\n"
plt_str += "==== SNDR/SFDR ====\n"
plt_str += f"ENOB = {stats['enob']['bits']} bits\n"
plt_str += f"SNDR = {stats['sndr']['dBFS']} dBFS ({stats['sndr']['dBc']} dBc)\n"
plt_str += f"SFDR = {stats['sfdr']['dBFS']} dBFS ({stats['sfdr']['dBc']} dBc)\n"
plt_str += f"Pspur = {stats['spur']['dBFS']} dBFS\n"
plt_str += f"fspur = {round(stats['spur']['freq']/1e6, 2)} MHz\n"
plt_str += f"fspur = {round(stats['spur']['freq']/xscale, 2)} {fscale}\n"
plt_str += f"Noise Floor = {stats['noise']['dBHz']} dBFS\n"
plt_str += f"NSD = {stats['noise']['NSD']} dBFS\n"
plt_str += "\n"
plt_str += "==== Harmonics ====\n"

for hindex, hdata in stats["harm"].items():
plt_str += f"HD{hindex} = {round(hdata['dB'] - full_scale, 1)} dBFS @ {hdata['freq']} MHz\n"
plt_str += f"HD{hindex} = {round(hdata['dB'] - full_scale, 1)} dBFS @ {hdata['freq']} {fscale}\n"

plt_str += "\n"

Expand All @@ -284,6 +300,7 @@ def analyze(
window="rectangular",
no_plot=False,
yaxis="fullscale",
fscale="MHz",
):
"""Perform spectral analysis on input waveform."""
(spectrum, stats) = plot_spectrum(
Expand All @@ -296,6 +313,7 @@ def analyze(
window=window,
no_plot=no_plot,
yaxis=yaxis,
fscale=fscale,
)

return (spectrum, stats)