AC Stability (Bode, PM/GM)

Compute Bode magnitude/phase and stability margins from an AC run.

RC Bode

Note: NGSpice names nodes as n1, n2, ... in the RAW file by default. Use v(n1) for the first node voltage (output in the RC examples).

Quick Bode

from cat.analysis import bode

# Run an AC sweep and get (f, mag_db, phase_deg)
f, mag_db, ph = bode(c, y_out="v(n1)", sweep_type="dec", n=201, fstart=10.0, fstop=1e6)

The circuit must include a small-signal AC source (e.g., VA() or Iac).

Margins and bandwidth

from cat.analysis import ac_gain_phase, bandwidth_3db, crossover_freq_0db, phase_margin, gain_margin_db

res = run_ac(c, "dec", 201, 10.0, 1e6)
f, g_db, ph = ac_gain_phase(res.traces, y_out="v(n1)")

bw = bandwidth_3db(res.traces, y_out="v(n1)")
wc = crossover_freq_0db(res.traces, y_out="v(n1)")
pm = phase_margin(res.traces, y_out="v(n1)")
gm = gain_margin_db(res.traces, y_out="v(n1)")
print(bw, wc, pm, gm)

Use plot_bode(ts, y) to plot the complex trace when available.