usefulweb.site Ohmforge AC Sweep (Bode plot)

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Ohmforge AC Sweep (Bode plot)

Frequency response of a circuit: Bode magnitude/phase, −3 dB corner and unity gain.

Subset: R C L V I D Q M E G K, .model, SIN/PULSE/PWL sources, engineering suffixes (k, m, u, n, p, meg). Node 0 is ground. Leave empty when you pass an Ohmforge project instead.

Alternative to the netlist: a .ohmforge.json project as saved by the app (format "ohmforge", version 1).

Name of the V or I source to excite (e.g. V1). Empty = keep the AC magnitudes from the netlist.

Report V(out)/V(ref) instead of V(out).

Hz

Empty = .ac line or 1 Hz.

Hz

Empty = .ac line or 10 MHz.

Empty = .ac line or 20.

Try an example: RC low-pass (fc ≈ 1.59 kHz) · Inverting op-amp, gain −10

How it works

Linearises the circuit at its DC operating point and solves the complex MNA equations across a logarithmic frequency sweep. Returns magnitude in dB and unwrapped phase of an output node (optionally relative to an input node), the peak gain, lower/upper −3 dB frequencies, the unity-gain frequency, a Bode chart and CSV.

  • The DC operating point is solved first; every nonlinear device is replaced by its small-signal conductances at that point (diode gd, BJT gm/gπ/go, MOSFET gm/gds, op-amp output slope).
  • Capacitors become admittances jωC, inductors impedances jωL in their branch equations, coupled inductors jωM; the complex system is solved by dense LU with partial pivoting at every frequency.
  • Magnitude is 20·log10|H|, phase is unwrapped to be continuous. The −3 dB points are found 3.01 dB below the peak by logarithmic interpolation; unity gain is the 0 dB crossing.

Teaching-grade simulation: device models are simplified (Ebers–Moll BJT, level-1 MOSFET, behavioural op-amps and 555) and part ratings are typical values. Verify real designs on the bench and against manufacturer data before building anything connected to mains voltage.

Sources

For scripts and AI agents

  • JSON API: POST https://ohmforgeacsweep.usefulweb.site/api/v1/calculate (same calculation as this page)
  • Interface description: OpenAPI 3.1 · AI guide: llms.txt
  • MCP server (Streamable HTTP): https://ohmforgeacsweep.usefulweb.site/mcp · tool name ohmforge_ac_sweep
Example request
curl -s -X POST https://ohmforgeacsweep.usefulweb.site/api/v1/calculate \
  -H 'content-type: application/json' \
  -d '{"netlist":"* RC low-pass, fc = 1/(2*pi*1k*100n) = 1591.5 Hz\nV1 in 0 DC 0 AC 1\nR1 in out 1k\nC1 out 0 100n\n.ac dec 20 10 1meg","output":"out","input":"V1"}'

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