## CircuitSim 1.5.0 The 1.5.0 release adds two new analysis capabilities — loop-gain stability (.STB) and Monte Carlo — plus in-world operating-point annotation on the K key, three new component blocks (Transformer, Transmission Line, Loop Probe), and direct support for KiCad and LTspice model libraries. It also brings an LTspice-style Measurement Builder, a pre-simulation circuit linter, and a netlist viewer. ### New Components **Transformer** — a 2×3 coupled-inductor block with one primary and one secondary winding (west pins = primary +/−, east pins = secondary +/−). The edit screen sets the coupling factor k (0 < k ≤ 1), primary inductance Lp, and secondary inductance Ls — all three sweepable with Param-block expressions. Each winding has an editable series resistance (default 1 mΩ; set 0 for a fully ideal winding). Note: the windings are galvanically isolated, so the secondary side needs its own DC path to ground (a resistor is enough) or ngspice will refuse to solve. **Transmission Line** — a 2×3 two-port block with two modes selected in its edit screen: *lossless* (characteristic impedance Z0 plus either a delay TD or a frequency F with normalized length NL; a freshly placed line defaults to Z0=50, TD=10ns) and *lossy LTRA* (per-length R, L, G, C plus the line length LEN; valid parameter combinations are RLC, RC, LC, and RG). All parameters accept `{param}` expressions for parametric sweeps. **Loop Probe** — a 2-pin block you drop in series inside a feedback loop. In every normal analysis it behaves as a transparent 0 V short and changes nothing; its purpose is the new .STB analysis. Orientation matters: the front face points toward the amplifier output — if your loop-gain plot looks inverted (tiny or negative dB where you expect gain), rotate the probe 180°. **Inductor series resistance** — standalone Inductor blocks gained an optional series-resistance field. Existing inductors stay ideal, but an ideal inductor straight across an ideal voltage source makes the DC operating point unsolvable ("singular matrix"), and a small Rser is the cure. ### New Analyses **.STB stability (loop-gain) analysis** — a new STB tab in the Simulate block, equivalent to Cadence Spectre's `stb` analysis. Place a Loop Probe in the feedback path, set the frequency range (same fields as AC), and run. The mod performs full Tian dual-injection — two AC runs (voltage and current injection) combined into the true loop gain — so the result is correct even at low- or high-impedance breaking points. You get Bode plots of loop-gain magnitude (dB) and phase (degrees) with phase unwrapping so the −180° crossing is visible, plus DC loop gain, unity-gain frequency (GBW), phase margin, and gain margin reported directly. **Monte Carlo** — a new "Monte Carlo runs" + "seed" row in the Simulate dialog, available for OP, AC, DC, and TRAN. Randomness comes from ngspice statistical distributions in Param blocks (`Rv = gauss(10k, 0.05, 3)`, plus agauss, unif, aunif, limit) and/or the new per-component tolerances below; every run re-rolls the values. AC/TRAN/DC runs overlay all iterations in the graph screen, OP runs plot each probe against run number, and every measured scalar (phase margin, GBW, ...) gets a mean / standard deviation / min / max summary in chat. A fixed seed makes runs reproducible; a blank seed picks a random one and tells you what it was. Capped at 300 runs. **Component tolerances** — ideal resistors, capacitors, and inductors now have a "Tolerance (%)" field in their edit screens, shown on the floating label (e.g. "1kΩ ±5%"). During Monte Carlo each toleranced device gets its own independent Gaussian draw with ±tolerance = 3σ; outside Monte Carlo the nominal value is used, so normal simulations stay deterministic. **Histograms** — graph screens gained a "Hist" toggle that re-bins the active curves' values into overlaid histograms — the natural way to look at Monte Carlo spreads. ### Operating-Point Annotation **K-key annotation** — after an .OP run, press K to float up to 4 chosen parameters over every device in the world: node voltages, currents, and for MOSFETs the full internal parameter set. "Edit Shown OP" picks which parameters are shown, per device type, from a grid of everything ngspice reports (IC MOSFETs expose ~65 parameters). Derived MOSFET figures of merit are computed for you and listed next to gm: gm/id, gm/gds (intrinsic gain), and fT = gm/(2π·cgg). Parametric and temperature OP sweeps produce one annotation frame per swept value, with `<` / `>` arrows to step through them and watch the bias points move. **Subcircuit OP projection** — while K annotation is active, any Subcircuit chip with .OP data floats a shrunk 3D copy of its inner circuit above the block, with each internal device's operating point annotated — you can see the bias of every transistor inside a chip without unpacking it. Note: chips converted before 1.5.0 don't carry the required device map; re-convert them once. **Subcircuit 3D preview** — the Subcircuit screen itself now renders a 3D preview of the chip's inner circuit, so you can see what a chip contains before placing it. ### Model Library Support Two new compatibility modes in the Simulate block make real vendor models usable directly: **KiCad mode (`ki`)** — point the paths box at KiCad's model libraries; it pre-fills the installed KiCad's built-in `Simulation_SPICE.sp` automatically, and the runner enables the same PSpice+LTspice translation KiCad itself uses. Discrete MOSFET/BJT/diode blocks auto-detect whether the library defines a `.model` card (e.g. VDMOS power FETs) or a `.subckt` macromodel (e.g. KiCad's BJTs) and emit the right SPICE device either way. The Amplifier block's pin order matches KiCad's 5-pin op-amp convention (IN+ IN− VCC VEE OUT) directly. **LTspice mode (`lt`)** — pre-fills the installed LTspice's component databases (`standard.dio` / `standard.bjt` / `standard.mos` — thousands of diode, BJT, and VDMOS cards) and reads vendor `.sub`/`.lib` macromodels. UTF-16 library files — which ngspice otherwise *silently* loads zero models from — are transcoded automatically, and LTspice `TABLE(...)` B-sources are rewritten to ngspice `pwl(...)`. Known limits: ADI-encrypted models (`<Binary File>`) and OTA-based macromodels (UniversalOpAmp2, newer ADI op-amps) only run inside LTspice itself. Also fixed in this area: ngspice's XSPICE code models (used by translated PSpice switches) now load reliably when ngspice is found via PATH. ### Simulation Workflow **Measurement Builder** — a "Measure…" button in the Commands block opens an LTspice-style editor with three tabs: Measure (build a single `meas` line from a form), Functions (expression palette for derived plots), and Presets (rise/fall time, propagation delay, period, overshoot, THD, slope-at-point, and a full AC amplifier report). Signal fields have a picker listing your live probes, sources, and plot names, and a Test button runs your configured analysis right there and shows the measured values before you save. **View Netlist** — a button in the Simulate block generates and displays the complete SPICE netlist without running the simulation, with one-click Copy. Useful for debugging or moving a circuit to desktop ngspice. **Circuit linter** — before each run the mod now checks for the classic silent killers and explains them in plain language: no Ground block placed, floating nodes (a wire to nowhere), and nodes with no DC path to ground (reachable only through capacitors or current sources). **Dual-waveform plots** — a plot screen can now show two different waveforms together on one plot. ### Other Changes - Simulations no longer hand you a written book with raw output after every run; results go to chat and the graph screens. - Fixed the Simulate block forgetting analysis parameters when switching between analysis types in its edit screen. - The separate subcircuit-projection key was removed — projections now ride along with the K annotation automatically. - New inventory item icons for the VCVS, VCCS, Amplifier, and Subcircuit blocks.

## CircuitSim 1.4.0 The 1.4.0 release lets you turn any circuit you build into a reusable subcircuit — convert a schematic into a portable chip and drop it into a new 5×5 Subcircuit block, exactly like the built-in Amplifier but defined entirely by you. It also adds behavioral (arbitrary) sources and a voltage-controlled switch, and reworks how IC/PDK parameters are configured. ### User-Defined Subcircuits **Subcircuit block** — a 5×5 block (like the Amplifier) that instantiates your own saved schematic as a single black-box component. It exposes 12 pins around its perimeter — two on each corner cell and one in the middle of each edge — numbered clockwise from the top-left. Wires connect only to the live pins; the top texture reflects the pin count and a floating name tag shows the loaded subcircuit. **Subcircuit Converter + Subcircuit Chip** — place the Converter block on a finished circuit, give it a name, and convert: the schematic is replaced by a portable Chip item. Right-click the ground with a chip to rebuild the entire circuit block-for-block, or insert it into a Subcircuit block to use it. **Probe "Subcircuit pin" toggle** — the voltage probe edit screen gains a checkbox (plus a pin-order number) that marks a net as an external terminal of the subcircuit. The probe's label becomes the pin name. **Under the hood** — conversion generates a self-contained `.subckt … .ends` definition and instantiates it with an `X` line, so subcircuits work across OP, AC, DC, TRAN, and NOISE analyses as well as parameter sweeps. The Subcircuit block's GUI has a chip slot and a scrollable, read-only netlist view. ### New Components **Behavioral (arbitrary) sources** — B-source blocks driven by a free-form expression (`V = …` for a voltage source, `I = …` for a current source). **VC Switch** — a voltage-controlled switch (ngspice `S` device / `SW` model) with configurable threshold, hysteresis, on/off resistances, and an optional initial state. Switches with identical parameters share one `.model` line. ### PDK / IC Components - The PDK choice (model prefix and MOSFET geometry) now lives on each IC component instead of the Simulate block. `none` / `placeholder` emit a bare `W/L/m` instance, while `sky130A` keeps the full geometry via a per-PDK formula table. - W/L are read as microns under `sky130A` and as SI meters otherwise; editor labels, field parsing, and in-world callouts were updated to match. NF is editable only under `sky130A`. - The device multiplier is emitted as ngspice's built-in `m=` for all IC devices. - The `hsa` compatibility mode now accepts multiple `.lib` paths in a single multi-line box, like `psa`. ### Example World - Updated with additional pre-built circuits. - **Note:** some examples reference `.lib` files by absolute path; update those to match your own PDK install before simulating them. ### Other Changes - README updated with a User-Defined Subcircuits guide and captions above the preview GIFs. - Removed leftover texture-fix helper scripts; minor texture fixes.

# CircuitSim 1.3.0 The 1.3.0 release adds discrete (single-package) transistors, BJT support, configurable diode models, and a big upgrade to the graph screen with measurement cursors. It also ships a playable example world so you can see working circuits without wiring anything yourself. ## New Components ### Discrete Transistors - **Discrete NMOS / PMOS** — single-block MOSFETs as an alternative to the multi-block IC MOSFETs, each with its own edit screen. - **Discrete NPN / PNP BJTs** — bipolar junction transistors. All four come with their own block, item, creative-tab entry, loot table, block model, edit screen, and network sync packet. ## Component Improvements - **Diode models** — the diode edit screen now has an optional `.MODEL` field. Leave it blank for the built-in basic SPICE diode, or enter a model name (e.g. `D1N4148_1`) to use a model from your library (PSpice). - **Voltage probe "name only" mode** — a new checkbox lets a voltage probe name and merge its net **without** plotting/printing it, useful for naming nodes you don't want cluttering the output. ## Graph Screen - **Measurement cursors** — toggle a pair of OrCAD-style vertical cursors per plot. Drag cursor 1 with the left mouse button and cursor 2 with the right; the readout shows X/Y at each cursor plus the dx/dy between them. - Independent cursor and log-axis toggles for the top and bottom plots. ## Simulation - **"None" compatibility mode** — you can now pick `none` when choosing the simulator compatibility mode. - Various netlist-builder and circuit-extractor updates to support the new components and diode models. ## Example World - The repo now ships a ready-to-play save in `example_world/` ("Zaza The Creator") with a set of pre-built example circuits — from simple passives up to controlled sources, the Amplifier block, and IC/PDK components. Copy the folder into your `saves/` directory to load it. - **Note:** some examples reference `.lib` files by absolute path; update those paths to match your own PDK install/OrCAD libraries before simulating them. ## Other Changes - New **Simulate Block edit screen** layout. - Mod icon changed to the amplifier texture. - README updated with animated GIF previews (non-inverting amp, Miller amp, MOSFET output characteristics) and an Example World section.