96 lines
3.3 KiB
JavaScript
96 lines
3.3 KiB
JavaScript
import { describe, it, expect } from 'vitest';
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import { runNetlist } from '../src/spice/SpiceEngine.js';
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/** Convert { real, img } to magnitude in dB. */
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function magDB(c) {
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return 20 * Math.log10(Math.sqrt(c.real * c.real + c.img * c.img));
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}
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function phaseDeg(c) {
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return Math.atan2(c.img, c.real) * 180 / Math.PI;
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}
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describe('ngspice — AC (small-signal) analysis', () => {
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it('RC low-pass: −3 dB at f_c = 1/(2πRC)', { timeout: 30_000 }, async () => {
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// R=1k, C=159.15nF → f_c = 1000 Hz exactly
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const netlist = `AC sweep RC low-pass
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V1 in 0 AC 1
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R1 in out 1k
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C1 out 0 159.155n
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.ac dec 20 10 1Meg
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.end`;
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const { vec } = await runNetlist(netlist);
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const freq = vec('frequency');
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const vout = vec('v(out)');
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// Find the frequency where magnitude = −3 dB
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const mag = vout.map(magDB);
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let f3db = null;
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for (let i = 0; i < freq.length - 1; i++) {
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if (mag[i] > -3 && mag[i + 1] <= -3) {
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const a = mag[i], b = mag[i + 1];
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const fa = freq[i].real ?? freq[i];
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const fb = freq[i + 1].real ?? freq[i + 1];
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f3db = fa + ((-3 - a) / (b - a)) * (fb - fa);
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break;
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}
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}
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expect(f3db).not.toBeNull();
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expect(f3db).toBeGreaterThan(900);
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expect(f3db).toBeLessThan(1100);
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// Low-frequency gain ≈ 0 dB
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expect(mag[0]).toBeGreaterThan(-0.5);
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// Well above cutoff: roll-off −20 dB/decade
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const highIdx = mag.length - 1;
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const decadesAbove = Math.log10((freq[highIdx].real ?? freq[highIdx]) / 1000);
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const expectedRolloff = -20 * decadesAbove;
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expect(mag[highIdx]).toBeLessThan(expectedRolloff + 2);
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expect(mag[highIdx]).toBeGreaterThan(expectedRolloff - 2);
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// Phase at cutoff ≈ −45°
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let fcIdx = 0;
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for (let i = 0; i < freq.length; i++) {
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if ((freq[i].real ?? freq[i]) >= 1000) { fcIdx = i; break; }
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}
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const ph = phaseDeg(vout[fcIdx]);
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expect(ph).toBeLessThan(-40);
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expect(ph).toBeGreaterThan(-50);
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});
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it('Parallel-tank RLC bandpass: peak at f₀ = 1/(2π√LC)', { timeout: 30_000 }, async () => {
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// L=1mH, C=1µF → f₀ ≈ 5033 Hz. Parallel LC to ground, R source.
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const netlist = `RLC bandpass
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V1 in 0 AC 1
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R1 in out 1k
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L1 out 0 1m
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C1 out 0 1u
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.ac dec 30 10 1Meg
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.end`;
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const { vec } = await runNetlist(netlist);
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const freq = vec('frequency');
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const vout = vec('v(out)');
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const mag = vout.map(magDB);
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let peakIdx = 0;
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for (let i = 1; i < mag.length; i++) if (mag[i] > mag[peakIdx]) peakIdx = i;
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const fpeak = freq[peakIdx].real ?? freq[peakIdx];
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const expected_f0 = 1 / (2 * Math.PI * Math.sqrt(1e-3 * 1e-6));
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// Peak of LC low-pass with R source is slightly below f0; allow wide band
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expect(fpeak).toBeGreaterThan(expected_f0 * 0.8);
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expect(fpeak).toBeLessThan(expected_f0 * 1.2);
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// Passive network: max gain ≤ 1 (0 dB). At resonance approaches 0 dB.
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expect(mag[peakIdx]).toBeGreaterThan(-1);
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expect(mag[peakIdx]).toBeLessThan(0.01);
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// Stop-band rejection at 10× the resonance frequency should be significant
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let farIdx = 0;
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for (let i = 0; i < freq.length; i++) {
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const f = freq[i].real ?? freq[i];
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if (f > expected_f0 * 10) { farIdx = i; break; }
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}
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if (farIdx > 0) {
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expect(mag[farIdx]).toBeLessThan(mag[peakIdx] - 15);
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}
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});
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});
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