{
  "spicebook_version": "2026-02-13",
  "metadata": {
    "title": "RC Lowpass Filter Analysis",
    "engine": "ngspice",
    "tags": ["filter", "passive", "beginner"],
    "created": "2026-02-13T00:00:00Z",
    "modified": "2026-02-13T00:00:00Z"
  },
  "cells": [
    {
      "id": "cell-intro",
      "type": "markdown",
      "source": "# RC Lowpass Filter\n\nA first-order passive RC lowpass filter with a cutoff frequency of approximately **1.59 kHz**.\n\nThe -3dB frequency is: f_c = 1 / (2 * pi * R * C)\n\nWith R = 1k and C = 100nF: f_c = 1 / (2 * pi * 1000 * 100e-9) = 1591 Hz",
      "outputs": []
    },
    {
      "id": "cell-ac",
      "type": "spice",
      "source": "RC Lowpass Filter - AC Analysis\nV1 in 0 AC 1\nR1 in out 1k\nC1 out 0 100n\n.ac dec 100 1 10meg\n.end",
      "outputs": []
    },
    {
      "id": "cell-explain-ac",
      "type": "markdown",
      "source": "## Interpreting the Bode Plot\n\nThe magnitude plot should show:\n- **Flat response** (0 dB) below the cutoff frequency\n- **-3 dB point** at approximately 1.59 kHz\n- **-20 dB/decade rolloff** above the cutoff\n\nThe phase should transition from 0 degrees to -90 degrees, passing through -45 degrees at the cutoff frequency.",
      "outputs": []
    },
    {
      "id": "cell-transient",
      "type": "spice",
      "source": "RC Lowpass Filter - Step Response\nV1 in 0 PULSE(0 1 0 1n 1n 0.5m 1m)\nR1 in out 1k\nC1 out 0 100n\n.tran 10u 3m\n.end",
      "outputs": []
    },
    {
      "id": "cell-explain-transient",
      "type": "markdown",
      "source": "## Step Response\n\nThe transient simulation shows the capacitor charging and discharging through the resistor.\n\nThe time constant is: tau = R * C = 1000 * 100e-9 = 100 us\n\nThe output reaches ~63% of the input voltage after one time constant, and ~95% after three time constants (300 us).",
      "outputs": []
    }
  ]
}