freechips/fullcustom/fullcustom-transistor.ipynb

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    "# Fullcustom analog design demo using Magic\n",
    "\n",
    "The environment path must be retrieved in order to provide _Magic_ with the technology files:"
   ]
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   "source": [
    "import os\n",
    "CONDA_PREFIX = os.environ['CONDA_PREFIX']"
   ]
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   "source": [
    "## Source files\n",
    "\n",
    "### Using the _Magic_ VLSI layout tool\n",
    "\n",
    "[_Magic_](http://opencircuitdesign.com/magic/) cells (`.mag`) are used to store and manage the layouts. They can be edited using _Magic_ commands or using _Magic_'s GUI.\n",
    "\n",
    "An existing _inverter_ design as well as its dependencies is imported and converted to _Graphic Design System_ (`.gds`) file for viewing and manufacturing and a _SPICE_ (`.spice`) file for simulation:"
   ]
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    "%%script magic -dnull -noconsole -rcfile {CONDA_PREFIX}/share/pdk/sky130A/libs.tech/magic/sky130A.magicrc\n",
    "\n",
    "load cad/mag/inverter.mag\n",
    "\n",
    "extract\n",
    "ext2spice lvs\n",
    "ext2spice cthresh 0\n",
    "ext2spice rthresh 0\n",
    "ext2spice -o cad/spice/inverter.spice\n",
    "\n",
    "gds labels no\n",
    "gds write cad/gds/inverter.gds"
   ]
  },
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   "source": [
    "### Display the inverter layout\n",
    "\n",
    "The `.gds` file can be converted to vector graphics for displaying:"
   ]
  },
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   "source": [
    "import gdstk\n",
    "import IPython.display\n",
    "\n",
    "library = gdstk.read_gds('cad/gds/inverter.gds')\n",
    "top_cells = library.top_level()\n",
    "top_cells[0].write_svg('cad/svg/inverter.svg', scaling=100)\n",
    "IPython.display.SVG('cad/svg/inverter.svg')"
   ]
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   "source": [
    "## Simulation\n",
    "\n",
    "### Using _SPICE_ simulation engine\n",
    "\n",
    "[_PySPICE_](https://pyspice.fabrice-salvaire.fr/releases/v1.4/overview.html) is a _Python_ implementation of several _SPICE_ simulation engines. The _SPICE_ engines are used to simulate analog circuits. A top-level test bench circuit must be built:"
   ]
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   "source": [
    "from PySpice.Spice.Netlist import Circuit, SubCircuit, SubCircuitFactory\n",
    "from PySpice.Unit import *\n",
    "\n",
    "# Declare the top-level circuit\n",
    "circuit = Circuit('Inverter')\n",
    "# Link to technology libraries\n",
    "circuit.lib(f'{CONDA_PREFIX}/share/pdk/sky130A/libs.tech/ngspice/sky130.lib.spice', 'tt')\n",
    "\n",
    "# Import and instantiate the CUT (Circuit Under Test)\n",
    "circuit.include('cad/spice/inverter.spice')\n",
    "circuit.X('Inverter', 'inverter', 'VDD','VSS','I','O');\n",
    "\n",
    "# Add voltage sources\n",
    "circuit.V('VSS', 'VSS', 0, 0)\n",
    "circuit.V('VDD', 'VDD', 'VSS', 1.8)\n",
    "# Add pulse source\n",
    "circuit.PulseVoltageSource(\n",
    "    'I', 'I', 'VSS',\n",
    "    initial_value=0@u_V, pulsed_value=1.8@u_V,\n",
    "    rise_time=10@u_ps, fall_time=10@u_ps,\n",
    "    pulse_width=40@u_ps, period=160@u_ps, delay_time=10@u_ps\n",
    ")\n",
    "\n",
    "# Create the simulation and simulate\n",
    "simulator = circuit.simulator()\n",
    "analysis = simulator.transient(step_time=1@u_ps, end_time=160@u_ps)"
   ]
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   "source": [
    "### Plot the waveform\n",
    "\n",
    "The output waveform can be plotted:"
   ]
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   "source": [
    "import matplotlib.pyplot as plt\n",
    "import numpy as np\n",
    "fig, ax = plt.subplots(figsize=(8,5))\n",
    "ax.grid(visible=True, which='major', axis='both');\n",
    "ax.grid(visible=True, which='minor', axis='both', linestyle=\"--\");\n",
    "ax.set_yticks(np.linspace(-1.0,2.5,8,endpoint=True));\n",
    "ax.set_yticks(np.linspace(-1.0,2.5,36,endpoint=True),minor=True);\n",
    "ax.set_xticks(np.linspace(0e-12,160e-12,9,endpoint=True));\n",
    "ax.set_xticks(np.linspace(0e-12,160e-12,17,endpoint=True),minor=True);\n",
    "ax.set_title('Inverter - Transient Simulation')\n",
    "ax.set_xlabel('Time [s]')\n",
    "ax.set_ylabel('Signal [V]')\n",
    "ax.plot(analysis.time,analysis.I)\n",
    "ax.plot(analysis.time,analysis.O)\n",
    "ax.legend(('Input (I)', 'Output (O)'))\n",
    "plt.tight_layout()\n",
    "plt.show()"
   ]
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   "cell_type": "markdown",
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   "source": [
    "## Graphical editor\n",
    "\n",
    "_Magic_ can be started specifying only one file (`.magicrc`) that sets everything up (layers, macros, DRC rules, etc.)! Both a console and a GUI are started. Some functions are only accessible using the command-line interface or using keybindings."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "!magic -rcfile {CONDA_PREFIX}/share/pdk/sky130A/libs.tech/magic/sky130A.magicrc"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# To have fun going further...\n",
    "\n",
    "Here are a couple ideas to spend a good time exploring those beautiful pieces of software:\n",
    "\n",
    " * Characterize an NMOS device or a PMOS device by applying voltage pulses on the different pads.\n",
    " * Start _Magic_ on another PDK and design another inverter.\n",
    " * Vary the devices' geometry; try to make the pull-up and the pull-down waveforms symmetrical.\n",
    " \n",
    " **Do not hesitate to open the `.mag` files to see how they are built and to adapt from them!**\n",
    " \n",
    " > Good luck and read the docs. 😉"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# References\n",
    "\n",
    "Inspired from:\n",
    "“Silicon Notebooks.” CHIPS Alliance, Apr. 08, 2023. Accessed: Apr. 10, 2023. [Online]. Available: https://github.com/chipsalliance/silicon-notebooks/blob/b65134a43b01ae31423f7ee87110740b2257ac42/analog-inverter-magic.ipynb (Apache License 2.0)"
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