"""Interdigital capacitor components."""
from __future__ import annotations
from itertools import chain
from math import ceil, floor
import gdsfactory as gf
from gdsfactory.component import Component
from gdsfactory.typings import LayerSpec
[docs]
@gf.cell
def interdigital_capacitor(
fingers: int = 4,
finger_length: float | int = 20.0,
finger_gap: float | int = 2.0,
thickness: float | int = 5.0,
layer: LayerSpec = "M1_DRAW",
) -> Component:
"""Generate an interdigital capacitor component with ports on both ends.
An interdigital capacitor consists of interleaved metal fingers that create
a distributed capacitance. This component creates a planar capacitor with
two sets of interleaved fingers extending from opposite ends.
See for example Zhu et al., `Accurate circuit model of interdigital
capacitor and its application to design of new quasi-lumped miniaturized
filters with suppression of harmonic resonance`, doi: 10.1109/22.826833.
Note:
``finger_length=0`` effectively provides a parallel plate capacitor.
The capacitance scales approximately linearly with the number of fingers
and finger length.
Args:
fingers: Total number of fingers of the capacitor (must be >= 1).
finger_length: Length of each finger in μm.
finger_gap: Gap between adjacent fingers in μm.
thickness: Thickness of fingers and the base section in μm.
layer: Layer specification for the capacitor geometry.
Returns:
Component: A gdsfactory component with the interdigital capacitor geometry
and two ports ('o1' and 'o2') on opposing sides.
"""
c = Component()
assert fingers >= 1, "Must have at least 1 finger"
width = 2 * thickness + finger_length + finger_gap # total length
height = fingers * thickness + (fingers - 1) * finger_gap # total height
points_1 = [
(0, 0),
(0, height),
(thickness + finger_length, height),
(thickness + finger_length, height - thickness),
(thickness, height - thickness),
*chain.from_iterable(
(
(thickness, height - (2 * i) * (thickness + finger_gap)),
(
thickness + finger_length,
height - (2 * i) * (thickness + finger_gap),
),
(
thickness + finger_length,
height - (2 * i) * (thickness + finger_gap) - thickness,
),
(thickness, height - (2 * i) * (thickness + finger_gap) - thickness),
)
for i in range(ceil(fingers / 2))
),
(thickness, 0),
(0, 0),
]
points_2 = [
(width, 0),
(width, height),
(width - thickness, height),
*chain.from_iterable(
(
(
width - thickness,
height - (1 + 2 * i) * thickness - (1 + 2 * i) * finger_gap,
),
(
width - (thickness + finger_length),
height - (1 + 2 * i) * thickness - (1 + 2 * i) * finger_gap,
),
(
width - (thickness + finger_length),
height - (2 + 2 * i) * thickness - (1 + 2 * i) * finger_gap,
),
(
width - thickness,
height - (2 + 2 * i) * thickness - (1 + 2 * i) * finger_gap,
),
)
for i in range(floor(fingers / 2))
),
(width - thickness, 0),
(width, 0),
]
c.add_polygon(points_1, layer=layer)
c.add_polygon(points_2, layer=layer)
c.add_port(
name="o1",
center=(0, height / 2),
width=thickness,
orientation=180,
layer=layer,
)
c.add_port(
name="o2",
center=(width, height / 2),
width=thickness,
orientation=0,
layer=layer,
)
return c
if __name__ == "__main__":
from qpdk import PDK
PDK.activate()
c = interdigital_capacitor()
c.show()
