"""Capacitive coupler components."""
from __future__ import annotations
from functools import partial
from itertools import chain
from math import ceil, floor
import gdsfactory as gf
from gdsfactory.component import Component
from gdsfactory.typings import CrossSectionSpec, LayerSpec
from qpdk.cells.waveguides import straight
from qpdk.helper import show_components
from qpdk.tech import LAYER
[docs]
@gf.cell
def interdigital_capacitor(
fingers: int = 4,
finger_length: float = 20.0,
finger_gap: float = 2.0,
thickness: float = 5.0,
etch_layer: LayerSpec | None = "M1_ETCH",
etch_bbox_margin: float = 2.0,
cross_section: CrossSectionSpec = "cpw",
half: bool = False,
) -> 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.
.. svgbob::
┌─┐───────┐┌─┐
│ │───────┘│ │
│ │ ┌──────│ │
┌│ │ └──────│ │┐
o1└│ │──────┐ │ │┘o2
│ │──────┘ │ │
│ │ ┌──────│ │
└─┘ └──────└─┘
See for example :cite:`leizhuAccurateCircuitModel2000`.
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.
etch_layer: Optional layer for etching around the capacitor.
etch_bbox_margin: Margin around the capacitor for the etch layer in μm.
cross_section: Cross-section for the short straight from the etch box capacitor.
half: If True, creates a single-sided capacitor (half of the interdigital capacitor).
Returns:
Component: A gdsfactory component with the interdigital capacitor geometry
and two ports ('o1' and 'o2') on opposing sides.
"""
c = Component()
# Used temporarily
layer = LAYER.M1_DRAW
if fingers < 1:
raise ValueError("Must have at least 1 finger")
width = (
2 * thickness + finger_length + finger_gap
if not half
else thickness + finger_length
) # 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),
]
c.add_polygon(points_1, layer=layer)
if not half:
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_2, layer=layer)
# Add etch layer bbox if specified
if etch_layer is not None:
etch_bbox = [
(-etch_bbox_margin, -etch_bbox_margin),
(width + etch_bbox_margin, -etch_bbox_margin),
(width + etch_bbox_margin, height + etch_bbox_margin),
(-etch_bbox_margin, height + etch_bbox_margin),
]
c.add_polygon(etch_bbox, layer=etch_layer)
# Add small straights on the left and right sides of the capacitor
straight_cross_section = gf.get_cross_section(cross_section)
straight_out_of_etch = straight(
length=etch_bbox_margin, cross_section=straight_cross_section
)
straight_left = c.add_ref(straight_out_of_etch).move(
(-etch_bbox_margin, height / 2)
)
if not half:
straight_right = c.add_ref(straight_out_of_etch).move((width, height / 2))
# Add WG to additive metal
c_additive = gf.boolean(
A=c,
B=c,
operation="or",
layer=layer,
layer1=layer,
layer2=straight_cross_section.layer,
)
# Take boolean negative
c_negative = gf.boolean(
A=c,
B=c_additive,
operation="A-B",
layer=etch_layer,
layer1=etch_layer,
layer2=layer,
)
# Combine results
c = gf.Component()
c.absorb(c << c_additive)
c.absorb(c << c_negative)
ports_config = [
("o1", straight_left["o1"]),
("o2", straight_right["o2"]) if not half else None,
]
for port_name, port_ref in filter(None, ports_config):
c.add_port(
name=port_name,
width=port_ref.width,
center=port_ref.center,
orientation=port_ref.orientation,
layer=LAYER.M1_DRAW,
)
# Center at (0,0)
c.move((-width / 2, -height / 2))
return c
[docs]
@gf.cell
def plate_capacitor(
length: float = 26.0,
width: float = 5.0,
gap: float = 7.0,
etch_layer: LayerSpec | None = "M1_ETCH",
etch_bbox_margin: float = 2.0,
cross_section: CrossSectionSpec = "cpw",
) -> Component:
"""Creates a plate capacitor.
A capacitive coupler consists of two metal pads separated by a small gap,
providing capacitive coupling between circuit elements like qubits and resonators.
.. svgbob::
______ ______
_________| | | |________
| | | |
| o1 pad1 | ====gap==== | pad2 o2 |
| | | |
|_________ | | _________|
|______| |______|
Args:
length: Length (vertical extent) of the capacitor pad in μm.
width: Width (horizontal extent) of the capacitor pad in μm.
gap: Gap between plates in μm.
etch_layer: Optional layer for etching around the capacitor.
etch_bbox_margin: Margin around the capacitor for the etch layer in μm.
cross_section: Cross-section for the short straight from the etch box capacitor.
Returns:
A gdsfactory component with the plate capacitor geometry.
"""
if width <= 0:
raise ValueError(f"width must be positive, got {width}")
if length <= 0:
raise ValueError(f"length must be positive, got {length}")
c = Component()
single_capacitor = plate_capacitor_single(
length=length,
width=width,
etch_layer=etch_layer,
etch_bbox_margin=etch_bbox_margin,
cross_section=cross_section,
)
c.add_ref(single_capacitor)
pad2 = c.add_ref(single_capacitor)
pad2.rotate(180)
pad2.move((width + gap, 0))
c.center = (0, 0)
# Ensure etch box between pads
if etch_layer is not None:
missing_width = gap - 2 * etch_bbox_margin
if missing_width > 0:
etch_bbox = [
(-missing_width / 2, -length / 2 - etch_bbox_margin),
(missing_width / 2, -length / 2 - etch_bbox_margin),
(missing_width / 2, length / 2 + etch_bbox_margin),
(-missing_width / 2, length / 2 + etch_bbox_margin),
]
c.add_polygon(etch_bbox, layer=etch_layer)
return c
[docs]
@gf.cell
def plate_capacitor_single(
length: float = 26.0,
width: float = 5.0,
etch_layer: LayerSpec | None = "M1_ETCH",
etch_bbox_margin: float = 2.0,
cross_section: CrossSectionSpec = "cpw",
) -> Component:
"""Creates a single plate capacitor for coupling.
This is essentially half of a :func:`~plate_capacitor`.
.. svgbob::
______
_________| |
| |
| o1 pad1 |
| |
|_________ |
|______|
Args:
length: Length (vertical extent) of the capacitor pad in μm.
width: Width (horizontal extent) of the capacitor pad in μm.
etch_layer: Optional layer for etching around the capacitor.
etch_bbox_margin: Margin around the capacitor for the etch layer in μm.
cross_section: Cross-section for the short straight from the etch box capacitor.
Returns:
A gdsfactory component with the plate capacitor geometry.
"""
if width <= 0:
raise ValueError(f"width must be positive, got {width}")
if length <= 0:
raise ValueError(f"length must be positive, got {length}")
c = Component()
layer = LAYER.M1_DRAW
points = [
(0, 0),
(0, length),
(width, length),
(width, 0),
]
c.add_polygon(points, layer=layer)
# Add etch layer bbox if specified
if etch_layer is not None:
etch_bbox = [
(-etch_bbox_margin, -etch_bbox_margin),
(width + etch_bbox_margin, -etch_bbox_margin),
(width + etch_bbox_margin, length + etch_bbox_margin),
(-etch_bbox_margin, length + etch_bbox_margin),
]
c.add_polygon(etch_bbox, layer=etch_layer)
# Add small straight on the left side of the capacitor
straight_cross_section = gf.get_cross_section(cross_section)
straight_out_of_etch = straight(
length=etch_bbox_margin, cross_section=straight_cross_section
)
straight_left = c.add_ref(straight_out_of_etch).move(
(-etch_bbox_margin, length / 2)
)
# Add WG to additive metal
c_additive = gf.boolean(
A=c,
B=c,
operation="or",
layer=layer,
layer1=layer,
layer2=straight_cross_section.layer,
)
# Take boolean negative
c_negative = gf.boolean(
A=c,
B=c_additive,
operation="A-B",
layer=etch_layer,
layer1=etch_layer,
layer2=layer,
)
# Combine results
c = gf.Component()
c.absorb(c << c_additive)
c.absorb(c << c_negative)
c.add_port(
name="o1",
width=straight_left["o1"].width,
center=straight_left["o1"].center,
orientation=straight_left["o1"].orientation,
layer=LAYER.M1_DRAW,
)
# Center at (0,0)
c.move((-width / 2, -length / 2))
return c
if __name__ == "__main__":
show_components(
plate_capacitor_single,
plate_capacitor,
interdigital_capacitor,
partial(interdigital_capacitor, half=True),
)
