"""Guard ring generators for sky130.
Provides pwell and nwell guard rings used to isolate NMOS and PMOS devices.
"""
import gdsfactory as gf
from sky130.layers import LAYER
from sky130.pcells.contact import contact_array
[docs]
@gf.cell
def pwell_guard_ring(
inner_width: float = 2.0,
inner_height: float = 2.0,
ring_width: float = 0.34,
spacing: float = 0.27,
) -> gf.Component:
"""P+ substrate guard ring for NMOS isolation.
Places a ring of tap (P+ diffusion) around an inner area of size
inner_width x inner_height. The ring is built from four rectangular
segments whose corners overlap so there are no gaps.
Layers applied:
- tapdrawing — ring body (substrate / well tap)
- psdmdrawing — P+ implant, extends 0.125 um beyond tap on every side
- li1drawing — local interconnect covering the tap ring
- licon1drawing — LiCon contacts along every edge (via contact_array)
A port named "VSS" is placed on the li1drawing layer at the centre of the
bottom edge, oriented downward (270 degrees).
Args:
inner_width: width of the inner area to be surrounded.
inner_height: height of the inner area to be surrounded.
ring_width: width of the tap ring.
spacing: gap between the inner area and the inner edge of the ring.
.. plot::
:include-source:
import sky130
c = sky130.pcells.pwell_guard_ring()
c.plot()
"""
return _guard_ring(
inner_width=inner_width,
inner_height=inner_height,
ring_width=ring_width,
spacing=spacing,
implant_layer=LAYER.psdmdrawing,
port_name="VSS",
add_nwell=False,
)
[docs]
@gf.cell
def nwell_guard_ring(
inner_width: float = 2.0,
inner_height: float = 2.0,
ring_width: float = 0.34,
spacing: float = 0.27,
) -> gf.Component:
"""N-well guard ring for PMOS isolation.
Same structure as pwell_guard_ring but adds an nwelldrawing region under
the entire ring (extending 0.18 um beyond tap on every side) and uses
nsdmdrawing (N+ implant) instead of psdmdrawing.
The supply port is named "VDD" instead of "VSS".
Args:
inner_width: width of the inner area to be surrounded.
inner_height: height of the inner area to be surrounded.
ring_width: width of the tap ring.
spacing: gap between the inner area and the inner edge of the ring.
.. plot::
:include-source:
import sky130
c = sky130.pcells.nwell_guard_ring()
c.plot()
"""
return _guard_ring(
inner_width=inner_width,
inner_height=inner_height,
ring_width=ring_width,
spacing=spacing,
implant_layer=LAYER.nsdmdrawing,
port_name="VDD",
add_nwell=True,
)
def _guard_ring(
inner_width: float,
inner_height: float,
ring_width: float,
spacing: float,
implant_layer,
port_name: str,
add_nwell: bool,
) -> gf.Component:
"""Shared implementation for pwell and nwell guard rings.
The inner area spans (0, 0) → (inner_width, inner_height).
Ring coordinates (all four segments use full-corner overlap):
- outer extent: -(spacing + ring_width) to inner_width + (spacing + ring_width)
- inner extent: -spacing to inner_width + spacing
The four rectangular tap segments are:
bottom: x_outer_left → x_outer_right, y from -(s+rw) → -s
top: x_outer_left → x_outer_right, y from ih+s → ih+s+rw
left: x from -(s+rw) → -s, y from -(s+rw) → ih+(s+rw)
right: x from iw+s → iw+s+rw, y from -(s+rw) → ih+(s+rw)
Implant (PSDM / NSDM) extends 0.125 um beyond tap.
N-well (nwell variant only) extends 0.18 um beyond tap.
"""
c = gf.Component()
s = spacing
rw = ring_width
iw = inner_width
ih = inner_height
implant_ext = 0.125
nwell_ext = 0.18
# Ring outer and inner bounds
x0 = -(s + rw) # outer left
x1 = iw + s + rw # outer right
y0 = -(s + rw) # outer bottom
y1 = ih + s + rw # outer top
# Four tap segments -------------------------------------------------------
# bottom and top segments span full outer width (corner overlap)
seg_bottom_x = x0
seg_bottom_y = -(s + rw)
seg_bottom_w = x1 - x0
seg_bottom_h = rw
seg_top_x = x0
seg_top_y = ih + s
seg_top_w = x1 - x0
seg_top_h = rw
# left and right segments span full outer height (corner overlap)
seg_left_x = -(s + rw)
seg_left_y = -(s + rw)
seg_left_w = rw
seg_left_h = ih + 2 * (s + rw)
seg_right_x = iw + s
seg_right_y = -(s + rw)
seg_right_w = rw
seg_right_h = ih + 2 * (s + rw)
def add_rect(layer, x, y, w, h):
rect = gf.components.rectangle(size=(w, h), layer=layer)
ref = c.add_ref(rect)
ref.move((x, y))
return ref
# --- tap (tapdrawing) ---
add_rect(LAYER.tapdrawing, seg_bottom_x, seg_bottom_y, seg_bottom_w, seg_bottom_h)
add_rect(LAYER.tapdrawing, seg_top_x, seg_top_y, seg_top_w, seg_top_h)
add_rect(LAYER.tapdrawing, seg_left_x, seg_left_y, seg_left_w, seg_left_h)
add_rect(LAYER.tapdrawing, seg_right_x, seg_right_y, seg_right_w, seg_right_h)
# --- implant (psdmdrawing or nsdmdrawing) extends 0.125 beyond tap ---
imp_ext = implant_ext
add_rect(
implant_layer,
x0 - imp_ext,
y0 - imp_ext,
(x1 - x0) + 2 * imp_ext,
(y1 - y0) + 2 * imp_ext,
)
# --- li1drawing (local interconnect) — same footprint as implant-less outer ring ---
# Li1 covers the ring body (tap footprint), also using full-extent rectangles
add_rect(LAYER.li1drawing, seg_bottom_x, seg_bottom_y, seg_bottom_w, seg_bottom_h)
add_rect(LAYER.li1drawing, seg_top_x, seg_top_y, seg_top_w, seg_top_h)
add_rect(LAYER.li1drawing, seg_left_x, seg_left_y, seg_left_w, seg_left_h)
add_rect(LAYER.li1drawing, seg_right_x, seg_right_y, seg_right_w, seg_right_h)
# --- nwelldrawing (nwell variant only) extends 0.18 beyond tap ---
if add_nwell:
nw_ext = nwell_ext
add_rect(
LAYER.nwelldrawing,
x0 - nw_ext,
y0 - nw_ext,
(x1 - x0) + 2 * nw_ext,
(y1 - y0) + 2 * nw_ext,
)
# --- licon1drawing contacts along each edge via contact_array ---
# Bottom edge
bot_cont = c.add_ref(
contact_array(
width=seg_bottom_w,
height=seg_bottom_h,
contact_layer=LAYER.licon1drawing,
)
)
bot_cont.move((seg_bottom_x, seg_bottom_y))
# Top edge
top_cont = c.add_ref(
contact_array(
width=seg_top_w,
height=seg_top_h,
contact_layer=LAYER.licon1drawing,
)
)
top_cont.move((seg_top_x, seg_top_y))
# Left edge
left_cont = c.add_ref(
contact_array(
width=seg_left_w,
height=seg_left_h,
contact_layer=LAYER.licon1drawing,
)
)
left_cont.move((seg_left_x, seg_left_y))
# Right edge
right_cont = c.add_ref(
contact_array(
width=seg_right_w,
height=seg_right_h,
contact_layer=LAYER.licon1drawing,
)
)
right_cont.move((seg_right_x, seg_right_y))
# --- Port on li1drawing at bottom edge centre, pointing down (270 deg) ---
bottom_centre_x = seg_bottom_x + seg_bottom_w / 2
bottom_edge_y = seg_bottom_y # bottom of the bottom tap segment
c.add_port(
name=port_name,
center=(bottom_centre_x, bottom_edge_y),
width=seg_bottom_w,
orientation=270,
layer=LAYER.li1drawing,
port_type="electrical",
)
return c
if __name__ == "__main__":
c = pwell_guard_ring()
c.show()
