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sky130: use special_nfet_01v8 model for sub-0.42um nfets #304

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sky130: use special_nfet_01v8 model for sub-0.42um nfets #304

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28 changes: 24 additions & 4 deletions compiler/modules/ptx.py
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Original file line number Diff line number Diff line change
Expand Up @@ -116,12 +116,32 @@ def create_layout(self):
# but this may be uncommented for debug purposes
# self.DRC()

def get_model_name(self):
"""
Return the device model name for this transistor's width.

Some technologies model narrow devices with a separate model. In
sky130, an nfet narrower than 0.42um is extracted as
sky130_fd_pr__special_nfet_01v8 rather than sky130_fd_pr__nfet_01v8
(see the "device msubcircuit" rules in sky130A.tech), so the netlist
must use the same name or LVS reports a device class mismatch on
every gate built from a minimum-width device.
"""
narrow_model = spice.get("{}_narrow".format(self.tx_type))
narrow_width = spice.get("{}_narrow_max_width".format(self.tx_type))
if narrow_model and narrow_width and self.tx_width < narrow_width:
return narrow_model

return spice[self.tx_type]

def create_netlist(self):
pin_list = ["D", "G", "S", "B"]
if self.tx_type == "nmos":
body_dir = "GROUND"
else:
body_dir = "POWER"

self.model_name = self.get_model_name()
dir_list = ["INOUT", "INPUT", "INOUT", body_dir]
self.add_pin_list(pin_list, dir_list)

Expand All @@ -133,7 +153,7 @@ def create_netlist(self):
self.channel_length = drc("minlength_channel")
if cell_props.ptx.model_is_subckt:
# sky130
main_str = "X{{0}} {{1}} {0} m={1} w={2} l={3} ".format(spice[self.tx_type],
main_str = "X{{0}} {{1}} {0} m={1} w={2} l={3} ".format(self.model_name,
self.mults,
self.tx_width,
self.channel_length)
Expand All @@ -142,7 +162,7 @@ def create_netlist(self):
area_str = "pd={0:.2f} ps={0:.2f} as={1:.2f}u ad={1:.2f}u".format(perimeter_sd,
area_sd)
else:
main_str = "M{{0}} {{1}} {0} m={1} w={2}u l={3}u ".format(spice[self.tx_type],
main_str = "M{{0}} {{1}} {0} m={1} w={2}u l={3}u ".format(self.model_name,
self.mults,
self.tx_width,
self.channel_length)
Expand All @@ -164,12 +184,12 @@ def create_netlist(self):
self.tx_width,
self.channel_length)
elif cell_props.ptx.model_is_subckt:
self.lvs_device = "X{{0}} {{1}} {0} m={1} w={2}u l={3}u".format(spice[self.tx_type],
self.lvs_device = "X{{0}} {{1}} {0} m={1} w={2}u l={3}u".format(self.model_name,
self.mults,
self.tx_width,
self.channel_length)
else:
self.lvs_device = "M{{0}} {{1}} {0} m={1} w={2}u l={3}u ".format(spice[self.tx_type],
self.lvs_device = "M{{0}} {{1}} {0} m={1} w={2}u l={3}u ".format(self.model_name,
self.mults,
self.tx_width,
self.channel_length)
Expand Down
8 changes: 8 additions & 0 deletions technology/sky130/tech/tech.py
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Original file line number Diff line number Diff line change
Expand Up @@ -711,6 +711,14 @@
spice = {}
spice["nmos"] = "sky130_fd_pr__nfet_01v8"
spice["pmos"] = "sky130_fd_pr__pfet_01v8"

# An nfet narrower than 0.42um is a different device in sky130: magic
# extracts it as sky130_fd_pr__special_nfet_01v8, so the netlist has to use
# that name below the threshold or netgen reports a device class mismatch.
# See the "device msubcircuit" lines in sky130A.tech. There is no equivalent
# split for pfets, so only the nmos is declared here.
spice["nmos_narrow"] = "sky130_fd_pr__special_nfet_01v8"
spice["nmos_narrow_max_width"] = 0.42
spice["power"]="vccd1"
spice["ground"]="vssd1"

Expand Down