mirror of https://github.com/VLSIDA/OpenRAM.git
433 lines
20 KiB
Python
433 lines
20 KiB
Python
import contact
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import design
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import debug
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from tech import drc, parameter, spice
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from ptx import ptx
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from vector import vector
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from math import ceil
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from globals import OPTS
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class pinv(design.design):
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"""
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This module generates gds of a parametrically sized inverter. The
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size is specified as the nmos size (relative to minimum) and a
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beta value for choosing the pmos size. The inverter's cell_height
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is usually the same as the 6t library cell. The route_output will
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route the output to the right side of the cell for easier access.
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"""
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c = reload(__import__(OPTS.config.bitcell))
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bitcell = getattr(c, OPTS.config.bitcell)
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unique_id = 1
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def __init__(self, size=1, beta=parameter["pinv_beta"], height=bitcell.height, route_output=True):
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# We need to keep unique names because outputting to GDSII
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# will use the last record with a given name. I.e., you will
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# over-write a design in GDS if one has and the other doesn't
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# have poly connected, for example.
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name = "pinv{0}".format(pinv.unique_id)
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pinv.unique_id += 1
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design.design.__init__(self, name)
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debug.info(2, "create pinv structure {0} with size of {1}".format(name, size))
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self.nmos_size = size
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self.pmos_size = beta*size
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self.beta = beta
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self.height = height
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self.route_output = route_output
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self.add_pins()
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self.create_layout()
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# for run-time, we won't check every transitor DRC/LVS independently
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# but this may be uncommented for debug purposes
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#self.DRC_LVS()
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def add_pins(self):
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"""Adds pins for spice netlist"""
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self.add_pin_list(["A", "Z", "vdd", "gnd"])
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def create_layout(self):
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"""Calls all functions related to the generation of the layout"""
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# These aren't for instantiating, but we use them to get the dimensions
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self.poly_contact = contact.contact(("poly", "contact", "metal1"))
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self.m1m2_via = contact.contact(("metal1", "via1", "metal2"))
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self.determine_tx_mults()
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self.create_ptx()
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self.setup_layout_constants()
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self.add_rails()
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self.add_ptx()
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# These aren't for instantiating, but we use them to get the dimensions
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self.nwell_contact = contact.contact(layer_stack=("active", "contact", "metal1"),
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dimensions=(1, self.pmos.num_contacts))
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self.pwell_contact = contact.contact(layer_stack=("active", "contact", "metal1"),
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dimensions=(1, self.nmos.num_contacts))
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self.extend_wells()
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self.extend_active()
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self.add_well_contacts()
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self.connect_well_contacts()
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self.connect_rails()
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self.connect_tx()
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self.route_pins()
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def determine_tx_mults(self):
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"""
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Determines the number of fingers needed to achieve the size within
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the height constraint. This may fail if the user has a tight height.
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"""
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# Do a quick sanity check and bail if unlikely feasible height
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# Sanity check. can we make an inverter in the height with minimum tx sizes?
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# Assume we need 3 metal 1 pitches (2 power rails, one between the tx for the drain)
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# plus the tx height
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nmos = ptx(tx_type="nmos")
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pmos = ptx(width=self.beta*drc["minwidth_tx"], tx_type="pmos")
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tx_height = nmos.height + pmos.height
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# rotated m1 pitch
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m1_pitch = self.poly_contact.width + drc["metal1_to_metal1"]
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metal_height = 4 * m1_pitch # This could be computed more accurately
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debug.check(self.height>tx_height + metal_height,"Cell height too small for our simple design rules.")
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# Determine the height left to the transistors to determine the number of fingers
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tx_height_available = self.height - metal_height
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# Divide the height according to beta
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nmos_height_available = 1.0/(self.beta+1) * tx_height_available
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pmos_height_available = tx_height_available - nmos_height_available
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# Determine the number of mults for each to fit width into available space
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self.nmos_width = self.nmos_size*drc["minwidth_tx"]
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self.pmos_width = self.pmos_size*drc["minwidth_tx"]
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nmos_required_mults = max(int(ceil(self.nmos_width/nmos_height_available)),1)
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pmos_required_mults = max(int(ceil(self.pmos_width/pmos_height_available)),1)
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# The mults must be the same for easy connection of poly
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self.tx_mults = max(nmos_required_mults, pmos_required_mults)
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# Recompute each mult width and check it isn't too small
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# This could happen if the height is narrow and the size is small
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# User should pick a bigger size to fix it...
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self.nmos_width = self.nmos_width / self.tx_mults
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debug.check(self.nmos_width>=drc["minwidth_tx"],"Cannot finger NMOS transistors to fit cell height.")
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self.pmos_width = self.pmos_width / self.tx_mults
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debug.check(self.pmos_width>=drc["minwidth_tx"],"Cannot finger PMOS transistors to fit cell height.")
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def create_ptx(self):
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"""Intiializes a ptx object"""
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self.nmos = ptx(width=self.nmos_width,
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mults=self.tx_mults,
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tx_type="nmos")
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self.add_mod(self.nmos)
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self.pmos = ptx(width=self.pmos_width,
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mults=self.tx_mults,
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tx_type="pmos")
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self.add_mod(self.pmos)
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def setup_layout_constants(self):
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"""Sets up constant variables"""
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# the well width is determined the multi-finger PMOS device width plus
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# the well contact width and enclosure
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self.well_width = self.pmos.active_position.x \
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+ self.pmos.active_width \
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+ drc["active_to_body_active"] \
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+ self.pmos.active_contact.width \
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+ drc["well_enclosure_active"]
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self.width = self.well_width
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def add_rails(self):
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"""Adds vdd/gnd rails to the layout"""
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rail_width = self.width
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rail_height = self.rail_height = drc["minwidth_metal1"]
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self.gnd_position = vector(0, - 0.5 * drc["minwidth_metal1"]) # for tiling purposes
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self.add_layout_pin(text="gnd",
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layer="metal1",
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offset=self.gnd_position,
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width=rail_width,
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height=rail_height)
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self.vdd_position = vector(0, self.height - 0.5 * drc["minwidth_metal1"])
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self.add_layout_pin(text="vdd",
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layer="metal1",
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offset=self.vdd_position,
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width=rail_width,
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height=rail_height)
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def add_ptx(self):
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"""Adds pmos and nmos to the layout"""
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# determines the spacing between the edge and nmos (rail to active
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# metal or poly_to_poly spacing)
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edge_to_nmos = max(drc["metal1_to_metal1"] \
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- self.nmos.active_contact_positions[0].y,
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0.5 * drc["poly_to_poly"] \
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- 0.5 * drc["minwidth_metal1"] \
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- self.nmos.poly_positions[0].y)
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self.nmos_position = vector(0, 0.5 * drc["minwidth_metal1"] + edge_to_nmos)
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offset = self.nmos_position + vector(0,self.nmos.height)
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self.add_inst(name="pinv_nmos",
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mod=self.nmos,
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offset=offset,
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mirror="MX")
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self.connect_inst(["Z", "A", "gnd", "gnd"])
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# determines the spacing between the edge and pmos
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edge_to_pmos = max(drc["metal1_to_metal1"] \
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- self.pmos.active_contact_positions[0].y,
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0.5 * drc["poly_to_poly"] \
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- 0.5 * drc["minwidth_metal1"] \
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- self.pmos.poly_positions[0].y)
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self.pmos_position = vector(0,
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self.height - 0.5 * drc["minwidth_metal1"]
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- edge_to_pmos - self.pmos.height)
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self.add_inst(name="pinv_pmos",
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mod=self.pmos,
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offset=self.pmos_position)
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self.connect_inst(["Z", "A", "vdd", "vdd"])
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def extend_wells(self):
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"""Extends the n/p wells to cover whole layout"""
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nmos_top_yposition = self.nmos_position.y + self.nmos.height
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# calculates the length between the pmos and nmos
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middle_length = self.pmos_position.y - nmos_top_yposition
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# calculate the middle point between the pmos and nmos
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middle_yposition = nmos_top_yposition + 0.5 * middle_length
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self.nwell_position = vector(0, middle_yposition)
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self.nwell_height = self.height - middle_yposition
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self.add_rect(layer="nwell",
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offset=self.nwell_position,
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width=self.well_width,
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height=self.nwell_height)
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self.add_rect(layer="vtg",
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offset=self.nwell_position,
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width=self.well_width,
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height=self.nwell_height)
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self.pwell_position = vector(0, 0)
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self.pwell_height = middle_yposition
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self.add_rect(layer="pwell",
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offset=self.pwell_position, width=self.well_width,
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height=self.pwell_height)
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self.add_rect(layer="vtg",
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offset=self.pwell_position,
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width=self.well_width,
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height=self.pwell_height)
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def extend_active(self):
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"""Extends the active area for n/p mos for the addition of the n/p well taps"""
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# calculates the new active width that includes the well_taps
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self.active_width = self.pmos.active_width \
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+ drc["active_to_body_active"] \
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+ self.pmos.active_contact.width
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# Calculates the coordinates of the bottom left corner of active area
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# of the pmos
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offset = self.pmos_position + self.pmos.active_position
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self.add_rect(layer="active",
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offset=offset,
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width=self.active_width,
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height=self.pmos.active_height)
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# Determines where the active of the well portion starts to add the
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# implant
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offset = offset + vector(self.pmos.active_width,0)
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implant_width = self.active_width - self.pmos.active_width
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self.add_rect(layer="nimplant",
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offset=offset,
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width=implant_width,
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height=self.pmos.active_height)
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# Calculates the coordinates of the bottom left corner of active area
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# of the nmos
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offset = self.nmos_position + self.nmos.active_position
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self.add_rect(layer="active",
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offset=offset,
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width=self.active_width,
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height=self.nmos.active_height)
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# Determines where the active of the well portion starts to add the
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# implant
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offset = offset + vector(self.pmos.active_width,0)
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implant_width = self.active_width - self.nmos.active_width
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self.add_rect(layer="pimplant",
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offset=offset,
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width=implant_width,
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height=self.nmos.active_height)
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def connect_poly(self):
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"""Connects the poly from nmos to pmos (as well if it is multi-fingered)"""
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# Calculates the y-coordinate of the top of the poly of the nmos
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nmos_top_poly_yposition = self.nmos_position.y \
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+ self.nmos.height \
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- self.nmos.poly_positions[0].y
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poly_length = self.pmos_position.y + self.pmos.poly_positions[0].y \
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- nmos_top_poly_yposition
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for position in self.pmos.poly_positions:
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offset = [position.x, nmos_top_poly_yposition]
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self.add_rect(layer="poly",
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offset=offset,
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width=drc["minwidth_poly"],
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height=poly_length)
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def connect_drains(self):
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"""Connects the drains of the nmos/pmos together"""
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# Determines the top y-coordinate of the nmos drain metal layer
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yoffset = self.nmos.height \
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- 0.5 * drc["minwidth_metal1"] \
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- self.nmos.active_contact_positions[0].y
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drain_length = self.height - yoffset + drc["minwidth_metal1"] \
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- (self.pmos.height
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- self.pmos.active_contact_positions[0].y)
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for position in self.pmos.active_contact_positions[1:][::2]:
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offset = [position.x + self.pmos.active_contact.second_layer_position.x,
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yoffset]
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self.drain_position = vector(offset)
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self.add_rect(layer="metal1",
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offset=offset,
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width=self.nmos.active_contact.second_layer_width,
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height=drain_length)
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def route_input_gate(self):
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"""Routes the input gate to the left side of the cell for access"""
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xoffset = self.pmos.poly_positions[0].x
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# Determines the y-coordinate of where to place the gate input poly pin
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# (middle in between the pmos and nmos)
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yoffset = self.nmos.height + (self.height
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- self.pmos.height - self.nmos.height
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- self.poly_contact.width) / 2
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offset = [xoffset, yoffset]
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self.add_contact(layers=("poly", "contact", "metal1"),
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offset=offset,
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rotate=90)
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# Determines the poly coordinate to connect to the poly contact
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offset = offset - self.poly_contact.first_layer_position.rotate_scale(1,0)
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self.add_rect(layer="poly",
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offset=offset,
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width=self.poly_contact.first_layer_position.y + drc["minwidth_poly"],
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height=self.poly_contact.first_layer_width)
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input_length = self.pmos.poly_positions[0].x - self.poly_contact.height
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# Determine the y-coordinate for the placement of the metal1 via
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self.input_position = vector(0, 0.5*(self.height - drc["minwidth_metal1"]
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+ self.nmos.height - self.pmos.height))
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self.add_layout_pin(text="A",
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layer="metal1",
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offset=self.input_position,
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width=input_length,
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height=drc["minwidth_metal1"])
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def route_output_drain(self):
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"""Routes the output (drain) to the right side of the cell for access"""
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# Determines the y-coordinate of the output metal1 via pin
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offset = vector(self.drain_position.x
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+ self.nmos.active_contact.second_layer_width,
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self.input_position.y)
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output_length = self.width - offset.x
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if self.route_output == True:
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# This extends the output to the edge of the cell
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self.add_layout_pin(text="Z",
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layer="metal1",
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offset=offset,
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width=output_length,
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height=drc["minwidth_metal1"])
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else:
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# This leaves the output as an internal pin (min sized)
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self.add_layout_pin(text="Z",
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layer="metal1",
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offset=offset)
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def add_well_contacts(self):
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"""Adds n/p well taps to the layout"""
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layer_stack = ("active", "contact", "metal1")
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# Same y-positions of the drain/source metals as the n/p mos
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well_contact_offset = vector(self.pmos.active_position.x
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+ self.active_width
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- self.nwell_contact.width,
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self.pmos.active_contact_positions[0].y)
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self.nwell_contact_position = self.pmos_position + well_contact_offset
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self.nwell_contact=self.add_contact(layer_stack,self.nwell_contact_position,(1,self.pmos.num_contacts))
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well_contact_offset = vector(self.nmos.active_position.x
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+ self.active_width
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- self.pwell_contact.width,
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self.nmos.active_contact_positions[0].y)
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self.pwell_contact_position = self.nmos_position + well_contact_offset
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self.pwell_contact=self.add_contact(layer_stack,self.pwell_contact_position,(1,self.nmos.num_contacts))
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def connect_well_contacts(self):
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"""Connects the well taps to its respective power rails"""
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# calculates the length needed to connect the nwell_tap to vdd
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nwell_tap_length = self.height \
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- 0.5 * drc["minwidth_metal1"] \
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- self.nwell_contact_position.y
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# obtains the position for the metal 1 layer in the nwell_tap
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offset = self.nwell_contact_position + \
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self.nwell_contact.second_layer_position.scale(1,0)
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self.add_rect(layer="metal1",
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offset=offset, width=self.nwell_contact.second_layer_width,
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height=nwell_tap_length)
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pwell_tap_length = self.pwell_contact_position.y \
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+ 0.5 * drc["minwidth_metal1"]
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offset = [self.pwell_contact_position.x
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+ self.pwell_contact.second_layer_position.x,
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0.5 * drc["minwidth_metal1"]]
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self.add_rect(layer="metal1",
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offset=offset,
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width=self.pwell_contact.second_layer_width,
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height=pwell_tap_length)
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def connect_rails(self):
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"""Connects the n/p mos to its respective power rails"""
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if self.tx_mults != 1:
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return
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# corrects offset to obtain real coordinates of the layer in question
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# in a contact object
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correct = vector(self.nmos.active_contact.width
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- self.nmos.active_contact.width,
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- drc["minwidth_metal1"]).scale(.5,.5)
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# nmos position of the source metals
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noffset = self.nmos_position + self.nmos.active_contact_positions[0] + correct
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offset = [self.nmos.active_contact.second_layer_position.x + noffset.x,
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0.5 * drc["minwidth_metal1"]]
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self.add_rect(layer="metal1", offset=offset,
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width=self.nmos.active_contact.second_layer_width,
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height=noffset.y)
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# corrects offset to obtain real coordinates of the layer in question
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# in a contact object
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correct = vector(self.pmos.active_contact.width
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- self.pmos.active_contact.width,
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self.pmos.active_contact.second_layer_height).scale(.5,1)
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# pmos position of the source metals
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offset = self.pmos_position + self.pmos.active_contact_positions[0]\
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+ correct + self.pmos.active_contact.second_layer_position
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temp_height = self.height - offset.y - 0.5 * drc["minwidth_metal1"]
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self.add_rect(layer="metal1",
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offset=offset,
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width=self.pmos.active_contact.second_layer_width,
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height=temp_height)
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def connect_tx(self):
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self.connect_poly()
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self.connect_drains()
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def route_pins(self):
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self.route_input_gate()
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self.route_output_drain()
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def input_load(self):
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return ((self.nmos_size+self.pmos_size)/parameter["min_tx_size"])*spice["min_tx_gate_c"]
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def analytical_delay(self, slew, load=0.0):
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from tech import spice
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r = spice["min_tx_r"]/(self.nmos_size/parameter["min_tx_size"])
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c_para = spice["min_tx_drain_c"]*(self.nmos_size/parameter["min_tx_size"])#ff
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return self.cal_delay_with_rc(r = r, c = c_para+load, slew = slew)
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