OpenRAM/compiler/pinv.py

import contact
import design
import debug
from tech import drc, parameter, spice
from ptx import ptx
from vector import vector
from math import ceil
from globals import OPTS

class pinv(design.design):
    """
    This module generates gds of a parametrically sized inverter. The
    size is specified as the nmos size (relative to minimum) and a
    beta value for choosing the pmos size.  The inverter's cell_height
    is usually the same as the 6t library cell.  The route_output will
    route the output to the right side of the cell for easier access.

    """
    c = reload(__import__(OPTS.config.bitcell))
    bitcell = getattr(c, OPTS.config.bitcell)

    unique_id = 1
    
    def __init__(self, size=1, beta=parameter["pinv_beta"], height=bitcell.height, route_output=True):
        # We need to keep unique names because outputting to GDSII
        # will use the last record with a given name. I.e., you will
        # over-write a design in GDS if one has and the other doesn't
        # have poly connected, for example.
        name = "pinv{0}".format(pinv.unique_id)
        pinv.unique_id += 1
        design.design.__init__(self, name)
        debug.info(2, "create pinv structure {0} with size of {1}".format(name, size))

        self.nmos_size = size
        self.pmos_size = beta*size
        self.beta = beta
        self.height = height
        self.route_output = route_output

        self.add_pins()
        self.create_layout()

        # for run-time, we won't check every transitor DRC/LVS independently
        # but this may be uncommented for debug purposes
        #self.DRC_LVS()

    def add_pins(self):
        """Adds pins for spice netlist"""
        self.add_pin_list(["A", "Z", "vdd", "gnd"])

    def create_layout(self):
        """Calls all functions related to the generation of the layout"""

        # These aren't for instantiating, but we use them to get the dimensions
        self.poly_contact = contact.contact(("poly", "contact", "metal1"))
        self.m1m2_via = contact.contact(("metal1", "via1", "metal2"))

        self.determine_tx_mults()
        self.create_ptx()
        self.setup_layout_constants()
        self.add_rails()
        self.add_ptx()

        # These aren't for instantiating, but we use them to get the dimensions
        self.nwell_contact = contact.contact(layer_stack=("active", "contact", "metal1"),
                                             dimensions=(1, self.pmos.num_contacts))
        self.pwell_contact = contact.contact(layer_stack=("active", "contact", "metal1"),
                                             dimensions=(1, self.nmos.num_contacts))

        self.extend_wells()
        self.extend_active()
        self.add_well_contacts()
        self.connect_well_contacts()
        self.connect_rails()
        self.connect_tx()
        self.route_pins()

    def determine_tx_mults(self):
        """
        Determines the number of fingers needed to achieve the size within
        the height constraint. This may fail if the user has a tight height.
        """
        # Do a quick sanity check and bail if unlikely feasible height
        # Sanity check. can we make an inverter in the height with minimum tx sizes?
        # Assume we need 3 metal 1 pitches (2 power rails, one between the tx for the drain)
        # plus the tx height
        nmos = ptx(tx_type="nmos")
        pmos = ptx(width=self.beta*drc["minwidth_tx"], tx_type="pmos")
        tx_height = nmos.height + pmos.height
        # rotated m1 pitch
        m1_pitch = self.poly_contact.width + drc["metal1_to_metal1"]
        metal_height = 4 * m1_pitch # This could be computed more accurately
        debug.check(self.height>tx_height + metal_height,"Cell height too small for our simple design rules.")

        # Determine the height left to the transistors to determine the number of fingers
        tx_height_available = self.height - metal_height
        # Divide the height according to beta
        nmos_height_available = 1.0/(self.beta+1) * tx_height_available
        pmos_height_available = tx_height_available - nmos_height_available
        

        # Determine the number of mults for each to fit width into available space
        self.nmos_width = self.nmos_size*drc["minwidth_tx"]
        self.pmos_width = self.pmos_size*drc["minwidth_tx"]
        nmos_required_mults = max(int(ceil(self.nmos_width/nmos_height_available)),1)
        pmos_required_mults = max(int(ceil(self.pmos_width/pmos_height_available)),1)
        # The mults must be the same for easy connection of poly
        self.tx_mults = max(nmos_required_mults, pmos_required_mults)

        # Recompute each mult width and check it isn't too small
        # This could happen if the height is narrow and the size is small
        # User should pick a bigger size to fix it...
        self.nmos_width = self.nmos_width / self.tx_mults
        debug.check(self.nmos_width>=drc["minwidth_tx"],"Cannot finger NMOS transistors to fit cell height.")
        self.pmos_width = self.pmos_width / self.tx_mults
        debug.check(self.pmos_width>=drc["minwidth_tx"],"Cannot finger PMOS transistors to fit cell height.")        
        
    def create_ptx(self):
        """Intiializes a ptx object"""
        self.nmos = ptx(width=self.nmos_width,
                        mults=self.tx_mults,
                        tx_type="nmos")
        self.add_mod(self.nmos)
        self.pmos = ptx(width=self.pmos_width,
                        mults=self.tx_mults,
                        tx_type="pmos")
        self.add_mod(self.pmos)

    def setup_layout_constants(self):
        """Sets up constant variables"""
        # the well width is determined the multi-finger PMOS device width plus
        # the well contact width and enclosure
        self.well_width = self.pmos.active_position.x \
                                  + self.pmos.active_width \
                                  + drc["active_to_body_active"] \
                                  + self.pmos.active_contact.width \
                                  + drc["well_enclosure_active"]
        self.width = self.well_width

    def add_rails(self):
        """Adds vdd/gnd rails to the layout"""
        rail_width = self.width
        rail_height = self.rail_height = drc["minwidth_metal1"]

        self.gnd_position = vector(0, - 0.5 * drc["minwidth_metal1"])  # for tiling purposes
        self.add_layout_pin(text="gnd",
                            layer="metal1",
                            offset=self.gnd_position,
                            width=rail_width,
                            height=rail_height)

        self.vdd_position = vector(0, self.height - 0.5 * drc["minwidth_metal1"])
        self.add_layout_pin(text="vdd",
                            layer="metal1",
                            offset=self.vdd_position,
                            width=rail_width,
                            height=rail_height)

    def add_ptx(self):
        """Adds pmos and nmos to the layout"""
        # determines the spacing between the edge and nmos (rail to active
        # metal or poly_to_poly spacing)
        edge_to_nmos = max(drc["metal1_to_metal1"] \
                           - self.nmos.active_contact_positions[0].y,
                           0.5 * drc["poly_to_poly"] \
                           - 0.5 * drc["minwidth_metal1"] \
                           - self.nmos.poly_positions[0].y)
        self.nmos_position = vector(0, 0.5 * drc["minwidth_metal1"] + edge_to_nmos)
        offset = self.nmos_position + vector(0,self.nmos.height)
        self.add_inst(name="pinv_nmos",
                      mod=self.nmos,
                      offset=offset,
                      mirror="MX")
        self.connect_inst(["Z", "A", "gnd", "gnd"])

        # determines the spacing between the edge and pmos
        edge_to_pmos = max(drc["metal1_to_metal1"] \
                           - self.pmos.active_contact_positions[0].y,
                           0.5 * drc["poly_to_poly"] \
                           - 0.5 * drc["minwidth_metal1"] \
                           - self.pmos.poly_positions[0].y)
        self.pmos_position = vector(0,
                                    self.height - 0.5 * drc["minwidth_metal1"]
                                    - edge_to_pmos - self.pmos.height)
        self.add_inst(name="pinv_pmos",
                      mod=self.pmos,
                      offset=self.pmos_position)
        self.connect_inst(["Z", "A", "vdd", "vdd"])

    def extend_wells(self):
        """Extends the n/p wells to cover whole layout"""
        nmos_top_yposition = self.nmos_position.y + self.nmos.height
        # calculates the length between the pmos and nmos
        middle_length = self.pmos_position.y - nmos_top_yposition
        # calculate the middle point between the pmos and nmos
        middle_yposition = nmos_top_yposition + 0.5 * middle_length

        self.nwell_position = vector(0, middle_yposition)
        self.nwell_height = self.height - middle_yposition
        self.add_rect(layer="nwell",
                      offset=self.nwell_position,
                      width=self.well_width,
                      height=self.nwell_height)
        self.add_rect(layer="vtg",
                      offset=self.nwell_position,
                      width=self.well_width,
                      height=self.nwell_height)

        self.pwell_position = vector(0, 0)
        self.pwell_height = middle_yposition
        self.add_rect(layer="pwell",
                      offset=self.pwell_position, width=self.well_width,
                      height=self.pwell_height)
        self.add_rect(layer="vtg",
                      offset=self.pwell_position,
                      width=self.well_width,
                      height=self.pwell_height)

    def extend_active(self):
        """Extends the active area for n/p mos for the addition of the n/p well taps"""
        # calculates the new active width that includes the well_taps
        self.active_width = self.pmos.active_width \
                          + drc["active_to_body_active"] \
                          + self.pmos.active_contact.width

        # Calculates the coordinates of the bottom left corner of active area
        # of the pmos
        offset = self.pmos_position + self.pmos.active_position
        self.add_rect(layer="active",
                      offset=offset,
                      width=self.active_width,
                      height=self.pmos.active_height)

        # Determines where the active of the well portion starts to add the
        # implant
        offset = offset + vector(self.pmos.active_width,0)
        implant_width = self.active_width - self.pmos.active_width
        self.add_rect(layer="nimplant",
                      offset=offset,
                      width=implant_width,
                      height=self.pmos.active_height)

        # Calculates the coordinates of the bottom left corner of active area
        # of the nmos
        offset = self.nmos_position + self.nmos.active_position
        self.add_rect(layer="active",
                      offset=offset,
                      width=self.active_width,
                      height=self.nmos.active_height)

        # Determines where the active of the well portion starts to add the
        # implant
        offset = offset + vector(self.pmos.active_width,0)
        implant_width = self.active_width - self.nmos.active_width
        self.add_rect(layer="pimplant",
                      offset=offset,
                      width=implant_width,
                      height=self.nmos.active_height)

    def connect_poly(self):
        """Connects the poly from nmos to pmos (as well if it is multi-fingered)"""
        # Calculates the y-coordinate of the top of the poly of the nmos
        nmos_top_poly_yposition = self.nmos_position.y \
                                  + self.nmos.height \
                                  - self.nmos.poly_positions[0].y

        poly_length = self.pmos_position.y + self.pmos.poly_positions[0].y \
                      - nmos_top_poly_yposition
        for position in self.pmos.poly_positions:
            offset = [position.x, nmos_top_poly_yposition]
            self.add_rect(layer="poly",
                          offset=offset,
                          width=drc["minwidth_poly"],
                          height=poly_length)

    def connect_drains(self):
        """Connects the drains of the nmos/pmos together"""
        # Determines the top y-coordinate of the nmos drain metal layer
        yoffset = self.nmos.height \
                  - 0.5 * drc["minwidth_metal1"] \
                  - self.nmos.active_contact_positions[0].y
        drain_length = self.height - yoffset + drc["minwidth_metal1"] \
                       - (self.pmos.height
                          - self.pmos.active_contact_positions[0].y)
        for position in self.pmos.active_contact_positions[1:][::2]:
            offset = [position.x + self.pmos.active_contact.second_layer_position.x,
                      yoffset]
            self.drain_position = vector(offset)
            self.add_rect(layer="metal1",
                          offset=offset,
                          width=self.nmos.active_contact.second_layer_width,
                          height=drain_length)

    def route_input_gate(self):
        """Routes the input gate to the left side of the cell for access"""

        xoffset = self.pmos.poly_positions[0].x
        # Determines the y-coordinate of where to place the gate input poly pin
        # (middle in between the pmos and nmos)
        yoffset = self.nmos.height + (self.height 
                     - self.pmos.height - self.nmos.height
                     - self.poly_contact.width) / 2
        offset = [xoffset, yoffset]
        self.add_contact(layers=("poly", "contact", "metal1"),
                      offset=offset,
                      rotate=90)

        # Determines the poly coordinate to connect to the poly contact
        offset = offset - self.poly_contact.first_layer_position.rotate_scale(1,0)
        self.add_rect(layer="poly",
                      offset=offset,
                      width=self.poly_contact.first_layer_position.y + drc["minwidth_poly"],
                      height=self.poly_contact.first_layer_width)

        input_length = self.pmos.poly_positions[0].x - self.poly_contact.height
        # Determine the y-coordinate for the placement of the metal1 via
        self.input_position = vector(0, 0.5*(self.height - drc["minwidth_metal1"] 
                                            + self.nmos.height - self.pmos.height))
        self.add_layout_pin(text="A",
                      layer="metal1",
                      offset=self.input_position,
                      width=input_length,
                      height=drc["minwidth_metal1"])

    def route_output_drain(self):
        """Routes the output (drain) to the right side of the cell for access"""
        # Determines the y-coordinate of the output metal1 via pin
        offset = vector(self.drain_position.x 
                        + self.nmos.active_contact.second_layer_width, 
                        self.input_position.y)
        output_length = self.width - offset.x
        if self.route_output == True:
            # This extends the output to the edge of the cell
            self.add_layout_pin(text="Z",
                                layer="metal1",
                                offset=offset,
                                width=output_length,
                                height=drc["minwidth_metal1"])
        else:
            # This leaves the output as an internal pin (min sized)
            self.add_layout_pin(text="Z",
                                layer="metal1",
                                offset=offset)


    def add_well_contacts(self):
        """Adds n/p well taps to the layout"""
        layer_stack = ("active", "contact", "metal1")
        # Same y-positions of the drain/source metals as the n/p mos
        well_contact_offset = vector(self.pmos.active_position.x 
                                         + self.active_width 
                                         - self.nwell_contact.width,
                                     self.pmos.active_contact_positions[0].y)
        self.nwell_contact_position = self.pmos_position + well_contact_offset
        self.nwell_contact=self.add_contact(layer_stack,self.nwell_contact_position,(1,self.pmos.num_contacts))

        well_contact_offset = vector(self.nmos.active_position.x 
                                               + self.active_width 
                                               - self.pwell_contact.width,
                                     self.nmos.active_contact_positions[0].y)
        self.pwell_contact_position = self.nmos_position + well_contact_offset
        self.pwell_contact=self.add_contact(layer_stack,self.pwell_contact_position,(1,self.nmos.num_contacts))

    def connect_well_contacts(self):
        """Connects the well taps to its respective power rails"""
        # calculates the length needed to connect the nwell_tap to vdd
        nwell_tap_length = self.height \
                           - 0.5 * drc["minwidth_metal1"] \
                           - self.nwell_contact_position.y
        # obtains the position for the metal 1 layer in the nwell_tap
        offset = self.nwell_contact_position + \
                 self.nwell_contact.second_layer_position.scale(1,0)
        self.add_rect(layer="metal1",
                      offset=offset, width=self.nwell_contact.second_layer_width,
                      height=nwell_tap_length)

        pwell_tap_length = self.pwell_contact_position.y \
                           + 0.5 * drc["minwidth_metal1"]
        offset = [self.pwell_contact_position.x
                  + self.pwell_contact.second_layer_position.x,
                  0.5 * drc["minwidth_metal1"]]
        self.add_rect(layer="metal1",
                      offset=offset,
                      width=self.pwell_contact.second_layer_width,
                      height=pwell_tap_length)

    def connect_rails(self):
        """Connects the n/p mos to its respective power rails"""
        if self.tx_mults != 1:
            return
        # corrects offset to obtain real coordinates of the layer in question
        # in a contact object
        correct = vector(self.nmos.active_contact.width 
                          - self.nmos.active_contact.width,
                         - drc["minwidth_metal1"]).scale(.5,.5)    
        # nmos position of the source metals
        noffset = self.nmos_position + self.nmos.active_contact_positions[0] + correct
        offset = [self.nmos.active_contact.second_layer_position.x + noffset.x,
                0.5 * drc["minwidth_metal1"]]
        self.add_rect(layer="metal1", offset=offset, 
                      width=self.nmos.active_contact.second_layer_width,
                      height=noffset.y)
        # corrects offset to obtain real coordinates of the layer in question
        # in a contact object
        correct = vector(self.pmos.active_contact.width
                         - self.pmos.active_contact.width,
                         self.pmos.active_contact.second_layer_height).scale(.5,1)
        # pmos position of the source metals
        offset = self.pmos_position + self.pmos.active_contact_positions[0]\
               + correct + self.pmos.active_contact.second_layer_position
        temp_height = self.height - offset.y - 0.5 * drc["minwidth_metal1"]
        self.add_rect(layer="metal1",
                      offset=offset,
                      width=self.pmos.active_contact.second_layer_width,
                      height=temp_height)

    def connect_tx(self):
        self.connect_poly()
        self.connect_drains()

    def route_pins(self):
        self.route_input_gate()
        self.route_output_drain()

    def input_load(self):
        return ((self.nmos_size+self.pmos_size)/parameter["min_tx_size"])*spice["min_tx_gate_c"]

    def analytical_delay(self, slew, load=0.0):
        from tech import spice
        r = spice["min_tx_r"]/(self.nmos_size/parameter["min_tx_size"])
        c_para = spice["min_tx_drain_c"]*(self.nmos_size/parameter["min_tx_size"])#ff
        return self.cal_delay_with_rc(r = r, c =  c_para+load, slew = slew)