import contact import design import debug from tech import drc, parameter, spice, info from ptx import ptx from vector import vector from math import ceil from globals import OPTS from utils import round_to_grid class pinv(design.design): """ Pinv generates gds of a parametrically sized inverter. The size is specified as the drive size (relative to minimum NMOS) and a beta value for choosing the pmos size. The inverter's cell height is usually the same as the 6t library cell and is measured from center of rail to rail.. 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["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 # Maybe minimize height if not defined in future? 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_supply_rails() self.add_ptx() self.extend_wells() self.add_well_contacts() self.connect_rails() self.route_input_gate() self.route_output_drain() 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. """ self.m1_width = drc["minwidth_metal1"] # 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=drc["minwidth_tx"], tx_type="pmos") tx_height = nmos.poly_height + pmos.poly_height # rotated m1 pitch or poly to active spacing min_channel = max(self.poly_contact.width + drc["metal1_to_metal1"], self.poly_contact.width + 2*drc["poly_to_active"]) # This is a poly-to-poly of a flipped cell # plus the extension beyond active in the ptx plus the drain/source connection self.top_bottom_cell_space = 0.5*drc["poly_to_poly"]+drc["poly_extend_active"] + 0.5*self.m1_width total_height = tx_height + min_channel + 2*self.top_bottom_cell_space debug.check(self.height> total_height,"Cell height {0} too small for simple min height {1}.".format(self.height,total_height)) # Determine the height left to the transistors to determine the number of fingers tx_height_available = self.height - min_channel - 2*self.top_bottom_cell_space # Divide the height in half. Could divide proportional to beta, but this makes # connecting wells of multiple cells easier. # Subtract the poly space under the rail of the tx nmos_height_available = 0.5 * tx_height_available - 0.5*drc["poly_to_poly"] pmos_height_available = 0.5 * tx_height_available - 0.5*drc["poly_to_poly"] debug.info(2,"Height avail {0} PMOS height {1} NMOS height {2}".format(tx_height_available, nmos_height_available, pmos_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... # We also need to round the width to the grid or we will end up with LVS property # mismatch errors when fingers are not a grid length and get rounded in the offset geometry. self.nmos_width = round_to_grid(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 = round_to_grid(self.pmos_width / self.tx_mults) debug.check(self.pmos_width>=drc["minwidth_tx"],"Cannot finger PMOS transistors to fit cell height.") def setup_layout_constants(self): """ Pre-compute some handy layout parameters. """ # the well width is determined the multi-finger PMOS device width plus # the well contact width and half well enclosure on both sides self.well_width = self.pmos.active_width + self.pmos.active_contact.width \ + drc["active_to_body_active"] + 2*drc["well_enclosure_active"] self.width = self.well_width # Height is an input parameter, so it is not recomputed. # This will help with the wells and the input/output placement self.middle_position = vector(0,0.5*self.height) def create_ptx(self): """ Create the PMOS and NMOS transistors. """ self.nmos = ptx(width=self.nmos_width, mults=self.tx_mults, tx_type="nmos", connect_poly=True, connect_active=True) self.add_mod(self.nmos) self.pmos = ptx(width=self.pmos_width, mults=self.tx_mults, tx_type="pmos", connect_poly=True, connect_active=True) self.add_mod(self.pmos) def add_supply_rails(self): """ Add vdd/gnd rails to the top and bottom. """ self.add_layout_pin_center_rect(text="gnd", layer="metal1", offset=vector(0.5*self.width,0), width=self.width) self.add_layout_pin_center_rect(text="vdd", layer="metal1", offset=vector(0.5*self.width,self.height), width=self.width) def add_ptx(self): """ Add PMOS and NMOS to the layout at the upper-most and lowest position to provide maximum routing in channel """ # place PMOS so it is half a poly spacing down from the top self.pmos_pos = self.pmos.active_offset.scale(1,0) \ + vector(0, self.height-self.pmos.active_height-self.top_bottom_cell_space) self.pmos_inst=self.add_inst(name="pinv_pmos", mod=self.pmos, offset=self.pmos_pos) self.connect_inst(["Z", "A", "vdd", "vdd"]) # place NMOS so that it is half a poly spacing up from the bottom self.nmos_pos = self.nmos.active_offset.scale(1,0) + vector(0,self.top_bottom_cell_space) self.nmos_inst=self.add_inst(name="pinv_nmos", mod=self.nmos, offset=self.nmos_pos) self.connect_inst(["Z", "A", "gnd", "gnd"]) def extend_wells(self): """ Extend the n/p wells to cover whole cell """ nwell_height = self.height - self.middle_position.y if info["has_nwell"]: self.add_rect(layer="nwell", offset=self.middle_position, width=self.well_width, height=nwell_height) self.add_rect(layer="vtg", offset=self.middle_position, width=self.well_width, height=nwell_height) if info["has_pwell"]: self.add_rect(layer="pwell", offset=vector(0,0), width=self.well_width, height=self.middle_position.y) self.add_rect(layer="vtg", offset=vector(0,0), width=self.well_width, height=self.middle_position.y) def route_input_gate(self): """ Route the input gate to the left side of the cell for access """ nmos_gate_pin = self.nmos_inst.get_pin("G") pmos_gate_pin = self.pmos_inst.get_pin("G") # Pick point on the left of NMOS and connect down to PMOS nmos_gate_pos = nmos_gate_pin.ll() + vector(0.5*drc["minwidth_poly"],0) pmos_gate_pos = vector(nmos_gate_pos.x,pmos_gate_pin.bc().y) self.add_path("poly",[nmos_gate_pos,pmos_gate_pos]) # Add the via to the cell midpoint along the gate left_gate_offset = vector(nmos_gate_pin.lx(),self.middle_position.y) contact_offset = left_gate_offset - vector(0.5*self.poly_contact.height,0) self.add_contact_center(layers=("poly", "contact", "metal1"), offset=contact_offset, rotate=90) self.add_layout_pin_center_segment(text="A", layer="metal1", start=left_gate_offset.scale(0,1), end=left_gate_offset) # This is to ensure that the contact is connected to the gate mid_point = contact_offset.scale(0.5,1)+left_gate_offset.scale(0.5,0) self.add_rect_center(layer="poly", offset=mid_point, height=self.poly_contact.first_layer_width, width=left_gate_offset.x-contact_offset.x) def route_output_drain(self): """ Route the output (drains) together. Optionally, routes output to edge. """ # Get the drain pins nmos_drain_pin = self.nmos_inst.get_pin("D") pmos_drain_pin = self.pmos_inst.get_pin("D") # Pick point at right most of NMOS and connect down to PMOS nmos_drain_pos = nmos_drain_pin.ur() - vector(0.5*self.m1_width,0) pmos_drain_pos = vector(nmos_drain_pos.x,pmos_drain_pin.bc().y) self.add_path("metal1",[nmos_drain_pos,pmos_drain_pos]) # Remember the mid for the output mid_drain_offset = vector(nmos_drain_pos.x,self.middle_position.y) output_length = self.width - mid_drain_offset.x if self.route_output == True: # This extends the output to the edge of the cell output_offset = mid_drain_offset.scale(0,1) + vector(self.width,0) self.add_layout_pin_center_segment(text="Z", layer="metal1", start=mid_drain_offset, end=output_offset) else: # This leaves the output as an internal pin (min sized) self.add_layout_pin(text="Z", layer="metal1", offset=mid_drain_offset) def add_well_contacts(self): """ Add n/p well taps to the layout and connect to supplies """ layer_stack = ("active", "contact", "metal1") # To the right a spacing away from the nmos right active edge nwell_contact_xoffset = self.nmos_pos.x + self.nmos.active_width + drc["active_to_body_active"] nwell_contact_yoffset = self.nmos_pos.y nwell_offset = vector(nwell_contact_xoffset, nwell_contact_yoffset) # Offset by half a contact in x and y nwell_offset += vector(0.5*self.nmos.active_contact.first_layer_width, 0.5*self.nmos.active_contact.first_layer_height) self.nwell_contact=self.add_contact_center(layers=layer_stack, offset=nwell_offset) self.add_path("metal1",[nwell_offset,nwell_offset.scale(1,0)]) # Now add the full active and implant for the PMOS nwell_offset = self.nmos_pos + vector(self.nmos.active_width,0) nwell_contact_width = drc["active_to_body_active"] + self.nmos.active_contact.width self.add_rect(layer="active", offset=nwell_offset, width=nwell_contact_width, height=self.nmos.active_height) self.add_rect(layer="pimplant", offset=nwell_offset, width=nwell_contact_width, height=self.nmos.active_height) # To the right a spacing away from the pmos right active edge pwell_contact_xoffset = self.pmos_pos.x + self.pmos.active_width + drc["active_to_body_active"] pwell_contact_yoffset = self.pmos_pos.y + self.pmos.active_height - self.pmos.active_contact.height pwell_offset = vector(pwell_contact_xoffset, pwell_contact_yoffset) # Offset by half a contact pwell_offset += vector(0.5*self.pmos.active_contact.first_layer_width, 0.5*self.pmos.active_contact.first_layer_height) self.pwell_contact=self.add_contact_center(layers=layer_stack, offset=pwell_offset) self.add_path("metal1",[pwell_offset,vector(pwell_offset.x,self.height)]) # Now add the full active and implant for the PMOS pwell_offset = self.pmos_pos + vector(self.pmos.active_width,0) pwell_contact_width = drc["active_to_body_active"] + self.pmos.active_contact.width self.add_rect(layer="active", offset=pwell_offset, width=pwell_contact_width, height=self.pmos.active_height) self.add_rect(layer="nimplant", offset=pwell_offset, width=pwell_contact_width, height=self.pmos.active_height) def connect_rails(self): """ Connect the nmos and pmos to its respective power rails """ nmos_source_pin = self.nmos_inst.get_pin("S") gnd_pin = self.get_pin("gnd") # Only if they don't overlap already if gnd_pin.uy() < nmos_source_pin.by(): self.add_rect(layer="metal1", offset=nmos_source_pin.ll(), height=-1*nmos_source_pin.by(), width=nmos_source_pin.width()) pmos_source_pin = self.pmos_inst.get_pin("S") vdd_pin = self.get_pin("vdd") # Only if they don't overlap already if vdd_pin.by() > pmos_source_pin.uy(): self.add_rect(layer="metal1", offset=pmos_source_pin.ll(), height=vdd_pin.by()-pmos_source_pin.by(), width=pmos_source_pin.width()) 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): 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)