# See LICENSE for licensing information. # # Copyright (c) 2016-2019 Regents of the University of California and The Board # of Regents for the Oklahoma Agricultural and Mechanical College # (acting for and on behalf of Oklahoma State University) # All rights reserved. # import pgate import debug from tech import drc, layer from vector import vector from sram_factory import factory import logical_effort from globals import OPTS class single_level_column_mux(pgate.pgate): """ This module implements the columnmux bitline cell used in the design. Creates a single columnmux cell with the given integer size relative to minimum size. Default is 8x. Per Samira and Hodges-Jackson book: Column-mux transistors driven by the decoder must be sized for optimal speed """ def __init__(self, name, tx_size=8, bitcell_bl="bl", bitcell_br="br"): debug.info(2, "creating single column mux cell: {0}".format(name)) self.tx_size = int(tx_size) self.bitcell_bl = bitcell_bl self.bitcell_br = bitcell_br pgate.pgate.__init__(self, name) def get_bl_names(self): return "bl" def get_br_names(self): return "br" def create_netlist(self): self.add_pins() self.add_ptx() def create_layout(self): # If li exists, use li and m1 for the mux, otherwise use m1 and m2 if "li" in layer: self.col_mux_stack = self.li_stack else: self.col_mux_stack = self.m1_stack self.pin_layer = self.bitcell.get_pin(self.bitcell_bl).layer self.pin_pitch = getattr(self, "{}_pitch".format(self.pin_layer)) self.pin_width = getattr(self, "{}_width".format(self.pin_layer)) self.pin_height = 2 * self.pin_width self.place_ptx() self.width = self.bitcell.width self.height = self.nmos_upper.uy() + self.pin_height self.connect_poly() self.add_bitline_pins() self.connect_bitlines() self.add_pn_wells() def add_ptx(self): self.bitcell = factory.create(module_type="bitcell") # Adds nmos_lower,nmos_upper to the module self.ptx_width = self.tx_size * drc("minwidth_tx") self.nmos = factory.create(module_type="ptx", width=self.ptx_width) self.add_mod(self.nmos) # Space it in the center self.nmos_lower = self.add_inst(name="mux_tx1", mod=self.nmos) self.connect_inst(["bl", "sel", "bl_out", "gnd"]) # This aligns it directly above the other tx with gates abutting self.nmos_upper = self.add_inst(name="mux_tx2", mod=self.nmos) self.connect_inst(["br", "sel", "br_out", "gnd"]) def add_pins(self): self.add_pin_list(["bl", "br", "bl_out", "br_out", "sel", "gnd"]) def add_bitline_pins(self): """ Add the top and bottom pins to this cell """ bl_pos = vector(self.pin_pitch, 0) br_pos = vector(self.width - self.pin_pitch, 0) # bl and br self.add_layout_pin(text="bl", layer=self.pin_layer, offset=bl_pos + vector(0, self.height - self.pin_height), height=self.pin_height) self.add_layout_pin(text="br", layer=self.pin_layer, offset=br_pos + vector(0, self.height - self.pin_height), height=self.pin_height) # bl_out and br_out self.add_layout_pin(text="bl_out", layer=self.pin_layer, offset=bl_pos, height=self.pin_height) self.add_layout_pin(text="br_out", layer=self.pin_layer, offset=br_pos, height=self.pin_height) def place_ptx(self): """ Create the two pass gate NMOS transistors to switch the bitlines""" # Space it in the center nmos_lower_position = self.nmos.active_offset.scale(0, 1) \ + vector(0.5 * self.bitcell.width- 0.5 * self.nmos.active_width, 0) self.nmos_lower.place(nmos_lower_position) # This aligns it directly above the other tx with gates abutting nmos_upper_position = nmos_lower_position \ + vector(0, self.nmos.active_height + max(self.active_space, self.poly_space)) self.nmos_upper.place(nmos_upper_position) if OPTS.tech_name == "sky130": self.add_implants() def connect_poly(self): """ Connect the poly gate of the two pass transistors """ # offset is the top of the lower nmos' diffusion # height is the distance between the nmos' diffusions, which depends on max(self.active_space,self.poly_space) offset = self.nmos_lower.get_pin("G").ul() - vector(0, self.poly_extend_active) height = self.nmos_upper.get_pin("G").by() + self.poly_extend_active - offset.y self.add_rect(layer="poly", offset=offset, height=height) # Add the sel pin to the bottom of the mux self.add_layout_pin(text="sel", layer="poly", offset=self.nmos_lower.get_pin("G").ll(), height=self.poly_extend_active) def connect_bitlines(self): """ Connect the bitlines to the mux transistors """ bl_pin = self.get_pin("bl") br_pin = self.get_pin("br") bl_out_pin = self.get_pin("bl_out") br_out_pin = self.get_pin("br_out") nmos_lower_s_pin = self.nmos_lower.get_pin("S") nmos_lower_d_pin = self.nmos_lower.get_pin("D") nmos_upper_s_pin = self.nmos_upper.get_pin("S") nmos_upper_d_pin = self.nmos_upper.get_pin("D") # Add vias to bl, br_out, nmos_upper/S, nmos_lower/D self.add_via_stack_center(from_layer=bl_pin.layer, to_layer=self.col_mux_stack[0], offset=bl_pin.bc()) self.add_via_stack_center(from_layer=br_out_pin.layer, to_layer=self.col_mux_stack[0], offset=br_out_pin.uc()) self.add_via_stack_center(from_layer=nmos_upper_s_pin.layer, to_layer=self.col_mux_stack[2], offset=nmos_upper_s_pin.center()) self.add_via_stack_center(from_layer=nmos_lower_d_pin.layer, to_layer=self.col_mux_stack[2], offset=nmos_lower_d_pin.center()) # bl -> nmos_upper/D on metal1 # bl_out -> nmos_upper/S on metal2 self.add_path(self.col_mux_stack[0], [bl_pin.ll(), vector(nmos_upper_d_pin.cx(), bl_pin.by()), nmos_upper_d_pin.center()]) # halfway up, move over mid1 = bl_out_pin.uc().scale(1, 0.4) \ + nmos_upper_s_pin.bc().scale(0, 0.4) mid2 = bl_out_pin.uc().scale(0, 0.4) \ + nmos_upper_s_pin.bc().scale(1, 0.4) self.add_path(self.col_mux_stack[2], [bl_out_pin.uc(), mid1, mid2, nmos_upper_s_pin.center()]) # br -> nmos_lower/D on metal2 # br_out -> nmos_lower/S on metal1 self.add_path(self.col_mux_stack[0], [br_out_pin.uc(), vector(nmos_lower_s_pin.cx(), br_out_pin.uy()), nmos_lower_s_pin.center()]) # halfway up, move over mid1 = br_pin.bc().scale(1, 0.5) \ + nmos_lower_d_pin.uc().scale(0, 0.5) mid2 = br_pin.bc().scale(0, 0.5) \ + nmos_lower_d_pin.uc().scale(1, 0.5) self.add_path(self.col_mux_stack[2], [br_pin.bc(), mid1, mid2, nmos_lower_d_pin.center()]) def add_implants(self): """ Add top-to-bottom implants for adjacency issues in s8. """ # Route to the bottom ll = (self.nmos_lower.ll() - vector(2 * [self.implant_enclose_active])).scale(1, 0) # Don't route to the top ur = self.nmos_upper.ur() + vector(self.implant_enclose_active, 0) self.add_rect("nimplant", ll, ur.x - ll.x, ur.y - ll.y) def add_pn_wells(self): """ Add a well and implant over the whole cell. Also, add the pwell contact (if it exists) """ # Add it to the right, aligned in between the two tx active_pos = vector(self.bitcell.width, self.nmos_upper.by() - 0.5 * self.poly_space) self.add_via_center(layers=self.active_stack, offset=active_pos, implant_type="p", well_type="p") # If there is a li layer, include it in the power stack self.add_via_center(layers=self.col_mux_stack, offset=active_pos) # Add the M1->..->power_grid_layer stack self.add_power_pin(name="gnd", loc=active_pos, start_layer="m1") # Add well enclosure over all the tx and contact if "pwell" in layer: self.add_rect(layer="pwell", offset=vector(0, 0), width=self.bitcell.width, height=self.height) def get_stage_effort(self, corner, slew, load): """ Returns relative delay that the column mux. Difficult to convert to LE model. """ parasitic_delay = 1 # This is not CMOS, so using this may be incorrect. cin = 2 * self.tx_size return logical_effort.logical_effort("column_mux", self.tx_size, cin, load, parasitic_delay, False)