Reduce split gate option in LVS

nam_nguyendac

Hi all,
I check reduction split gate option in Klayout.

Case 1: I use nand2x2 cell


Extracted circuit:
M$1 5 2 1 8 PCH L=0.04U W=0.55U AS=0.0495P AD=0.0385P PS=1.185U PD=0.83U
M$3 5 3 1 8 PCH L=0.04U W=0.55U AS=0.04125P AD=0.05225P PS=0.85U PD=1.205U
M$5 4 2 6 9 NCH L=0.04U W=0.255U AS=0.02535P AD=0.01785P PS=0.73U PD=0.395U
M$6 6 2 7 9 NCH L=0.04U W=0.255U AS=0.01785P AD=0.01785P PS=0.395U PD=0.395U
M$7 7 3 1 9 NCH L=0.04U W=0.255U AS=0.01785P AD=0.0204P PS=0.395U PD=0.415U
M$8 1 3 4 9 NCH L=0.04U W=0.255U AS=0.0204P AD=0.02535P PS=0.415U PD=0.73U
After reduction:
M$1 5 2 1 7 PCH L=0.04U W=0.55U AS=0.0495P AD=0.0385P PS=1.185U PD=0.83U
M$3 5 3 1 7 PCH L=0.04U W=0.55U AS=0.04125P AD=0.05225P PS=0.85U PD=1.205U
M$5 4 2 6 8 NCH L=0.04U W=0.51U AS=0.0432P AD=0.0357P PS=1.125U PD=0.79U
M$7 4 3 1 8 NCH L=0.04U W=0.51U AS=0.03825P AD=0.04575P PS=0.81U PD=1.145U

this option works perfectly in this case !!!!

Case 2: I use nand2x4 cell

After reduction:
M$1 6 1 3 7 PCH L=0.04U W=1.1U AS=0.088P AD=0.077P PS=2.015U PD=1.66U
M$5 6 2 3 7 PCH L=0.04U W=1.1U AS=0.077P AD=0.088P PS=1.66U PD=2.015U
M$9 4 1 5 8 NCH L=0.04U W=0.765U AS=0.06155P AD=0.05355P PS=1.52U PD=1.185U
M$12 5 1 9 8 NCH L=0.04U W=0.255U AS=0.01785P AD=0.01785P PS=0.395U PD=0.395U
M$13 9 2 3 8 NCH L=0.04U W=0.255U AS=0.01785P AD=0.01785P PS=0.395U PD=0.395U
M$14 3 2 4 8 NCH L=0.04U W=0.765U AS=0.05355P AD=0.06105P PS=1.185U PD=1.52U

But target netlist:
M$1 6 1 4 7 PCH L=0.04U W=1.1U AS=0.088P AD=0.077P PS=2.015U PD=1.66U
M$5 6 2 4 7 PCH L=0.04U W=1.1U AS=0.077P AD=0.088P PS=1.66U PD=2.015U
M$9 3 1 5 8 NCH L=0.04U W=1.02U AS=0.0794P AD=0.0714P PS=1.915U PD=1.58U
M$13 3 2 4 8 NCH L=0.04U W=1.02U AS=0.0714P AD=0.0789P PS=1.58U PD=1.915U

This option does not work perfectly in this case. It is only reduced for PMOS (PCH) and NMOS is not thorough. Can you help me fix this problem ?

Thank you very much

Matthias

Hi,

The second case is lacking the symmetry requirement: there are basically two separate nodes in the low-side branch on the nand (the two serial transistors). But they are not interchangeable as one node is between two 3x transistors while the other one is between two 1x transistors.

Formally this prevents the reduction algorithm to join these nodes. There is no easy fix except for extending the algorithm. But I have no good idea how to do this currently. An option is to create a virtual connection through labels (use 'connect_implicict("nand2x4", "your_label")').

Matthias

nam_nguyendac

Thank you so much for your information

dai

Hi,
to resolve the issue i read netlist and join_net to joint the points like that, after that use device combine again. it work like expected. Here is my script

#find path
def findPath(netIgr, net, path, joined)

  nnet = nil
  nid = -1

  net.each_terminal do |tm|
    sNet = tm.device.net_for_terminal(0)
    gNet = tm.device.net_for_terminal(1)
    dNet = tm.device.net_for_terminal(2)
    if sNet.cluster_id == netIgr.cluster_id || dNet.cluster_id == netIgr.cluster_id ;next ;end;
    nnet = dNet
    if nnet.cluster_id == net.cluster_id
      nnet = sNet     
    end
    if path.length == 0
      path.push(nnet.cluster_id)
    else
      path[0] = nnet.cluster_id
    end

    path.push(gNet.cluster_id)
    break
  end

  if nnet == nil || !joined.include?(nnet.cluster_id) && nnet.terminal_count >2 || nnet.pin_count>0 ; return; end

  findPath(net, nnet, path, joined)
end

def pathCompare(p1,p2)
  #puts "p1_length:" + p1.length.to_s + " p2_length:" + p2.length.to_s
  if p1 == nil || p2 == nil || p1.length == 0; return false; end
  for i in 0..(p1.length - 1)
    if p1[i] != p2[i] ; return false; end
  end
  return true
end

any = true
while(any)
devices.clear
any = false
  top_cir.each_device do |dev|
  #S-D-G-B: 0-1-2-3
  if dev.device_class.name.match(reg) 
    next
  end

  s_net = dev.net_for_terminal(0)
  g_net = dev.net_for_terminal(1)
  d_net = dev.net_for_terminal(2)
  b_net = dev.net_for_terminal(3)
  if filterDevDmy
    if s_net.cluster_id == d_net.cluster_id && s_net.cluster_id == g_net.cluster_id
      devRemove.push(dev)
      next
    end
  end
  key_gdb = "%s_%s_%s"  %[g_net.expanded_name,d_net.expanded_name,b_net.expanded_name]
  key_gsb = "%s_%s_%s"  %[g_net.expanded_name,s_net.expanded_name,b_net.expanded_name]

  net_pair0 = nil
  net_pair0_p = nil
  i = nil
  key = ""

  if d_net.terminal_count != 2 && s_net.terminal_count != 2
    next
  end

  if devices.key?(key_gdb)
    i = devices[key_gdb]
    key = key_gdb
    net_pair0 = s_net
    net_pair0_p = d_net
  end

  if devices.key?(key_gsb)
    i = devices[key_gsb]
    key = key_gsb
    net_pair0 = d_net
    net_pair0_p = s_net
  end

  if net_pair0 == nil || i == nil
    if d_net.terminal_count == 2 && d_net.pin_count == 0 && d_net.pin_count == 0 && d_net.subcircuit_pin_count == 0
      devices[key_gsb] = Hash.new
      devices[key_gsb]["net"] = d_net
      devices[key_gsb]["id"] = dev.id
    end

    if s_net.terminal_count == 2 && s_net.pin_count == 0 && s_net.pin_count == 0 && s_net.subcircuit_pin_count == 0
      devices[key_gdb] = Hash.new
      devices[key_gdb]["net"] = s_net
      devices[key_gdb]["id"] = dev.id
    end
    next
  end

  net_pair = i["net"]
  ddev = top_cir.device_by_id(i["id"])
  net_pair_p = ddev.net_for_terminal(0)
  if net_pair_p.cluster_id == net_pair.cluster_id
    net_pair_p = ddev.net_for_terminal(2)
  end
  g1 = nil
  g2 = nil
  sd1 = -1
  sd2 = -2
  tc1 = 0
  tc2 = 0
  if net_pair.terminal_count ==0 || net_pair.pin_count>0 || net_pair0.pin_count>0; next; end

  net_pair.each_terminal do |tm|

    if tm.device.id !=i["id"] && !tm.device.device_class.name.match(reg)
      g1 = tm.device.net_for_terminal(1) #net G of device
      if tm.device.net_for_terminal(0).cluster_id != net_pair.cluster_id
        sd1 = tm.device.net_for_terminal(0).cluster_id
        tc1 = tm.device.net_for_terminal(0).terminal_count
      else
        sd1 = tm.device.net_for_terminal(2).cluster_id
        tc1 = tm.device.net_for_terminal(2).terminal_count
      end
    end

  end


  net_pair0.each_terminal do |tm|
    if tm.device.id != dev.id && !tm.device.device_class.name.match(reg)
      g2 = tm.device.net_for_terminal(1) #net G of device
      if tm.device.net_for_terminal(0).cluster_id != net_pair0.cluster_id
        sd2 = tm.device.net_for_terminal(0).cluster_id
        tc2 = tm.device.net_for_terminal(0).terminal_count
      else
        sd2 = tm.device.net_for_terminal(2).cluster_id
        tc2 = tm.device.net_for_terminal(2).terminal_count
      end
    end
  end

  if g1 == nil || g2 == nil; next; end

  if g1.cluster_id == g2.cluster_id && g1 != nil && net_pair0.cluster_id != net_pair.cluster_id && (sd1 == sd2 && tc1 !=2 || (tc1 == tc2 && tc1 == 2))
    net_joined = net_joined + net_pair0.expanded_name + " vs " + net_pair.expanded_name + "\n" 
    pt1 = Array.new
    pt2 = Array.new
    findPath(net_pair0_p,net_pair0,pt1,netJoined)
    findPath(net_pair_p,net_pair,pt2,netJoined)

    if pathCompare(pt1, pt2)
      log "Join:" + net_pair0.expanded_name + " / " + net_pair.expanded_name + " => " + pt1.to_s + " / " + pt2.to_s
      top_cir.join_nets(net_pair0, net_pair)
      i["net"] = net_pair0 #because net_pair merged s_net so it is not exist more
      netJoined.push(net_pair0.cluster_id)
      any = true
    end
  end

end
end

dai