10.6.5. Nominal design

We are going to find the values of design parameters for which the design requirements specified in definitions.py are satisfied at nominal operating conditions and with the typical process variation MOS models. The script is in file 02-nominal-design.py in folder demo/design/miller/

# Nominal design

from definitions import *
from pyopus.design.cbd import CornerBasedDesign
from pyopus.evaluator.aggregate import formatParameters
# If MPI is imported an application not using MPI will behave correctly
# (i.e. only slot 0 will run the program) even when started with mpirun/mpiexec
from pyopus.parallel.mpi import MPI
from pyopus.parallel.cooperative import cOS


if __name__=='__main__':
	# Prepare statistical parameters dictionary with nominal values (0)
	nominalStat={ name: 0.0 for name, desc in statParams.items() }
	
	# Prepare operating parameters dictionary with nominal values
	nominalOp={ name: desc['init'] for name, desc in opParams.items() }
	
	# Prepare initial design parameters dictionary
	initialDesign={ name: desc['init'] for name, desc in designParams.items() }
	
	# Prepare one corner, module 'tm', nominal op parameters, defined for all heads
	corners={
		'nom': {
			'params': nominalOp, 
			'modules': ['tm']
		}
	}
	
	# Prepare parallel environment
	cOS.setVM(MPI(mirrorMap={'*':'.'}))
	
	# Design it, nominal statistical parameters are treated as fixed parameters
	cbd=CornerBasedDesign(
		designParams, heads, analyses, measures, corners, 
		fixedParams=[nominalStat], variables=variables, norms={ 'area': 100e-12 }, 
		initial=initialDesign, 
		method='global', 
		evaluatorOptions={'debug': 0}, 
		debug=1
	)
	
	# Run optimization
	atDesign, aggregator, analysisCount = cbd()
	
	# Print design parameters and performance measures
	print(formatParameters(atDesign))
	print(aggregator.formatResults())
	
	# Finalize cOS parallel environment
	cOS.finalize()
	
# Result 
#           c_out:   2.0125484638530715e-12
#          diff_l:   9.0173130168525476e-07
#          diff_w:   1.3748137933373763e-05
#          load_l:   3.1959280853504449e-06
#          load_w:   8.9130317977231035e-05
#          mirr_l:   1.9427037931893832e-06
#         mirr_ld:   2.4749186739319866e-06
#          mirr_w:   7.9105009110997434e-05
#         mirr_wd:   2.0887405636991897e-05
#         mirr_wo:   3.8316438575060692e-05
#           out_l:   2.7397889227076129e-06
#           out_w:   1.3868429320545923e-05
#           r_out:   1.7894053483506941e+04

The script first prepares dictionaries with nominal statistical parameter values (0), nominal operating parameter values and initial design parameter values. The nominal corner named nom is defined. This corner adds the ‘tm’ module to the input netlist for the simulator and specifies the nominal values of operating parameters.

Next, the cooperative multitasking OS is initialized. It uses MPI as the backend and starts every task in its own local folder which contains the copies of all files from the current folder (mirrorMap argument to MPI).

A pyopus.design.cbd.CornerBasedDesign object is created from designParams, heads, analyses, measures, variables defined in definitions.py and the corners variable constructed in this script. The bounds on design parameters are apecified in the designParams variable. The fixedParams argument specifies the nominal statistical parameter values. These parameters do not change during optimization. The initial design is specified with the initial argument. For the process of optimization the global method is used (parallel SADE optimizer). The debug argument makes the optimizer print its progress during optimization.

The design requirements are specified in the measures variable with lower and upper members of the dictionary describing a performance measure. Only performance measures for which at least one of these two values is specified will be subject to optimization.

For the area performance measure the value of the norm is specified with the norms argument. In our case 1 penalty will be assigned for every 100um2 above the target value for the area. For other performance measures the norm is equal to the absolute value of the respetive lower or upper design requirement. If both of these requirements are specified the greater absolute value of both is used. If a norm is zero it is set to one.

The optimization can be run in parallel on 5 local CPUs by typing

mpirun -n 5 python3 02-nominal-design.py

The parallelization will happen at the optimizer level where multiple candidate solutions will be evaluated in parallel. Of the 5 CPUs one will be the master and the remaining 4 will be workers. This means that we can expect a speedup of up to 4. One can also include CPUs of remote machines in the process of optimization. Read the Using the virtual machine abstraction layer and the Algorithm parallelization tutorials on how to do this.

During optimization messages are printed that show the progress of the optimizer. When the optimization is finished the values of the design parameters obtained by the optimizer are printed

  c_out:    4.496976e-12
 diff_l:    3.237868e-06
 diff_w:    1.541743e-05
 load_l:    3.077559e-06
 load_w:    5.160282e-05
 mirr_l:    2.677943e-06
mirr_ld:    3.758176e-06
 mirr_w:    5.644932e-05
mirr_wd:    8.414813e-06
mirr_wo:    3.312984e-05
  out_l:    1.272839e-06
  out_w:    1.719281e-05
  r_out:    2.216717e+04

followed by the circuit’s performance.

    area  <  9.000e-09    |      1.448e-09    nom : 0
    cmrr  >  9.000e+01    |      1.288e+02    nom : 0
    gain  >  6.000e+01    |      8.015e+01    nom : 0
    isup  <  1.000e-03    |      1.703e-04    nom : 0
overshdn  <  1.000e-01    |      1.540e-03    nom : 0
overshup  <  1.000e-01    |      1.538e-02    nom : 0
      pm  >  5.000e+01    |      8.152e+01    nom : 0
psrr_vdd  >  6.000e+01    |      7.855e+01    nom : 0
psrr_vss  >  6.000e+01    |      9.414e+01    nom : 0
  slewdn  >  2.000e+06    |      2.292e+06    nom : 0
  slewup  >  2.000e+06    |      2.272e+06    nom : 0
   swing  >  1.000e+00    |      1.218e+00    nom : 0
  tsetdn  <  1.000e-06    |      4.325e-07    nom : 0
  tsetup  <  1.000e-06    |      4.100e-07    nom : 0
    ugbw  >  1.000e+07    |      2.530e+07    nom : 0
 vds_drv  >  0.000e+00    |      1.498e-01    nom : 0
 vgs_drv  >  0.000e+00    |      6.355e-02    nom : 0

In the left half of the printout the design requirements are summarized. The first column of the right half lists the obtained circuit’s performance followed by the corner where this performance was obtained and the penalty contribution to the final value of the cost function. Because all design requirements are satisfied all penalty contributions are 0.

Note that due to the random nature of the delays on the network parallel runs may yield different solutions for the same design problem.