Safe Operating Area Check

 

Introduction

CMOS devices are designed to operate under defined operating conditions, these conditions are defined in the Operating Conditions section in the Process Parameter document. Violating operating conditions could lead to a degradation, malfunction or even to the destruction of the device.

The Safe Operating Area Check (SOAC) traces the operating point of each device in a simulated design and reports violations when the safe operating region is left. The Safe Operating Area Checker uses Verilog-A modules to trace the voltages of each device, therefore a Cadence Verilog-A license is required.

The warnings are written to the standard spectre output log: <Sim>/<circuitName>/spectre/schematic/psf/spectre.out

After the simulator terminates the SOAC Tool can be started, this tool reads the output file and shows all SOAC violations in a separat window in Cadence. It allows a cross-probing between error message, waveforms and schematic.

Usage/Analog Artist Integration

Each device included in the Process Parameter Document has a SOAC model. The SOAC models are defined in a separate directory in the spectre model path. Simulation with SOAC is mandatory in H35 and therefore the SOAC models are set by default when starting spectre. Using the HIT-Kit will not require any additional steps to setup a Safe Operating Area Check.
Check the model path before using SOAC. The model path has to include soac to set the soac models.

  • Check the Model Libraries:

      Setup->Model Libraries ...

    modellibraries

  • Also check the Simulation Files:
      Setup->Simulation files ...

    simulationFiles
    Note: The mcparams.scs files is required to include the SOAC models.

  • The model path can also be changed by selecting:

      CIW->HIT-Kit utilities->Change Model Files:->Set/Unset SOAC Models

    Change

 

Before starting the simulation the Substrate node has to be defined

For some Devices checks between a Device pin and the substrate exist. The checker uses a global node psub! as Substrate, therefore a global node psub! has to be defined in the schematic.
This node is referenced in the models and must be given a specified voltage to the ground by a voltage source.

If the substrate is at 0 V specify a 0V - voltage source (this is also useful for probing of the substrate current):  

 

psub

 

During the simulation every violation to the SOA is written in the simulator output log file.

<simulation directory>/<circuit name>/spectre/schematic/psf/spectre.out 


SOAC: M2.soac_m1    		  modn50h V(G,S): LEAVING@  0us      ;
SOAC: M2.soac_m1    		  modn50h V(G,B): LEAVING@  0us      ;
SOAC: M0.M_subinst_01.soac_m1     modp50h V(G,S): LEAVING@  0us      ;
SOAC: M0.M_subinst_01.soac_m1     modp50h V(G,B): LEAVING@  0us      ;
SOAC: M3.M_subinst_01.soac_m1     modpim V(D,S):  LEAVING@  0.04us   ;
SOAC: M3.M_subinst_01.soac_m1     modpim V(D,B):  LEAVING@  0.04us    ;
SOAC: M3.M_subinst_01.soac_m1     modpim V(G,S):  LEAVING@  0.80926us ;
SOAC: M3.M_subinst_01.soac_m1     modpim V(G,B):  LEAVING@  0.80926us ;

Note: for Corner Analysis the spectre.out file can be found under:
<simulation directory>/<circuit name>/spectre/schematic/Corner<number>/spectre.out

 

Safe Operating Area Graphical User Interface

The graphical user interface for SOAC can be started after the spectre Simulation has finished: Schematic Window

    HIT-Kit Utilities->SOAC Tool

SOAC

 

The SOAC PostProcessor shows the list of operating area violations and enables a cross-probing between schematic and waveform. Selecting a line in the SOAC tool will automatically highlight the involved device in the schematic and the node-voltages are displayed in the waveforms window.
The Designer can now examine the violation and, if applicable, he can mark the error as fixed - if he is sure that this violation can be neglected.
There are different buttons to filter the data which is displayed in the SOAC tool.

  • Error File: - enables the designer to select the SOAC spectre.out to be examined
  • Show WaveForms - Waveform display is turned off by default
  • Sort by - sorting of the list by Time, Instance and Parameter
  • Show - filters the data to be displayed, selections can be:
    • All - shows all violations
    • REDUCED_LT - only shows devices which have a REDUCED LIFETIME
    • Only not fixed - shows only violations which have not been marked as fixed
    • Only fixed - shows violations which have been marked as fixed
    • Leaving only - shows only the violation when Device is leaving the SOA
    • Entering only - shows only the violation when Device is entering the SOA
  • Toggle line un/fixed - marks the selected line as fixed or unfixed
  • Mark Device as fixed - marks all lines involving the the selected Device as fixed
  • Mark as fixed: Time [us] - marks all violations with a duration shorter than the specified value as fixed
  • Cols show/unshow - displayed columns can be configured
  • Merge Duplicated - duplicated lines can be merged
  • All not fixed - marks all lines as not fixed
  • Details - shows currents through device if available

 

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