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Ringing in transient simulation.

YutaoLiu

Dear all,

I encountered an unexpected ringing while running transient simulation for a high-speed receiver.

I am using ADE Assembler and the version is ICADV12.3-64b.

The detail is as following,

There are CTLE, source follower, interleaving switch and SAR ADC in series in my test bench. The differential input of CTLE is proved by an ideal voltage source through 50Ohm ideal resistor.  And there are also 8 "vpulse" voltage source realizing 8 phase 8GHz clock driving interleaving switches. There is some s-parameter file to model the induction inside CTLE. And there are a few tens of ideal voltage sources providing dc control signals. I saw unexpected ringing on top of the CTLE input signal in the transient waveform.

In order to debug this issue, I remove all circuitry after the source follower. So there are only input voltage source, CTLE, source follower and 8 clock voltage sources (which are open), and some dc control voltage source in the test bench. The ringing remained there.

If I removed those 8 clock voltage sources in the schematic, or did not save their waveform , the ringing went away.

Below is the my transient simulation setup parameters
start = 0 s
outputstart = 0 s
stop = 10 ns
step = 10 ps
maxstep = 200 ps
ic = all
useprevic = no
skipdc = no
reltol = 1e-03
abstol(V) = 1 uV
abstol(I) = 1 pA
abstol(U) = 1 u
temp = 27 C
tnom = 27 C
tempeffects = all
errpreset = moderate
method = traponly
lteratio = 3.5
relref = sigglobal
cmin = 0 F
gmin = 1 pS
rabsshort = 1 mOhm

Do you have any idea about this issue?

Thanks and regards,

Yutao

Parents

  • Dear Yutao,

    It would be helpful to see the spectre.out file to understand if any warnings were issued. This will also provide the version of the tool you are using

    I can think of a number of possible issues but cannot further resolve them without more information. Common issues include the S -parameter file you are using, the errpreset setting in light of your circuit requirements, the value of maxstep, the integration method chosen with your errpreset, and your actual circuit. I cannot ascertain which, if any, might be good candidates to study without more information.

    Other questions that come to mind ...

    1. What do you consider "unexpected ringing"?

    2. When in the simulation does the ringing occur?

    3. Is your S-parameter file accurate to frequencies well beyond your high speed" receiver signal bandwidth?

    4. Does your S-parameter file include a DC term?

    Shawn

  • in reply to ShawnLogan

    Hi Shawn,

    Thanks for your reply.

    I attached the spectre.out file and the snapshot of the CTLE input signaltransient waveform below. 

    Fullscreen spectre.txt Download 
    Spectre (R) Circuit Simulator
Version 18.1.0.spe.345 64bit -- 23 Apr 2019
Copyright (C) 1989-2019 Cadence Design Systems, Inc. All rights reserved worldwide. Cadence and Spectre are registered trademarks of Cadence Design Systems, Inc. All others are the property of their respective holders.

Includes RSA BSAFE(R) Cryptographic or Security Protocol Software from RSA Security, Inc.

User: yutaoliu   Host: fmci70071   HostID: 600AAC1B   PID: 136299
Memory  available: 34.3441 GB  physical: 405.0262 GB
Linux   : SUSE Linux Enterprise Server 11 (x86_64)
CPU Type: Intel(R) Xeon(R) Gold 6136 CPU @ 3.00GHz
        Socket: Processors [Frequency]
        0:       0 [3001.0],  1 [3001.0],  2 [1200.0],  3 [1200.0],  4 [1200.0]
                 5 [1200.0],  6 [1200.0],  7 [1200.0],  8 [1200.0],  9 [1200.0]
                10 [1200.0], 11 [1200.0]
        1:      12 [1200.0], 13 [1200.0], 14 [1200.0], 15 [1200.0], 16 [1200.0]
                17 [1200.0], 18 [1200.0], 19 [1200.0], 20 [1200.0], 21 [1200.0]
                22 [1200.0], 23 [1200.0]
        
System load averages (1min, 5min, 15min) : 5.1 %, 3.2 %, 2.6 %
HPC is enabled


Simulating `input.scs' on fmci70071 at 8:59:59 AM, Thur Aug 27, 2020 (process id: 136299).
Current working directory: /nfs/fm/disks/fm_act_00053/users/yutaoliu/serdes_10_ytliu/simulation/serdesafe_ihdk_sch/serdesafe_top_testbench_maestro/maestro_1/results/maestro/Interactive.2104.RO/1/serdesafesim_ihdk_sch:serdesafe_CTLE_OPHPF:1/netlist
Environment variable:
    CMI_CONFIG=/nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/cmiconfig_18.1.0.2
Command line:
    /p/hdk/cad/mmsim/18.1.0.spe.345/tools/bin/spectre -64 input.scs  \
        +escchars +log ../psf/spectre.out -format psfxl -raw ../psf  \
        +aps -mt +lqtimeout 900 -maxw 5 -maxn 5 +preset=mx-f +logstatus

Loading /p/hdk/cad/mmsim/18.1.0.spe.345/tools.lnx86/cmi/lib/64bit/5.0/libinfineon_sh.so ...
Loading /p/hdk/cad/mmsim/18.1.0.spe.345/tools.lnx86/cmi/lib/64bit/5.0/libphilips_o_sh.so ...
Loading /p/hdk/cad/mmsim/18.1.0.spe.345/tools.lnx86/cmi/lib/64bit/5.0/libphilips_sh.so ...
Loading /p/hdk/cad/mmsim/18.1.0.spe.345/tools.lnx86/cmi/lib/64bit/5.0/libsparam_sh.so ...
Loading /p/hdk/cad/mmsim/18.1.0.spe.345/tools.lnx86/cmi/lib/64bit/5.0/libstmodels_sh.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libctrk.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libdio2.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libgbnw.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libibjt.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/librtrk.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libstinw.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libumos3.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libumos4.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libumos5.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libvctrk.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libvdnmos.so ...
Loading /nfs/fm/disks/fm_act_00053/users/abalanku/flc.tc1/models/rg/cmi/libvtrk.so ...
Reading file:  /nfs/fm/disks/fm_act_00053/users/yutaoliu/serdes_10_ytliu/simulation/serdesafe_ihdk_sch/serdesafe_top_testbench_maestro/maestro_1/results/maestro/Interactive.2104.RO/1/serdesafesim_ihdk_sch:serdesafe_CTLE_OPHPF:1/netlist/input.scs

Notice from spectre during circuit read-in.
    Pre_Configuration file used: /p/hdk/cad/mmsim/18.1.0.spe.345/tools.lnx86/spectre/etc/configs/preset.precfg
    Configuration file used: `/p/hdk/cad/mmsim/18.1.0.spe.345/tools.lnx86/spectre/etc/configs/preset.cfg'.

Reading link:  /p/hdk/cad/mmsim/18.1.0.spe.345
Reading link:  /p/hdk/cad
Reading link:  /p
Reading file:  /nfs/site/disks/hdk_cad_16/cad/mmsim/18.1.0.spe.345/tools.lnx86/spectre/etc/configs/mapsubckt.cfg
Reading file:  /nfs/site/disks/hdk_cad_16/cad/mmsim/18.1.0.spe.345/tools.lnx86/spectre/etc/configs/spectre.cfg
Reading file:  /nfs/site/disks/hdk_cad_16/cad/mmsim/18.1.0.spe.345/tools.lnx86/spectre/etc/configs/preset.precfg
Reading link:  /p/hdk/cad/vmac/18.08.27.p32
Reading file:  /nfs/site/disks/hdk_cad_18/cad/vmac/18.08.27.p32/release/ade_utils/bin/spectre_gnd_vss.scs
Reading link:  /p/hdk/archive/ihdk/Barak.TC3
Reading link:  /p/hdk/archive/ihdk
Reading link:  /p/hdk/archive
Reading file:  /nfs/fm/disks/fm_act_00053/arc/Barak.TC3/proj_files/latest/sim/corners.scs
Reading link:  /p/hdk/cad/pdk/cpdk7581_r0.8HP1_19ww26.3_FLC
Reading file:  /nfs/site/disks/hdk_cad_18/cad/pdk/cpdk7581_r0.8HP1_19ww26.3_FLC/models/core/spectre/p1275_81_var.scs
Reading file:  /nfs/site/disks/hdk_cad_18/cad/pdk/cpdk7581_r0.8HP1_19ww26.3_FLC/models/custom/spectre/intel75mfcwrapper.scs
Reading file:  /nfs/site/disks/hdk_cad_18/cad/pdk/cpdk7581_r0.8HP1_19ww26.3_FLC/models/custom/spectre/intel75custom.scs
Reading link:  /nfs/fm/disks/fm_act_00053/users/yutaoliu/serdes_10_ytliu/simulation/serdesafe_ihdk_sch/serdesafe_top_testbench_maestro/maestro_1/results/maestro/Interactive.2104.RO/1/serdesafesim_ihdk_sch:serdesafe_CTLE_OPHPF:1/netlist/netlist
Reading file:  /nfs/fm/disks/fm_act_00053/users/yutaoliu/serdes_10_ytliu/simulation/serdesafe_ihdk_sch/serdesafe_top_testbench_maestro/maestro_1/results/maestro/Interactive.2104.RO/psf/serdesafesim_ihdk_sch:serdesafe_CTLE_OPHPF:1/netlist/netlist
Reading file:  /nfs/site/disks/hdk_cad_16/cad/mmsim/18.1.0.spe.345/tools.lnx86/spectre/etc/configs/preset.cfg
Time for NDB Parsing: CPU = 752.046 ms, elapsed = 7.18587 s.
Time accumulated: CPU = 808.049 ms, elapsed = 7.18588 s.
Peak resident memory used = 90.3 Mbytes.


Notice from spectre during circuit read-in.
    "input.scs" 7: Redeclaration of the global node `vss'.
Warning from spectre during circuit read-in.
    WARNING (SFE-2649): Remove instance `vvssz49xzz' in top level because its terminals are connected together.
    WARNING (SFE-2649): Remove instance `vvssz49xzz2' in top level because its terminals are connected together.
    WARNING (SFE-2649): Remove instance `mqn105' in subckt `f8xlesdclpe2000qnxunx' because its terminals are connected together.
    WARNING (SFE-2649): Remove instance `mqn106' in subckt `f8xlesdclpe2000qnxunx' because its terminals are connected together.
    WARNING (SFE-2649): Remove instance `mqn103' in subckt `f8xlesdclpe2000qnxunx' because its terminals are connected together.
        Further occurrences of this warning will be suppressed.
Warning from spectre in `e8xldcpip0n4000xn3unx_prim':`i0.bias.c_stab.xftti1', in `e8xldcpip0n4000xn3unx':`i0.bias.c_stab', in `serdesadcnsf_inbuf_nsf_bias':`i0.bias', in `serdesadcnsf_inbuf_nsf':`i0', during hierarchy flattening.
    WARNING (SFE-103): "/p/hdk/cad/pdk/cpdk7581_r0.8HP1_19ww26.3_FLC/models/core/spectre/p1275_81_var.scs" 490095: Subcircuit parameter `level', defined for subcircuit `p', has been ignored because it is invalid. Check the parameters that are defined for the instantiated subcircuit and rerun the simulation.

Reading file:  /nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p
Reading file:  /nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_pad_top_redo_4.s12p
Reading file:  /nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st1_top_ind_all_copy_ver2.s9p
Reading file:  /nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st2_top_ind_only_copy_final.s8p
Time for Elaboration: CPU = 648.042 ms, elapsed = 654.507 ms.
Time accumulated: CPU = 1.45609 s, elapsed = 7.84051 s.
Peak resident memory used = 160 Mbytes.


Warning from spectre during hierarchy flattening.
    WARNING (SPECTRE-17101): The value 'psf' specified using the 'checklimitdest' option will no longer be supported in future releases.
Notice from spectre in `serdesafe_st3_top_testbench2':`afe_core.st3_top', in `serdesafe_core_testbench':`afe_core', during hierarchy flattening.
    Nport compression is disabled on instance afe_core.st3_top.NPORT0 because its used port ratio 0.800000 is greater than 0.800000.
Notice from spectre in `serdesafe_pad_top_testbench5':`afe_core.pad_top', in `serdesafe_core_testbench':`afe_core', during hierarchy flattening.
    Nport compression is disabled on instance afe_core.pad_top.NPORT0 because its used port ratio 0.833333 is greater than 0.800000.
Notice from spectre in `serdesafe_st1_top_testbench_ind':`afe_core.st1_top', in `serdesafe_core_testbench':`afe_core', during hierarchy flattening.
    Nport compression is disabled on instance afe_core.st1_top.NPORT0 because its port number 9 is smaller than 10.
        
Notice from spectre in `serdesafe_st2_top_testbench_4':`afe_core.st2_top', in `serdesafe_core_testbench':`afe_core', during hierarchy flattening.
    Nport compression is disabled on instance afe_core.st2_top.NPORT0 because its port number 8 is smaller than 10.
        



Warning from spectre during hierarchy flattening.
    WARNING (SPECTRE-8527): There are some nodes and instances removed from the netlist topology check. Check the circuit and correct the topology. Or use preserve_inst to keep them if necessary.

***********************************************
  Total removed instances 18 ( dangling 10, terminals connected together 8)  

Warning from spectre during hierarchy flattening.
    WARNING (SPECTRE-8529): Dangling instance. V105 is removed.
    WARNING (SPECTRE-8529): Dangling instance. V30 is removed.
    WARNING (SPECTRE-8528): Terminals are connected together. afe_core.pad_top.I36.i51.xftti0.c2 is removed.
    WARNING (SPECTRE-8528): Terminals are connected together. afe_core.pad_top.I36.i51.xftti0.c3 is removed.
    WARNING (SPECTRE-8528): Terminals are connected together. afe_core.st3_cntrl.odacmrr<1>.qn4.q0.qn0_turbo_m2 is removed.
    WARNING (SPECTRE-8528): Terminals are connected together. afe_core.st3_cntrl.odacmrr<0>.qn4.q0.qn0_turbo_m2 is removed.
    WARNING (SPECTRE-8528): Terminals are connected together. afe_core.st1_cntrl.odacmrr<1>.qn4.q0.qn0_turbo_m2 is removed.
        Further occurrences of this warning will be suppressed.
    WARNING (SPECTRE-8529): Dangling instance. i0.r0 is removed.
    WARNING (SPECTRE-8529): Dangling instance. i0.r2 is removed.
    WARNING (SPECTRE-8529): Dangling instance. i0.r4 is removed.
        Further occurrences of this warning will be suppressed.


  Total removed nodes 10 ( dangling nodes 10, floating nodes 0 )

Warning from spectre during hierarchy flattening.
    WARNING (SPECTRE-8530): Dangling node. st2_psw2<5> is removed.
    WARNING (SPECTRE-8530): Dangling node. st1_psw2<5> is removed.
    WARNING (SPECTRE-8530): Dangling node. net016 is removed.
    WARNING (SPECTRE-8530): Dangling node. net015 is removed.
    WARNING (SPECTRE-8530): Dangling node. net018 is removed.
        Further occurrences of this warning will be suppressed.
    WARNING (SPECTRE-8531): Floating node. net054 is removed.
    WARNING (SPECTRE-8531): Floating node. st3_ggain2n<4> is removed.
    WARNING (SPECTRE-8531): Floating node. st3_ggain2n<3> is removed.
    WARNING (SPECTRE-8531): Floating node. st3_ggain2n<2> is removed.
    WARNING (SPECTRE-8531): Floating node. st3_ggain2n<1> is removed.
        Further occurrences of this warning will be suppressed.

***********************************************
Time for EDB Visiting: CPU = 540.033 ms, elapsed = 541.811 ms.
Time accumulated: CPU = 1.99612 s, elapsed = 8.38243 s.
Peak resident memory used = 214 Mbytes.


Notice from spectre during initial setup.
    In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st2_top_ind_only_copy_final.s8p', the maximum passivity violation is 3.0933 % at 100 GHz.
Warning from spectre during initial setup.
    WARNING (CMI-2839): In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st1_top_ind_all_copy_ver2.s9p', S5_9 may be discontinuous at 57.45 GHz.
Notice from spectre during initial setup.
    In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st1_top_ind_all_copy_ver2.s9p', the maximum passivity violation is 2.46725 % at 100 GHz.
    In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_pad_top_redo_4.s12p', the maximum passivity violation is 3.38048 % at 100 GHz.
Warning from spectre during initial setup.
    WARNING (CMI-2839): In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', S9_9 may be discontinuous at 2.875 GHz.
    WARNING (CMI-2839): In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', S9_10 may be discontinuous at 2.875 GHz.
    WARNING (CMI-2839): In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', S10_10 may be discontinuous at 2.875 GHz.
Notice from spectre during initial setup.
    In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', the maximum passivity violation is 1.98119 % at 100 GHz.
Warning from spectre during initial setup.
    WARNING (SPECTRE-8281): `outp' is not a node nor an instance name.
    WARNING (SPECTRE-8286): Ignoring invalid item `outp' in save statement.
    WARNING (SPECTRE-8281): `outn' is not a node nor an instance name.
    WARNING (SPECTRE-8286): Ignoring invalid item `outn' in save statement.
    WARNING (SPECTRE-8281): `net0117' is not a node nor an instance name.
    WARNING (SPECTRE-8286): Ignoring invalid item `net0117' in save statement.
    WARNING (SPECTRE-8281): `net0118' is not a node nor an instance name.
    WARNING (SPECTRE-8286): Ignoring invalid item `net0118' in save statement.
    WARNING (SPECTRE-8281): `cbump_P_30f' is not a node nor an instance name.
        Further occurrences of this warning will be suppressed.
    WARNING (SPECTRE-8286): Ignoring invalid item `cbump_P_30f' in save statement.
        Further occurrences of this warning will be suppressed.
Notice from spectre during topology check.
    Only one connection to the following 36 nodes:
        th_clk<4>
        th_clk<5>
        th_clk<6>
        th_clk<7>
        th_clk<1>
        Further occurrences of this notice will be suppressed.
    No DC path from node `afe_core.pad_top.I39.itimer_gated.noconn<0>' to ground, Gmin installed to provide path.
    No DC path from node `afe_core.st2_top.st2_rln2.nc_d' to ground, Gmin installed to provide path.
    No DC path from node `afe_core.st2_top.st2_rlp2.nc_d' to ground, Gmin installed to provide path.
    No DC path from node `afe_core.st2_top.gm_core.st1_gm.I23.net5' to ground, Gmin installed to provide path.
    No DC path from node `afe_core.st2_top.gm_core.st1_gm.I22.net5' to ground, Gmin installed to provide path.
        Further occurrences of this notice will be suppressed.


Global user options:
         psfversion = 1.1.0
            vabstol = 1e-06
            iabstol = 1e-12
               temp = 27
               gmin = 1e-12
             rforce = 1
           maxnotes = 5
           maxwarns = 5
             digits = 5
               cols = 80
             pivrel = 0.001
           sensfile = ../psf/sens.output
     checklimitdest = psf
               save = selected
           currents = selected
          useprobes = yes
             reltol = 0.005
               tnom = 27
             scalem = 1
              scale = 1

Scoped user options:

Circuit inventory:
              nodes 11072
          capacitor 8716  
               dio2 3077  
               gbnw 2088  
            isource 13    
              nport 4     
           resistor 3484  
               rtrk 12    
              umos5 35492 
            vsource 121   

Analysis and control statement inventory:
               info 7     
               tran 1     

Output statements:
             .probe 0     
           .measure 0     
               save 1     


Notice from spectre during initial setup.
    49 vsources are short because their absolute value is less than or equal to 'vabsshort'.
    Spectre preset=mx-f Enabled.
    67 notices suppressed.
    48 warnings suppressed.

Time for parsing: CPU = 460.028 ms, elapsed = 491.043 ms.
Time accumulated: CPU = 2.45615 s, elapsed = 8.87358 s.
Peak resident memory used = 238 Mbytes.

~~~~~~~~~~~~~~~~~~~~~~
Pre-Simulation Summary
~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~

************************************************
Transient Analysis `tran': time = (0 s -> 20 ns)
************************************************

Notice from spectre during transient analysis `tran'.
    tran: Loosening Newton tolerances when using trapezoidal rule might give anomalous results.
Warning from spectre during DC solution estimation, during IC analysis, during transient analysis `tran'.
    WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st2_top_ind_only_copy_final.s8p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency).
    WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st1_top_ind_all_copy_ver2.s9p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency).
    WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency).
    WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_pad_top_redo_4.s12p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency).

Trying `homotopy = gmin' for initial conditions.

Notice from spectre during IC analysis, during transient analysis `tran'.
    Bad pivoting is found during DC analysis. Option dc_pivot_check=yes is recommended for possible improvement of convergence.

DC simulation time: CPU = 6.70042 s, elapsed = 6.71082 s.

Opening the PSFXL file ../psf/tran.tran.tran ...
Important parameter values:
    start = 0 s
    outputstart = 0 s
    stop = 20 ns
    step = 20 ps
    maxstep = 400 ps
    ic = all
    useprevic = no
    skipdc = no
    reltol = 5e-03
    abstol(V) = 1 uV
    abstol(I) = 1 pA
    abstol(U) = 1 u
    temp = 27 C
    tnom = 27 C
    tempeffects = all
    errpreset = moderate
    method = trap
    lteratio = 3.5
    relref = allglobal
    cmin = 0 F
    gmin = 1 pS
    rabsshort = 1 mOhm

Reading link:  /nfs/site/home/yutaoliu
Reading file:  /nfs/fm/disks/fm_home_a1fs/yutaoliu/.cadence/mmsim/108c7afe8e4e96d9a543f18b4c7f4f18.bin

Notice from spectre during transient analysis `tran'.
    Nport afe_core.st2_top.NPORT0: Reuse impulse responses from the file `108c7afe8e4e96d9a543f18b4c7f4f18.bin' in the directory of `/nfs/site/home/yutaoliu/.cadence/mmsim/'.

Reading file:  /nfs/fm/disks/fm_home_a1fs/yutaoliu/.cadence/mmsim/956d6faee98104c9e43b56b0c1bd0006.bin

Notice from spectre during transient analysis `tran'.
    Nport afe_core.st1_top.NPORT0: Reuse impulse responses from the file `956d6faee98104c9e43b56b0c1bd0006.bin' in the directory of `/nfs/site/home/yutaoliu/.cadence/mmsim/'.

Reading file:  /nfs/fm/disks/fm_home_a1fs/yutaoliu/.cadence/mmsim/a6e6e4631c82e69049efe67a6694cf2a.bin

Notice from spectre during transient analysis `tran'.
    Nport afe_core.st3_top.NPORT0: Reuse impulse responses from the file `a6e6e4631c82e69049efe67a6694cf2a.bin' in the directory of `/nfs/site/home/yutaoliu/.cadence/mmsim/'.

Reading file:  /nfs/fm/disks/fm_home_a1fs/yutaoliu/.cadence/mmsim/4320f3465557e0103ab9050cc4610527.bin

Notice from spectre during transient analysis `tran'.
    Nport afe_core.pad_top.NPORT0: Reuse impulse responses from the file `4320f3465557e0103ab9050cc4610527.bin' in the directory of `/nfs/site/home/yutaoliu/.cadence/mmsim/'.


Output and IC/nodeset summary:
                 save   21      (voltage)

    tran: time = 500 ps       (2.5 %), step = 1.888 ps    (9.44 m%)
    tran: time = 1.415 ns    (7.07 %), step = 1.145 ps    (5.73 m%)
    tran: time = 1.501 ns    (7.51 %), step = 1.09 ps     (5.45 m%)
    tran: time = 2.354 ns    (11.8 %), step = 1.77 ps     (8.85 m%)
    tran: time = 2.5 ns      (12.5 %), step = 1.232 ps    (6.16 m%)
    tran: time = 3.365 ns    (16.8 %), step = 1.405 ps    (7.02 m%)
    tran: time = 3.5 ns      (17.5 %), step = 1.267 ps    (6.33 m%)
    tran: time = 4.364 ns    (21.8 %), step = 2.136 ps    (10.7 m%)
    tran: time = 4.5 ns      (22.5 %), step = 1.496 ps    (7.48 m%)
    tran: time = 5.369 ns    (26.8 %), step = 1.847 ps    (9.23 m%)
    tran: time = 5.5 ns      (27.5 %), step = 1.324 ps    (6.62 m%)
    tran: time = 6.375 ns    (31.9 %), step = 1.886 ps    (9.43 m%)
    tran: time = 6.5 ns      (32.5 %), step = 1.229 ps    (6.15 m%)
    tran: time = 7.373 ns    (36.9 %), step = 1.797 ps    (8.98 m%)
    tran: time = 7.501 ns    (37.5 %), step = 1.181 ps    (5.91 m%)
    tran: time = 8.365 ns    (41.8 %), step = 1.262 ps    (6.31 m%)
    tran: time = 8.5 ns      (42.5 %), step = 1.89 ps     (9.45 m%)
    tran: time = 9.346 ns    (46.7 %), step = 997.4 fs    (4.99 m%)
    tran: time = 9.501 ns    (47.5 %), step = 1.22 ps      (6.1 m%)
    tran: time = 10.35 ns    (51.7 %), step = 1.072 ps    (5.36 m%)
    tran: time = 10.5 ns     (52.5 %), step = 1.885 ps    (9.42 m%)
    tran: time = 11.34 ns    (56.7 %), step = 1.379 ps    (6.89 m%)
    tran: time = 11.5 ns     (57.5 %), step = 1.881 ps    (9.41 m%)
    tran: time = 12.35 ns    (61.8 %), step = 1.277 ps    (6.39 m%)
    tran: time = 12.5 ns     (62.5 %), step = 1.368 ps    (6.84 m%)
    tran: time = 13.35 ns    (66.8 %), step = 1.311 ps    (6.55 m%)
    tran: time = 13.5 ns     (67.5 %), step = 1.887 ps    (9.44 m%)
    tran: time = 14.35 ns    (71.7 %), step = 1.317 ps    (6.59 m%)
    tran: time = 14.5 ns     (72.5 %), step = 1.177 ps    (5.89 m%)
    tran: time = 15.36 ns    (76.8 %), step = 1.898 ps    (9.49 m%)
    tran: time = 15.5 ns     (77.5 %), step = 1.535 ps    (7.67 m%)
    tran: time = 16.34 ns    (81.7 %), step = 1.503 ps    (7.52 m%)
    tran: time = 16.5 ns     (82.5 %), step = 1.355 ps    (6.77 m%)
    tran: time = 17.35 ns    (86.8 %), step = 1.389 ps    (6.95 m%)
    tran: time = 17.5 ns     (87.5 %), step = 1.89 ps     (9.45 m%)
    tran: time = 18.37 ns    (91.8 %), step = 1.196 ps    (5.98 m%)
    tran: time = 18.5 ns     (92.5 %), step = 1.538 ps    (7.69 m%)
    tran: time = 19.34 ns    (96.7 %), step = 1.349 ps    (6.75 m%)
    tran: time = 19.5 ns     (97.5 %), step = 1.415 ps    (7.08 m%)
Number of accepted tran steps =             14894

Maximum value achieved for any signal of each quantity: 
V: V(afe_core.st2_top.gm_core.st1_gm.i01.i13.i1_turbo_m2.i2_turbo_m4.dg16r.source1<0>_turbo_m4:int_g) = 1.501 V
I: I(V2:p) = 62.03 mA
U: U(afe_core.st3_top.NPORT0:t10) = 3.897 m

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Post-Transient Simulation Summary
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


During simulation, the CPU load for active processors is :
        Spectre 12 (97.1 %)     14 (1.1 %)      15 (1.2 %)      
        Other    0 (6.0 %)       1 (5.3 %)       2 (1.3 %)       3 (1.3 %)
                 4 (1.5 %)       5 (2.1 %)       8 (1.1 %)       9 (1.3 %)
Initial condition solution time: CPU = 6.70042 s, elapsed = 6.71102 s.
Intrinsic tran analysis time:    CPU = 232.175 s, elapsed = 232.537 s.
Total time required for tran analysis `tran': CPU = 238.891 s (3m  58.9s), elapsed = 239.268 s (3m  59.3s).
Time accumulated: CPU = 241.371 s (4m  1.4s), elapsed = 248.181 s (4m  8.2s).
Peak resident memory used = 288 Mbytes.

finalTimeOP: writing operating point information to rawfile.

Opening the PSF file ../psf/finalTimeOP.info ...
modelParameter: writing model parameter values to rawfile.

Opening the PSF file ../psf/modelParameter.info ...
element: writing instance parameter values to rawfile.

Opening the PSF file ../psf/element.info ...
outputParameter: writing output parameter values to rawfile.

Opening the PSF file ../psf/outputParameter.info ...
designParamVals: writing netlist parameters to rawfile.

Opening the PSFASCII file ../psf/designParamVals.info ...
primitives: writing primitives to rawfile.

Opening the PSFASCII file ../psf/primitives.info.primitives ...
subckts: writing subcircuits to rawfile.

Opening the PSFASCII file ../psf/subckts.info.subckts ...

Aggregate audit (9:04:11 AM, Thur Aug 27, 2020):
Time used: CPU = 245 s (4m  4.9s), elapsed = 252 s (4m  11.9s), util. = 97.2%.
Time spent in licensing: elapsed = 5.68 s.
Peak memory used = 305 Mbytes.
Simulation started at: 8:59:59 AM, Thur Aug 27, 2020, ended at: 9:04:11 AM, Thur Aug 27, 2020, with elapsed time (wall clock): 252 s (4m  11.9s).
spectre completes with 0 errors, 46 warnings, and 28 notices.

    1. What do you consider "unexpected ringing"?

    When I simulated the CTLE and the rest of the circuit separately, I did not see the ringing. And in the chip test, I also don't see the ringing at the CTLE input node. So I don't think it is the real circuit problem. Moreover, the ringing happens even if the clock sources are not connected to any other circuitry as I mentioned. After some experiment on the test bench, I also found that the ringing shows up only when there are 4 or more different phase clock source in the test bench. 

    2. When in the simulation does the ringing occur?

    According to the waveform, the ringing happens right after the clock signal appears. (I set some delay for the clocks)

    3. Is your S-parameter file accurate to frequencies well beyond your high speed" receiver signal bandwidth?

    I will double check with the CTLE owner. But in the test bench, the input signal of CTLE is only 2.5GHz, far below than the CTLE bandwidth we targets.

    4. Does your S-parameter file include a DC term?

    I think so. Because the CTLE input waveform looks fine when I simulate it alone or I removed the sampling clock voltage source.

    Thanks and regards,

    Yutao

  • in reply to YutaoLiu

    Dear Yutao,

    YutaoLiu said:
    I attached the spectre.out file and the snapshot of the CTLE input signaltransient waveform below. 

    Thank you for the spectre.out file, your plot, and your additional information - all are quite helpful to me anyway!

    I believe one possible problem is indeed the S parameter file. Note that in your spectre.out file it contains a number of warnings relative to the file:

    "Notice from spectre during transient analysis `tran'.
        tran: Loosening Newton tolerances when using trapezoidal rule might give anomalous results.
    Warning from spectre during DC solution estimation, during IC analysis, during transient analysis `tran'.
        WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st2_top_ind_only_copy_final.s8p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency).
        WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st1_top_ind_all_copy_ver2.s9p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency).
        WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency).
        WARNING (CMI-2134): Risky extrapolation to DC of data given in S-parameter file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_pad_top_redo_4.s12p'. This may cause convergence or accuracy issues in simulator. Please extend the data to include DC point (0 frequency)."

    As I suspected, the last warning (bold text) indicates the file does not have a DC term. Prior to these warnings, there are a number of passivity and potential discontinuity warnings:

    "    In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st1_top_ind_all_copy_ver2.s9p', the maximum passivity violation is 2.46725 % at 100 GHz.
        In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_pad_top_redo_4.s12p', the maximum passivity violation is 3.38048 % at 100 GHz.
    Warning from spectre during initial setup.
        WARNING (CMI-2839): In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', S9_9 may be discontinuous at 2.875 GHz.
        WARNING (CMI-2839): In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', S9_10 may be discontinuous at 2.875 GHz.
        WARNING (CMI-2839): In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', S10_10 may be discontinuous at 2.875 GHz.
    Notice from spectre during initial setup.
        In file `/nfs/fm/disks/fm_act_00069/users/shivak/io_de/serdesafe_st3_top_ind_only_copy.s10p', the maximum passivity violation is 1.98119 % at 100 GHz."

    It may be obvious to you, but the way a transient simulator uses an S-parameter file is to create a time domain model from the frequency domain information. SInce the transient simulation includes DC, without a DC term, the time domain model may not accurately model behavior. It is also clear there is some type of discontinuity at 2.875 GHz of the S-parameter file. My concern is the resulting time domain model spectre creates may not be physical and hence can cause unexpected simulation results - which could be the source of your ringing.

    A couple of quick experiments come to mind:

    1. Replace your S-parameter model of the CTLE inductor with a circuit model for an ideal inductor with a series real resistor. This is not intended to provide a good model of your CTLE inductor, but rather to run the simulation without your S-parameter file to determine if it may be the dominant reason for your anomalous simulation result. If it is, I might suggest the S-parameter file be replaced with one that has a DC term and, perhaps, less measurement error (which could lead to the "discontinuity" noted in the spectre.out file). As a further note, you commented that the ringing does not happen under all simulations - and this is entirely possible as a specific set of circuit conditions may excite the ringing you are observing.

    2. In addition, I might suggest increasing your accuracy setting to cx (essentially an errpreset of "conservative") or, alternately, set the integration method to "gear2only" to reduce the likelihood of ringing with the trapezoidal integration and a "moderate" accuracy setting.

    Other experts monitoring this forum will probably have additional - and better - suggestions. However, these came to mind immediately to me after reading your added information.

    Shawn

  • in reply to ShawnLogan

    Hi Shawn,

    Appreciate you suggestion. I will try it out.

    I take a look at the S-parameter files for inductors inside CTLE. And the data covers from 100MHz to 110GHz. The step size is roughly 20/dec, I think.

    You mentioned "S-parameter file accurate to frequencies well beyond your high speed" receiver signal bandwidth" . What is the criteria for that? Could you give me an example?

    Thanks and regards,

    Yutao

  • in reply to YutaoLiu

    Dear Yutao,

    YutaoLiu said:
    I will try it out.

    Great!

    YutaoLiu said:
    You mentioned "S-parameter file accurate to frequencies well beyond your high speed" receiver signal bandwidth" . What is the criteria for that? Could you give me an example?

    Please examine pages 7 and 10 of Tawna Wilsey's excellent note on the attributes of an S-parameter file that will provide a more robust time domain simulation result at URL:

    https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1O3w000009bgt4EAA&pageName=ArticleContent

    These two pages include information on the need for low frequency parameters  in the file and the criteria for determining the maximum frequency.

    Shawn

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