completely wrong gain of a simple circuit consisting of 3 cascaded inverting amplifiers

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Sergei
2014-05-03
2014-05-03
  • Sergei
    Sergei
    2014-05-03

    Hello, I have created a simple circuit consisting of 3 cascaded amplifies with gains -1, -1, -1000.

    Simulation exhibits gain in -120 .. -112db range. I can't understand why.

    Netlist:

    # Qucs 0.0.17  /home/sergei/junk/op_amp_try_1.sch
    
    .Def:OpAmps_opa27_TI_ _net0 _net1 _net2 _net3 _net4
    Sub:X1 _net0 _net1 _net2 _net3 _net4 gnd Type="opa27_TI_cir"
    .Def:End
    .Def:opa27_TI_cir _netP_INN _netP_INP _netP_OUT _netP_VCC _netP_VEE _ref
      .Def:OPA27_TI _ref _netP_INP _netP_INN _netP_VCC _netP_VEE _netP_OUT
      C:C1 _net11 _net12 C="2.079e-11"
      C:C2 _net6 _net7 C="1.143e-10"
      C:CEE _net10 _net99 C="0"
      Diode:DC _net53 _netP_OUT Is="8e-16" N="1" M="0.5" Cj0="1e-14" Vj="0.7"
      Diode:DE _netP_OUT _net54 Is="8e-16" N="1" M="0.5" Cj0="1e-14" Vj="0.7"
      Diode:DLP _net91 _net90 Is="8e-16" N="1" M="0.5" Cj0="1e-14" Vj="0.7"
      Diode:DLN _net90 _net92 Is="8e-16" N="1" M="0.5" Cj0="1e-14" Vj="0.7"
      VCVS:EGND1 _netP_VCC _net999 _ref _ref G="0.5"
      VCVS:EGND2 _netP_VEE _net99 _net999 _ref G="0.5"
      CCCS:FB1 _net9 _net7 _net99 _cnet0 G="1.095e+07"
      CCCS:FB2 _netP_VCC _net7 _net99 _cnet1 G="-1e+07"
      CCCS:FB3 _net54 _net7 _net99 _cnet2 G="1e+07"
      CCCS:FB4 _net91 _net7 _net99 _cnet3 G="1e+07"
      CCCS:FB5 _ref _net7 _net99 _cnet4 G="-1e+07"
      VCCS:GA _net11 _net6 _ref _net12 G="0.004638"
      VCCS:GCM _net10 _ref _net6 _net99 G="2.608e-09"
      Idc:IEE _netP_VEE _net10 I="0.00024"
      CCVS:HLIM _net7 _net90 _ref _cnet5 G="1000"
      BJT:Q1 _netP_INN _net11 _net13 _ref Type="npn" Is="8e-16" Bf="7990" Nf="1" Nr="1" Ikf="0" Ikr="0" Vaf="0" Var="0" Ise="0" Ne="1.5" Isc="0" Nc="2" Br="1" Rbm="0" Irb="0" Cje="0" Vje="0.75" Mje="0.33" Cjc="0" Vjc="0.75" Mjc="0.33" Xcjc="1" Cjs="0" Vjs="0.75" Mjs="0" Fc="0.5" Vtf="0" Tf="0" Xtf="0" Itf="0" Tr="0"
      BJT:Q2 _netP_INP _net12 _net14 _ref Type="npn" Is="8e-16" Bf="7990" Nf="1" Nr="1" Ikf="0" Ikr="0" Vaf="0" Var="0" Ise="0" Ne="1.5" Isc="0" Nc="2" Br="1" Rbm="0" Irb="0" Cje="0" Vje="0.75" Mje="0.33" Cjc="0" Vjc="0.75" Mjc="0.33" Xcjc="1" Cjs="0" Vjs="0.75" Mjs="0" Fc="0.5" Vtf="0" Tf="0" Xtf="0" Itf="0" Tr="0"
      R:R2 _net6 _net9 R="100k"
      R:RC1 _netP_VCC _net11 R="215.6"
      R:RC2 _netP_VCC _net12 R="215.6"
      R:RE1 _net13 _net10 R="0.005395"
      R:RE2 _net14 _net10 R="0.005395"
      R:REE _net10 _net99 R="833500"
      R:RO1 _net8 _netP_OUT R="35"
      R:RO2 _net7 _net99 R="35"
      R:RP _netP_VCC _netP_VEE R="10870"
      Vdc:VB _cnet0 _ref U="0"
      Vdc:VC _cnet1 _net53 U="1.2"
      Vdc:VE _cnet2 _netP_VEE U="1.2"
      Vdc:VLIM _cnet5 _net8 U="0"
      Vdc:VLP _cnet3 _ref U="25"
      Vdc:VLN _cnet4 _net92 U="25"
      .Def:End
      Sub:X1 _ref _netP_INP _netP_INN _netP_VCC _netP_VEE _netP_OUT Type="OPA27_TI"
    .Def:End
    
    .DC:DC1 Temp="26.85" reltol="0.001" abstol="1 pA" vntol="1 uV" saveOPs="no" MaxIter="150" saveAll="no" convHelper="none" Solver="CroutLU"
    R:R1 amp_input _net0 R="4.7k" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    Vdc:V2 _net1 gnd U="15V"
    Vdc:V3 gnd _net2 U="15V"
    Sub:OP1 _net0 gnd _net3 _net1 _net2 Type="OpAmps_opa27_TI_"
    R:R4 _net3 _net4 R="4.7k" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    Sub:OP2 _net4 _net5 _net6 _net1 _net2 Type="OpAmps_opa27_TI_"
    R:R7 gnd _net5 R="2.2K" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    Vac:V4 amp_input gnd U="1e-6V" f="1 GHz" Phase="0" Theta="0"
    Sub:OP3 _net7 _net8 amp_output _net1 _net2 Type="OpAmps_opa27_TI_"
    R:R10 gnd _net8 R="2.2K" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    R:R8 _net6 _net7 R="4.7k" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    .AC:AC1 Type="log" Start="1Hz" Stop="1MHz" Points="199" Noise="no"
    R:R3 _net3 _net0 R="4.7K" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    R:R5 _net6 _net4 R="4.7K" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    Eqn:Eqn1 dbov="dB(amp_output.v / amp_input.v)" ph="phase(amp_output.v)" Export="yes"
    R:R9 amp_output _net7 R="4700K" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
    

    Regards,
    Sergei.