bellona
Junior Member level 2
Hi, I'm using Calibre PEX and Cadence Spectre to do post-layout simulation of an OPAMP. I'm using Charterd 0.35um technology. The pre-layout simulation is alright and i also passed LVS. But the Post-layout simulation is not correct, the biasing point of these transistors looks weird.
Take a current mirror for example: MP10 and MP0 forms a current mirror, (W/L)10=(30um/3um) and (W/L)0=(120um/3um),MP10 have 3 fingers while MP0 have 10 fingers. In post simulation the id of MP10 is (-8.37424u*3)about 25uA but that of MP0 is (-33.6371u*12) over 400uA, this really puzzles me since their Vdsat are the same and they are all working in saturation, i think the id of MP0 should be about 100uA. Can anbody help me? Thank you
***********************************************
*Pre-layout simulation
***********************************************
string OP("/I3/MP10" "??")
gm 157.24u
id -31.2366u
vds -407.893m
vdsat -295.064m
vgs -1.21116
vth -855.268m
string OP("/I3/MP0" "??")
gm 569.993u
id -120.807u
vds -291.556m
vdsat -295.064m
vgs -1.21116
vth -855.268m
***********************************************
*Post-layout simulation
***********************************************
string OP("/I3/MP10__3@2" "??")
gm 81.9997u
id -8.37424u
vds -295.526m
vdsat -158.418m
vgs -1.02411
vth -855.268m
string OP("/I3/MP0__12@2" "??")
gm 330.044u
id -33.6371u
vds -340.88m
vdsat -158.418m
vgs -1.02411
vth -855.268m
Take a current mirror for example: MP10 and MP0 forms a current mirror, (W/L)10=(30um/3um) and (W/L)0=(120um/3um),MP10 have 3 fingers while MP0 have 10 fingers. In post simulation the id of MP10 is (-8.37424u*3)about 25uA but that of MP0 is (-33.6371u*12) over 400uA, this really puzzles me since their Vdsat are the same and they are all working in saturation, i think the id of MP0 should be about 100uA. Can anbody help me? Thank you
***********************************************
*Pre-layout simulation
***********************************************
string OP("/I3/MP10" "??")
gm 157.24u
id -31.2366u
vds -407.893m
vdsat -295.064m
vgs -1.21116
vth -855.268m
string OP("/I3/MP0" "??")
gm 569.993u
id -120.807u
vds -291.556m
vdsat -295.064m
vgs -1.21116
vth -855.268m
***********************************************
*Post-layout simulation
***********************************************
string OP("/I3/MP10__3@2" "??")
gm 81.9997u
id -8.37424u
vds -295.526m
vdsat -158.418m
vgs -1.02411
vth -855.268m
string OP("/I3/MP0__12@2" "??")
gm 330.044u
id -33.6371u
vds -340.88m
vdsat -158.418m
vgs -1.02411
vth -855.268m