Input bias current specification

[ioannis]

Hello,

i want to specify the charakteristics of an amplifier!

Therefore ai have writen a script in hspice which is specifying the
Iput Offset Voltage Vos and the Input Bias Current Ios. I know, that
for specifiyng the Vos, ihave to put two exactly same Voltage sources
(as it is shown bellow) on the invering and non-inverting inputs of
the amplifier and measure the output Voltage.


****Voltage Sources******
VDD VDD 0 0
VSS VSS 0 0
*************************

****Stimuli***********************************************************
VinnDut_Vos 0 innDut_Vos dc .1 *sin(0, 0.1, 5Hz,0,0,0)
VinpDut_Vos 0 inpDut_Vos dc .1 *sin(0, 0.1, 5Hz,0,0,0)
vbiasDut_Vos vbiasDut_Vos 0 5
**********************************************************************

What shall i have to do when measure the input bias current? Shall i
do it in the same way?

I have distinguished two cases:
a) very low Input bias curernt
b) normal low input bias current?

For the first case i have writen for the operatin circuit this
script:

**** Input Bias Offset (Ios) specification
**** Ios=I_B(+)-IB(-)
**** I_B=C*(\delta(out)/(\delta(t))


**** a) Extremly low Ios*****


VinnDut_Ios_low 0 innDut_Ios_low dc 1 *sin(0, 0.1, 5Hz,0,0,0)
VinpDut_Ios_low 0 inpDut_Ios_low dc 1 *sin(0, 0.1, 5Hz,0,0,0)
VbiasDut_Ios_low vbiasDut_Ios_low 0 5

*Circuit for measuring extremely low Ios*

*Rsp 0 inpDut_Ios_low 1 *short out Capacitor C1 to test
I_B(-)
Rsm innDut_Ios_low outDut_Ios_low 1 *short out Capacitor C2
to test I_B(+)
C2 innDut_Ios_low outDut_Ios_low 1u
C1 0 inpDut_Ios_low 1u


and for the second case this one:


**** b)Normal Ios *****

*Input Sources*

VinnDut_IosNorm 0 innDut_Ios_Norm dc .1
*sin(0, 0.1, 5Hz,0,0,0)
VinpDut_IosNorm 0 inpDut_Ios_Norm dc .1
*sin(0, 0.1, 5Hz,0,0,0)
vbiasDut_IosNorm vbiasDut_Ios_Norm 0 5
vbiasGen_IosNorm vbiasGen_Ios_Norm 0 5


*Device Under Test(DUT)*

XDutIosNorm VDD VSS vbiasDut_Ios_Norm inpDut_Ios_Norm innDut_Ios_Norm
outDut_Ios_Norm DA

*General OpAmp Type*

XGenIosNorm VDD VSS vbiasGen_IosNorm 0 innGen_Ios_Norm
outGen_Ios_Norm DA

*Circuit for measuring normal Ios*

RoutDut_Ios_Norm outDut_Ios_Norm innGen_Ios_Norm 10k
Rm 0 1 100
Rp 0 3 100
Rbn 1 innDut_Ios_Norm 1 *Rbn short out to test IB(+)
Rbp 3 inpDut_Ios_Norm 1000K *Rbp short out to test IB(-)
R2 3 outGen_Ios_Norm 100
CinGen innGen_Ios_Norm outGen_Ios_Norm 1u



Can anyone tell me if i have to put the same input voltages, in the
same way with i did for the Vos specification?
Or shall i have to test the Vos without input Voltages?

Regards

Ioannis

P.S. Do anyone know a hspice forum?