ELE 541 Electronic Testing II

Lab 1 Ammeter Simulation

Evaluate the ammeter shown in Figure 1. The opamp has a gain of 108, an input impedance of 100 MEG, an input offset voltage of 1 mV, and an input offset current of 100 pA. Run SPICE simulations to determine the effect of the nonideal opamp on the ammeter accuracy.

Figure 1.   Ammeter circuit


Figure 2   Opamp model

Opamp SPICE Subcircuit 

.subckt opamp  1 2 3
* opamp input impedance is 100MEG
Rin     1       2       100MEG
VOS     1       4       1E-3
IOS     4       2       1e-10
*
* A voltage controlled voltage source models the opamp.
* V+ in is node 1,  V- in is node 2, and   Output is node 3
* The gain is 1E8
EOPAMP  5       0       4       2       1E8
ROUT    5       3       100
.ends