Question 8.18: Verify Ex. 8.17 using SPICE. Use a voltage-controlled voltag......

The schematic used for simulations is seen in Fig. 8.37. Instead of connecting the op-amp’s noninverting input (the + input) to ground directly, we connect it to ground via a zero volt DC supply so that, in the simulation, we have an “input.” (Recall comments about how the AC magnitude of this input source affects the input-referred noise calculation on the bottom of page 227.) The SPICE netlist is

Comment line; the first line of a netlist is ignored by SPICE

.noise         V(Vout,0)               Vplus         dec         100          1         1000G

Vplus         Vplus     0                dc                 0            ac           1

Rf               Vout       Vminus    100k

Cf               Vout       Vminus                     1000pf

Eopamp                   Vout            0            Vplus      Vminus   100MEG

.print noise all
.end

The SPICE output is

TEMP=27 deg C
inoise_total = 4.142190e-12
onoise_total = 4.142190e-12

For the 1,000 pF capacitor, this gives 2.03 μV. Resimulating with the 1 pF capacitor, gives 64.3 μV.