Problem 6.7 - Ideal Op-Amp Voltage-to-Current Converter
*
* Two ideal op amps in the noninverting configuration shown
* completely isolate the load from the voltage source.
* The voltage at node 3 must be equal to the source voltage when the
* op amp in the feedback loop is an ideal unity-gain voltage-follower.
* The load current is therefore I(RL) = V(3)/R1 = V1/R1.
*
* Use PROBE to obtain a graph of the load current (the current
* through load resistance RL) as a function of the source voltage
* for a variable load resistance and a variable source voltage.
* Obtain a graph with both V(1) and V(3) plotted vs. RL, and
* a third graph showing a plot of the load voltage V(2,3) vs. RL.
*
* Note that because of the ideal op amp's infinite input
* resistance, the source V1 and the controlled source at node
* 4 are "floating." That is, there is only one circuit device
* connected at node 1 and at node 4 and therefore there is no
* dc path to ground. A resistance must be added at each of the
* nodes so that PSpice will run, but the resistances must be
* located in such a way that they do not change the results
* of the circuit analysis.
*
* ===> To verify that you have connected the added resistances in such
* a way that they do not affect the analysis, edit your program to
* change the resistances to some low value, say 100 ohms, and re-run
* the analysis. The results should be unchanged.
*
.OPT NOPAGE
V1 1 0 DC 1
RS1 ??? ??? 1E6 ; Resistance added to provide dc path to
; ground at node 1. Enter the correct
; node numbers.
EA1 2 0 ??? ??? 1E10 ; Enter the control voltage node numbers.
EA2 4 0 ??? ??? 1E10 ; Enter the control voltage node numbers.
RS2 4 0 1E6 ; Resistance added to provide dc path to
; ground at node 4.
RL 2 3 RLOAD 1
R1 3 0 1k
.MODEL RLOAD RES(R=1)
.DC RES RLOAD(R) ??? ??? ??? ; Complete the .DC sweep statement for RL.
.STEP V1 ; Complete the .STEP command for source V1.
.PROBE
.PRINT DC V(1) V(3) I(RL)
.END