Hints, Suggestions and Partial Answers

Hints, suggestions and partial answers:

Lab report experiment 4 and Prelab report for experiment 5 are due:

Sec 003: 10/17

Sec 502: 10/17

Sec 001: 10/18

Sec 502: 10/21

PRE-LAB 5
* Important amplifier relation:
V_out
G = ------
V_in
So V_out = G * V_in
The above is ALWAYS true, regardless of the type of amplifier (as long as the amplifier operates in the "linear region").
* Important Op-amp rules:
1. No current flows into or out of the input terminals (pin 2 and pin 3
on the uA 741) due to the op-amp's very high input impedance at these
terminals.
2. With negative feedback and under normal operating conditions (i.e.,
with the output NOT in saturation, the op-am "forces" the same
potential between the input terminals (i.e., there is a "virtual
short" between pins 2 and 3).

* Simulate each circuit in SPICE to verify your hand calculations.
1. Remember to rename ground to "0"
2. Consider using only ONE ground node by connecting all ground points together.
PL5.0.1:
Use the inverting amplifier gain equation (5-1):
R_f
G = ------= -10/4.7
R_i
Thus, V_out = (-10/4.7) * V_in
By hand calculations:
The current through R_i = the current through R_f (rule 1 and KCL).
The potential at the right end of R_i is 0V (rule 2).
PL5.0.2:
Use the non-inverting amplifier gain equation (5-2):
R_i + R_f
G = + ------
R_i
Thus, V_out = (+14.7/4.7) * V_in
By hand calculations:
The current through R_i = the current through R_f (rule 1 and KCL).
The potential at the right end of R_i is 2V (rule 2).
PL5.0.3:
Use the differential amplifier gain equation (5-3):
R_f
V_out = -----(V_1 - V_2)
R_i
By hand calculations:
Use a voltage divider (4V source, R_2 and R_1) to find the potential at pin 3.
The potential at the right end of R_i is the same as that at pin 2 (rule 2).
The current through R_i = the current through R_f (rule 1 and KCL).
PL5.0.4:
Use the summing amplifier gain equation (5-1):
R_3 R_4
V_out = ------* V_3 ------* V_4
R_f R_f
By hand calculations:
The potential at the right end of the input resistors (R_1, R_2, . . . ) is the
same as that at pin 2, i.e., 0V (rule 2).
The sum of the current through of the input resistors = the current through R_f
(rule 1 and KCL).
LAB 5 HINTs:
* Build the second circuit (Figure 5-2) first
* Build the first circuit (Figure 5-1) next:
simply switch the position of the 2V input and the ground input
(i.e., switch the inputs to pin 3 and pin 2).
* Do NOT remove any components to build the third circuit (Figure 5-3):
simply add the 4V input and the series resistor circuit involving pin 3.
* Remove only components in the series resistor circuit involving pin 3:
simply add the 1V input and the connecting 3.3 K-ohm resistor.
* Use the HP power supplies for + 10V and -10V power to the op-amp(s):
TOP HP: + ==> +10V, - ==> ground
BOTTOM HP: + ==> ground, - ==> -10V
* Use the Keithly power supplies for + 2V, +4V and +1V inputs to the op-amp(s).
* Remember to tie ALL grounds (HP power supplies, Keithly power supplies, resistor circuits) to a common point.