Op Amps II

The purpose of the lab is explore the effects of a varying input voltages, and feedback resistors on the output voltage on an inverting Op Amp.

Procedure:
We first consider this simple circuit.

Resistor	Nominal Value	Meaured Value
R_1	10 kΩ	9.91 kΩ
R_F	100 kΩ	97.7 kΩ

Building the Circuit

Finished circuit with the 12V rails

Using the pot, we varied V_in and recorded the output.

V_in (Desired)	V_in (Actual)	V_out (Measured)	V_RF (Measured)	I_op (Calculated)
0.25 V	0.24 V	-2.41 V	2.46 V	-0.0246 mA
0.5 V	0.50 V	-4.90 V	4.87 V	-0.0502 mA
1.0 V	1.00 V	-10.04 V	9.86 V	-0.1028 mA

I_cc = 0.874 mA
I_ee = -0.981 mA
I_cc + I_ee = -0.107 mA
P_cc = V*I = 10.488 mW
P_ee = 11.772 mW

Next we add a 1k resistor like shown below

Part 2 Circuit Diagram

The final circuit

However, we only took measurements when V_in = 1V.

V_in (Desired)	V_out (Measured)	V_RF (Measured)	I_op (Calculated)	I_cc (Measured)	I_ee (Measured)
1.0 V	-9.99 V	9.72 V	-0.102 mA	0.887 mA	-0.987 mA

I_ee + I_cc = -0.1 mA
P_cc = 10.644 mW
P_ee = 11.844 mW

Bonus:

R_f was swapped with a variable resistor

The gain becomes -5 when R_f = 50 kΩ
Measured R_f = 49.9 kΩ

V_in (Desired)	V_out (Measured)	V_RF (Measured)	I_op (Calculated)	I_cc (Measured)	I_ee (Measured)
1.0 V	-5.03 V	4.99 V	-0.101 mA	0.885 mA	-0.985 mA

I_ee + I_cc = -0.1 mA

Conclusion:
The results are as expected because the ratio of the feedback resistors gives a gain of -10. V_in does not change the gain, only the resistors. KCL held, so the experiment was a success. To get a gain of 5, the ratio of R_i:R_f had to be 1:5, therefore R_f = 50 kΩ.