LAB 1 Analog eletronics

741 OP Amp

ECE 312

Lab #1

02/03/2016

Matheus Diniz Ferreira

Samuel Hardy

Introduction:

        For this experiment will be using the Op Amp 741 to build a difference amplifier circuit. After doing all the calculations with the theoretical value of the resistor and inputs, all the resistors values are going to be measured and the circuit is gonna be powered up. After the circuit is on, all the inputs and outputs are going to be measured.

Theory:

        It’s predicted that on the steps 2 and 3 the amplifier will output a Vo = 0 and on the step 6 attaching VI1 to ground and inputting 500 mVpp 1 kHz on VI2 it’s expected to get 5 v on the output given that differential-mode gain (ad)  is 10.

        

Materials & Instruments:

• Function Generator

• Op Amp 741

• Wires

• 1k and 10k ohms resistors

• +15 and -15 voltage power

• Breadboard

• Oscilloscope

• Wire Stripper

Procedure: 

1. For the first step of the lab, we will use a 741 op amp to build the difference amplifier circuit shown below.  The selected resistors are R1=R3=1k ohms and R2=R4=10k ohms. We measured the resistors to see their true values. In the Measurements section we can see the values.

 

[pic 1]

 

[pic 2]

[pic 3]

Common-Mode Gain

2. The theoretical common-mode gain is given by

 

                                                                [pic 4]         (1)                        

 

The nominal common-mode gain is [pic 5].  We measured all four resistor values and got and acm of 0.030081

 

3. We applied a 500 mVpp 1kHz input sine wave at both [pic 6] and [pic 7], measured all the values  and got 14.8 mV as and output.

4. We applied a 500 mVpp 1 kHz input sine wave at [pic 8] with [pic 9] grounded.  Using our measured values for [pic 10] and [pic 11] we determined that the Ad = 9.91119.

Data & Measurements:

Table for the resistors used for the lab.

	Theory	Measured
R1	1 k[pic 12]	983.66 [pic 13]
R2	10 k[pic 14]	9.869 k[pic 15]
R3	1 k[pic 16]	983 [pic 17]
R4	10 k[pic 18]	10.057 k[pic 19]

Table of the computed theoretical value for the common-mode gain from the equation (1) with our 4 measured values of the resistors. (Step 2)

	Theory	Measured
Gain for the Common Mode (Acm)	0V	17.628 mV/V  or 0.017628

Table for the values for the Gain of the Common Mode. (Step 3)

	Theory	Measured
Gain for the Common Mode (Acm)	0V	30.081 mV or 0.030081

Table for the values for the gain obtained from the common mode on step 4

	Theory	Measured
Gain for the Common Mode	0V	8.81 mV/V  or 0.00884

Picture of the sines waves collected from the Oscilloscope from step 3 of the lab 01.

[pic 20]

On this measurement were applied 500 mVpp 1kHz input sine wave at both VI1 and VI2 and the output gave us 14.8mV, giving an acm of 0.030081 when the expected value for acm was 0.

The blue wave means the output and the yellow one is the input of our circuit.

Picture taken from the Oscilloscope based on the step number 6 of the lab 01.

[pic 21]

For this experiment we applied a 500mVpp (peek-to-peek) with a 1KHz sine wave on VI2 only, as we applied the VI1 to the ground.

The blue wave means the output and the yellow one is the input of our circuit.

Theory Comparison & Conclusion:

	Theory	Measured
R1	1 k[pic 22]	983.66 [pic 23]
R2	10 k[pic 24]	9.869 k[pic 25]
R3	1 k[pic 26]	983 [pic 27]
R4	10 k[pic 28]	10.057 k[pic 29]

Table of the computed theoretical value for the common-mode gain from the equation (1) with our 4 measured values of the resistors. (Step 2)