EE312- assignment #2

King Abdulaziz University
Faculty of Engineering

Department of Electrical and Computer Engineering
Spring 2021

EE312

Electronics II

Assignment #2

Name: Abdullah Mohammed
Id. # Algarni

1635459

Instructor: Dr. Sami Alghamdi

Introduction:

Ideal op-amp is not real, it is for understanding the concept of the op-amp so in this
assignment we will dealing with nonideal op-amp. These problems help us to
understand more about op-amp in real life.

Problems:

P1: How many identical amplifiers in cascade each of voltage gain of 9 V/V needed
to have a total gain of 59,049 V/V? You must use gains in dB in your analysis.

The gain: = 9( ) total gain = 59,049



So the number "n" for identical amplifiers is

Figure 1:P1 solution

So we should have 5 identical amplifiers

P2: Analyze the circuit of multiple feedback shown below and find the gain terms of
n.

Figure 2: p2 circuit

First step here is applying KCL at node V1 and V2 to find its equations as following:

Figure 3:volts at v1 and v2

After that we have to substituting 1 and 2 and then we get gain in term of n:

Figure 4:gain in terms of n

P3. Using LTspice, simulate the following signals using an inverting amplifier
AD713 op amp (SR=20V/u) with a gain of A and a sine wave input v = a sin(2πf.t):

First of all we have to design inverting amplifier with AD713 op amp and add
frequency fs at 31.4159khz.

The procedure of this experiment will to use the values in the table above to decide
which Rf and Rs should we use.

Starting our process by first values:
a =2, A = 5
so the gain is 5 and by knowing the gain we can choose the values of resistances

Rf = 5k , Rs = 1k → = 5

1

for vcc and -vcc we will choose 15, -15 as save and that will not have saturation if it
above 10V, as shown in this figure below.

Figure 5:circuit of NO. 1

The DC operating points and waveform:

Figure 6:DC points of 1

For transition time we choose 100u to make it clear.

Figure 7:waveform of 1

2) a =1, A = 10

Rf = 10k , Rs = 1k → = 10

1

for vcc and -vcc we will choose 15. -15 as save and that will not have saturation if it
above 10V same as 1, the circuit shown in this figure below.

The DC operating points and waveform:

Figure 8:circuit of NO. 2

Figure 9:DC points of 2

Figure 10:waveform of 2

2) a =6, A = 5
Rf = 5k , Rs = 1k → = 5

1

for vcc and -vcc we will choose 35, -35 as save and that will not have saturation if it
above 30V, the circuit shown in this figure below.

Figure 11:circuit of NO. 3

The DC operating points and waveform:

Figure 12:DC points of 3

Figure 13:waveform of

P4. Calculate the worst-case DC offset of the design shown when the op amps are
identical and have Ib=50nA, Ios=1nA, Vos=2.0 mV. (Hint: Terminals of stage 2 are
balanced).

Figure 14:P4 circuit

In this problem we notice that stage 2 is balanced, so by using superposition:
When IB is connected we can find V2:

Figure 15:When IB is connected

Then, when Vos is connected:

Figure 16:when Vos is connected

So the worst case DC offset is 5.005V.
P5. The input voltage to the design shown below is: Vs = 10 cos (400,000t)

Figure 17:p5 circuit

Find the followings:
a) v1, v2, and vo
b) The op amps’ minimum bandwidth (BW) to correctly amplify the input.
c) The op amps’ minimum Slew Rate (SR)
a)

Figure 18: a) solution

b)
Bandwidth = 400k rad/s

c)

Figure 19:c) solution

Conclusion:
In this assignment we have use an op-amp in nonideal mode. These problems let us
know how to deal with op-amps we will face in real life and how it is work. When
solving these problems, I got more knowledge about op-amps analysis.