Class Activity (week 6)

In this week many different kinds of Op-amps are introduced by the Professor Mason.

Figure 1: Voltage as a Time Function

When g(t) = 2.5 +2.5*sin(wt)  , this means first two parts are added and then those are multiplied.

When g(t) = 2.5*(1 + sin(wt) ) , this means first two parts are multiplied and then those are added.

Mathematically there is no different between situation 1 and 2, but electrically those have different 

meaning.

Figure 2: The Sum of Two voltages

The summation, subtraction, and multiplication of two voltages or currents are as the mathematical 

functions. 

Figure 3: The Input and Output Voltages an Inverting Op-amp

The gain is bigger than one, it is negative. When Vin = - 100 mV, Vo = (-3)*(-100) = 300 mV.

When Vin = 100 mV, Vo = -300 mV, but the lowest saturation voltage of op-amp is zero, so Vo = 0.

Figure 4: The Input and Output Voltages an Non-Inverting Op-amp

Vo = (33/133)*(1.33)*V2 , Vo = (0.33)*( V2)

The gain is less than one, but it is positive. When Vin = 5V, Vo = (0.33)*(5) = 1.65 V

When Vin = -5 V, Vo = (0.33)*(-5) = -1.65 V, but the lowest saturation voltage of  the non-inverting

op-amp is zero, so Vo = 0. 

Figure 5: A Non-Inverting Op-amp

Gain = Vo/Vin = 1 + (Rf/Rs) , If Rf << Rs → Gain = 1. (This is a buffer)

Figure 6: A Inverting Op-amp

Figure 7: A Summing op-amp

The output voltage is function of two input voltages. Also, output voltage is weighted by R3/R1 and 

R3/R2. In other words, the output voltage is a weight function.

Figure 8: A Summing Amplifier

If R1 = R2 = 2*R3  →  Vo = - (Va + Vb)/2. The output voltage is average of its input voltages.

Figure 9: A Real Circuit of an Summing Amplifier

Figure 10: A Summing Amplifier with Three input 

Figure 11: A Non-Inverting Summing  Amplifier

The gain of inverting amplifiers are A1 and A2. Also, the output voltages of these amplifies are the 

input voltages a summing amplifier. 

Vo1 = - (6/2)*V1 , Vo2 = -(8/4)*V2 , Vo = (-10)*[(Vo1/5) + (Vo2/15)] , Vo = 6*V1 + (4/3)*V2

Figure 12: A Cascade Amplifier

Vin = 20 mV  →  Amplifier → Vo = 350 mV

Gain 1 = 1 + (12/3) , Gain 2 = 1 + (10/4) , Total Gain = A1*A2 , Vo = (A1*A2)*Vin

Vo = [1 + (12/3)]*[(1 + (10/4)]* Vin , Vo = 350 mV