May 2019 StudentZone Quiz Solution

Question 1:

How do you measure and computed the slew rate in the unity-gain buffer configuration? Compare this with the value listed in the OP97 data sheet.

Answer 1:

Slew rate is defined as the maximum rate of change (slope) of the output voltage that the op-amp can deliver (change of voltage per unit of time).

The easiest way to measure the slew rate using the unity-gain buffer is to apply a square wave at the input.

Considering the unity-gain buffer configuration described in the lab activity, apply at the input a square wave having the frequency = 500Hz, minV = 0.5V, maxV=4.5V. Plot the input and the output voltages, then zoom in on the rising edge of the signal.

We can notice that the output voltages (CB-H) reaches the maximum value slower than the input voltage.

By computing the slope of the output signal (V/µs) based on the plot example above we obtain the slew rate as follows:

 

 

Question 2:

Summing circuit: using superposition, derive the expected transfer characteristic for the circuit of - find the output voltage in terms of Vin0, Vin1, Vin2 and Vin3. Compare the predictions of the ideal relationship with your data.

Answer 2:

Consider the positive and negative input of the operational amplifier.

Question 3:

Comparator: What would happen if the polarity of Vref is reversed?

Answer 3:

If the polarity of Vref is reversed, then the negative input of the operational amplifier will become -2.5V. Since the entire input signal applied at the positive input of the operational amplifier is larger than the negative input, the output will be always “high” (5V).