May 2023 StudentZone Quiz Solution

Question 1:

Using the values and formulas provided in the laboratory directions compute the following parameters:

• Forward current through the IR LED. (use datasheet of the QED-123)
• Cut-off frequency of the high-pass filter.
• Cut-off frequency of the second stage low-pass filter.
• Cut-off frequency of the third stage low-pass filter.
• Gain of the third stage amplifier

Answer 1:

• Forward current through the IR LED can be computed using the following forumla (the datasheet value for the forward volage of the QED-123 is 1.7V):

I_F = 7mA

• Cut-off frequency of the high-pass filter can be computed using the following formula:

F_c1 = 0.33Hz

• Cut-off frequency of the second stage low-pass filter can be computed using the following formula:

F_c2 = 3.3Hz

• Cut-off frequency of the third stage low-pass filter can be computed using the following formula:

F_c3 = 3.3Hz

• Gain of the third stage amplifier

A_V = - 470

Question 2:

What parameters change if R₅ is modified?

Answer 2:

If R₅ is modified, this will affect the gain of the third stage amplifier.

Question 3:

What parameters change if R₆ is modified?

Answer 3:

If R₆ is modified, this will affect both the gain of the third stage amplifier and the cut-off frequency of the third stage low-pass filter.