Bill Chun Wai Hung

Lab 7 Prelab

Q1) Compute the cutoff frequency of the low pass filter of figure 1 considering it disconnected form the amplifier.

Low Pass Filter

R2 = 4k ohm

C2 = 1u ohm

f2 = 40 Hz

Result

High Pass Filter

R1 = 8k ohm

C1 = 1n ohm

f1 = 20kHz

Result

Q2) Compute the cutoff frequency of the low pass filter of figure 1 When it is connected to the amplifier.

Low Pass

First calculate the Thevenin Resistance of the Amplifier

R(TH) =Vt/It

-Vt/R_L – Vo/R3=0

Vt = -Vo* R_L/R3

It = -Vo/R₃

R(TH) =Vt/It = R_L

High Pass

-Vt/R_H – Vo/R3=0

Vt = -Vo* R_H/R3

It = -Vo/R₃

R(TH) =Vt/It = R_H

Q3) The cutoff frequency of the input resistance of the amplifier should be very small in order to have the cutoff frequency to remain unchanged. Because the gain of the amplifier = -R3/ R_L

So Ra should be very large.

Q4) The high pass filter data is shown above.

Q5)

R3/Ra=1

R3=Ra

R3/(Ra+10k) = 0.3

R3/(R3+10k) = 0.3

0.7 R3 = 3k

R3 = 4.29k

Ra = 4.29k

R3 = 4.29k

R1= 8k

C1 = 1n

R2 = 4k

C2 = 1u

The Circuit Diagram

The Result Plot