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.

R2 = 4k ohm

C2 = 1u ohm

f2 = 40 Hz

Result

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.

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/R_{3}

R(TH) =Vt/It = R_{L}

-Vt/R_{H }– Vo/R3=0

Vt = -Vo* R_{H}/R3

It = -Vo/R_{3}

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