Can you help me with question number 6?

It really confuses me.

ECE 205 Spring 2015: Homework 9
Due Wednesday 4/6 by 5:00 PM:
1)
2)
3)
4)
5)
6)

KnI 7.1
KnI 7.8
KnI 7.11
KnI 9.13
KnI 9.22
Consider circuit 1, as follows, which shows a filter which relates the input voltage Vi to the
output voltage Vo.

Circuit 1

a) As we did in class, plot the linear magnitude response |()| and the phase response ?() as
a function of linear frequency. Your plot should show what happens at DC, what happens at the
cutoff frequency ( ), and what happens at high frequency where ? . Label in both
b) Now consider what happens to the circuit when there is a load (for example, it is attempting to
drive a pair of 500 ? headphones). This is shown in circuit 2. Plot the magnitude response and
phase response in the same way, relating Vo to Vin.
c) What can we say about the effect of a resistive load on a passive high pass filter? Specifically,
which way does the cutoff frequency shift? How might we restore the original cutoff frequency
if this effect is unintended?

Circuit 2

ECE 205 Spring 2015: Homework 9
7) Given the circuit and the plots of Vout (red) and Vin (blue) below.
a. Find the magnitude response |()| from the graph. This should be in units of V/V.
b. Find the phase response ?() from the graph. This should be in units of radians or
degrees.
c. Use your result from either to find the value of capacitor C1 in the circuit below. V_in is
a sine wave at 1kHz with a magnitude of 1 V.

Vout and Vin
1.00
0.80
0.60
0.40

Volts

0.20
0.00

-0.20

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

-0.40
-0.60
-0.80
-1.00

seconds
V_in

V_out

0.0014

0.0016

0.0018

0.002