Quiz 4 performance

1

Max. is 28/30. Average is 23

Please note the unique 3 digit code at the 2nd page of your Quiz 4You can use this to track your grade at the class website.

Chapter 8: Frequency Response

for

8.1 BODE PLOTS

Logarithmic frequency scales:

For f << fb, |Av(f)|dB =0

For f >> fb

For f = fb

Phase of Av(f):

Fig. 8.3: Bode plot for the low-pass RC filter

Fig. 8.3: Bode plot for the low-pass RC filter

The Magnitude Bode Plot: The Phase Bode Plot:

Note: The actual responses are usually approximated by the asymptotes

The Magnitude and Phase Bode Plots

The results is a ratio of polynomials in s, we have a pole at s = -1/(R1+R2)C, and a zero at s = -1/R2C

Magnitude of Av(f) =

In decibels:

Let

We have,

Bode Plot for an RC Circuit with one pole and one zero

Example 8.1:

Steps: 1.Plot each of the functions 2.Note the corner frequencies3.Determine the superimposed plot based on the corner frequencies

The Magnitude Bode Plot

The Phase Bode Plot

At a very high frequencies, the capacitor behaves as a short circuit, then the circuit reduces to a resistive voltage divider with a gain of

Simple checks of the Bode Plots:

Thus the gain is -20 dB at high frequencies, similar to what we have plotted.

Magnitude of Av(f):

Example

In decibels,

Magnitude Plots

9

Phase Plots

FET Common Source Amplifier model at High Frequencies

where

Thus to obtain higher value of upper freq:

1.Reduce Cgs and Cds

2.Reduce Rsig and RL