# Bode plot

Discussion in 'Homework Help' started by markmc001, Apr 26, 2009.

1. ### markmc001 Thread Starter Member

Mar 10, 2008
12
0
Hi all,
I have some questions to answer for my HNC homework, but am having a little trouble understanding the example we were given. I have top draw out some asymptotic bode diagrams.

In the example given the bode diagram was derived from the following formula:
Vo / Vin (jω) = 3 / (1+j3ω)(1+j4ω)

I know that the break points are at 0.25 and 0.33 as these can be found by inverting the constants 3 and 4, but I am not sure how to find the start point, which in this case is 9.5dB.

Any help would be much appreciated.
Mark

2. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
The formula you need to apply is:

$Gain_{(dB)}\large\ =\ 20*log_{10}(3)$

The 3 used above is the voltage gain taken from the transfer function.

hgmjr

Last edited: Apr 26, 2009
3. ### markmc001 Thread Starter Member

Mar 10, 2008
12
0
Thats great. That should get me started. Thanks for your help.
MM

4. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
674
The reason for this is that when ω=0 (DC), the numerator is 1.