# Bode Frequency response

Discussion in 'Homework Help' started by james_dean, Jan 7, 2011.

1. ### james_dean Thread Starter New Member

Jan 7, 2011
3
0
Looking for help on past exam papers for exam next week.

Sketch to scale the approximate and actual bode frequency response for a d.c amplifier witth a cutoff frequency of 100khz and a passband gain of 10. why is the amplitude express in dbs??? at what frequency is the gain 0 db??

any help would be great.
thanks

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
When you plot a bode plot, you plot all the zeros and poles and then you find the resultant bode plot. If the gain was not in dB, you would need to multiply all these plots to get the resultant bode plot. However, by expressing the gain in dB you just add all these plots.
Also, it is easier to plot small and large gain responses on the same figure since their dB values won't be far apart.

gain dB=20log(gain)

To find the at which frequency the gain equals 0dB (or 1) use the transfer function or the bode plot. Remember that after the cut-off frequency, the gain will roll off with a rate of 20dB/decade.