Hi.who could remind me how to find the dc gain of a transfer that has a zero in the origin. I need to find the transfer func from a bode plot that start at -30db and and grows in 20 db because it has the zero in the origin. F(0)=0 so how it start at -30 db.thanks

 

What is the Bode plot x axis value at the zero value ? Is it 0 Hertz ?

In other words is the Bode plot a horizontal line from DC to ~ Fzero/10
or is it still changing at a 20 db rate ?

Post the bode plot might make sense.

Regards, Dana.

 

For a transfer function: 0 dB means that the output is identically equal to the input. Why?

\(10\cdot log_{10}(1)=0\)

 

What is the Bode plot x axis value at the zero value ? Is it 0 Hertz ?

In other words is the Bode plot a horizontal line from DC to ~ Fzero/10
or is it still changing at a 20 db rate ?

Post the bode plot might make sense.

Regards, Dana.

Here the bode plot

 

So start with basics, what simple circuit exhibits a high pass response ?

Laplace, how do you write out a zero, denominator or numerator ?

The plot does not indicate there is anything at DC, rather its telling you
something is continuing to roll off at 20 db/decade rate as freq drops.

Regards, Dana.

 

The horizontal axis is logarithmic. There is no "origin on a logarithmic scale because:

\(log_{10}(0+)\rightarrow -\infty\)

 

I dont under stand both of you.the transfer func strats at -30db.and a zero (must be on numeretor thats the defintion)and the 20 db is the proof.now how the hell i can start in -30 db if 20log(H(o)=0)=-inf
Where the -30 db hide ?

 

I dont under stand both of you.the transfer func strats at -30db.and a zero (must be on numeretor thats the defintion)and the 20 db is the proof.now how the hell i can start in -30 db if 20log(H(o)=0)=-inf
Where the -30 db hide ?

It doesn't start a 0 on the horizontal axis. Look very closely and notice that the left hand edge of the magnitude graph has an x-coordinate of 10^-1. That is 0.1 Hz. You cannot have an x-coordinate of 0 on a logarithmic scale.

At a frequency of 0.1 Hz, the output is down 30 dB from the input.