band pass filter

[sperelat]

I'm trying to simulate pulse transmitted through bandpass filter
(actually ,it is APD that has band pass type frequency response)

One of the problem is that the frequency respons is not like a
typical
band pass filter.


It is like a high-pass filter for low frequency and,like a low-pass
filter


for high frequency.


I don't know how to get the


transfer function of such a filter,


Can I just multiply transfer funtions of two-filters?

 

[Tom Bruhns]

I'm trying to simulate pulse transmitted through bandpass filter
(actually ,it is APD that has band pass type frequency response)

One of the problem is that the frequency respons is not like a
typical
band pass filter.

It is like a high-pass filter for low frequency and,like a low-pass
filter

for high frequency.

I don't know how to get the

transfer function of such a filter,

Can I just multiply transfer funtions of two-filters?

Is it a linear, time-invariant system? If so, then yes. But...beware
that the transfer functions you have for the two filters were almost
certainly developed for those filters driven from particular source
impedances, and operating into particular load impedances. Generally
those are resistive sources and loads. When you cascade passive
reflective filters (e.g. LC ladder filters), the first filter no
longer "sees" a pure load resistance, and the second filter no longer
"sees" a pure source resistance.

These days, it's convenient to use computer simulations for filter
evaluation. There are several good programs specifically devoted to
filters of various types, and Spice (e.g. LTSpice) can do a reasonable
job with most filters.

Cheers,
Tom