How to understand and get the response time of a filter?

[agump]

Hi, I am engaged in a filter design and have read some books about the filter. I am now knowing that I must apply the input to the filter for some time. But I can't know where to get the time. Please give me some help , thanks.
Best regards.
Agump

 

[ionp]

Most introductory filter designs are intended to allow the passage of some frequencies while restricting the passage of others.

Testing such a filter would generally be done by applying a sine wave at the input, with a frequency chosen to demonstrate either passage or restriction.

What kind of filter are you designing? Low pass? High pass? Band pass?

There are filters of types other than frequency selective, but less likely for a first attempt.

 

[Kral]

agump,
To get the frequency response of a filter (or any linear time-invariant system), simply sibstitute jw for s in the transfer function.
.
To get the step response, multiply the transfer function by 1/s. Expand the resultant expression using partial fractions, and then obtain the time response using a table of LaPlace transforms. Any good text on LaPlace transforms will give you the details.
Regards,
Kral

 

[ericsully]

There is actually a free tool you can get to measure response time http://www.real-user-monitoring.com

 

[WimRFP]

Hello,

I don't know what type of filters you are designing and what you mean with "response time", but some things can be said.

When you think of the time it takes before the output of the filter is stable, this delay time is proportional with 1/BW, and some other factors (like allowable envelope distortion).

So a filter with a Center frequency = 100 MHz and BW = 1 MHz, will have the same delay time as a filter with Center frequency = 1 GHz and BW = 1 MHz.

You may know that the faster the envelope/frequency/phase of a sinusoidal signal changes, the more spectrum that signal occupies. So a narrow band filter will only pass the low frequency sidebands, hence the output envelope (and frequency or phase of output) will vary slowly.

When you understand the behavior of low pass filters, a band pass filter can be seen as a shifted (in frequency) version of a low pass filter.

 

[Kral]

agump,
The tool that ericsully refers to is for measuring web response, not time response of an electrical filter
Regards,
Kral