hi all, i wonder that how can i use multisim to calculate all the resistors' values while i am attempting to change the cutoff frequency of a filter.

 

I use a free download program called FilterPro from the TI website to design the filter. I sometimes put the finished filter into LTSpice to find how it does combined with other parts of an overall circuit, or with different capacitor/resistor values.

 

thank you for your reply,Mike.however, it seems to me your answer is not what i am looking for. so, everybody, any clues about how to generate automatically the value of the resistors to the new filter using any software when i find the cutoff frequency of the original one. thank you.

 

It would help if you got a bit more specific on the filter? There are huge numbers of designs out there, any answer we gave would be a guess best case.

 

thank you for your reply,Mike.however, it seems to me your answer is not what i am looking for. so, everybody, any clues about how to generate automatically the value of the resistors to the new filter using any software when i find the cutoff frequency of the original one. thank you.

The answer is as I said: Spice (Multisim) is a way of ANALYzing an existing circuit design; it has no intrinsic built-in capability for synthesizing active filter circuit from basic specs like number of poles, cuttoff, impedance, etc.

FilterPro is a CAD program which specifically creates an opamp-based active-filter when you put in basic specs like number of poles, high, low, bandpass, cut-off frequency, impedance, etc. FilterPro creates a schematic which can be simulated in Spice.

 

It would help if you got a bit more specific on the filter? There are huge numbers of designs out there, any answer we gave would be a guess best case.

thank you for your reply, Bill. here comes my attachment on a lowpass filter with 10K cutoff frequency. how can you figure out these specs on it if i want cutoff frequency to be 150Hz

 

The answer is as I said: Spice (Multisim) is a way of ANALYzing an existing circuit design; it has no intrinsic built-in capability for synthesizing active filter circuit from basic specs like number of poles, cuttoff, impedance, etc.

FilterPro is a CAD program which specifically creates an opamp-based active-filter when you put in basic specs like number of poles, high, low, bandpass, cut-off frequency, impedance, etc. FilterPro creates a schematic which can be simulated in Spice.

thank you for your help, Mike. i am still confused about the filterPro software;is it a software that can help me figure out specs from the exsiting filter rather than design a new filter in accordance with the specs.

i have attached my lowpass filter which needs to be designed as 150Hz cutoff frequency one.

 

...my attachment on a lowpass filter with 10K cutoff frequency. how can you figure out these specs on it if i want cutoff frequency to be 150Hz

You are asking a different question now! If you have a working filter at one frequency, and want to scale it to another frequency, read this.