Check my bandpass filter with frequency from 10 to 20 kHz

[naspek]

Band pass filter

hey there..

i'm trying to design a bandpass filter with pass band frequency from 10 kHz to 20 kHz and gain = 1
however, my circuit didnt give me the correct graph.. my circuit is correct?

 

[FvM]

Re: Band pass filter

The low pass has a correct 20 kHz cut-off butterworth characteristic, the high pass should be 10k butterworth, but has completely
wrong dimensioning. Where did you get values? Seems like you did a transform in the wrong direction. A standard butterworth would
have equal capacitors and 1:2 ratio resistors. E.g. C1=C2=5.6 nF, R1=4k, R2=2k

 

[keith1200rs]

Band pass filter

Both filters have the same values - just connected differently!

Keith

 

[naspek]

Re: Band pass filter

The low pass has a correct 20 kHz cut-off butterworth characteristic, the high pass should be 10k butterworth, but has completely
wrong dimensioning. Where did you get values? Seems like you did a transform in the wrong direction. A standard butterworth would
have equal capacitors and 1:2 ratio resistors. E.g. C1=C2=5.6 nF, R1=4k, R2=2k

what do u mean by wrong dimensioning?
i calculated the values..
the values for resistors and capacitors for high pass section are the same with the
low pass section right?

Added after 55 seconds:

Both filters have the same values - just connected differently!

Keith

i did connect it differently right?

 

[Audioguru]

Band pass filter

The lowpass filter cuts the highs and the highpass cuts the lows. The cutoff frequency of both filters is almost the same so all frequencies are reduced.

A bandpass filter has no loss at the peak frequency then the highs and lows are reduced.

 

[keith1200rs]

Band pass filter

You said you wanted 10-20kHz but you have a 20kHz low pass and 20kHz high pass. Double the capacitor values in the high pass to reduce the frequency to 10kHz.

Keith

 

[naspek]

Re: Band pass filter

You said you wanted 10-20kHz but you have a 20kHz low pass and 20kHz high pass. Double the capacitor values in the high pass to reduce the frequency to 10kHz.

Keith

didn't work.. still the same.. =(

 

[LvW]

Re: Band pass filter

hey there..

i'm trying to design a bandpass filter with pass band frequency from 10 kHz to 20 kHz and gain = 1
however, my circuit didnt give me the correct graph.. my circuit is correct?

A bandpass is described by four parameters:
*mid frequency (center)
*bandwidth
*Approximation (ripple in the pass band) for filter orders equal to or higher than 4
*gain at center frequency

Therefore, what do you want? To answer your question it is not sufficient to know that the circuit "didn'n give the correct graph" without knowing the specification.

 

[naspek]

Re: Band pass filter

ok.. thanks LvW..

1st, the pass band is from 10kHz to 20kHz..
so.. my mid frequency, fc must be 15kHz right?

my fl=10kHz and my fh = 20kHz..
fl and fh must cut -3dB.. which mean, at -3dB is my fl and fh

my roll off rate is at least -40dB/decade..

 

[keith1200rs]

Re: Band pass filter

You said you wanted 10-20kHz but you have a 20kHz low pass and 20kHz high pass. Double the capacitor values in the high pass to reduce the frequency to 10kHz.

Keith

didn't work.. still the same.. =(

Hmm. Could you post the results and new circuit?

Keith

 

[LvW]

Re: Band pass filter

1st, the pass band is from 10kHz to 20kHz..
so.. my mid frequency, fc must be 15kHz right?
my fl=10kHz and my fh = 20kHz..
fl and fh must cut -3dB.. which mean, at -3dB is my fl and fh
my roll off rate is at least -40dB/decade..

OK, some comments seems to be appropriate:

1.) In general, you have two choices: (a) Series connection of two bandpass stages or (b) series connection of a lowpass and a highpass (as you did).
2.) Because of the rather large bandwidth (10 kHz with mid frequency around 15 kHz) alternative (b) seems to be the best one.
3.) However, the exact design is not very easy:
You cannot design the corner frequencies for both stages separately to 10kHz resp. 20 kHz, since both stages influence each other. More than that, if the mid band gain has to be "1", you cannot use unity gain Sallen-Key stages (each having a gain of only unity).
4.) Exact Design: Apply the bandpass-lowpass transformation, find the low pass poles of a 4th order transfer function, transform back to bandpass and design both stages of second order using multi-feedback or Sallen-Key (with gain) topology.
This is a rather challenging process.
5.) Or use one of the filter design programs (filter-solutions.com offer a demo version which suits to your requirements)

Good luck

Added after 2 hours 45 minutes:

Addendum to 2): Series connection of two different (!) bandpass stages is also possible, however, the design procedure is not much less if compared with the LP-HP approach (BP-LP transformation before).

 

[mirawani]

Band pass filter

hi...i need a help for modify my bandpass filter layout using ads...how i want to crop the layout shape???

 

[bpf168]

Re: Band pass filter

Why not use one single bandpass filter insteed of Series a highpass filter and a lowpass filter. A bandpass filter is easy for design, easy tune, and easy calculate. Please refer to: **broken link removed**