RC Band pass filter help

[ChronoFish]

Hello,

I have a pulsed signal where each pulse is made up of a sine wave of 8 cycles at 29kHz. What is the best configuration of resistors
and capacitors to get a 27khz - 32khz band pass filter? Does anyone have an excel spreadsheet they would be willing to share or
know of an online calculator that can help solve this?

Thanks!
CF

 

[MikeM]

ChronoFish wrote:

Hello,

I have a pulsed signal where each pulse is made up of a sine wave of 8 cycles at 29kHz. What is the best configuration of resistors
and capacitors to get a 27khz - 32khz band pass filter? Does anyone have an excel spreadsheet they would be willing to share or
know of an online calculator that can help solve this?

Look at TI's website. Lots of analog filter design help there.

I have cobbled together something which you can play with to get a final
circuit.

1. Download and install LTSpice/SwitcherCADIII from http://www.linear.com/software/

2. cut and paste everything below the _____________ into a text file
called "bpf.asc".

3. Run SwitcherCADIII

4. File/OPEN bpf.asc

5. click on the little running man

6. After it runs, click on waveforms at V(out), V(mod), V(in)

7. You can play with values and resim it...

_______________________________________________________________________

Version 4
SHEET 1 880 680
WIRE -144 64 -112 64
WIRE -112 128 -112 64
WIRE -112 64 -80 64
WIRE -112 0 -112 64
WIRE -16 64 16 64
WIRE -112 -64 -112 -112
WIRE -112 -112 16 -112
WIRE 80 64 16 64
WIRE -112 208 -112 256
WIRE 144 80 192 80
WIRE 192 80 192 -112
WIRE 192 -112 16 -112
WIRE 112 48 112 -32
WIRE 112 -32 320 -32
WIRE 112 112 112 208
WIRE 112 208 320 208
WIRE 320 -16 320 -32
WIRE 320 64 320 80
WIRE 320 176 320 208
WIRE 320 80 256 80
WIRE 320 80 320 96
WIRE 256 80 256 112
WIRE 192 -112 256 -112
WIRE 80 96 48 96
WIRE -224 64 -272 64
WIRE -528 224 -528 208
WIRE -448 96 -528 96
WIRE -528 96 -528 128
WIRE -272 64 -304 64
WIRE 16 -112 16 -64
WIRE 16 64 16 16
WIRE 48 96 48 128
FLAG 48 128 0
FLAG -112 256 0
FLAG 256 112 0
FLAG 256 -112 out
IOPIN 256 -112 Out
FLAG -528 224 0
FLAG -272 64 In
FLAG -528 96 mod
SYMBOL res -128 48 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 8.423K
SYMBOL res 0 -80 R0
SYMATTR InstName R2
SYMATTR Value 92.66K
SYMBOL cap -128 -64 R0
SYMATTR InstName C1
SYMATTR Value 3.3n
SYMBOL res -128 112 R0
SYMATTR InstName R3
SYMATTR Value 288.5
SYMBOL cap -16 48 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 330p
SYMBOL Opamps\\1pole 112 80 R0
SYMATTR InstName U1
SYMBOL Misc\\battery 320 -32 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 10
SYMBOL Misc\\battery 320 80 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 10
SYMBOL SpecialFunctions\\modulate -448 32 R0
WINDOW 3 -42 -77 Left 0
SYMATTR InstName A1
SYMATTR Value mark=30k space=30k
SYMBOL voltage -528 112 R0
WINDOW 3 38 56 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value PULSE(0 1 50u 1u 1u 265u)
TEXT -8 272 Left 0 !.tran 500u
TEXT -416 208 Left 0 ;Second order BPF, \nButterworth response, \ncenter
freq=30Khz,\nBandwidth=2Khz
TEXT -8 232 Left 0 ;OpAmp GBW >1.5Mhz

 

[Ben Bradley]

In sci.electronics,sci.electronics.design, "ChronoFish"
<deja@chronofish.com> wrote:

Hello,

I have a pulsed signal where each pulse is made up of a sine wave of 8 cycles at 29kHz. What is the best configuration of resistors
and capacitors to get a 27khz - 32khz band pass filter?

What Q do you want? Are those frequencies the -3dB points? Or are
you asking us?

Does anyone have an excel spreadsheet they would be willing to share or
know of an online calculator that can help solve this?

There probably are some, once you decide what circuit configuration
you want. The Active Filter Cookbook is a good read for this.

Thanks!
CF

-----
http://mindspring.com/~benbradley

 

[Ban]

ChronoFish wrote:

Hello,

I have a pulsed signal where each pulse is made up of a sine wave of
8 cycles at 29kHz. What is the best configuration of resistors and
capacitors to get a 27khz - 32khz band pass filter? Does anyone have
an excel spreadsheet they would be willing to share or know of an
online calculator that can help solve this?

Thanks!
CF

If you want a bandpass-filter, there are 2 possibilities. Either an active
filter which requires at least one opamp with supply(+5 or +3.3V might do)
or a passive filter which needs coils in addition to resistors and
capacitors but no opamp. Also the filter will make additional cycles at the
end of the burst. The more selective it is, the more it rings.
The passive filter will amplify the burst around 10times when having the
small required bandwith, loads the source quite a bit (you will need a high
current driver) and. the inductivities are bulky. The attenuation is very
good -30dB at double/half the frequency.


|| ___
o----||---+---UUU------+----------o
330n|| | 1.8mH | |
| | |
C| --- .-.
C| --- | |
C| 15n| | |Rload=1k
100uH | | '-'
| | |
o---------+------------+----------o
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


--
ciao Ban
Bordighera, Italy

 

[MikeM]

Ban wrote:

ChronoFish wrote:

Hello,

I have a pulsed signal where each pulse is made up of a sine wave of
8 cycles at 29kHz. What is the best configuration of resistors and
capacitors to get a 27khz - 32khz band pass filter? Does anyone have
an excel spreadsheet they would be willing to share or know of an
online calculator that can help solve this?

Thanks!
CF


If you want a bandpass-filter, there are 2 possibilities. Either an active
filter which requires at least one opamp with supply(+5 or +3.3V might do)
or a passive filter which needs coils in addition to resistors and
capacitors but no opamp. Also the filter will make additional cycles at the
end of the burst. The more selective it is, the more it rings.
The passive filter will amplify the burst around 10times when having the
small required bandwith, loads the source quite a bit (you will need a high
current driver) and. the inductivities are bulky. The attenuation is very
good -30dB at double/half the frequency.


|| ___
o----||---+---UUU------+----------o
330n|| | 1.8mH | |
| | |
C| --- .-.
C| --- | |
C| 15n| | |Rload=1k
100uH | | '-'
| | |
o---------+------------+----------o

Here is an LTSpice sim of Ban's circuit. It has a lower Q, and therefore
wider bandwidth than the OPAmp version I posted. I modified the
MODULATE source so that it presents three different bursts (at 20Khz, 30Khz, and
40Khz, respectively). Ban's circuit also has a faster risetime, but less
attenuation of the out-of-band frequencies at 20 and 40 Khz.

MikeM

Cut and paste the following into LCbpf.asc and open it with LTSpice
_______________________________________________________________________________

Version 4
SHEET 1 880 680
WIRE 128 48 160 48
WIRE 288 48 336 48
WIRE 336 48 464 48
WIRE 528 48 528 80
WIRE 528 160 528 224
WIRE 528 224 336 224
WIRE 336 160 336 224
WIRE 336 224 160 224
WIRE 336 96 336 48
WIRE 160 96 160 48
WIRE 160 48 208 48
WIRE 160 176 160 224
WIRE 336 256 336 224
WIRE 464 48 528 48
WIRE -480 304 -480 288
WIRE -480 176 -480 208
WIRE -224 144 -256 144
WIRE -400 112 -560 112
WIRE -560 112 -560 208
WIRE -560 288 -560 304
WIRE -400 176 -480 176
WIRE -224 144 -160 144
WIRE -16 144 -80 144
WIRE 64 48 -16 48
WIRE -16 48 -16 144
FLAG 336 256 0
FLAG 464 48 out
FLAG -480 304 0
FLAG -224 144 In
FLAG -480 176 mod
FLAG -560 304 0
SYMBOL ind 144 80 R0
SYMATTR InstName L1
SYMATTR Value 100u
SYMBOL ind 192 64 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 5 56 VBottom 0
SYMATTR InstName L2
SYMATTR Value 1.8m
SYMBOL res 512 64 R0
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL cap 64 64 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C1
SYMATTR Value 330n
SYMBOL cap 352 160 R180
WINDOW 0 24 64 Left 0
WINDOW 3 24 8 Left 0
SYMATTR InstName C2
SYMATTR Value 15n
SYMBOL res -176 160 R270
WINDOW 0 32 56 VTop 0
WINDOW 3 0 56 VBottom 0
SYMATTR InstName R2
SYMATTR Value 50
SYMBOL SpecialFunctions\\modulate -400 112 R0
WINDOW 3 -42 -77 Left 0
SYMATTR Value mark=19.5k space=39.5k
SYMATTR InstName A1
SYMBOL voltage -480 192 R0
WINDOW 3 38 56 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(0 1 50u 1u 1u 265u 600u)
SYMATTR InstName V1
SYMBOL voltage -560 192 M0
WINDOW 3 -444 156 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PWL(0 0 600u 0 601u 0.5 1200u 0.5 1201u 1)
TEXT -80 352 Left 0 !.tran 1.8m
TEXT -408 296 Left 0 ;R2 is a resonable value of source resistance

 

[ChronoFish]

"MikeM" <trashcan@yahoo.com> wrote in message news:c3nfsv$k6q$1@coward.ks.cc.utah.edu...

Ban wrote:

ChronoFish wrote:

Hello,

I have a pulsed signal where each pulse is made up of a sine wave of
8 cycles at 29kHz. What is the best configuration of resistors and
capacitors to get a 27khz - 32khz band pass filter? Does anyone have
an excel spreadsheet they would be willing to share or know of an
online calculator that can help solve this?

Thanks!
CF


If you want a bandpass-filter, there are 2 possibilities. Either an active
filter which requires at least one opamp with supply(+5 or +3.3V might do)
or a passive filter which needs coils in addition to resistors and
capacitors but no opamp. Also the filter will make additional cycles at the
end of the burst. The more selective it is, the more it rings.
The passive filter will amplify the burst around 10times when having the
small required bandwith, loads the source quite a bit (you will need a high
current driver) and. the inductivities are bulky. The attenuation is very
good -30dB at double/half the frequency.


|| ___
o----||---+---UUU------+----------o
330n|| | 1.8mH | |
| | |
C| --- .-.
C| --- | |
C| 15n| | |Rload=1k
100uH | | '-'
| | |
o---------+------------+----------o


Here is an LTSpice sim of Ban's circuit. It has a lower Q, and therefore
wider bandwidth than the OPAmp version I posted. I modified the
MODULATE source so that it presents three different bursts (at 20Khz, 30Khz, and
40Khz, respectively). Ban's circuit also has a faster risetime, but less
attenuation of the out-of-band frequencies at 20 and 40 Khz.

MikeM

Cut and paste the following into LCbpf.asc and open it with LTSpice

You guys are great. That was more than I could ask for as far as effort on your part. Thanks so much!

-CF