# bandpass filter

Discussion in 'Electronic Design' started by John, Sep 28, 2003.

1. ### JohnGuest

hello I need a schematic of bandpass filter of 14.5 khz. If anyone can help thanks.

2. ### John PopelishGuest

WE need to know a lot more about the details to give any useful advice
(what bandwidth, in band ripple, out of band rejection, active or
passive, what supplies are available, must this filter pass
significant power, etc.) But if you want to read into some active
filter possibilities, look at:

http://www.national.com/an/AN/AN-779.pdf

At this frequency range, I like the biquad, 3 opamp design for

http://www-k.ext.ti.com/SRVS/Data/ti/KnowledgeBases/analog/document/faqs/ssbqbphq.htm

3. ### BanGuest

Here is a small circuit, which allows tuning with a single resistor R3,
while maintaining gain and bandwidth.

design equations:
fr= 1/(2*pi*C) sqrt((R1+R3)/(R1*R2*R3))
gain: -Ar=R2/2R1
Q= pi*R2*C*fr
B= 1/(pi*R2*C)
+--------+--------+
| .-. |
--- | |R2 |
--- | | |
|C '-' |
___ | || | |\ |
o-|___|-+---||---+---|-\ |
R1 | ||C | >-+--o
| +--|+/
.-. | |/
| |R3 ===
| | GND
'-'
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

ciao Ban

4. ### BanGuest

hello I need a schematic of bandpass filter of 14.5 khz. If anyone
forgot to mention that the operational amplifier needs a open loop gain of
greater than 2*Q^2 at the resonance frequency. This is particulary difficult
to obtain for higher values of Q. On the other hand the circuit is pretty
immune against self_oscillation at fr even with components not exactly the
calculated value.
Of course a must is the right bypass and frequency correction of the opamp
to avoid high frequency oscillations.

ciao Ban

5. ### BrianGuest

John,
While you didn't supply a lot of needed information, I will give you two examples of
circuits (with their response curves). If you will give more information, then we can
give you a circuit to match your needs. See the circuits at
http://www.fncwired.com/BandpassExample
hope this helps,
Brian

6. ### Jim ThompsonGuest

See "GyratorFilterBP.pdf" on the S.E.D/Schematics page of my website.

...Jim Thompson