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