On Tue, 2004-10-12 at 21:00, Wan Zulhelmi Wan Ahmad Kamar wrote:
> Hi, I've designed a 40khz bandpass filter.  When I simulate it on
> pspice, the center frequency is 40khz.  However on breadboard, the
> center frequency seems to be at 37khz and not at 40khz.  Can this be
> ignored or do i really need it at 40 khz since my ultrasonic
> transducer is at 40khz.  Any suggestions on what's the problem with my
> circuit?  Here's my circuit.  Thanks in advance.

Remember, pspice is just a simulator, it uses models to approximate what
happens in the real world.

It is entirely possible that a real world circuit will behave different
from simulation. In your case I'd say it's working pretty close to
simulation! Note that in pspice usually your components are "exact", a
100kohm resistor is exactly 100kohm. Unfortunately in real life this is
rarely the case, a 100kohm resistor may be 98kohm, a 1uF cap might be
1.2uF.

There is no problem with your circuit, you just have to tweak the
components a little to get the performance you want. Please do not rely
soley on simulation, I have had cases where real world behaviour was FAR
different then simulation (oscillators are a good device to confuse a
simulator). TTYL

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