On Mar 23, 3:39*pm, "dave.harper" wrote:
I'm trying to come up with a filter or converter that takes a square
wave input and outputs something closer to a sign wave (varying
between ~1.9kHz and 2.1kHz). *It can have some distortion, but I'm
trying to eliminate the sharp leading and trailing edge. *One option
I'm pursuing is a bandpass filter (2 caps and 2 resistors), which
looks to give a reasonable output, but still not quite as smooth as
I'd like. *I've also considered using a counter feeding a bank of
resistors, but finding a method for it to start counting up with it
hits 0 and down when it hits the high value might be more difficult.

Originally, I had used a wein-bridge oscillator with op-amps to make
the sine wave, but due to the environment, EMI was a problem and it
damped out the oscillations (even with ferrite beads and modest
shielding). *So I'd like to avoid using op-amps (since they are
apparently sensitive to EMI) if possible.

Any suggestions?

Thanks in advance!
Dave

Start with a triangle wave, there are less harmonics to filter out.
How bad is the EMI? I like the Wein-bridge. Try using an FET opamp
for it. The only problem I've had with the wien bridge was motor-
boating of the frequency. This was finally solved by using good low
dissipation caps. (Ohh I have seen EMI fuzz.. but only with BJT
opamps.)

George H.