[sdiy] Single vs Dual Op Amp Supplies

[Tom Wiltshire]

On 8 Mar 2009, at 05:45, Matthew Smith wrote:
>
> As my signal is not going either side of a zero voltage - it is  
> always positive - is there any reason not to use such a device?

The voltage offset. The best reason for using the dual-rail op-amps  
is that you can get the signal moving either side of 0V and not have  
any DC shift.

> Can this be done with a single 5V supply?  If not, how do I get  
> half of my 0-5V signal "below the line" to go into a split supply  
> op amp?

You need to add -2.5V DC to cancel the 2.5VDC shift that your  
squarewave has. A simple inverting mixer will do, but since the mixer  
inverts, you need to connect it to +2.5V instead.

David is right too; the integrator will produce an output amplitude  
that halves for each octave increase in frequency. This has to be  
compensated somehow. There's loads of "DCO" stuff on the web and in  
the SDIY archive that offers one way, or otherwise you could use some  
kind of variable gain circuit after the integrator.

Regards,
Tom