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previous: Ed Rembold Ummm, R.G.Now I'm not the s... -- 1/12/2001 3:45 AM View Thread

Re: Phase Reverser at GEO

1/12/2001 4:35 PM
R.G. on the roadRe: Phase Reverser at GEO
Yeah, Ed, I know it wasn't the most lucid bit of writing in the world. I wanted to get down the bones of the issue and then flesh them in as time permitted.  
There are indeed multiple ways to skin cats. This is just one, there are others. I'm not familiar with using a DPDT to phase reverse - is this to select the output of an inverter or follower?  
That's clearly a valid way to do phase reversing, but it needs either a follower and an inverter plus an SPDT switch to do the selecting. You can get by by making the inverting gain-of-one circuit be an "effect" in its own right and selecting either the input (noninverted) or the output (inverted). The advantage with the +1/-1 circuit is that you get the change with only an SPST switch to ground, which may be easier than the SPDT or DPDT to implement.  
You could also do a phase splitter and then choose between the true/inverted outputs with either a manual or electronic switch. These are a little tricker to set up and will inevitably have a smaller signal swing than most opamp circuits, but they do work, and you have both outputs simultaneously.  
Like most "classical" opamp circuits, yeah, the text books do assume a bipolar supply, and there are special considerations for single supply. The big thing is making the bias voltage really, really steady. Sometimes the two-resistors-and-a-capacitor thing won't do and you have to make a more solid, lower impedance one. That's possible, and in fact TI makes a three-pin TO-92 device intended to be a high performance power supply splitter with low impedance just to do that job. Can't buy them anywhere (I've tried) but they are made. Probably pure unobtanium crystals 8-)  
Obviously, I didn't get to breadboard the circuits. They are correct as to the theory, and I have built a working single supply phase flopper before for a magnetometer I put together and that did work well. However, I believe that some variant of that will work correctly, and in succeeding installments I'll get working circuits illustrated.