leeb_965,
I believe that you have a very conventional instrumentation amp circuit; it should work OK, within its limitations.
For production use, a single integrated part usually costs less at any chosen performance level, but it is no sin to make your own using op-amps.
Any recommendation to you would depend on your particular circumstances. We don't know what your circuit needs to do, or what your expected annual production rate might be.
That said, I'll try to help with your questions.
I'm a little confused by your description of what's happening.
First, V1 and V2 do not appear to be labeled on your drawings.
And you say they equal pure numbers. Could you mean DC voltages? AC voltages? And relative to what reference point?
Nowhere in the linked schematic do I see a place with " 0.1 X gain". I see 21 X voltage gain, followed by plus and minus 1X voltage gain.
The pictorial diagram shows "inputs from ac signal generator". What sort of generator? Does it have a balanced output, with the average fixed at zero volts DC?
You might read up on "input common mode voltage range"; your asymmetrical clipping on the output may have to do with this.
This particular circuit, with fairly low power supply voltages, will not accept very large input signals. The LF353 inputs are not guaranteed to work closer to either supply than 4V, so you have only a plus or minus 2 volt range from ground potential. Similarly, the outputs may quit at 3V away from each supply. Divide what's left by 21, and you have an input voltage of only 143mV peak. Real parts will do somewhat better than the MIN numbers off the data sheet, but this is no rail to rail part. ( They really kinda had plus and minus 15 volts in mind for the power.)
These limitations might be mitigated by higher supply voltages, or by op amps with rail to rail I/O. Moving the gain to the second stage could help improve the common mode input range.
So I suggest that you keep both the common and differential mode input signals small, for the circuit shown.
And look out for the DC bias on the inputs if you are working with AC inputs. Op-amps have small but non-zero input currents that have to come from something off the left hand edge of your schematic.
A good way to see what's going on is to ditch the AC on the inputs, and use a couple of pots connected across plus and minus 300mV, or so. You can measure the inputs and output and see if the result is as expected.
I hope this is of help to you.
shrtrnd,
Yes. Burr Brown was a good outfit. And the LF353 original source was similarly swallowed-up; the ten gallon hat people have been to Santa Clara, too.
Ted
