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I replaced the 5534 op-amp in the PI board with an AD8031 to see how they compare. I am interested in using the 8031 because it will run on a single 5V supply.
There was no feedback capacitor on the board and the 8031 has a wider bandwidth. So the noise at the output of the amplifier was slightly higher with the 8031. It is a little hard to judge noise amplitude especially when the bandwidth changes, but it looks like it jumped 20 to 30%.
The interesting thing is that the transition at coil turn off looks much cleaner and the 8031 settles faster. I had to readjust the coil damping, but with it adjusted for the 8031 I got better settling than I could get from the 5534 at any setting.
The 8031 has no offset adjustment but the output offset was only 350 mV at a gain of 450. That is less than 1 mV at the input and should be easy to adjust out.
I could not check it with a minus supply of 0V so there is still one big question remaining. What happens when the input goes one diode drop below the negative supply? I know that if the input goes more than one diode drop below there will be a phase reversal at the output. The question is, will the drop across the clamp diode be large enough to trigger the phase reversal and if so, does it take any longer to recover from that than it takes to recover from hitting the rails?
Robert
There was no feedback capacitor on the board and the 8031 has a wider bandwidth. So the noise at the output of the amplifier was slightly higher with the 8031. It is a little hard to judge noise amplitude especially when the bandwidth changes, but it looks like it jumped 20 to 30%.
The interesting thing is that the transition at coil turn off looks much cleaner and the 8031 settles faster. I had to readjust the coil damping, but with it adjusted for the 8031 I got better settling than I could get from the 5534 at any setting.
The 8031 has no offset adjustment but the output offset was only 350 mV at a gain of 450. That is less than 1 mV at the input and should be easy to adjust out.
I could not check it with a minus supply of 0V so there is still one big question remaining. What happens when the input goes one diode drop below the negative supply? I know that if the input goes more than one diode drop below there will be a phase reversal at the output. The question is, will the drop across the clamp diode be large enough to trigger the phase reversal and if so, does it take any longer to recover from that than it takes to recover from hitting the rails?
Robert
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