I broke the loop on this TIA circuit and wanted to run an AC simulation to check stability on the Bode plot.
However, I keep getting this irregular circuit error about the current through L1. Any idea how to correct this problem?
Hey Erik,
1st of all, let's make sure we knnow about the input C to this device, here is what is in the datasheet, 25pF is pretty high,
next, the LG setup you showed is in the lit, but less desirable as it isolates the Zout from the feedback network. Here I set up using the original LMP7701 model for the loop broken at the input, when you do that you have to add the input C manually, but the Zout sees the right load, could not read you load R, I have 100ohm here, 85deg phase margin is real good,
And then, I drop in what might be a model update for the LMP7704-SP to this LG sim, looks the same, and runs fine,
here is an article showing why you want to do the LG this way instead of what you had, only matters if the model has a reactive open loop output Z, but more prudent anyway.
And this last file, in TINA V9
Erik,
Your method is correct and should yield identical results as Michael obtained. There must be some bug in your schematic that gives the error. I entered your schematic and got 86 degrees phase margin - see below.
Below I have attached the schematic for your convenience.
The output injection method works most of the time, I prefer an approach that works all of the time.
If the model has a correct open loop output impedance, the method injecting into the output network will isolate that impedance from the feedback network - doesn't matter a lot of the time, but sometimes it does. In any case the design is likely very stable.
here is a a Zol test on the model, kind of odd looking,
