Can you identify this opamp from its simplified schematic and PSRR plot?
Posted 10th September 2015 at 01:28 AM by abraxalito
Updated 21st September 2015 at 12:23 AM by abraxalito
Updated 21st September 2015 at 12:23 AM by abraxalito
In my search for opamps with better real-world PSRR behaviour, I came across this beauty. For now I'll just post up its simplified schematic and PSRR plot - if any of you know of it please put your deduction in the comments. I may add more clues later if nobody nails it early on.
The reason I find this part interesting is its cascoded output stage - I believe this is what leads to the 'hump' in the positive rail PSRR. I've never seen that behaviour on any other device.
Well over a hundred views now and not one single stab at the answer. Its the industrial-strength version of the now obsolete LM308, a Bob Widlar special with super-beta input stage. The output stage cascode I take it isn't primarily to improve the PSRR rather its due to the high maximum operating voltage (72V). TI does still have the DS on its website though it doesn't put in an appearance in parametric search as its been obsolete for a while. Even more interesting is its decompensated variant which TI no longer has the DS for but still can be found online.
The reason I find this part interesting is its cascoded output stage - I believe this is what leads to the 'hump' in the positive rail PSRR. I've never seen that behaviour on any other device.
Well over a hundred views now and not one single stab at the answer. Its the industrial-strength version of the now obsolete LM308, a Bob Widlar special with super-beta input stage. The output stage cascode I take it isn't primarily to improve the PSRR rather its due to the high maximum operating voltage (72V). TI does still have the DS on its website though it doesn't put in an appearance in parametric search as its been obsolete for a while. Even more interesting is its decompensated variant which TI no longer has the DS for but still can be found online.
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It was a later design, I use the simplify input stage of LM108 with JFET-BJT Cascode Current Source or I should say BJT-JFET, and Full Wilson Current Mirror
Posted 4th June 2016 at 02:04 AM by TavoNice