Other Parts Discussed in Thread: TL081, TL072, TL082,
I'm modeling the input impedance of a simple non-inverting stage and finding that the impedance is very different from other TI JFET input opamps. Here is the simulation:
Running an ac sim on the above gives me:
The input impedance as shown in the bottom trace drops to 1.1Meg at 20kHz.
This all makes sense given an input capacitance of 6pF but similar simulations with TL072 and TL081 show very different behaviour with the impedance holding at 2Meg beyond 10MHz.
So why the difference? Is it that the TL072 and TL082 models do not model input capacitance?