I have a signal that can potentially swing +-15 volts maybe, and I'm going into a 4-pole Sallen-Key filter, then an ADC with swing range 0 to 4.096. So I added a dual diode, BAV99, at the input of the first opamp, connecting to clamp rails of 0 and 4.1. The filter input resistors add up to about 10K.
This works, but it's not safe over temperature. Turns out a BAV99 leaks around 5 nA at room temp alone.
The collector-base junction of a cheap transistor, like a BCX70, leaks about 150 fA at room temp, -5 volts, kinda hard to measure.
Transistors are so much better diodes than diodes. Do they still make diodes by dicing up featureless wafers, exposing the damaged edges? Barbaric. Or are they just big junctions?
Maybe I'll test some high-voltage dual diodes; they might leak less. I could use the BCX70 or BFT25 junctions (we created a PADS schematic symbol for a transistor used as a diode) but it will take two parts.
Central makes a "low-leakage" SOT-23 dual diode, samples coming.