Is there any circuit for triggering? I want to input a signal with a series events, when an event cross a threshold, the circuit out put a triggering signal such as a TTL. I need to have two thresholds. When my signal is positive rising cross a threshold, the circuit send a triggering signal; when my signal is negative falling cross a negative threshold, the circuit send a triggering signal. Thank you.

Thank you for your inquiry.

You’re describing the function of a device they call an Analog Voltage Comparator

A regular comparator will detect when the circuit is rises above and below one threshold.

Two comparators can be used if you have a different rising threshold than the falling threshold, which is called windowing.

Here is an article on using comparators as level detectors.

You could also do this with an analog to digital converter on a microcontroller.

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Thank you, Kristof. Does Digikey sell this kinds of windowing device, or parts of it so that I can easily assemble one?