Debugging odd push button behavior

[monteie]

I have the following circuit, and I noticed something I've never seen before on my scope when I release the button. I have attached the schematic and the waveform. The button is IC has an internal pullup to 1.8V.

As you can see, when I release the button, the voltage rises to about mid level for a few microseconds and then proceeds to rise to 1.8v. At first I though it was mechanical bounce in the switch, but that theory wasn't consistent with what I've seen before. Anyone have any idea would could be going on here?

 

[KlausST]

Hi,

* to "what" IC?
* where is the pullup?
* is it a simple mechanical pushbutton?
* where did you measure the signal?

Klaus

 

[monteie]

The IC is SPEAr300 from ST

Pullup is configured in the IO. I also assume there is ESD clamping inside

It's a small mechanical push button on a flex. Off-mom

Measured the signal at the IC


Thanks!
Eric

 

[c_mitra]

Can you disconnect the IC and test the signal? Where the other end of the switch going? Connect that to the Vcc, if possible. I cannot see the charging/ discharging of the capacitor.