I recently acquired an oscilloscope as I've been having some odd issues with multiplexing simple one color LED matrices with the TLC5940 Mux library. Standard setup using 1-of8 decoder into 8 p-channel FETs for each row, and then having each column tied to output pins 1->8 on the TLC5940. (And yes, the TLC5940 is decoupled.)
In the following image, the yellow channel is one of the p-channel FETs, and the blue channel is that FET's corresponding decoder output pin. The yellow channel is positioned at 0V and the blue channel is placed at -5V.
I cannot come up with a reason as to why the random noise is occurring all of the sudden - I've ruled out crosstalk as it's happening on every FET. I imagine that this issue is what is causing ghosting/flickering around my patterns that I am trying to draw to the matrix.
Thanks for any possible help!