I am trying to use a CD4051BM multiplexer to alternate between two 6MHz signals in order to read them separately with a frequency counter, but I can't manage to get the correct output. I have designed a small PCB where the CD4051BM is connected to an ATMega 2560 which is doing the counting. The CD4051BM is supplied with 12V and the inputs are for the two signals are in Y0 and Y3 so in order to get the Y0 and Y3 signals i need 000 and 011 on the respective select channels CBA. This input signals have an amplitude of 5Vp-p, however on the output channel of the MUX I am getting a 1Vp-p signal and that is not enough amplitude for the ATMega 2560 to do the counting properly, is there a reason for this voltage drop? How can I solve this?
Here I attach an image of the CD4051BM board layout :