I strongly suspect that PSoC 5LP can only deal with positive signals.
You are positively right with your assumption. Any signal into the PSoC has to be >= GND and <= VDDA.
1. For AC signals you may use RC-shifting network (check this thread and EDN reference inside)
2. use capacitive input similar to shown on the picture attached.
3. Please look into Cypress ANs attached (Precision Rectifier, Modulation-Demodulation, SIO Tips)
Thanks for confirming, Bob Marlowe!
odissey1, I'll consider all these material that you posted, then I'll make some experiments and tests with them. Thanks a lot!