I have found an interesting simultaneous wireless information and power transfer concept where two MOSFETs are used as switches to switch two other resonant capacitors. Because of the switching in the secondary circuit, current amplitude changes can be noticed in the primary circuit. I believe this modulation method is called BASK (Binary Amplitude Shift Keying). Back telemetry is what I am interested in.
What I understand so far is that when the extra capacitors, that are added parallel to the LC circuit, are switched, they will change the resonant frequency of the secondary side, therefore, the current amplitude of the primary side will change.
I tried simulating this circuit and I came up with two questions:
What could be the second MOSFET for (Figure 1)? I do not see any difference in the current amplitude of the primary side after removing it.
Why the amplitude decreases rather than increases when MOSFET is switched (Figure 2)? The only thing I came up with is that perhaps depletion instead of enhancement MOSFETs are used in the offered concept, but also then I am not sure why it would be better in this way if that is the case.
Any ideas/answers would be much appreciated! Thank you.