The FETs need a significant gate voltage (relative to the source) to turn on. Without a separate gate control for the top FETs, they will be far less efficient that schottky diodes and never conduct at 0.5V.
I cannot read the FET numbers in the diagram so cannot look up the specifications.
Note that with 0.5V RMS in and a hypothetical perfect rectifier, you would only get 0.707V out of that circuit and not 1.5V
I think we need to know what your load is, how you plan on stepping up a 0.5vAC source to 1.55vdc. Rectifying, even with an ideal rectifier, does not get a 0.5 v sine wave (rms, peak, peak-to-peak, average) to 1.55v. I don't know how you are getting there.
how much current are you hoping to deliver to your load - and what is your load?
And Sheldon Copper from The Big Bang Theory was completely wrong about the best number being 73The best number is, 0.5^0.5. Or, as crutschow approximates,
ok, but are you trying to...
- build an energy harvesting system (hand-cranked generator or similar) to rectify and then use the power? In this case it wouldn't make any sense to add battery operated components to actively rectify the signal.
Or,
- monitor an AC signal from another system so you can add batteries or other power supply to power microcontroller, Mosfets and more?