Hi

I am designing a wireless biomedical implant in TSMC's 0.18um CMOS process (It is very similar to RFID design). RF frequency is 13.56MHz. My question is about the half-wave rectifier of my transponder. I doubt which of the following structures will give better results:

1) Using  P+/N-well diode (P+ connected to antenna and N-well connected to Vdd)
2)  Using P-sub/n+ diode (P-sub is obviously ground, and n+ is connected to antenna.

I know that it's better that the rectifying diode has lower ON voltage and higher reverse breakdown voltage as well as lower series resistance, but I don't which of the above structures better satisfies these requirements.

I greatly appreciate it if you inform me about other things I should consider for the design of rectifier.

Many thanks,