I am designing a high frequency passive RFID tag-like device that receiving 27MHz wireless power, use it to power a onboard MCU and a low power transmitter. The estimated current drain is about 50mA. You may say this is a huge amount power for a passive RFID tag, moreover, the distance between the reader and tag will be 46cm maximum. However, in our application, we will have a powerful(25W) reader for this application. My specific question here is about the power receiver. I have two available options. First one use diode and capacitor for a voltage multiplier, which is very common seen on RFID article, then follow by overvoltage protection and linear regulator, like this in following picture: Comments:
Because of the high frequency of incoming power, I can use rather small(100nF) capacitor in voltage multiplier.
I add an overvoltage protection on linear regulator input(LT3065's Vin max up to 45V) for situation where the tag is occasionally brought too close to reader. M1 will start to draw excessive current when LT3065's input larger than about 20V.
I will use schottky diode whose trr<<40nS for this 27MHz input power.
I don't know how to deal with the transmitter and receiver coil, so I just left the receiver coil to a sine signal with a roughly(guess) amplitude. How can I model its parameter, like Rser? I noted the output of voltage multiplier depends on it.
So, will this circuit work?
********updated on 2.13:
I found a signal generator with maximum 1W output power to simulate the transmitter. For convenience and test purpose, I used a NFC antenna transmitter coil(2.1uH at 13.56MHz) at hand with the signal frequency changed to 13.56MHz. For maximum transmitting current, I add a capacitor(actually three, according to this app note by Atmel, for better trimming) serial with the transmitter coil for serial resonance at 13.56MHz. So the transmitter circuit just looks like below. Because the signal generator's output impedance is 50Ohm, and ought to be used with 50Ohm load. 100mW output power means about 6.3V amplitude on sine wave voltage source(Am I right?). So I will get about 120mA(I actual measured about 100mA with a serial 5Ohm resistor with oscilloscope) transmit coil current for the transmitter. Is this approach for optimal(longest) operating distance right? Should I use a power amplifier whose output impedance is much smaller instead of 50Ohm for a larger transmitter coil current?