design of rectifier for ultra low input power

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arezu

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Hi,
I want to design a rectifier using schottky diode (HSMS285x) for an ultra low input power (-20dBm) at 700MHz.
It is strange that efficiency is better with single diode than voltage doubler circuit or/and bridge diode, although half-wave is lost in single diode circuit!!!
but on high input power level (>10dBm), efficiency is direct proportion to the number of stages and diodes However, on the low input power level is in the inverse proportion.
why?!!
 

Even a Schottky loses a large portion of the waveform before
it begins to conduct, and the penalty applies at each stage in
a multiplier ladder. The only good rectifier for very low amplitude
inputs is a zero-VT MOSFET and even this will suffer on the
leak-back phase. A synchronous rectifier would be best but
that's a chicken / egg deal, can't work until the commutation
circuitry has powered up.

A resonant input circuit may help you, ringing up until the
diode starts to steal energy from the tank. A resonant
transformer with voltage gain, even better.
 

You cannot have a diode rectifier that rectifies without a forward drop or does not have a reverse leakage. That is forbidden by Maxwell's demon.

To rectify ultra low input power (perhaps much lower than the room temperature) you will need a source of energy- in terms of jargon, you will be needing active circuits.
 

The best signal diode for low level, high frequency signals is often a Back Diode (a tunnel diode operated in the reverse direction).
It has a very low forward drop at small currents. and it has a square-law characteristic which means the output rectified DC voltage is proportional to the signal power (the square of the voltage).
The are used extensively in a satellite system I worked on for detecting microwave signals in the GHz region.
 

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