How to power the Tag chip?

Folks,

Power recieved by the tag antenna is around few mirco watts (may be 10 uW).
Further this is rectified and voltage multipliers are used to increase the voltage level. This is one side of the coin.

How much power is required by the Tag chip? The tag chip has different modules like REctifier, Multiplier, Modulator and demodulator. What is the power requirement of those modules?
Rectifier can convert ac-dc with an efficiency of max 40-50%. Then voltage multipliers are used. Until what extent (level of i/p), the voltage has to be multiplied? I mean to ask whats the limit of voltage multipliers to be used.

The modulated signal sent from the reader antenna is receieved by the tag antenna. The same signal is sent to demodulator of tag. In order to demodulate 10uW of signal whatever received by tag antenna, one needs a high sensitive demod. How much power does demodulator consumes? Whats the power that gets dissipated?

I have googled but didn't get required info.
Hope someone can clarify this.

If anyone has documented their earlier work reg power analysis, please post it.

Thanks!