RF ID Tag

I'm no electrical engineer, but given the amount of power that your circuit is consuming, you might just want to consider a battery as a power source. I did a quick google search and did some maths... An "N" Cell battery ought to power your device continuously for almost 30,000 hours. However, I reserve every right to be completely wrong.

Why not use the radiated energy as the power source?

So when the tag is near the target the radiated field is used to power it, similar to having a 'ghost' power supply.

John.

Have you tried TI, National Semiconductor, or Power Integrations Websites? They have a number of simple circuits for micropower. I can't recommend anything specific since you didn't mention input voltage on the AC side and output voltage on the DC side. Many of these circuits are also available in a preassembled kit which can get you up to speed pretty quick. I suggest looking for those circuits designed for the new LED's which consume power in the range you are looking at. For that matter, you could buy an LED based nightlight and disconnect the LED's and tap into the power there as well.

When it comes to RFID schemes there are a number of home grown approaches, so your operating voltage and current will affect your battery life. If it is optimized around the battery's normal voltage range (as it starts to wear down) then you will maximize your amp/hour life of your battery. There are a number of effects which will change your actual realized battery life: temp, duty cycle, and max current to name a few.

Another option, depending on your skill, is to modify or buy an existing multi-output voltage Wall-wart - yes, they are like big warts on the wall. Since your power requirement is quite low, you could also try a spare cell phone charger, some of which are unbelievably compact (like the Sanyo's).

Hope one of these ideas helps.

Thanks for the ideas, they actually helped a lot! When I was looking at manufacturers who made the ADC's they all operated at a way higher wattage than I needed. I still need to do more calculations for other values (such as AC input and DC output) based on the specs I'm given, so once I do that I'll have a better idea of what i can use.

A tranceiver is also being build with the tag by other people in the group. The tag is powered by the power that's transferred in the AC signal it receives, so I don't need a battery for my design, I just need to work with what I'm given and have enough power left to send a signal back.

Thanks again for all your help! Any more suggestions are definitly welcome!