I am designing a SIM card with RF radio included. The radio with its CPU needs minimum 2.7V to run. The current consumption is my problem: - for a period of 50msec (during transmission), it requires 100mA or more - for the same period afterwards, there is an idle period where it needs less than 10mA
The SIM card is plugged into any cell phone, which supplies on the SIM connector 3V/50mA guaranteed.
My idea is to take advantage of my radio idle period, charge something up, and add that charge to my high demand period.
In short: - supply to SIM card from the phone is 3V / 50mA (no more current allowed) - the SIM circuit requires 2.7V minimum, but the consumption needs to alternate between 10/100mA (50mA supply is not sufficient)
Sound like 'just add a capacitor'... but here is my last obstacle: SIM card is TINY, we have a total of about 8 x 10mm
We have tried to use a charge-pump to hold the 2.7V for as long as possible, but unless we are wrong, the capacitance needed is 1mF which we do not see how to do in the small size we have available.
Anybody has any smart idea how to solve this?