Circuit for "waking up" a microprocessor power supply, in particular for an ID card in a car remote control system

Claim 1

In a portable card including a microprocessor, RF receiving means for receiving a RF signal for waking-up said microprocessor, said signal being transmitted by an on-board electronic module of an automotive vehicle adapted to control given functions of said vehicle, RF transmitting means for transmitting to said electronic module an RF identification signal, and a low capacity battery for powering said portable card, a wake-up circuit for switching said microprocessor from a sleeping state to a woken-state, wherein said signal transmitted from said electronic module to said portable card comprises a given plural number of successive control pulses of given period, and wherein said circuit comprises: converter means for outputting a variable electric signal, connected to said receiving means and including means for increasing the level of said variable electric signal, different from said pulses, by a predetermined value from a reference level each time a first pulse is received by said circuit from said receiving means, means for increasing the level of said variable electric signal by said predetermined value from its actual level each time a subsequent pulse is received by said circuit from said receiving means, and means for gradually decreasing the level of said variale electric signal between the reception of two subsequent pulses, and means for comparing the level of said variable electric signal with a predetermined threshold value and for producing a wake-up signal for said microprocessor only when said level has reached said threshold value, whereby said microprocessor is woken-up only when a given plural number of control pulses have been received and the frequency of said control pulses is not less than a predetermined frequency.