Waferscale Integration, Inc.

Chang Hee Hong

Boaz Eitan

John H Pasternak

A switching circuit for switching between a main power supply and a battery power supply includes a comparator, a p-channel battery power transfer transistor, a p-channel main power transfer transistor and an inverter. The comparator operates on the main power supply and is connected on input to the main power supply and to the battery power supply. The comparator compares the voltage level of the main power supply with the voltage level of the battery power supply and provides a selection signal which is low when the voltage level of the battery power supply is higher than the voltage level of the main power supply. The p-channel battery power transfer transistor is controlled by the selection signal and transfers the battery supply signal to a switched power supply node. The inverter operates on the battery power supply and inverts the voltage level of the selection signal. The p-channel main power transfer transistor is controlled by the inverter and transfers the main power supply to the switched power supply node.

Backup battery switch

The present invention is a battery backed output buffer which provides a well-defined signal, even during battery power. The buffer includes a regular output buffer for providing output data during operation with a main power supply and for switching to a tri-state during battery power. The buffer also includes a configurable battery backed output buffer which provides a predetermined output signal during battery operation and produces a signal in the tri-stated during main power operation.

Battery backed configurable output buffer

A unit for maintaining the value of information regarding the state of a device during battery power includes one local latch per bit of state to be maintained. The latch is powered by a switched power supply which switches between main and battery power supplies. The latch latches the value of the bit of state when the value of the bit of state is valid and the power of the device is significant and maintains the value otherwise, typically during battery operation.

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Fremont, CA, United States of America

Chang Hee Hong