Abstract: A Complementary Metal Oxide Semiconductor (CMOS) power switching circuit and a method for operating a CMOS power switching circuit are described. In one embodiment, a CMOS power switching circuit includes a voltage selection circuit configured to output the highest output voltage between an output voltage of a primary power supply and an output voltage of a backup power supply and a control circuit configured to connect a load circuit to either the primary power supply or the backup power supply by comparing the output voltage of the primary power supply with a power supply switchover level that is set as a function of the highest output voltage. The backup power supply serves as a voltage reference to set the power supply switchover level only when the output voltage of the primary power supply is lower than the output voltage of the backup power supply. Other embodiments are also described.

Abstract: An electronic timekeeping circuit and a method for operating an electronic timekeeping circuit are described. In one embodiment, an electronic timekeeping circuit includes power supplies and timekeeping circuit components that are grouped into power supply domains. Power is supplied to each of the power supply domains by a corresponding one of the power supplies. Timekeeping registers are duplicated for each of the power supply domains. The timekeeping registers are synchronized between the power supply domains if one of the timekeeping registers is modified or if one of the power supplies is turned off and subsequently turned back on. Other embodiments are also described.

Abstract: A Complementary Metal Oxide Semiconductor (CMOS) power switching circuit and a method for operating a CMOS power switching circuit are described. In one embodiment, a CMOS power switching circuit includes a voltage selection circuit configured to output the highest output voltage between an output voltage of a primary power supply and an output voltage of a backup power supply and a control circuit configured to connect a load circuit to either the primary power supply or the backup power supply by comparing the output voltage of the primary power supply with a power supply switchover level that is set as a function of the highest output voltage. The backup power supply serves as a voltage reference to set the power supply switchover level only when the output voltage of the primary power supply is lower than the output voltage of the backup power supply. Other embodiments are also described.

Abstract: An electronic timekeeping circuit and a method for operating an electronic timekeeping circuit are described. In one embodiment, an electronic timekeeping circuit includes power supplies and timekeeping circuit components that are grouped into power supply domains. Power is supplied to each of the power supply domains by a corresponding one of the power supplies. Timekeeping registers are duplicated for each of the power supply domains. The timekeeping registers are synchronized between the power supply domains if one of the timekeeping registers is modified or if one of the power supplies is turned off and subsequently turned back on. Other embodiments are also described.