US 7,460,966 B1Granted

Microcontroller that maintains capacitors of an analog circuit in a charged state during low power operation

AssigneeZilog, Inc.

InventorHidefumi Hattori

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Abstract

An analog circuit of a microcontroller includes a switch that is coupled in series with a capacitor of the analog circuit. During nominal power mode operation, an operational voltage is present on the capacitor. The switch is conductive so that the capacitor is switched into the analog circuit and so that the capacitor operates as part of the analog circuit. At the beginning of sleep mode operation, the switch is made nonconductive thereby effectively switching the capacitor out of the analog circuit and storing the operational voltage on the capacitor. When the analog circuit is powered up again after sleep mode operation, the switch is made conductive to switch the capacitor back into the analog circuit. Because the capacitor still holds a substantial voltage, analog circuit wake up time is reduced because the time required to charge the capacitor up to its operational voltage is reduced.

Claims20

Dependent claims

A method comprising:

(a) operating a microcontroller in a nominal power mode, wherein the microcontroller comprises a digital circuit and an analog circuit, wherein in the nominal power mode both the digital circuit and the analog circuit are powered, wherein the analog circuit comprises a capacitor and a switch, the switch being coupled in series with the capacitor, the capacitor having a capacitance of at least one half picofarad, wherein a first voltage is present across the capacitor when the microcontroller is operating in the nominal power mode;
(b) terminating microcontroller operation in the nominal power mode and beginning microcontroller operation in a low power mode, wherein said terminating and beginning comprises:
(b1) making the switch substantially nonconductive such that the first voltage is stored on the capacitor;
(b2) unpowering the analog circuit;
and
(b3) unpowering the digital circuit;
(c) operating the microcontroller in the low power mode, wherein during the low power mode the switch is substantially nonconductive;
and
(d) terminating microcontroller operation in the low power mode and beginning microcontroller operation in the nominal power mode, wherein said terminating and beginning comprises:
(d1) making the switch substantially conductive, wherein immediately before the switch is made substantially conductive a non-zero second voltage was present across the capacitor;
(d2) powering the analog circuit;
and
(d3) powering the digital circuit.

10 more elements

Dependencies are inferred from the claim text.