Self-start circuits for low-power clock oscillators

Details Self-start circuits for low-power clock oscillators Self-start circuits for low-power clock oscillators

1999-11-30

2001-02-20

Mis, David (Department: 2817)

Oscillators

Electromechanical resonator

Crystal

C331S1160FE, C331S173000, C327S142000

Reexamination Certificate

active

06191662

ABSTRACT:

BACKGROUND
The present invention relates to oscillators and more specifically, to self-start circuits for such oscillators.
The popularity of portable computers and hand-held devices has made it desirable for new computer products to operate with low power. To accommodate these low power requirements, computer chips often employ circuits that determine when to enter or exit the low-power state.
FIG. 1
shows a typical system power supply
100
with a controller, such as an input/output (I/O) controller
102
.
The I/O controller
102
also contains power state control logic
104
and a real-time clock (RTC)
106
, as well as other peripheral devices (not shown). The controller
102
powers off (zero voltage) the I/O section of the chip during low-power states while the RTC
106
remains powered by either an auxiliary supply
118
or by a battery
118
. The RTC
106
is in a different power “well” than the rest of the chip, which allows the RTC
106
to be powered separately. Also in this separate power well is the power state control logic
104
that controls the power state of the system power supply
100
.
In most systems with low-power states, the power supply
100
has a main supply
120
and an auxiliary supply
118
. The main supply
120
is enabled when the {overscore (PwrEn)} input is active. The {overscore (PwrEn)} input is controlled by the LP STATE signal
122
of the power state control logic
104
. The controller
102
has internal timers and other inputs (not shown) that determine when to enter or exit the low-power state. VccAUX
118
is always active as long as the supply is plugged into the wall AC power in a desktop system or the main battery is present in a portable system.
The battery
114
provides back up to the auxiliary supply
118
if the supply is unplugged from the wall or the main battery is removed from the portable system. The auxiliary
118
and battery
114
supplies are “OR'ed” together by a diode network
108
,
110
. Since VccAUX
118
is always higher than the battery voltage while the supply
118
is on, it supplies current to VccRTC
124
. If the auxiliary supply
118
fails, the battery
114
supplies the current to VccRTC
124
. The resistor
112
in series with the diode
110
is a safety requirement for lithium batteries.
VccRTC
120
supplies power to the RTC
106
and to the power state control
104
. Both blocks need to have power in order to keep system time and state during lower-power states when the main supply voltages
120
are shut down.
Resume reset (ResumeRST)
126
is an input that detects if the voltage level on the VccRTC
124
has failed because the battery
114
is dead or absent and VccAUX
118
is off. The RC delay on ResumeRST
126
is used to reset the state of the power state control logic
104
, which allows the system to boot up. The ResumeRST signal
126
also enables a START signal to the RTC to ensure that the oscillator
116
is running.
When a battery is replaced or first inserted by a consumer or manufacturer, the oscillator may not self-start and thus needs “kicking.” Since the consequences of the oscillator not starting, especially in the hands of the consumer, are expensive, it is advisable to take as many opportunities as possible to ensure that the oscillator is running.
SUMMARY
A clock circuit includes an oscillator having a biasing node that causes the oscillator to enter a low-power state. The clock circuit also includes a kick-start circuit and a first mechanism. The kick-start circuit operates to provide an excitation to the oscillator, where the excitation enables the oscillator to start its oscillation. The first mechanism is configured to inhibit kick-start based on certain conditions, such as when the oscillator reaches a particular level capable of sustaining oscillation by itself or when the oscillator is already running.


REFERENCES:
patent: 5557243 (1996-09-01), Ho

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