Oscillators – Automatic frequency stabilization using a phase or frequency... – Plural oscillators controlled
Reexamination Certificate
1999-09-29
2001-04-03
Grimm, Siegfried H. (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Plural oscillators controlled
C331S014000, C331S016000, C331S025000, C713S501000
Reexamination Certificate
active
06211740
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to switching a clocked device from an initial frequency to a target frequency.
When switching the frequency of a device's internal clock from an initial to a target frequency, the target frequency should remain in phase with a master external clock. In microprocessors and other clocked devices, this is done using a phase locked loop (“PLL”).
Typically, frequencies are changed in a clocked device by placing the device in an idle state, changing the frequency to the target frequency, and locking the device's PLL in phase with the target frequency. The length of the idle state required for the changing and locking to occur slows down device operation.
SUMMARY OF THE INVENTION
In general, in one aspect of the invention, a clocked device is switched from an initial frequency to a target frequency by locking a first PLL to the target frequency while a second PLL is driving a clock distribution network at the initial frequency. The first PLL is then substituted for the second PLL on the clock distribution network.
Among the advantages of the invention may be one or more of the following. Frequency switching can be effected relatively seamlessly, with little or no idle time between operation at different frequencies (called “switching latency”). Reductions in idle time make it possible to change device frequencies gradually, thereby reducing transient currents in the device.
Frequency switching also permits devices to change their operational speed and power consumption. For example, operation at higher frequencies requires more power than operation at lower frequencies. Accordingly, it is possible to cause the device to enter a low-power mode by switching from a high to a low device operational frequency.
Other advantages and features of the invention will become apparent from the following description and the claims.
REFERENCES:
patent: 4659999 (1987-04-01), Motoyama et al.
patent: 5434888 (1995-07-01), Fukuchi
patent: 5838205 (1998-11-01), Ferraiolo et al.
Dai Xia
Wong Keng
Fish & Richardson P.C.
Grimm Siegfried H.
Intel Corporation
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