SYSTEMS AND METHODS FOR COMPENSATING FOR VARIATIONS OF THE OUTPUT OF A REAL-TIME CLOCK

• US 20090160569A1
• Filed: 12/19/2008
• Published: 06/25/2009
• Est. Priority Date: 12/20/2007
• Status: Active Grant

• Current Assignee: Pentad Design
• Original Assignee: Pentad Design Corporation
• Inventors: Gros, Richard A.
• Granted Patent: US 7,791,418 B2
• Time in Patent Office: Days
• US Class Current: 331/176
• CPC Class Codes: G04G 3/02 Circuits for deriving low frequency timing pulses from pulses of higher frequency pulse frequency dividers in general H03K23/00 - H03K29/00
• CPC Class Codes: G04G 3/04 Temperature-compensating arrangements
• CPC Class Codes: H03L 1/00 Stabilisation of generator output against variations of physical values, e.g. power supply
• CPC Class Codes: H03L 1/026 by using a memory for digitally storing correction values H03L1/025 takes precedence

Abstract

Method and systems are provided for adjusting real-time clocks to compensate for frequency offset, temperature effects, and/or aging effects.

Claims

1. A method for correcting offset of a real-time clock, comprising:

determining a frequency of an output of an oscillator, the frequency being represented as an integer (i) portion and a non-integer (ni) portion; and

counting a first number (a) of “

i”

oscillations and counting a second number (b) of “

i+x”

oscillations by dithering between “

i” and

“

i+x”

oscillations;

wherein an average of the first number (a) of “

i”

oscillations and the second number (b) of “

i+x”

oscillations is an effective number of oscillations that is approximately the same as the determined frequency.

2. The method of claim 1, wherein x=1.

3. The method of claim 1, wherein x>

1.

4. The method of claim 1, further comprising compensating for a frequency variation of the real-time clock caused by ambient temperature without knowing the ambient temperature.

5. The method of claim 1, wherein counting the second number (b) further comprises counting a second number (b) of “

i+1”

oscillations.

6. The method of claim 1, wherein counting the second number (b) further comprises counting a second number (b) of “

i+2”

oscillations.

7. The method of claim 1, wherein the first number (a) is greater than the second number (b).

8. The method of claim 1, wherein the second number (b) is greater than the first number (a).

9. The method of claim 1, wherein the first number (a) and the second number (b) are equal.

10. The method of claim 1, wherein all of the first number (a) of “

i”

oscillations are counted followed by all of the second number (b) of “

i+x”

oscillations.

11. The method of claim 1, wherein one of the first number (a) of “

i”

oscillations is counted followed by one of the second number (b) of “

i+x”

oscillations.

12. The method of claim 1, wherein “

ni”

is a fraction or a decimal.

13. A method for correcting offset of an oscillator of a real-time clock, comprising:

determining a frequency of an output of an oscillator, the frequency being represented as an integer (i) portion and a non-integer (ni) portion; and

counting a first number (a) of “

i”

oscillations and counting a second number (b) of “

i+1”

oscillations by dithering between “

i”

oscillations and “

i+1”

oscillations;

wherein an average of the first number (a) of “

i”

oscillations and the second number (b) of “

i+x”

oscillations is an effective number of oscillations that is the same as or approximately the same as the determined frequency.

14. A method for correcting offset of an oscillator of a real-time clock, comprising:

determining a frequency of an output of an oscillator, the frequency being represented as an integer (i) portion and a non-integer (ni) portion; and

counting a first number (a) of “

i”

oscillations and counting a second number (b) of “

i+1”

oscillations by dithering between “

i”

oscillations and “

i+x”

oscillations;

wherein a ratio of (first number (a)*i)+(second number (b)*(i+x)/(first number (a)+second number (b)) is an effective number of oscillations that is the same as or approximately the same as the determined frequency.

15. A real-time clock, comprising:

a frequency source,

a counter coupled to the frequency source and being configured to generate a count value based on an output of the frequency source; and

a controller coupled to the counter and being configured to adjust the counter to reflect the actual output of the frequency source by reading the count value from the counter based on the actual output of the frequency source to determine an actual frequency of the output of the frequency source, the frequency being represented as an integer (i) portion and a non-integer (ni) portion, counting a first number (a) of “

i”

oscillations and counting a second number (b) of “

i+1”

oscillations by dithering between “

i”

oscillations and “

i+1”

oscillations, wherein a ratio of (a*i)+(b*(i+1)/(a+b) is the same as or approximately the same as the determined frequency.

16. A system for compensating for age-induced frequency variations of an oscillator, comprising:

a counter;

a controller coupled to the counter; and

a non-volatile memory coupled to the controller,

wherein an age of the oscillator is tracked using the non-volatile memory, and the output of the non-volatile memory is provided to the controller, the controller adjusting the counter based on the output of the controller.

17. The system of claim 16, wherein the non-volatile memory is flash memory.

18. A system for correcting frequency variations of an oscillator, comprising:

a counter;

a controller coupled to the counter;

an analog-to-digital converter coupled to the controller;

a temperature sensor coupled to the analog-to-digital converter, wherein analog data from the temperature sensor is provided to the analog-to-digital converter, the analog-to-digital converter transforms the analog data into digital data, the digital data being provided to the controller, the controller being configured to adjust the counter based on the digital output of the analog-to-digital converter without knowing the temperature; and

a flash memory coupled to the controller, wherein an age of the oscillator is tracked using the flash memory, an output of the flash memory is provided to the controller, and the controller is configured to adjust the counter to compensate for the age of the oscillator based on the output of the controller related to the flash memory.

19. A method for calibrating a plurality of real time clocks, comprising,

receiving a plurality of real time clocks;

calibrating each real time clock using an off-chip frequency counter, an on-chip temperature measurement element and an on-chip analog-to-digital converter; and

programming each real time clock with customized calibration data.

20. A method for calibrating a real time clock, comprising,

receiving a real time clock having an on-chip temperature measurement element;

inserting the real time clock into an environmental chamber;

exposing the real time clock inside the environmental chamber to a plurality of temperatures;

measuring each temperature of the plurality of temperatures using the on-chip temperature sensor;

detecting the frequency of the output of each real time clock at each measured temperature;

determining a curve fit function based on the measured temperatures and frequencies; and

programming the real time clock with the determined curve fit function.

21. The method of claim 20, determining the curve fit function being based on data output by an analog-to-digital converter.

22. A method for calibrating and adjusting a real time clock, comprising:

calibrating the real time clock by

inserting the real time clock into an environmental chamber;

exposing an oscillator of the real time clock inside the environmental chamber to a plurality of temperatures;

measuring each temperature of the plurality of temperatures using an on-chip temperature sensor of the real time clock;

detecting the frequency of the output of the oscillator at each measured temperature;

determining a curve fit function based on the measured temperatures and frequencies;

programming the real time clock with the determined curve fit function;

correcting offset of the oscillator of the real-time clock by determining a frequency of an output of the oscillator, the frequency being represented as an integer (i) portion and a non-integer (ni) portion;

counting a first number (a) of “

i”

oscillations and counting a second number (b) of “

i+x”

oscillations by dithering between “

i” and

“

i+x”

oscillations, wherein an average of the first number (a) of “

i”

oscillations and the second number (b) of “

i+x”

oscillations is an effective number of oscillations that is approximately the same as the determined frequency; and

compensating for age-induced frequency variations of the oscillator using flash memory.