Integrated circuit identification system

• US 6,230,270 B1
• Filed: 01/02/1998
• Issued: 05/08/2001
• Est. Priority Date: 01/03/1997
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Laczko, Frank L. Sr.
• Primary Examiner(s): Dharia, Rupal
• Application Number:
  US09/002,464
• Time in Patent Office: 1,222 Days
• Field of Search: 377/28, 377/20, 348/525, 348/476, 348/180, 327/149, 327/151, 327/153, 340/825.25, 713/200
• US Class Current: 726/34
• CPC Class Codes: G06F 11/006 Identification G06F11/2289 takes precedence
• CPC Class Codes: G11C 16/22 Safety or protection circuits preventing unauthorised or accidental access to memory cells

Abstract

An improved integrated circuit including decryption functions employs a method for determining if its environment has been modified, by providing a first VCXO as part of the integrated circuit, providing a second VCXO, adjusting one of the VCXOs in a first preselected manner, determining a first frequency count of the adjusted VCXO during a first preselected time interval using the other VCXO, adjusting the one of the VCXOs in a second preselected manner, determining a second frequency count of the adjusted VCXO during the first preselected time interval using the other VCXO, averaging the first and second frequency count to provide an average frequency count, adjusting the average frequency count in a predetermined manner, and comparing the adjusted average frequency count to a previously stored, determined, or provided average frequency count to determine if the environment of the integrated circuit has been modified.

Claims

1. A method for determining if a system in which an integrated circuit is operating has been altered, changed or modified, comprising:

providing a first voltage controlled crystal oscillator (“

VCXO”

) as part of said integrated circuit,

providing a second VCXO as part of said system or said integrated circuit,

adjusting one of said VCXOs in a first preselected manner,

determining a first frequency count of said adjusted VCXO during a first preselected time interval determined by said other VCXO, and

comparing said frequency count to a previously stored, determined or provided frequency count to determine if said system in which said circuit is operating has been altered, changed or modified.

2. The method of claim 1, wherein said determining step includes monitoring output cycles of said adjusted VCXO and determining how many of said adjusted VCXO output cycles occur during the time interval.

3. The method of claim 1, including defining the time interval, said defining step including monitoring output cycles of said other VCXO, ascertaining a period of time occupied by a predetermined number of consecutive output cycles of said other VCXO, and using said ascertained period of time as the time interval.

4. The method of claim 3, wherein said ascertaining step includes producing a first indication of a beginning of said period of time, counting a predetermined number of consecutive output cycles of said other VCXO that occur immediately after said first indication and, when said counting step reaches said predetermined number, providing a second indication of an end of said period of time.

5. The method of claim 4, wherein said determining step includes monitoring output cycles of said adjusted VCXO and determining how many of said adjusted VCXO output cycles occur between said first indication and said second indication.

6. The method of claim 3, wherein said ascertaining step includes dividing the output of said other VCXO.

7. A method for determining if an environment in which an integrated circuit operates has been modified, comprising:

providing a first voltage controlled crystal oscillator (“

VCXO”

) as part of said integrated circuit,

providing a second VCXO as part of said environment or said integrated circuit,

adjusting one of said VCXOs in a first preselected manner,

determining a first frequency count of said adjusted VCXO during a first preselected time interval determined by said other VCXO,

adjusting said one of said VCXOs in a second preselected manner,

determining a second frequency count of said adjusted VCXO during said first preselected time interval determined by said other VCXO,

averaging said first and second frequency count to provide an average frequency count,

adjusting said average frequency count in a predetermined manner, and

comparing said adjusted average frequency count to a previously determined average frequency count to determine if said environment in which said circuit operates has been modified.

8. The method of claim 7, wherein said determining steps include monitoring output cycles of said adjusted VCXO and determining how many of said adjusted VCXO output cycles occur during the time interval.

9. The method of claim 7, including defining the time interval, said defining step including monitoring output cycles of said other VCXO, ascertaining a period of time occupied by a predetermined number of consecutive output cycles of said other VCXO, and using said ascertained period of time as the time interval.

10. The method of claim 9, wherein said ascertaining step includes producing a first indication of a beginning of said period of time, counting a predetermined number of consecutive output cycles of said other VCXO that occur immediately after said first indication and, when said counting step reaches said predetermined number, providing a second indication of an end of said period of time.

11. The method of claim 10, wherein said determining steps include monitoring output cycles of said adjusted VCXO and determining how many of said adjusted VCXO output cycles occur between said first indication and said second indication.

12. The method of claim 9, wherein said ascertaining step includes dividing the output of said other VCXO.

13. A method for generating a unique electronic signature for an integrated circuit, comprising:

providing a first voltage controlled crustal oscillator (“

VCXO”

) as part of said integrated circuit,

providing a second VCXO as a part of said integrated circuit or an external circuit associated with said integrated circuit,

adjusting one of said VCXOs in preselected manner, and

determining a unique electronic characteristic from said adjusted VCXO during a preselected time interval determined by said other VCXO.

14. The method of claim 13, including defining the time interval, said defining step including monitoring output cycles of said other VCXO, ascertaining a period of time occupied by a predetermined number of consecutive output cycles of said other VCXO, and using said ascertained period of time as the time interval.

15. The method of claim 14, wherein said ascertaining step includes producing a first indication of a beginning of said period of time, counting a predetermined number of consecutive output cycles of said other VCXO that occur immediately after said first indication and, when said counting step reaches said predetermined number, providing a second indication of an end of said period of time.

16. The method of claim 14, wherein said ascertaining step includes dividing the output of said other VCXO.

17. Circuitry for generating a unique electronic signature for an integrated circuit, comprising:

a first voltage controlled crystal oscillator (VCXO) which is a portion of said integrated circuit;

a second VCXO which is a portion of said integrated circuit or an external circuit associated with said integrated circuit;

a counter coupled to said first VCXO for producing a frequency count of said first VCXO by counting output cycles of said first VCXO; and

said counter also coupled to said second VCXO and responsive to output cycles produced by said second VCXO for counting a number of output cycles of said first VCXO that occur during a time interval derived from said output cycles of said second VCXO.

18. The circuitry of claim 17, including a further counter coupled to said second VCXO for deriving said time interval by counting a predetermined number of consecutive output cycles of said second VCXO, said further counter having an output coupled to said first-mentioned counter for indicating when said predetermined number of output cycles of said second VCXO have been counted.

19. The circuitry of claim 18, wherein said further counter includes a divider circuit.