Calibration of integrated circuit time constants

• US 6,842,710 B1
• Filed: 08/22/2002
• Issued: 01/11/2005
• Est. Priority Date: 08/22/2002
• Status: Active Grant

• Current Assignee: Tamiras Per Pte Ltd LLC (Intellectual Ventures LLC)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Jensen, Brent R., Gehring, Mark Richard
• Primary Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US10/226,911
• Time in Patent Office: 873 Days
• Field of Search: 702/107, 702/85, 702/65, 324/601, 324/615, 324/658, 324/711, 327/344, 327/337
• US Class Current: 702/107
• CPC Class Codes: G01R 31/2884 using dedicated test connectors, test elements or test circuits on the IC under test G01R31/2855 takes precedence
• CPC Class Codes: H03H 11/1291 Current or voltage controlled filters
• CPC Class Codes: H03H 2210/021 Amplifier, e.g. transconductance amplifier
• CPC Class Codes: H03H 2210/043 by measuring time constant

Abstract

A method and system for calibrating a time constant within an integrated circuit. A voltage storage element is charged, and the time required to achieve a reference voltage on the storage element is measured. The measured time is compared to a desired time. It necessary, an adjustable impedance is modified to change the charging time, and the cycle may be repeated until the charging time matches the desired time. In this novel manner, an actual RC time constant, as rendered in a particular integrated circuit, is measured and potentially adjusted to match a desired time constant. Advantageously, configuration information of the adjustable impedance may be communicated to other circuitry within the integrated circuit to enable such circuitry to implement the same RC time constant in analog signal processing. Consequently, embodiments of the present invention overcome incidences of wide tolerance in passive components implemented in integrated circuits. Beneficially, no external test equipment is required.

Claims

1. A method of calibrating an integrated circuit time constant comprising:

charging a voltage storage element on said integrated circuit;

measuring a charge time required for a voltage of said voltage storage element to match a reference voltage;

adjusting an impedance on said integrated circuit to make said charge time approximately equal to a desired time constant value, wherein said adjusting comprises successive approximation; and

based on an adjustment configuration determined by said adjusting, configuring a second circuit on said integrated circuit to have substantially said desired time constant value.

2. The method of calibrating a time constant as described in claim 1 wherein said voltage storage element is a capacitive element.

3. The method of calibrating a time constant as described in claim 1 wherein said impedance comprises a plurality of substantially passive elements.

4. The method of calibrating a time constant as described in claim 3 wherein said plurality of substantially passive elements are selectively combinable to form a range of impedances.

5. The method of calibrating a time constant as described in claim 3 wherein said plurality of substantially passive elements comprise a binary sequence of element values.

6. The method of calibrating a time constant as described in claim 3 wherein said plurality of substantially passive elements are resistive.

7. The method of calibrating a time constant as described in claim 3 wherein said plurality of substantially passive elements are capacitive.

8. The method of calibrating a time constant as described in claim 1 wherein said measuring comprises incrementing a counter until said voltage stored on said voltage storage element matches a reference voltage.

9. The method of calibrating a time constant as described in claim 1 further comprising initializing a voltage stored on said voltage storage element to be substantially ground.

10. The method of calibrating a time constant as described in claim 9 further comprising repeating said initializing, charging, measuring and adjusting if said time is less than said desired time constant.

11. The method of claim 1 wherein said adjusting comprises switching a plurality of switchable capacitors to obtain said charge time.

12. An electronic circuit for calibrating a time constant comprising:

a current source having a current output that is determined by a resistance and a voltage reference;

a variable impedance coupled to said current source;

a voltage storage element coupled to said current source for charging by said current source;

a voltage comparator coupled to said voltage reference and to said voltage storage element for comparing a voltage of said voltage storage element to a voltage of said voltage reference;

a counter coupled to said voltage comparator to measure the charge time required for said voltage of said voltage storage element to substantially equal said voltage of said voltage reference; and

a circuit for adjusting said variable impedance until said charge time is substantially equal to a desired time constant, wherein said adjusting comprises successive approximation.

13. The electronic circuit as described in claim 12 further comprising a switch for initializing a voltage on said voltage storage element to be substantially ground.

14. The electronic circuit as described in claim 12 wherein said voltage storage element comprises said variable impedance.

15. The electronic circuit as described in claim 12 wherein said resistance comprises said variable impedance.

16. The electronic circuit as described in claim 12 wherein said variable impedance comprises a first plurality of substantially passive elements wherein said passive elements are selectively combinable to form a range of impedances.

17. The electronic circuit as described in claim 16 wherein said first plurality of substantially passive elements comprise a binary sequence of element values.

21. The electronic circuit as described in claim 16 wherein said successive approximation comprises sequentially switching elements of said variable impedance.

18. In an electronic circuit, a method of calibrating a time constant comprising:

charging a voltage storage element of said electronic circuit;

measuring a time required for a voltage of said voltage storage element to match a reference voltage as a charge time wherein said charge time is dependent on a impedance; and

adjusting said impedance of said electronic circuit to make said charge time approximately equal a desired time constant, wherein said adjusting comprises successive approximation.

19. The method of calibrating a time constant as described in claim 18 wherein said impedance comprises a plurality of substantially passive elements.

20. The method of calibrating a time constant as described in claim 19 wherein said plurality of substantially passive elements are selectively combinable to form a range of impedances.