Test system including a local trigger signal generator for each of a plurality of test instruments

• US 5,717,704 A
• Filed: 04/16/1996
• Issued: 02/10/1998
• Est. Priority Date: 04/16/1996
• Status: Expired due to Term

• Current Assignee: Xcerra Corporation (COHU Incorporated)
• Original Assignee: LTX Corp. (COHU Incorporated)
• Inventors: Rosenfeld, Eric H.
• Primary Examiner(s): Nguyen, Hoa T.
• Application Number:
  US08/633,172
• Time in Patent Office: 665 Days
• Field of Search: 371/25.1, 371/20.1, 371/21.1, 371/21.2, 371/22.1, 324/158.1, 324/158 R, 324/73.1, 324/750
• US Class Current: 714/736
• CPC Class Codes: G01R 13/32 Circuits for displaying non-recurrent functions such as transients; Circuits for triggering; Circuits for synchronisation; Circuits for time-base expansion
• CPC Class Codes: G01R 31/2882 Testing timing characteristics
• CPC Class Codes: G01R 31/31922 Timing generation or clock distribution G01R31/3191 takes precedence

Abstract

A local trigger signal generator is provided for each of a plurality of test instruments in a test system. The disclosed test system includes a master clock generator that defines a start time t₀ and generates a periodic master clock signal characterized by a master clock oscillation frequency f_mc and a corresponding period T_mc. The master clock generator generates a clock network signal that is representative of the master clock signal and the start time t₀. The system further includes a set of n test instruments TIN1, TIN2, . . . TINn. An ith one of the test instruments TINi includes a local clock receiver for receiving the clock network signal and defining therefrom a local start time t₀ i and for generating therefrom a local timestamp signal LTSSi, where the local timestamp signal LTSSi is representative of a number of time intervals having a length substantially equal to the period T_mc occurring after the local start time t₀ i. The ith test instrument also stores one or more local trigger values and generates one or more local trigger signals LTGSi when the local timestamp signal LTSSi equals one or more of the local trigger values.

Claims

1. A test system for testing a device under test (DUT), said system comprising:

A. a master clock generator for defining a start time t₀ and for generating a periodic master clock signal characterized by a master clock oscillation frequency f_mc and a period T_mc and for generating a clock network signal representative of said master clock signal and of said start time t₀ ; and

B. a set of n test instruments TIN1, TIN2, . . . TINn, where n is an integer, an ith one of said test instruments TINi including a local clock receiver LCRi for receiving said clock network signal and for defining therefrom a local start time t₀ i and for generating therefrom a local timestamp signal LTSSi representative of a number of time intervals having a length substantially equal to said period T_mc occurring after said local start time t₀ i, said ith test instrument including means for storing one or more local trigger values and including means for generating one or more local trigger signals LTGSi when said local timestamp signal LTSSi equals one or more of said local trigger values, for all i from one to n.

2. A system according to claim 1, wherein one or more of said test instruments includes means, responsive to one of said local trigger signals, for applying a stimulus signal to said DUT.

3. A system according to claim 1, wherein one or more of said test instruments includes means, responsive to one of said local trigger signals, for receiving a responsive signal from said DUT and for measuring said responsive signal.

4. A system according to claim 1, further comprising a clock distribution network for distributing said clock network signal to each of said test instruments.

5. A system according to claim 4, wherein said clock distribution network comprises a non-homogeneous medium.

6. A system according to claim 4, wherein said clock distribution network comprises a homogeneous medium.

7. A system according to claim 4, wherein said clock distribution network comprises a transmission medium coupled to said master clock generator and to one of said test instruments, said transmission medium being selected from the group consisting of wire, wireless, cable, printed circuit, optical, fiber optic, infrared, and waveguide type transmission mediums.

8. A system according to claim 1, wherein said master clock generator includes means for generating a start signal indicative of said start time t₀.

9. A system according to claim 8, wherein said master clock generator includes means for modulating said start signal onto said master clock and thereby generating a modulated signal, and wherein said clock network signal comprises said modulated signal.

10. A system according to claim 8, wherein said clock network signal includes said master clock signal and said start signal.

11. A system according to claim 8, wherein said master clock generator includes counter means for receiving said start signal and said master clock signal and for generating a master timestamp signal representative of a number of periods T_mc of said master clock signal occurring after said start time t₀, and wherein said clock network signal comprises said master timestamp signal.

12. A system according to claim 1, wherein at least one of said test instruments includes a local event message generator for generating an event message in response to a particular event, said event message being representative of said particular event.

13. A system according to claim 12, wherein said event message is further representative of an occurrence time of said particular event.

14. A system according to claim 13, wherein said occurrence time is indicated by a sampled value of one of said local timestamp signals.

15. A system according to claim 12, wherein one or more of said test instruments includes a local event receiver for receiving said event message, said one or more of said test instruments further including means for generating one or more local trigger signals in response to said event message.

16. A system according to claim 15, further including an event message network for receiving said event message from said at least one of said test instrument and for transmitting said event message to others of said test instruments.

17. A system according to claim 16, wherein said event message network is homogeneous.

18. A system according to claim 16, wherein said event message network is non-homogeneous.

19. A system according to claim 16, wherein said event message network comprises a transmission medium being selected from the group consisting of wire, wireless, cable, printed circuit, optical, fiber optic, infrared, and waveguide type transmission mediums.

20. A system according to claim 12, further including a shared event coordinator for receiving event messages from said at least one of said test instruments and for detecting an occurrence of a predefined sequence of said event messages and for generating an event message in response to said sequence.

21. A system according to claim 1, wherein a jth one of said test instruments, TINJ, includes time interpolator means for receiving a jth one of said local timestamp signals, LTSSj, and for generating therefrom an improved resolution local timestamp signal IRTSSj, said improved resolution local timestamp signal IRTSSj having a most significant portion that is substantial equal to said local timestamp signal LTSSj, and said improved resolution local timestamp signal IRTSSj having a least significant portion that is representative of fractional increments of said local timestamp signal LTSSj, wherein j is an integer greater than or equal to one and less than or equal to n.

22. A system according to claim 21, wherein said jth test instrument TINj includes means for generating one or more of said local trigger signals LTGSj when said improved resolution local timestamp signal IRTSSj equals one or more of said local trigger values.

23. A system according to claim 1, wherein said DUT is characterized by a time reference frame and wherein one of said test instruments is characterized by a time reference frame that is defined by its local timestamp signal, said system further including means for measuring a time offset between said time reference frame of said DUT and said time reference frame of said one test instrument.

24. A system according to claim 23, wherein said local trigger values include offset components to compensate for said time offset between said time reference frame of said DUT and said time reference frame of said one test instrument.

25. A system according to claim 23, wherein said one test instrument includes a local event message generator for generating an event message in response to a particular event, said event message being representative of said particular event.

26. A system according to claim 25, wherein said event message is further representative of an occurrence time of said particular event.

27. A system according to claim 25, wherein said one test instrument includes means for sampling its local timestamp signal and generating a timestamp value when said one test instrument detects an occurrence of said particular event.

28. A system according to claim 27, wherein said event message includes said timestamp value.

29. A system according to claim 27, wherein said one test instrument includes means for generating an adjusted timestamp as a function of said timestamp value and of said time offset.

30. A system according to claim 29, wherein said event message includes said adjusted timestamp.

31. A system according to claim 1, further including logging means for recording said one or more trigger signals.

32. A system according to claim 24, wherein said logging means further includes means for recording selected portions of said local timestamp signals.

33. A system according to claim 1, further including additional test instruments that operate independently of said clock network signal.