Parametric measurement of high-speed I/O systems

1. A method of using a phase comparator to test an input/output (I/O) circuit of a device under test, the method comprising:

receiving a signal at the device under test;

in the phase comparator, generating a phase signal in response to the signal;

feeding the phase signal from the phase comparator to a loop filter;

extracting the phase signal from the phase comparator prior to the loop filter; and

determining parametric information pertaining to the I/O circuit of the device under test from the phase signal extracted from the phase comparator prior to the loop filter.

2. The method of claim 1 , in which:

the I/O circuit comprises the phase comparator; and

the determining is performed internally to the device under test.

3. The method of claim 2 , in which:

the device under test additionally comprises a test access port; and

the method additionally comprises outputting the parametric information via the test access port.

4. The method of claim 1 , in which the determining is performed externally of the device under test.

5. The method of claim 4 , in which:

the I/O circuit comprises the phase comparator;

the device under test additionally comprises a test access port; and

the method additionally comprises outputting the phase signal via the test access port.

6. The method of claim 5 , additionally comprising subjecting the phase signal to data reduction prior to the outputting.

7. The method of claim 1 , in which:

the I/O circuit comprises a receiver circuit, the receiver circuit comprising the phase comparator and having an input coupled to the phase comparator;

the method additionally comprises:

providing a transmitter circuit having an input and an output, and

coupling the output of the transmitter circuit to the input of the receiver circuit; and

the receiving comprises receiving the signal at the input of the transmitter circuit.

8. The method of claim 6 , in which the I/O circuit additionally comprises the transmitter circuit.

9. The method of claim 1 , in which:

the I/O circuit comprises a transmitter circuit having an input and an output;

the method additionally comprises:

providing a phase comparator external to the device under test, and

coupling the output of the transmitter circuit to the input of the phase comparator; and

the receiving comprises receiving the signal at the input of the transmitter circuit.

10. The method of claim 1 , additionally comprising subjecting the phase signal to data reduction prior to the determining.

11. The method of claim 10 , in which the data reduction comprises one of filtering and compressing.

12. The method of claim 1 , in which the determining comprises determining one of transmitter random jitter (rj), transmitter deterministic jitter (dj) and transmitter harmonic jitter as the parametric information.

13. The method of claim 1 , in which the determining comprises determining one of receiver clock and data recovery proportional and integral loop constants, receiver input offset, receiver functional failure, receiver parametric failure, receiver equalization performance in-band harmonic frequency contamination, out-of-band harmonic frequency contamination and loop phase hunting behavior as the parametric information.

14. The method of claim 1 , in which:

the receiving comprises receiving the signal at the I/O circuit;

the I/O circuit comprises the phase comparator; and

the parametric information represents deviations between transition timings of the phase signal and nominal transition timings.

15. The method of claim 14 , in which the signal has a known transition timing accuracy.

16. The method of claim 1 , in which the parametric information additionally comprises average power spectral density.

17. The method of claim 1 , in which the receiving comprises receiving a pseudo-random bit sequence as the signal.

18. The method of claim 1 , in which the receiving comprises:

providing a bit sequence; and

periodically offsetting the bit sequence in phase by non-integer unit intervals to generate the signal.

19. The method of claim 1 , in which the receiving comprises:

providing a bit sequence; and

sinusoidally modulating the bit sequence in phase to generate the signal.

20. The method of claim 1 , in which the receiving comprises:

providing an input signal; and

subjecting the input signal to waveform degradation to provide the signal.

21. The method of claim 1 , in which the receiving comprises:

providing an input signal;

pre-emphasizing the input signal to provide a pre-emphasized input signal;

transmitting the pre-emphasized input signal to the device under test via a transmission medium, the transmitting subjecting the pre-emphasized input signal to waveform degradation; and

calibrating the pre-emphasizing to compensate for the waveform degradation.

22. The method of claim 21 , in which:

the transmitting comprises transmitting the pre-emphasized input signal through the transmission medium from a proximal end of to a distal end;

the pre-emphasizing applies a first pre-emphasis; and

the calibrating comprises:

terminating the distal end of the transmission medium with a reflecting termination,

at the proximal end of the transmission medium, subtracting the pre-emphasized input signal from a superposition of a de-emphasized reflected signal and the pre-emphasized input signal to obtain the de-emphasized reflected signal, the de-emphasized reflected signal resulting from reflection of the pre-emphasized input signal at the termination;

equalizing the de-emphasized reflected signal with a second equalization to obtain a reflected signal, the second equalization equal to the first equalization; and

adjusting the first equalization and the second equalization until the reflected signal matches the input signal.

23. The method of claim 1 , in which the extracting comprises converting a linear phase signal to a digital phase signal.

24. A test system for testing a device under test comprising an input/output (I/O) circuit, the test system comprising:

a phase tracking circuit comprising a phase comparator and a loop filter, the phase comparator operable to generate a phase signal and to feed the phase signal to the loop filter; and

a processing circuit connected to receive from the phase comparator prior to the loop filter the phase signal generated by the phase comparator, the processing circuit operable to determine parametric information pertaining to the I/O circuit from the phase signal received from the phase comparator prior to the loop filter.

25. The test system of claim 24 , in which the processing circuit is external to the device under test.

26. The test system of claim 24 , in which:

the I/O circuit comprises a receiver circuit; and

the phase tracking circuit constitutes part of the receiver circuit.

27. The test system of claim 26 , in which the processing circuit is internal to the device under test.

28. The test system of claim 26 , in which:

the processing circuit is external to the device under test; and

the test system additionally comprises a connection between the phase comparator and the processing circuit.

29. The test system of claim 26 , in which the processing circuit comprises a data reduction circuit internal to the device under test and an analyzer external to the device under test.

30. The test system of claim 29 , additionally comprising a communication link between the data reduction circuit and the analyzer.

31. The test system of claim 26 , in which:

the receiver circuit comprises an input; and

the test system additionally comprises a stress circuit preceding the input of the receiver circuit.

32. The test system of claim 26 , in which:

one of the I/O circuit and the test system comprises a transmitter circuit having an output; and

the phase tracking circuit has an input coupled to the output of the transmitter circuit.

33. The test system of claim 32 , in which the I/O circuit comprises the transmitter circuit.

34. The test system of claim 32 , in which the transmitter circuit is external to the device under test.

35. The test system of claim 32 , additionally comprising a stress circuit between the output of the transmitter circuit and the input of the receiver circuit.

36. The test system of claim 35 , additionally comprising an additional phase tracking circuit between the output of the transmitter circuit and the input of the stress circuit.

37. The test system of claim 36 , in which:

the I/O circuit comprises the transmitter circuit;

the additional phase tracking circuit comprises an additional phase comparator, the additional phase comparator generating an additional phase signal; and

the processing circuit is additionally connected to receive the additional phase signal and is additionally operable to determine additional parametric information pertaining to the I/O circuit from the additional phase signal.

38. The test system of claim 24 , in which:

the I/O circuit comprises a receiver circuit and a receiver equalizer connected in tandem with the receiver circuit;

the parametric information pertains to the receiver equalizer; and

the test system additionally comprises an equalizer controller connected to receive the parametric information and operable in response thereto to provide an equalizer control signal to the receiver equalizer.

39. An integrated circuit comprising the test system of claim 24 .

40. An electronic device, comprising:

an input/output circuit comprising a phase tracking circuit, the phase tracking circuit comprising a phase comparator and a loop filter, the phase comparator operable to generate a phase signal and to feed the phase signal to the loop filter; and

a signal path extending from the phase comparator prior to the loop filter to convey the phase signal to a location external to the phase tracking circuit.

41. The electronic device of claim 40 , in which the signal path extends to a location external to the input/output circuit.

42. The electronic device of claim 40 , in which the phase signal comprises an early phase signal component and a late phase signal component.