1. A method for measuring jitter in a digital input signal, the method comprising:
producing a digital reference signal having a predetermined frequency offset from that of said digital input signal;
detecting a first occurrence of a predetermined phase relationship between said digital input signal and said digital reference signal;
detecting subsequent occurrence of said predetermined phase relationship between said digital input signal and said digital reference signal; and
determining the time difference between said first occurrence and said subsequent occurrence, to determine a measurement of jitter present in said digital input signal.
2. The method of claim 1 wherein the step of producing said digital reference signal comprises:
measuring the frequency of said digital input signal to produce a frequency measurement; and
using the frequency measurement to produce said digital reference signal having a frequency which is offset therefrom by a predetermined amount.
3. The method of claim 1 wherein the step of detecting a first occurrence of a predetermined phase relationship between said digital input signal and said digital reference signal and the step of detecting subsequent occurrence of said predetermined phase relationship between said digital input signal and said digital reference signal comprise detecting coincidence of similar edges of said digital input signal and said digital reference signal.
4. The method of claim 1 wherein the step of detecting subsequent occurrence of said predetermined phase relationship between said digital input signal and said digital reference signal comprises:
detecting over a plurality of said subsequent occurrences a maximum time difference value and a minimum time difference value; and
determining from said maximum time difference value and said minimum time difference value a total peak-to-peak jitter measurement.
5. The method of claim 4 wherein said predetermined frequency offset is varied between test cycles to facilitate detection of fixed frequency jitter based on a frequency that would beat with a fixed frequency offset.
6. The method of claim 1 further comprising pre-scaling the digital input signal to increase the resolution of jitter measurement.
7. An apparatus for measuring jitter in a digital input signal, the apparatus comprising:
a receiving arrangement for receiving a digital input signal;
a reference signal arrangement for producing a digital reference signal having a predetermined frequency offset from that of said digital input signal;
a phase detecting arrangement for detecting a first occurrence of a predetermined phase relationship between said digital input signal and said digital reference signal and subsequent occurrence of said predetermined phase relationship between said digital input signal and said digital reference signal; and
a determining arrangement for determining the time difference between said first occurrence and said subsequent occurrence, to determine a measurement of jitter present in said digital input signal.
8. The apparatus of claim 7 wherein said reference signal arrangement comprises:
a measuring arrangement for measuring the frequency of said digital input signal to produce a frequency measurement; and
a signal producing arrangement for producing from said frequency measurement said digital reference signal having a frequency which is offset therefrom by a predetermined amount.
9. The apparatus of claim 8 wherein said measuring arrangement comprises a frequency counter.
10. The apparatus of claim 8 wherein said signal producing arrangement comprises a programmable oscillator.
11. The apparatus of claim 7 wherein said phase detecting arrangement comprises an edge detecting arrangement for detecting coincidence of similar edges of said digital input signal and said digital reference signal.
12. The apparatus of claim 7 wherein said phase detecting arrangement comprises:
a minimummaximum detecting arrangement for detecting over a plurality of said subsequent occurrences a maximum time difference value and a minimum time difference value; and
a jitter determining arrangement for determining from said maximum time difference value and said minimum time difference value a total peak-to-peak jitter measurement.
13. The apparatus of claim 12 wherein said minimummaximum detecting arrangement comprises:
a counter arrangement driven by said reference signal;
a maximum register arrangement for holding a value in said counter arrangement when said phase detecting arrangement detects a said second occurrence;
a maximum comparator arrangement for comparing a value in said maximum register arrangement with a value in said counter arrangement when said phase detecting arrangement detects a said subsequent occurrence and if said counter arrangement value is greater than said maximum register arrangement value storing said counter arrangement value in said maximum register arrangement;
a minimum register arrangement for holding a value in said counter arrangement when said phase detecting arrangement detects a said subsequent occurrence; and
a minimum comparator arrangement for comparing a value in said minimum register arrangement with a value in said counter arrangement when said phase detecting arrangement detects a said second occurrence and if said counter arrangement value is less than said minimum register arrangement value storing said counter arrangement value in said minimum register arrangement.
14. The apparatus of claim 7 wherein the apparatus is substantially comprised in a field programmable gate array.
15. The apparatus of claim 7 wherein the apparatus is arranged to sense jitter in a telecommunications pulse code modulation (PCM) signal.
16. The apparatus of claim 7 wherein said predetermined frequency offset is varied between test cycles to facilitate detection of fixed frequency jitter based on a frequency that would beat with a fixed frequency offset.
17. The apparatus of claim 7 further comprising a pre-scaling arrangement for pre-scaling the received digital input signal to increase the resolution of jitter measurement.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A billiard table ball pick-up box, comprising a bottom bracket (7) and a side cover located above the bottom bracket (7), wherein the side cover comprises a cover plate (1), a left side plate (2) and a right side plate (3) located on both sides of the cover plate, and a scoreboard (4) located on the top of the cover plate, characterized in that the left side plate (2), the right side plate (3) and the scoreboard (4) are all hinged with the cover plate (1), wherein a cover body is formed integrally when the left side plate, the right side plate and the scoreboard are curved together with the cover plate respectively along the hinge point in the same direction.
2. The billiard table ball pick-up box according to claim 1, characterized in that a mounting plate (5) is arranged on the left side plate (2) and the right side plate (3), wherein mounting holes are arranged on the mounting plate.
3. The billiard table ball pick-up box according to claim 2, characterized in that the left side plate (2) and the right side plate (3) are provided with a lug (6) for positioning.
4. The billiard table ball pick-up box according to claim 3, characterized in that the edge connecting the left side plate (2), the right side plate (3) and the cover plate (1) is curved, wherein the cover plate is bent into an arc elastically along the curved edge.
5. A billiard table ball pick-up box, comprising a bottom bracket (7) and a side cover located above the bottom bracket (7), wherein the side cover comprises a cover plate (1), a left side plate (2) and a right side plate (3) located on both sides of the cover plate, and a scoreboard (4) located on the top of the cover plate, characterized in that one side of the left side plate (2) and the right side plate (3) is spliced with both sides of the cover plate (1) respectively, wherein the included angle between the left side plate, the right side plate and the cover plate is 80-120\xb0 respectively, and the scoreboard is hinged with the cover plate.
6. The billiard table ball pick-up box according to claim 5, characterized in that one or more connection holes (8) are arranged on the edge of both sides of the cover plate (1) and a convex structure (9) engaging with the connection holes is arranged on the edge connecting the left side plate (2), the right side plate (3) and the cover plate, wherein the left side plate and the right side plate are fixed on the cover plate by inserting the connection holes via the convex structure.
7. The billiard table ball pick-up box according to claim 6, characterized in that the edge connecting the left side plate (2), the right side plate (3) and the cover plate (1) is curved, wherein the cover plate is bent into an arc elastically along the curved edge.
8. The billiard table ball pick-up box according to claim 7, characterized in that a mounting plate (5) is arranged on the left side plate (2) and the right side plate (3), wherein mounting holes are arranged on the mounting plate.
9. The billiard table ball pick-up box according to claim 8, characterized in that the left side plate (2) and the right side plate (3) are provided with a lug (6) for positioning.
10. The billiard table ball pick-up box according to claim 5, characterized in that one or more cylindrical mounting holes (10) are arranged on both sides of the cover plate (1) in the side direction and a connection column (11) engaging with the cylindrical mounting holes is arranged on the edge connecting the left side plate (2), the right side plate (3) and the cover plate, wherein the left side plate and the right side plate are fixed on the cover plate by inserting the cylindrical mounting holes via the connection column.
11. The billiard table ball pick-up box according to claim 10, characterized in that the edge connecting the left side plate (2), the right side plate (3) and the cover plate (1) is curved, wherein the cover plate is bent into an arc elastically along the curved edge.
12. The billiard table ball pick-up box according to claim 11, characterized in that a mounting plate (5) is arranged on the left side plate (2) and the right side plate (3), wherein mounting holes (51) are arranged on the mounting plate.
13. The billiard table ball pick-up box according to claim 12, characterized in that the left side plate (2) and the right side plate (3) are provided with a lug (6) for positioning.