Teledyne-lecroy QPHY-DDR2 Manuel d'utilisateur télécharger pdf (Page 36)

36 QPHY-DDR2-OM-E Rev A

tJIT(per), Clock Period Jitter

Applicable only to 667 and 800 MHz device only.

tJIT(per) is defined as the largest deviation of any single tCK from tCK(avg). This test compares the average clock

period (over 200 cycles) with each period inside the window. The smallest and largest values must be within

limits.

tJIT(per) = Min/max of {tCKi - tCK(avg)} where i=1 to 200

Measured on both the rising and the falling edge.

There are different limit depending on whether the DLL is already locked or not:

 tJIT(per) defines the single period jitter when the DLL is already locked.

 tJIT(per,lck) uses the same definition for single period jitter, during the DLL locking period only.

A configuration variable allows to define which limit to use.

tJIT(cc), Cycle to Cycle Period Jitter

Applicable only to 667 and 800 MHz device only.

tJIT(cc) is defined as the difference in clock period between two consecutive clock cycles. This test compares the

smallest and largest values of the difference between any two consecutive clock cycles inside a 200 cycles

window.

tJIT(cc) = Min/max of {tCKi+1 – tCKi} where i = 1 to 199

Measured on both the rising and the falling edge.

There are different limit depending on whether the DLL is already locked or not:

 tJIT(cc) defines the cycle to cycle jitter when the DLL is already locked.

 tJIT(cc,lck) uses the same definition for cycle to cycle jitter, during the DLL locking period only.

A configuration variable allows to define which limit to use.

tERR(n per), Cumulative Error

Applicable only to 667 and 800 MHz device only.

tERR is defined as the cumulative error across multiple consecutive cycles from tCK(avg). This test compares the

average clock period (over 200 cycles) with each n-bit period inside the window. The smallest and largest values

must be within limits.

There are 6 different tests:

tERR(2per), tERR (3per), tERR (4per), tERR (5per), tERR (6-10per) and tERR (11-50per)

tERR(nper) = Min/max of {SUM(tCKi) - n x tCK(avg)}

where i=1 to n and:

n = 2 for tERR(2per)

n = 3 for tERR(3per)

n = 4 for tERR(4per)

n = 5 for tERR(5per)

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Teledyne-lecroy QPHY-DDR2 Manuel d'utilisateur Page 36