Teledyne LeCroy QPHY-LPDDR2 - Manual (Page 40)

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QPHY-LPDDR2-OM-G Rev B
tJIT(duty), Half Period Jitter
tJIT(per), Clock Period Jitter
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
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
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 12 different tests:
tERR( n per) (n → 2,3,4,5,6,7,8,9,10,12,13,14…49,50)
tERR(nper) = Min/max of {SUM(tCKi) - n x tCK(avg)}
where i=1 to n and: