Rev. 1.11 - UBiio

Internet Data Sheet
7.3 Jitter Definition and Clock Jitter Specification
HY[B/I]18T256[40/80/16]0B[C/F](L)
256-Mbit Double-Data-Rate-Two SDRAM
Generally, jitter is defined as “the short-term variation of a signal with respect to its ideal position in time”. The following table
provides an overview of the terminology.
TABLE 56
Average Clock and Jitter Symbols and Definition
Symbol Parameter Description Units
t CK.AVG Average clock period t CK.AVG is calculated as the average clock period within any consecutive
200-cycle window:
ps
tCK.AVG
=
N
1
N
---. ⎛ ⎞
⎜
⎜∑
tCK ⎟
j ⎟
⎝ ⎠
j = 1
(1)
N=200
t JIT.PER Clock-period jitter t JIT.PER is defined as the largest deviation of any single t CK from t CK.AVG :
t JIT.PER = Min/Max of {t CKi – t CK.AVG } where i = 1 to 200
ps
t JIT.PER defines the single-period jitter when the DLL is already locked.
t JIT.PER is not guaranteed through final production testing.
t JIT (PER, LCK)
t JIT.CC
Clock-period jitter
during DLL-locking
period
Cycle-to-cycle clock
period jitter
t JIT (PER,LCK) uses the same definition as t JIT.PER , during the DLL-locking
period only.
t JIT (PER,LCK) is not guaranteed through final production testing.
t JIT.CC is defined as the absolute difference in clock period between two
consecutive clock cycles:
t JIT.CC = Max of ABS{t CKi+1 – t CKi }
ps
ps
t JIT.CC defines the cycle- to- cycle jitter when the DLL is already locked.
t JIT.CC is not guaranteed through final production testing.
t JIT (CC, LCK)
t ERR.2PER
Cycle-to-cycle clock
period jitter during
DLL-locking period
Cumulative error
across 2 cycles
t JIT (CC,LCK) uses the same definition as t JIT.CC during the DLL-locking
period only.
t JIT (CC,LCK) is not guaranteed through final production testing.
t ERR.2PER is defined as the cumulative error across 2 consecutive cycles
from t CK.AVG :
ps
ps
i+
n–
1
⎛ ⎞
tERR( 2per) = ⎜
∑ tCK ⎟
⎜
j ⎟
⎝ ⎠
j = i
– n ×
tCK( avg)
(2)
n=2 for t ERR (2per)
where i = 1 to 200
Rev. 1.11, 2007-07 59
11172006-LBIU-F1TN