Datasheet

AD9553
Rev. A | Page 26 of 44
JITTER TOLERANCE
Jitter tolerance is the ability of the AD9553 to maintain lock in
the presence of sinusoidal jitter. The AD9553 meets the input
jitter tolerance mask per Telcordia GR-253-CORE (see Figure 32).
The acceptable jitter tolerance is the region above the mask. The
trace showing the performance of the AD9553 in Figure 32
represents the limitations of the test equipment because the
AD9553 did not indicate loss of lock, even with the test
equipment injecting its maximum jitter level.
1k
0.1
1
10
100
0.01 0.1 1 10 100 1k 10k
INPUT JITTER AMPLITUDE (U
LPP
)
JITTER FREQUENCY (kHz)
08565-030
AD9553
MASK
Figure 32. Jitter Tolerance
OUTPUT/INPUT FREQUENCY RELATIONSHIP
The frequency at OUT1 and OUT2 depends on the frequency at
the input to the PLL, the PLL feedback divider value (N), and the
output divider values (P
0
, P
1
, and P
2
). The equations that define
the frequency at OUT1 and OUT2 (f
OUT1
and f
OUT2
, respectively)
are as follows:








×
=
10
1
PP
N
FPFDf
OUT








×
=
20
2
PP
N
FPFDf
OUT
where:
FPFD is the frequency at the reference input of the PFD.
N is the feedback divider value.
P
0
is the VCO prescaler divider value.
P
1
is the OUT1 divider value.
P
2
is the OUT2 divider value.
The operating frequency range of the PFD places a limitation
on FPFD as follows:
13.3 kHz ≤ FPFD ≤ 100 MHz
Note that for applications using the frequency selection pins in
conjunction with the XTAL input for the holdover function, the
maximum value of FPFD is 50 MHz (twice the 25 MHz default
crystal frequency).
FPFD depends on the input frequency to the AD9553, the
configuration of the multiplexers for the ÷5 prescaler and ×2
frequency multiplier, and the value of the R
X
divider (either R
A
,
R
B
, or R
XO
) as follows:
X
X
R
K
fFPFD ×=
where:
f
X
is equal to f
REFA
, f
REFB
, or f
XTAL
.
K is the scale factor per Table 22.
FPFD is the frequency at the input to the phase frequency
detector.
Table 22. K as a Function of Input Multiplexer Configuration
Input ÷5 ×2 K
REFA Bypassed Bypassed 1
Active Bypassed 1/5
Bypassed Active 2
Active Active 2/5
REFB Bypassed Bypassed 1
Active Bypassed 1/5
Bypassed Active 2
Active Active 2/5
XTAL N/A
1
N/A
1
2
1
N/A means not applicable.
This leads to the complete frequency translation formula








×








=
10
1
PP
N
R
K
ff
X
X
OUT








×








=
20
2
PP
N
R
K
ff
X
X
OUT
Specific numeric constraints apply as follows. Note that the
symbol
∈
indicates that the constraint is an element of one in
the series from the list within the curly brackets.
K






∈ 2,1,
5
2
,
5
1
K
X
∈
{1, 2, …, 16,384}
N
∈
{32, 33, …, 1,048,576}
P
0
∈
{5, 6, …, 11}
P
1
∈
{1, 2, …, 63}
P
2
∈
{1, 2, …, 63}
Additional constraints apply. One constraint is related to the
VCO and the other to the ×2 frequency multipliers in the REFA
and REFB paths. The VCO constraint is a consequence of its
limited bandwidth. However, the ×2 frequency multiplier
constraint only applies when the ÷5 prescalers are bypassed, but
it also requires that R
A
and R
B
are large enough to satisfy the
FPFD constraint. The additional constraints are as follows:
3350 MHz ≤ f
OUT1
× P
0
× P
1
≤ 4050 MHz
3350 MHz ≤ f
OUT2
× P
0
× P
2
≤ 4050 MHz
f
REFA/REFB
≤ 125 MHz (×2 multiplier with ÷5 bypassed)