11274-001 AMI Semiconductor, Inc., 11274-001 Datasheet - Page 30

• Manufacturer Part Number: 11274-001
• Description: Logic and Timing, Programmable Line Lock Clock Generator IC, Tape and Reel
• Manufacturer: AMI Semiconductor, Inc.

FS6131-01
FS6131-01
FS6131-01
FS6131-01
Programmable Line Lock Clock Generator IC
Programmable Line Lock Clock Generator IC
Programmable Line Lock Clock Generator IC
Programmable Line Lock Clock Generator IC
11.0
A signal reflection will occur at any point on a PC-board
trace where impedance mismatches exist. Reflections
cause several undesirable effects in high-speed applica-
tions, such as an increase in clock jitter and a rise in
electromagnetic emissions from the board. Using a prop-
erly designed series termination on each high-speed line
can alleviate these problems by eliminating signal reflec-
tions.
11.1
If a PECL interface is desired, the transmission line must
be terminated using a Thévenin, or dual, termination. The
output stage can only sink current in the PECL mode,
and the amount of sink current is set by a programming
resistor on the LOCK/IPRG pin. Source current is pro-
vided by the pull-up resistor that is part of the Thévenin
termination.
Figure 27: Thévenin Termination (PECL)
Thévenin termination uses two resistors per transmission
line. The parallel resistance of the termination resistors
should be sized to equal the transmission line imped-
ance, taking into account the driver sink current, the de-
sired rise and fall times, and the V
of the load.
R
i
PECL Mode Output
IPRG
PECL Output Mode
Applications Information
from
PLL
{
CLKP
CLKN
z
O
IH
z
z
L
L
and V
R
R
p1
p2
V
CC
IL
R
R
n1
n2
specifications
V
CC
LOAD
30
11.1.1
In PECL mode, the output driver does not source current,
so the V
nating resistors using the equation
where R
sistor, and V
The resistor ratio must also match the line impedance via
the equation
where z
Combining these equations, and solving for R
If the load’s V
the line impedance is 75 , then R
stituting into the equation for line impedance and solving
for R
To solve for the load’s V
programmed via the IPRG pin. If the desired V
1.6, choose V
rent of 25mA through the 82
drop. The sink current is programmed via the IPRG pin,
where the ratio of IPRG current to output sink current is
1:4. An IPRG programming resistor of 750
generates 6.6mA, or about 27mA output sink current.
p2
gives a value of 880 (choose 910 ).
L
p1
IH
is the line impedance.
Example Calculation
value is determined by the ratios of the termi-
is the pull-up resistor, R
NMH
IH(min)
CC
R
is the desired noise margin, and
V
p
– 2.0 for some extra margin. A sink cur-
1
NMH
= V
V
z
z
IH
L
L
CC
V
IL
– 0.6, choose a V
, an output sink current must be
V
CC
z
R
L
CC
R
p
æ
ç ç
è
1
p
V
1
R
resistor generates a 2.05V
R
CC
V
p
R
V
p
1
NMH
R
2
p
NMH
2
p2
p1
p
V
1
R
.
NMH
is the pull-down re-
is about 82 . Sub-
p
2
ö
÷ ÷
ø
NMH
p1
at V
= 0.45V. If
IH
gives
= V
DD
= 5V
CC
–