fs6131 AMI Semiconductor, Inc., fs6131 Datasheet - Page 33

• Manufacturer Part Number: fs6131
• Description: Fs6131-01g Programmable Line Lock Clock Generator Ic
• Manufacturer: AMI Semiconductor, Inc.

FS6131-01/FS6131-01g Programmable Line Lock Clock Generator IC
11.1.1 Example Calculation
In PECL mode, the output driver does not source current, so the V
the equation
where R
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
for line impedance and solving for R
To solve for the load's V
some extra margin. A sink current of 25mA through the 82W resistor generates a 2.05V 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 750W at V
6.6mA, or about 27mA output sink current.
11.2 CMOS Output Mode
If a CMOS interface is desired, a transmission line is typically terminated using a series termination. Series termination adds no dc
loading to the driver, and requires less power than other resistive termination methods. In addition, no extra impedance exists from the
signal line to a reference voltage, such as ground.
As shown in Figure 23, the sum of the driver's output impedance (z
impedance (z
When the source impedance (z
of the full signal amplitude.
AMI Semiconductor
www.amis.com
L
p1
is the line impedance.
is the pull-up resistor, R
L
IH(min)
). That is,
= V
Specifications subject to change without notice
– Rev. 3.0, Jan. 08
CC
- 0.6, choose a V
IL
, an output sink current must be programmed via the IPRG pin. If the desired V
O
+R
p2
S
is the pull-down resistor and V
) is matched to the line impedance, then by voltage division the incident wave amplitude is one-half
p2
gives a value of 880W (choose 910W).
NMH
DRIVER
= 0.45V. If the line impedance is 75W, then R
p1
gives
V
Figure 23: Series Termination (CMOS)
R
i
V
p
1
=
NMH
=
z
V
V
O
z
z
IH
R
(
L
L
=
z
S
=
+
O
=
V
(
=
z
CC
33
V
z
+
R
R
NMH
O
IH
L
CC
S
R
z
p
R
⎛
⎜ ⎜
⎝
value is determined by the ratios of the terminating resistors using
×
+
1
L
is the desired noise margin, and
p
V
S
1
+
−
O
R
−
R
R
CC
) and the series termination resistance (R
)
V
p
R
S
p
V
+
z
1
LINE
R
NMH
2
)
p
−
O
NMH
+
z
z
2
p
L
V
L
1
R
NMH
p
=
2
V
2
⎞
⎟ ⎟
⎠
RECEIVE
p1
is about 82W. Substituting into the equation
IH
= V
CC
- 1.6, choose V
S
) must equal the line
DD
= 5V generates
CC
Data Sheet
- 2.0 for