MAX9209 Maxim, MAX9209 Datasheet - Page 14

• Manufacturer Part Number: MAX9209
• Description: The MAX9209/MAX9213 serialize 21 bits of LVTTL/LVCMOS parallel input data to three LVDS outputs
• Manufacturer: Maxim

Voltage droop and the DSV of transmitted symbols
cause signal transitions to start from different voltage
levels. Because the transition time is finite, starting the
signal transition from different voltage levels causes
timing jitter. The time constant for an AC-coupled link
needs to be chosen to reduce droop and jitter to an
acceptable level.
The RC network for an AC-coupled link consists of the
LVDS receiver termination resistor (R
output resistor (R
itors (C). The RC time constant for two equal-value
series capacitors is (C x (R
RC time constant for four equal-value series capacitors
is (C x (R
Programmable DC-Balanced
21-Bit Serializers
Figure 15. Four Capacitors per Link, AC-Coupled, DC-Balanced Mode
14
PWRDWN
TxCLK IN
______________________________________________________________________________________
TxIN
Selection of AC-Coupling Capacitors
T
+ R
7
7
7
O
Applications Information
)) / 4 (Figure 15).
O
), and the series AC-coupling capac-
(7 + 2):1
(7 + 2):1
(7 + 2):1
PLL
21:3 SERIALIZER
MAX9209
MAX9213
T
+ R
O
)) / 2 (Figure 14). The
T
), the LVDS driver
R
R
R
R
O
O
O
O
TxOUT
TxCLK OUT
SURFACE-MOUNT CAPACITORS
HIGH-FREQUENCY CERAMIC
R
ance (usually 100Ω) and R
driver design, with a minimum value of 78Ω (see the DC
Electrical Characteristics table). This leaves the capaci-
tor selection to change the system time constant.
In the following example, the capacitor value for a
droop of 2% is calculated. Jitter due to this droop is
then calculated assuming a 1ns transition time:
where:
C = AC-coupling capacitor (F)
t
DSV = digital sum variation (integer)
ln = natural log
D = droop (% of signal amplitude)
R
B
T
T
= bit time (s)
C = -(2 x t
= termination resistor (Ω)
is required to match the transmission line imped-
100Ω
100Ω
100Ω
100Ω
R
R
R
R
RxCLK IN
T
T
T
T
=
=
=
=
RxIN
B
x DSV) / (ln (1 - D) x (R
3:21 DESERIALIZER
MAX9210
MAX9214
O
is determined by the LVDS
1:(9 - 2)
1:(9 - 2)
1:(9 - 2)
PLL
T
+ R
O
7
7
7
)) (Eq 1)
RxOUT
PWRDWN
RxCLK OUT