MAX9242 Maxim, MAX9242 Datasheet - Page 17

• Manufacturer Part Number: MAX9242
• Description: The MAX9242/MAX9244/MAX9246/MAX9254 deserialize three LVDS serial-data inputs into 21 single-ended LVCMOS/LVTTL outputs
• Manufacturer: Maxim

R
(usually 100Ω) and R
ver design (the minimum differential output resistance of
78Ω for the MAX9209/MAX9213 serializers is used in
the following example). This condition leaves the capac-
itor selection to change the system time constant.
In the following example, the capacitor value for a 2%
droop is calculated. Jitter due to this droop is then cal-
culated 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
R
Equation 1 is for two series capacitors (Figure 19). The bit
time (t
Figure 18. DC-Coupled Link, Non-DC-Balanced Mode
B
T
T
O
= bit time (s)
C = -(2 x t
is required to match the transmission line impedance
= termination resistor (Ω)
= output resistance (Ω)
PWRDWN
TxCLK IN
B
) is the period of the parallel clock divided by 9.
TxIN
B
7
7
7
x DSV) / (ln (1 - D) x (R
______________________________________________________________________________________
21-Bit Deserializers with Programmable
O
PLL
7:1
7:1
7:1
is determined by the LVDS dri-
MAX9209/MAX9213
21:3 SERIALIZER
Spread Spectrum and DC Balance
T
+ R
R
O
O
)) (Eq 1)
TxOUT
TxCLK OUT
TRANSMISSION LINE
The DSV is 10. See equation 3 for four series capacitors
(Figure 20).
The capacitor for 2% maximum droop at 16MHz parallel
rate clock is:
Jitter due to droop is proportional to the droop and
transition time:
where:
t
t
D = droop (% of signal amplitude)
Jitter due to 2% droop and assumed 1ns transition time is:
The transition time in a real system depends on the fre-
quency response of the cable driven by the serializer.
J
T
C = -(2 x t
C = -(2 x 6.95ns x 10) / (ln (1 - 0.02) x (100Ω + 78Ω))
C = 0.038µF
= jitter (s)
= transition time (s) (0 to 100%)
100Ω
100Ω
100Ω
100Ω
RxCLK IN
R
RxIN__
T
MAX9242/MAX9244/MAX9246/MAX9254
B
x DSV) / (ln (1 - D) x (R
3:21 DESERIALIZER
t
J
t
J
= t
= 1ns x 0.02
t
J
T
= 20ps
x D (Eq 2)
1:7 FIFO
1:7 FIFO
1:7 FIFO
PLL1 +
SSPLL
T
+ R
O
7
7
7
))
RxOUT_
PWRDWN
RxCLK OUT
17