DS90CR213_05 Datasheet, PDF (11/15 Pages) Texas Instruments – 21-Bit Channel Link-66 MHz

DS90CR213 Pin Description—Channel Link Transmitter (Continued)
Pin Name
PWR DOWN
V_CC
GND
PLL V_CC
PLL GND
LVDS V_CC
LVDS GND
I/O No.
Description
I
1 TTL level input. Assertion (low input) TRI-STATES the outputs, ensuring low current at power
down.
I
4 Power supply pins for TTL inputs.
I
5 Ground pins for TTL inputs.
I
1 Power supply pin for PLL.
I
2 Ground pins for PLL.
I
1 Power supply pin for LVDS outputs.
I
3 Ground pins for LVDS outputs.
DS90CR214 Pin Description—Channel Link Receiver
Pin Name
RxIN+
RxIN−
RxOUT
RxCLK IN+
RxCLK IN−
RxCLK OUT
PWR DOWN
V_CC
GND
PLL V_CC
PLL GND
LVDS V_CC
LVDS GND
I/O No.
Description
I
3 Positive LVDS differential data inputs.
I
3 Negative LVDS differential data inputs.
O
21 TTL level outputs.
I
1 Positive LVDS differential clock input.
I
1 Negative LVDS differentiaI clock input.
O
1 TTL level clock output. The rising edge acts as data strobe.
I
1 TTL Ievel input. Locks the previous receiver output state.
I
4 Power supply pins for TTL outputs.
I
5 Ground pins for TTL outputs.
I
1 Power supply for PLL.
I
2 Ground pin for PLL.
I
1 Power supply pin for LVDS inputs.
I
3 Ground pins for LVDS inputs.
Applications Information
The Channel Link devices are intended to be used in a wide
variety of data transmission applications. Depending upon
the application the interconnecting media may vary. For
example, for lower data rate (clock rate) and shorter cable
lengths (< 2m), the media electrical performance is less
critical. For higher speed/long distance applications the me-
dia’s performance becomes more critical. Certain cable con-
structions provide tighter skew (matched electrical length
between the conductors and pairs). Twin-coax for example,
has been demonstrated at distances as great as 5 meters
and with the maximum data transfer of 1.38 Gbit/s. Addi-
tional applications information can be found in the following
National Interface Application Notes:
AN = ####
AN-1041
AN-1035
AN-806
AN-905
AN-916
Topic
Introduction to Channel Link
PCB Design Guidelines for LVDS and
Link Devices
Transmission Line Theory
Transmission Line Calculations and
Differential Impedance
Cable Information
CABLES
A cable interface between the transmitter and receiver needs
to support the differential LVDS pairs. The 21-bit CHANNEL
LINK chipset (DS90CR213/214) requires four pairs of signal
wires and the 28-bit CHANNEL LINK chipset (DS90CR283/
284) requires five pairs of signal wires. The ideal cable/
connector interface would have a constant 100Ω differential
impedance throughout the path. It is also recommended that
cable skew remain below 350 ps (@ 66 MHz clock rate) to
maintain a sufficient data sampling window at the receiver.
In addition to the four or five cable pairs that carry data and
clock, it is recommended to provide at least one additional
conductor (or pair) which connects ground between the
transmitter and receiver. This low impedance ground pro-
vides a common mode return path for the two devices. Some
of the more commonly used cable types for point-to-point
applications include flat ribbon, flex, twisted pair and Twin-
Coax. All are available in a variety of configurations and
options. Flat ribbon cable, flex and twisted pair generally
perform well in short point-to-point applications while Twin-
Coax is good for short and long applications. When using
ribbon cable, it is recommended to place a ground line
between each differential pair to act as a barrier to noise
coupling between adjacent pairs. For Twin-Coax cable ap-
plications, it is recommended to utilize a shield on each
cable pair. All extended point-to-point applications should
also employ an overall shield surrounding all cable pairs
regardless of the cable type. This overall shield results in
improved transmission parameters such as faster attainable
speeds, longer distances between transmitter and receiver
and reduced problems associated with EMS or EMI.
The high-speed transport of LVDS signals has been demon-
strated on several types of cables with excellent results.
However, the best overall performance has been seen when
using Twin-Coax cable. Twin-Coax has very low cable skew
and EMI due to its construction and double shielding. All of
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