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AS1153/55

Data Sheet - A p p l i c a t i o n s

!

Use cables and connectors with matched differential impedance (typically 100

Ω) to minimize impedance mis-

matches.

!

Balanced cables such as twisted pair offer superior signal quality and tend to generate less EMI due to magnetic

field canceling effects. Balanced cables pick up noise as common mode, which is rejected by the LVDS receiver.

!

Avoid the use of unbalanced cables such as ribbon cable or simple coaxial cable.

Termination

Due to the high data rates of LVDS drivers, matched termination will prevent the generation of any signal reflections,

and reduce EMI.

!

The AS1157/58 has integrated termination resistors connected across the inputs of each receiver. The value of the

integrated resistor is specified in Table 3.

!

The AS1153/55 requires an external termination resistor. The termination resistor should match the differential

impedance of the transmission line and be placed as close to the receiver inputs as possible. Termination resis-

tance values may range between 90 to 132

Ω depending on the characteristic impedance of the transmission

medium. Use 1% surface-mount resistors.

Board Layout

The device should be placed as close to the interface connector as possible to minimize LVDS trace length.

!

Keep the LVDS and any other digital signals separated from each other to reduce crosstalk.

!

Use a four-layer PC board that provides separate power, ground, LVDS signals, and input signals.

!

Isolate the input LVDS signals from each other and the output LVCMOS/LVTTL signals from each other to prevent

coupling.

!

Separate the input LVDS signals from the output signals planes with the power and ground planes for best results.

Figure 20. Propagation Delay and Transition Time Test Circuit

INx+

50

Ω

50

Ω

INx-

OUT

Pulse

Generator**

* 50

Ω required for pulse generator.

** When testing the AS1157/58, adjust the pulse generator out-

put to account for internal termination resistor.

Receiver

AS1153/55, AS1157/58