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GS2985 Multi-Rate SDI Reclocker with Equalization &

De-emphasis

Data Sheet

36663 - 5

July 2012

21 of 45

Proprietary & Confidential

4.5 Crystal Buffer

The GS2985 features a crystal buffer supporting a Gennum recommended external 27MHz

crystal. The GS2985 requires an external 27MHz reference clock for correct operation. This

reference clock is generated by connecting a crystal to the XTAL- and XTAL+ pins of the device.

Alternately, a 27MHz external clock source can be connected to the XTAL- pin of the device,

while the XTAL+ pin should be left floating.

4.6 LOS (Loss Of Signal) Detection

The LOS (Loss Of Signal) status pin is an active-high output that indicates when the serial digital

input signal selected at the 4:1 input mux is invalid. In order for this output to be asserted,

transitions must not be present for a period of tLA = 5 - 10μs. After this output has been asserted,

LOS will de-assert within tLD = 0 - 5μs after the appearance of a transition at the DDIx input. See

Figure 4-1.

This signal is HIGH (signal lost), when the number of data edges within a window is below a

defined threshold. The output is automatically muted when LOS is detected.

This signal is LOW (signal valid), when the number of data edges within a window is above a

defined threshold. See Table 4-4.

The LOS function is operational for all operating modes of the device.

Figure 4-1: LOS Signal Timing

The LOS detector has two major modes. In legacy mode, a simple edge-based detector is used to

monitor the received signal at the output of the data slicer. Since the incoming signal has

undergone considerable gain by this point, the legacy detector can be more susceptible to false

de-assertion of LOS for unused channels which experience significant cross-talk from adjacent

active channels.

Table 4-4: LOS Operation

LOS

Signal

HIGH

Invalid

LOW

Valid

DATA

LOS

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