GS2965 datasheet(18/41 Pages) SEMTECH

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GS2965 Multi-Rate SDI Reclocker with Equalization &

De-emphasis

Data Sheet

52462 - 4

July 2012

18 of 41

Proprietary & Confidential

4.5 Crystal Buffer

The GS2965 features a crystal buffer supporting a Gennum recommended external

27MHz crystal. The GS2965 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 2:1 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 mode can be selected using the host interface, in register TOP_1. 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.

The new LOS detector uses a measure of both signal amplitude and duration to minimize

false detection of the impulse like signals that are characteristic of cross-talk. In this

Table 4-4: LOS Operation

LOS

Signal

HIGH

Invalid

LOW

Valid

DATA

LOS

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