GS2965 Datasheet, PDF (18/41 Pages) Gennum Corporation – Uses standard 27MHz crystal

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 t_LA = 5 - 10μs. After this output
has been asserted, LOS will de-assert within t_LD = 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.
Table 4-4: LOS Operation
LOS
HIGH
LOW
Signal
Invalid
Valid
The LOS function is operational for all operating modes of the device.
t _LA
t _LD
DATA
LOS
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
GS2965 Multi-Rate SDI Reclocker with Equalization &
De-emphasis
Data Sheet
52462 - 4
July 2012
18 of 41
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