GS2985 Datasheet, PDF (24/45 Pages) Gennum Corporation – Uses standard 27MHz crystal

Table 4-7: Output De-emphasis
DEn_EN pin
HIGH
LOW
Status of Output n
Output De-emphasis
ON
Output De-emphasis
OFF
When DEn_EN is set LOW or left unconnected, the de-emphasis for output n is OFF. When HIF
is HIGH, these DE_EN controls select between OFF and a setting that compensates for roughly
five inches of trace.
All other settings are available only via the host interface.
When a DEn_EN pin is tied HIGH, the output de-emphasis for output n is ON.
The default de-emphasis setting upon power-up is 0dB (OFF).
NOTE: Changing the de-emphasis setting will vary both V1 & V2 (see Figure 4-2).
Tx signal after de-emphasis
0.6
V1
0.4
0.2
V2
0
De-emphasis (dB)
=20 log (V1/V2)
-V2
-0.2
-0.4
-V1
-0.6 11110000 pattern
268
269
270
271
272
273
274
275
UI
Figure 4-2: De-emphasis Waveform
4.10 Automatic and Manual Data Rate Selection
The GS2985 can be configured to manually lock to a specific data rate or automatically search
for and lock to the incoming data rate. The AUTO/MAN pin selects Automatic data rate
detection mode (AUTO mode) when HIGH and manual data rate selection mode (MANUAL
mode) when LOW.
In AUTO mode, the SS[1:0] bi-directional pins become outputs and the bit pattern indicates the
data rate at which the PLL is currently locked to (or previously locked to). The search algorithm
GS2985 Multi-Rate SDI Reclocker with Equalization &
De-emphasis
Data Sheet
36663 - 5
July 2012
24 of 45
Proprietary & Confidential