GS2985 Datasheet, PDF (19/45 Pages) Gennum Corporation – Uses standard 27MHz crystal

4. Detailed Description
The GS2985 is a multi-standard reclocker for serial digital SDTV signals operating at 270Mb/s,
and HDTV signals operating at 1.485Gb/s, 1.485/1.001Gb/s, 2.97Gb/s and 2.97/1.001Gb/s.
4.1 Serial Data Input
The GS2985 features four differential input buffers.
The serial data input signal is connected to the DDI0/DDI0, DDI1/DDI1, DDI2/DDI2 and
DDI3/DDI3 input pins of the device.
Input signals can be single-ended or differential, DC or AC-coupled.
The input circuit is self-biasing, to allow for simple AC or DC-coupling of input signals to the
device.
The serial digital data inputs are also compatible when DC-coupled with LVPECL or CML
differential outputs from crosspoint switches which operate from 3.3V or 2.5V supplies. This
includes but is not limited to: GS2974A, GS2974B, and GS2984 equalizers.
4.2 Modes of Operation
The GS2985 has two modes of operation: Legacy Mode (HIF = HIGH) and SPI Mode (HIF = LOW).
In Legacy Mode, chip functions are controlled via pins only, and offers limited control of input
equalization and output de-emphasis.
In SPI mode, access is gained to additional EQ and DE settings as well as access to additional
features such as LOS adjustment, polarity invert, auto-mute, etc.
4.3 Input Trace Equalization
The GS2985 features adjustable trace equalization to compensate for PCB trace dielectric losses
at 1.5GHz.
The trace equalization has three peak-gain settings. The maximum peak gain value is optimized
for compensating the high-frequency losses associated with 25 inches of 5-mil stripline in FR4
material. For boards with different striplines or materials, users can experiment to find the EQ
setting which optimizes their system performance.
These settings are accessible via the serial host interface.
Each serial digital input; DDI, DDI includes a pin EQn_EN to turn its trace equalizer on or off.
When a pin EQn_EN is tied LOW or left unconnected, the trace equalization for input n is set to
the Low Range.
When an EQn_EN pin is tied HIGH, and input n is selected, the trace equalization for input n is
set to the Medium Range.
GS2985 Multi-Rate SDI Reclocker with Equalization &
De-emphasis
Data Sheet
36663 - 5
July 2012
19 of 45
Proprietary & Confidential