GS2989 Datasheet, PDF (10/19 Pages) Gennum Corporation – Dual-Slew-Rate, Dual-Output Cable Driver with 3Gb/s Capability

4. Detailed Description
4.1 Serial Data Input
The GS2989 features a differential input buffer with on-chip 100Ω differential
termination.
The serial data input signal is connected to the DDI and DDI input pins of the device.
Input signals can be single-ended or differential, DC or AC-coupled.
The serial data input buffer is capable of operation with any binary coded signal that
meets the input signal level requirements, in the range of 270Mb/s to at least 2.97Gb/s.
The input circuit is self-biasing to allow for simple AC or DC-coupling of input signals to
the device.
4.2 Input Trace-equalization
The GS2989 features fixed trace-equalization to compensate for PCB trace dielectric
losses.
NOTE: This feature is not available in SD mode, and therefore trace-equalization must
be disabled when operating in this mode.
The trace-equalization has two settings, OFF and ON. ON invokes a typical 3dB gain
value at 1.5GHz. This value is optimized for compensating the high-frequency losses
associated with approximately 10 inches of 5-mil stripline in FR4 material.
Table 4-1: Input Trace-Equalization
EQ_EN
0
1
Floating
Function
Typical 3dB Trace Equalization
Trace Equalization OFF
Trace Equalization OFF
4.3 Serial Data Output
The GS2989 features dual current-mode differential output drivers capable of driving
up to 1800mVpp single-ended into a 1m length of 75Ω cable terminated at both ends.
The output signal amplitude or swing is user configurable using an external RSET
resistor.
The SDO1/SDO1 and SDO2/SDO2 pins of the device provide the serial data outputs.
4.3.1 Slew Rate Selection (Rise/Fall Time Requirement)
The GS2989 supports two user-selectable output slew rates.
GS2989 Dual-Slew-Rate, Dual-Output Cable Driver
with 3Gb/s Capability
Data Sheet
52133 - 4
December 2010
10 of 19