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PDF GS2984 Data sheet ( Hoja de datos )

Número de pieza GS2984
Descripción Adaptive Cable Equalizer
Fabricantes Gennum 
Logotipo Gennum Logotipo



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GS2984 Adaptive Cable Equalizer
Key Features
• SMPTE 424M, SMPTE 292M and SMPTE 259M
compliant
• Automatic cable equalization
• Multi-standard operation from 143Mb/s to 2.97Gb/s
• Performance optimized for 270Mb/s, 1.485Gb/s and
2.97Gb/s. Typical equalized length of Belden 1694A
cable:
Š 140m at 2.97Gb/s
Š 200m at 1.485Gb/s
Š 400m at 270Mb/s
• Supports DVB-ASI at 270Mb/s
• Manual bypass (useful for low data rates with slow
rise/fall times)
• Programmable carrier detect with squelch threshold
adjustment
• Differential outputs support DC coupling to 3.3V and
2.5V CML logic
• 0/6 dB gain boost selection pin
• Standard EIA/JEDEC logic control and status signal
levels
• Single 3.3V power supply operation
• 195mW power consumption (typical)
• Wide temperature range of -40ºC to +85ºC
• Small footprint QFN package (4mm x 4mm)
Š Drop-in compatible with the GS2974
• Pb-free and RoHS compliant
Applications
• SMPTE 424M, SMPTE 292M and SMPTE 259M coaxial
cable serial digital interfaces
Description
The GS2984 is a high-speed BiCMOS integrated circuit
designed to equalize and restore signals received over 75Ω
coaxial cable.
The device is designed to support SMPTE 424M,
SMPTE292M and SMPTE 259M, and is optimized for
performance at 270Mb/s, 1.485Gb/s and 2.97Gb/s.
The GS2984 features DC restoration to compensate for the
DC content of SMPTE pathological test patterns.
The Carrier Detect output pin (CD) indicates whether a
valid input signal has been detected. It can be connected
directly to the MUTE pin to mute the output on loss of
carrier. A voltage programmable threshold, which can be
changed via the SQ_ADJ pin, forces CD high when the
input signal amplitude falls below the threshold. This
allows the GS2984 to distinguish between low-amplitude
SDI signals and noise at the input of the device.
The equalizing and DC restore stages are disengaged when
the BYPASS pin is HIGH. No equalization occurs in Bypass
mode.
The GS2984 includes a gain selection pin (GAIN_SEL)
which, when tied HIGH, compensates for 6dB flat
attenuation.
The differential outputs can be DC-coupled to Gennum
3.3V cable drivers and reclockers and to industry-standard
3.3V and 2.5V CML logic using the CMSET pin.
The GS2984 is footprint and drop-in compatible with
existing GS2974 designs, with no additional application
changes required.
The device is available in a 16-pin, 4mm x 4mm QFN
package.
Power consumption of the GS2984 is typically 195mW.
The GS2984 is Pb-free, and the encapsulation compound
does not contain halogenated flame retardant.
This component and all homogeneous subcomponents are
RoHS compliant.
GS2984 Adaptive Cable Equalizer
Data Sheet
50985 - 3
March 2010
www.gennum.com
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1 page




GS2984 pdf
Table 1-1: GS2984 Pin Descriptions (Continued)
Pin Number
8
Name
SQ_ADJ
Timing
Analog
Type
Input
9
CMSET
Not
Input
Synchronous
10, 11
12
SDO, SDO
VEE_D
Analog
Analog
Output
Power
13
VCC_D
Analog
Power
14
MUTE
Not
Input
Synchronous
15 CD Not Output
Synchronous
16
VCC_A
Analog
Power
Center Pad
Power
Description
Squelch Adjust.
Adjusts the approximate amount of cable equalized before CD goes
low. See Section 4.4 and Section 4.5. (Internal pull-down).
CONTROL SIGNAL INPUT
levels are LVCMOS/LVTTL compatible. (3.3V Tolerant)
Controls output common mode level. (Internal pull-down).
See Section 4.7.
Equalized serial digital differential output.
Most negative power supply for the digital circuitry and output
buffer.
Connect to GND.
Most positive power supply for the digital I/O pins of the device.
Connect to +3.3V DC.
CONTROL SIGNAL INPUT
levels are LVCMOS/LVTTL compatible. (3.3V Tolerant)
Controls output behaviour on SDO and SDO. (Internal pull-down).
See Section 4.5.
STATUS SIGNAL OUTPUT
Signal levels are LVCMOS/LVTTL compatible.
Indicates the presence of an input signal.
See Section 4.5.
Most positive power supply for the analog circuitry of the device.
Connect to +3.3V DC.
Internally bonded to VEE_A.
GS2984 Adaptive Cable Equalizer
Data Sheet
50985 - 3
March 2010
5 of 20

5 Page





GS2984 arduino
4.2 Cable Equalization
The input signal passes through a variable gain equalizing stage, whose frequency
response closely matches the inverse of the cable loss characteristic. In addition, the
variation of the frequency response with control voltage imitates the variation of the
inverse cable loss characteristic with cable length.
The edge energy of the equalized signal is monitored by a detector circuit which
produces an error signal corresponding to the difference between the desired edge
energy and the actual edge energy. This error signal is integrated by both an internal and
an external AGC filter capacitor providing a steady control voltage for the gain stage. As
the frequency response of the gain stage is automatically varied by the application of
negative feedback, the edge energy of the equalized signal is kept at a constant level
which is representative of the original edge energy at the transmitter. The equalized
signal is also DC restored, effectively restoring the logic threshold of the equalized signal
to its correct level independent of shifts due to AC coupling.
4.3 Serial Digital Outputs
The digital output signals have a nominal voltage of 800mVpp differential, or 400mVpp
single-ended when terminated with 50Ω as shown in Figure 4-1.
+200mV
SDO
VCM = 2.9V
typical
-200mV
SDO
50 50
+200mV
VCM = 2.9V
typical
-200mV
Figure 4-1: Typical Output Voltage Levels (for 3.3V Common Mode)
GS2984 Adaptive Cable Equalizer
Data Sheet
50985 - 3
March 2010
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