GS1508-CTAE3 View Datasheet(PDF) - Gennum -> Semtech

Part Name

Description

Manufacturer

GS1508-CTAE3

HD-LINX™ HDTV Cable Driver

Gennum -> Semtech 

3. Detailed Description

3.1 Input Interfacing

SDI/SDI are high-impedance differential inputs (see Figure 4-1 for equivalent input

circuit).

Several conditions must be observed when interfacing to these inputs:

1. The differential input signal amplitude must be between 150 and 800mVpp.

2. The common mode voltage range must be as specified in the DC Electrical

Characteristics table. For a 400mV input from the GS1504 HD cable equalizer, this

corresponds to a common mode voltage range of between 2.7V and 4.8V.

3. For input trace lengths longer than approximately 1cm, the inputs should be

terminated as shown in the Typical Application Circuit.

The GS1508 inputs are self biased, allowing for simple AC-coupling to the device. For

serial digital HDTV, a minimum capacitor value of 4.7μF should be used to allow

coupling of pathological test signals. A tantalum capacitor is recommended.

3.2 Output Interfacing

The GS1508 outputs are current-mode, and will drive 800mV into a 75Ω load. These

outputs are protected from accidental static damage with internal static protection

diodes.

The SMPTE 292M standard requires that the output of a cable driver have a source

impedance of 75Ω and a return loss of at least 15dB between 5MHz and 1.485GHz.

In order for an HD SDI output circuit using the GS1508 to meet this specification, the

output circuit shown in the Typical Application Circuit is recommended.

The values of LCOMP and CCOMP will vary depending on PCB layout, but typical values are

12nH and 0.5pF respectively. The small value of CCOMP can be easily swamped by

parasitic PCB capacitance, so it is recommended that the ground plane be removed

under the GS1508 output circuitry (see the Application Information section in this data

sheet for further details). A 4.7μF capacitor is used for AC-coupling the output of the

GS1508. This value is chosen to ensure that pathological signals can be coupled without

a significant DC component occurring.

GS1508 HD-LINX™ HDTV Cable Driver

Data Sheet

9500 - 6

August 2010

5 of 14

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