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GS1578ACNE3 View Datasheet(PDF) - Gennum -> Semtech

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GS1578ACNE3 Datasheet PDF : 15 Pages
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4. Detailed Description
GS1578A Data Sheet
4.1 Input Interfacing
SDI/SDI are high impedance differential inputs. The equivalent input circuit is shown
in Figure 3-1.
Several conditions must be observed when interfacing to these inputs:
• The differential input signal amplitude must be between 300 and 2000mVpp.
• The common mode voltage range must be as specified in the DC Electrical
Characteristics on page 5.
• For input trace lengths longer than approximately 1cm, the inputs should be
terminated as shown in the Typical Application Circuit.
The GS1578A inputs are self-biased, allowing for simple AC coupling to the device.
For serial digital video, a minimum capacitor value of 4.7µF should be used to allow
coupling of pathological test signals. A tantalum capacitor is recommended.
SD/HD Input Pin
The GS1578A SDO rise and fall times can be set to comply with both SMPTE
259M/344M and SMPTE 292M. For all SMPTE 259M standards, or any data rate
that requires longer rise and fall time characteristics, the SD/HD pin must be set
HIGH by the application layer. For SMPTE 292M standards and signals which
require faster rise and fall times, this pin should be set LOW.
4.2 Output Interfacing
The GS1578A 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, SMPTE 344M and SMPTE 259M standards require 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 SDI output circuit using the GS1578A to meet this specification, the
output application circuit shown in Typical Application Circuit on page 12 is
recommended.
The value of LCOMP will vary depending on the PCB layout, with a typical value of
5.6nH. A 4.7µF capacitor is used for AC coupling the output of the device. This
value is chosen to ensure that pathological signals can be coupled without a
significant DC component occurring. Please see Application Information on
page 12 for more details.
33657 - 4 March 2006
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