GS1528 Data Sheet
3. Detailed Description
3.1 Input Interfacing
S
DI/SDI are high impedance differential inputs. (See Figure 2-1 1 for equivalent
input circuit).
Several conditions must be observed when interfacing to these inputs:
1. The differential input signal amplitude must be between 300 and 2000mVpp.
2. The common mode voltage range must be as specified in the Table 1-1: DC
Electrical Characteristics.
3. For input trace lengths longer than approximately 1cm, the inputs should be
terminated as shown in the Typical Application Circuit.
The GS1528 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.
3.2 SD/HD
The GS1528 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 to
a HIGH INPUT. For SMPTE 292M standards and signals which require faster rise
and fall times, this pin should be set to a LOW INPUT.
3.3 Output Interfacing
The GS1528 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 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 SDI output circuit using the GS1528 to meet this specification, the
output circuit shown in the Typical Application Circuit is recommended.
The value of L
will vary depending on the PCB layout, with a typical value of
COMP
5.6nH (see the Application Information on page 11 in this data sheet for further
details). A 4.7µF capacitor is used for AC coupling the output of the GS1528. This
value is chosen to ensure that pathological signals can be coupled without a
significant DC component occurring.
16632 - 5 June 2005
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GENNUM [ GENNUM CORPORATION ]
