5. Detailed Description
5.1 Input Interfacing
SDI/SDI are high impedance differential inputs. The equivalent input circuit is shown in
Figure 4-1
.
Several conditions must be observed when interfacing to these inputs:
•
•
•
The differential input signal amplitude must be between 300 and 2000mVp-p.
The common mode voltage range must be as specified in Table 2.2.
For input trace lengths longer than approximately 1cm, the inputs should be
terminated as shown in the Typical Application Circuit.
The GS1528A/9068A 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 (GS1528A only):
The GS1528A 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.
5.2 Output Interfacing
The GS1528A/9068A 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 GS1528A/9068A to meet this specification,
the output application circuit shown in Typical Application Circuits on page 14 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 14 for more details.
GS1528A/GS9068A HD-LINX® II Multi-Rate Dual
Slew-Rate Cable Driver
10 of 18
Data Sheet
Proprietary & Confidential
30953 - 6
August 2010
GENNUM [ GENNUM CORPORATION ]
