GS9078A Data Sheet
34165 - 4 March 2006 8 of 14
4. Detailed Description
4.1 Input Interfacing
S
DI/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 GS9078A 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.
4.2 Output Interfacing
The GS9078A 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 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 540MHz.
In order for an SDI output circuit using the GS9078A to meet this specification, the
output application circuit shown in Typical Application Circuit on page 11 is
recommended.
The value of L
COMP
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 11 for more details.
