GS1528A / GS9068A Data Sheet

30953 - 4

January 2006

9 of 16

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 2000mVpp.

•

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

•

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 75

Ω

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 75

Ω 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 Section 6.2 is recommended.

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 Section 6.0 for more details.