AD8113JSTZ datasheet(19/28 Pages) AD

19 / 28 page

REV. A

AD8113

–19–

late, and the bandwidth limitations of the devices will com-

pound. In addition, the extra devices will consume more current

and take up more board space. Once again, the overall system

design specifications will determine how to make the various

trade-offs.

Multichannel Video and Audio

The good video specifications of the AD8113 make it an ideal

candidate for creating composite video crosspoint switches. These

can be made quite dense by taking advantage of the AD8113’s

high level of integration and the fact that composite video requires

only one crosspoint channel per system video channel. There are,

however, other video formats that can be routed with the AD8113,

requiring more than one crosspoint channel per video channel.

Some systems use twisted-pair wiring to carry video or audio sig-

nals. These systems utilize differential signals and can lower costs

because they use lower cost cables, connectors, and termination

methods. They also have the ability to lower crosstalk and reject

common-mode signals, which can be important for equipment that

operates in noisy environments, or where common-mode voltages

are present between transmitting and receiving equipment.

In such systems, the audio or video signals are differential; there

are positive and negative (or inverted) versions of the signals.

These complementary signals are transmitted onto each of the

two wires of the twisted pair, yielding a first order zero common-

mode voltage. At the receive end, the signals are differentially

received and converted back into a single-ended signal.

When switching these differential signals, two channels are

required in the switching element to handle the two differential

signals that make up the video or audio channel. Thus, one

differential video or audio channel is assigned to a pair of

crosspoint channels, both input and output. For a single AD8113,

eight differential video or audio channels can be assigned to the

16 inputs and 16 outputs. This will effectively form an 8

× 8

differential crosspoint switch.

Programming such a device will require that inputs and outputs be

programmed in pairs. This information can be deduced through

inspection of the programming format of the AD8113 and the

requirements of the system.

There are other analog video formats requiring more than one

analog circuit per video channel. One two-circuit format that is

commonly being used in systems such as satellite TV, digital

cable boxes, and higher quality VCRs, is called S-video or Y/C

video. This format carries the brightness (luminance or Y)

portion of the video signal on one channel and the color (chromi-

nance, chroma, or C) on a second channel.

Since S-video also uses two separate circuits for one video channel,

creating a crosspoint system requires assigning one video channel

to two crosspoint channels as in the case of a differential video

system. Aside from the nature of the video format, other aspects

of these two systems will be the same. Stereo audio can also be

routed in a paired-channel arrangement similar to a two-channel

video system.

RTERM

IN 00–15

IN 16–31

IN 32–47

IN 48–63

IN 64 –79

IN 80–95

IN 96 –111

IN 112 –127

RANK 2

32:16 NONBLOCKING

(32:32 BLOCKING)

RANK 1

AD8113)

128:32

RTERM

AD8113

OUT 00 –15

NONBLOCKING

ADDITIONAL

16 OUTPUTS

(SUBJECT

TO BLOCKING)

AD8113

Figure 12. Nonblocking 128

× 16 Audio Array (128 × 32 Blocking)

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