AD8115AST datasheet(17/26 Pages) AD

17 / 26 page

AD8114/AD8115

–17–

REV. 0

two AD8115s to create a nonblocking, gain-of-two, 128

× 16

crosspoint that restricts the wire-ORing at the output to only

four outputs.

Additionally, by using the lower eight outputs from each of the

two Rank 2 AD8115s, a blocking 128

× 32 crosspoint array can

be realized. There are, however, some drawbacks to this tech-

nique. The offset voltages of the various cascaded devices will

accumulate and the bandwidth limitations of the devices will

compound. 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 tradeoffs.

Multichannel Video

The excellent video specifications of the AD8114/AD8115 make

them ideal candidates for creating composite video crosspoint

switches. These can be made quite dense by taking advantage of

the AD8114/AD8115’s high level of integration and the fact that

composite video requires only one crosspoint channel per sys-

tem video channel. There are, however, other video formats that

can be routed with the AD8114/AD8115 requiring more than

one crosspoint channel per video channel.

Some systems use twisted-pair wiring to carry video signals.

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 video signals are differential; there is a

positive and negative (or inverted) version 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 channel. Thus, one differential

video channel is assigned to a pair of crosspoint channels, both

input and output. For a single AD8114/AD8115, eight differential

video 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 by

inspection of the programming format of the AD8114/AD8115

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.

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

AD8114)

128:32

RTERM

AD8115

OUT 00–15

NONBLOCKING

ADDITIONAL

16 OUTPUTS

(SUBJECT

TO BLOCKING)

AD8114

Figure 43. Nonblocking 128

× 16 Array (128 × 32 Blocking)

AD8115AST датащи(PDF) 17 Page - Analog Devices

AD8115AST датащи(HTML) 17 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

датащи скачать

ссылки URL