AD8114AST datasheet(21/32 Pages) AD

21 / 32 page

AD8114/AD8115

Rev. B | Page 21 of 32

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

Ω

AD8115

OUT 00Ð15

NONBLOCKING

ADDITIONAL

16 OUTPUTS

(SUBJECT

TO BLOCKING)

AD8114

Figure 49. Nonblocking 128 × 16 Array (128 × 32 Blocking)

Using additional crosspoint devices in the design can lower the

number of outputs that must be wire-OR’ed together. Figure 49

shows a block diagram of a system using eight AD8114s and

two AD8115s to create a nonblocking, gain-of-2, 128 × 16

crosspoint that restricts the wire-OR’ing 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

technique. 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

system 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

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