AD8107 datasheet(17/28 Pages) AD

17 / 28 page

AD8106/AD8107

Rev. 0 | Page 17 of 28

Figure 46 illustrates this concept for a 32 × 5 crosspoint array.

AD8106

AD8107

RTERM

IN 00–15

AD8106

AD8107

IN 16–31

Figure 46. A 32 × 5 Crosspoint Array Using Two AD8106s or Two AD8107s

The inputs are uniquely assigned to each of the 32 inputs of the

two devices and terminated appropriately. The outputs are wire-

OR’ed together in pairs. The output from only one of a wire-OR’ed

pair should be enabled at any given time. The device program-

ming software must be properly written to cause this to happen.

At some point, the number of outputs that are wire-OR’ed becomes

too great to maintain system performance. This varies according

to which system specifications are most important. It also

depends on whether the matrix consists of AD8106s or AD8107s.

The output disabled impedance of the AD8106 is much

higher than that of the AD8107. As a result, its disabled

parasitics have a smaller effect on the one output that is

enabled. For example, a 128 × 5 crosspoint can be created

with eight AD8106s/AD8107s. This design has 128 separate

inputs and the corresponding outputs of each device wire-

OR’ed together in groups of eight.

Using additional crosspoint devices in the design can lower the

number of outputs that must be wire-OR’ed together. Figure 47

shows a block diagram of a system using eight AD8106s and

two AD8107s to create a nonblocking, gain-of-two, 128 × 5

crosspoint that restricts the wire-OR’ing at the output to only

four outputs.

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

two Rank 2 AD8107s, a blocking 128 × 10 crosspoint array can

be realized. There are, however, some drawbacks to this technique.

The offset voltages of the various cascaded devices accumulate

and the bandwidth limitations of the devices compound. The

extra devices also consume more current and take up more

board space. Once again, the overall system design specifica-

tions determine which tradeoffs should be made.

RANK 2

16:8 NONBLOCKING

(16:16 BLOCKING)

RANK 1

(8 × AD8106)

128:16

AD8107

AD8106

OUT 00–04

NONBLOCKING

ADDITIONAL

5 OUTPUTS

(SUBJECT TO

BLOCKING)

1kΩ

IN 00–15

RTERM

IN 16–31

RTERM

IN 32–47

RTERM

IN 48–63

RTERM

IN 64–79

RTERM

IN 80–95

RTERM

IN 96–111

RTERM

IN 112–127

RTERM

Figure 47. A Gain-of-Two 128 × 5 Nonblocking Crosspoint Array (128 × 10 Blocking)

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