ISL59533 Datasheet, PDF(21/24 Page) Intersil Corporation – 32x32 Video Crosspoint with Differential Inputs

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ISL59533 Datasheet, PDF (21/24 Pages) Intersil Corporation – 32x32 Video Crosspoint with Differential Inputs

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ISL59533

Gain Setting

The gain of each output may be set to 1 or 2 using the gain set word. It is in the same format as the output enable control word:

TABLE 5. GAIN SET FORMAT

B15 B14 B13 B12 B11 B10 B9

N0 Gn+7 Gn+6 Gn+5 Gn+4 Gn+3 Gn+2 Gn+1 Gn

Input to Output Selection

Individual outputs receive their input selection choice using the input/output control word. Its format is:

TABLE 6. INPUT/OUTPUT WORD

B15 B14 B13 B12 B11 B10 B9

For a given binarily selected output, as specified by the O's, an input channel is assigned by the binarily selected I's. Thirty-two

transmissions of the input/output control words will be required to set up all outputs.

Broadcast Mode

The broadcast mode routs one input to all 32 outputs. It has a memory bit that remembers its state. The configuration of

input/output assignments that existed before setting broadcast mode is kept in memory and when broadcast mode is disabled the

previous configuration is restored. The broadcast control word format is:

TABLE 7. BROADCAST WORD

B15 B14 B13 B12 B11 B10 B9

EB sets or resets the broadcast mode memory bit. The I's binarily select the input channel to be broadcast to all outputs.

Note: Going from broadcast mode to normal crosspoint mode can alter the input/output configuration. All input/output

selections currently must be re-sent after a broadcast-to-non-broadcast transition.

Bandwidth Considerations

Wide frequency response (high bandwidth) in a video

system means better video resolution. Four sets of

frequency response curves are shown in Figure 47.

Depending on the switch configurations, one can get

between 250MHz to 350MHz bandwidth. A short discussion

of the trade-offs followsâincluding matrix configuration,

output buffer gain selection, channel selection, and loading.

Mux, Av = 2

Mux, Av = 1

-2

Broadcast,

Av = 2

Broadcast,

-4

Av = 1

-6

-8

-10

100

Frequency [MHz]

1000

32 outputs. The parasitic capacitance of all 32 channels

loads down the input and reduces bandwidth in broadcast

mode. In addition, output buffer gain of +2 has higher

bandwidth than gain of +1 due to internal device

compensation. Therefore, the highest bandwidth set-up is

multiplexer mode and output buffer gain of +2.

The relative location of the input and output channel also has

significant impact on the device bandwidth. Again this is due

to the layout of the device. When the input and output

channels are further away, there are additional parasitics as

a result of the distance and lower bandwidth results.

The bandwidth does not change significantly with resistive

loading as shown in Figure 3 in the typical performance

curves. However, it does change greatly with capacitance

loading, Figure 4 in typical performance curves. This is most

significant when laying out the PCB. If the PCB trace

between the output of the crosspoint switch and the back

termination resistor is not minimized, additional parasitic

capacitance severely distorts the frequency response.

FIGURE 47. FREQUENCY RESPONSE FOR VARIOUS MODES

In multiplexer mode, the input only drives one output

channel, while in broadcast mode the same input drives all

To emphasize how critical the PCB layout is to performance,

letâs compare the two boards presented in Figures 48 and

49. Figure 48 shows a larger engineering evaluation board

where the termination resistor is far away from the device

because of the use of a socket. The board in Figure 48 is a

FN6222.0

March 13, 2006

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