PRELIMINARY TECHNICAL DATA

REV. PrF 09/2003

AD5380

–33–

FIBRE

A D 5380,

40-C hannel,

14-BitDA C

DW DM

IN

DW DM

OU T

FIBRE

AD D

PO R TS

DRO P

PO R TS

FIBRE

Attenuator

Attenuator

Attenuator

Attenuator

AW G

AW G

.

.

.

.

.

.

.

.

.

N:1 Multiplexer

TIA/LOG AM P

(A D 8304/5)

16-BIT AD C

Photo-diodes

CO NTRO LLER

l

l

l

l

1

2

n-1

n

.

.

.

....

....

Optical

Sw itch

A D G 731

(40:1 MU X)

A D 7671

(0-5V,1M SPS)

Figure 20 . OADM using the AD5380 as part of an Optical Attenuator

Optical Attenuators

The AD5380 based on its high channel count, high resolution, monotonic behaviour and high level of integration is ide-

ally targetted at optical attenuation applications used in dynamc gain equilizers, variable optical attenuators (VOA) and

Optical Add-Drop Mutliplexers (OADM). In these applications each wavelength is individually extracted using an ar-

rayed wavequide and its power monitored using a photo-diode, transimpedance amplifier and ADC in a close loop

control system. The AD5380 controls the optical attenuator for each wavelength ensuring that the power is equilized in

all wavelengths before being multiplexed onto the fibre. This prevents information loss and saturation from occurring at

amplification stages further along the fibre.

Utilizing the AD5380 FIFO

The AD5380 FIFO mode optimizes total system update rate in applications where a large number of channels need to be

updated. FIFO mode is only available when the parallel interface mode is selected. The FIFOEN pin is used to enable

the FIFO. The status of the FIFOEN pin is sampled during the initialisation sequence, therefore the FIFO status can

only be changed by resetting the device. An example of where a large number of channels need to be updated in a short

period of time would be in a telescope that provides for the cancellation of atmospheric distortion. In these systems as

many as 400channels need to be updated in a window of 40us. 400 channels necessitates the use of 10* AD5380 devices.

With FIFO mode enabled the data write cycle time is 40ns, therefore each group consisting of 40 channels can be fully

loaded 1.6us. In FIFO mode a complete group of 40 channels will update in 14.4us. Therefore the time taken to update

all 400channels will equate to 14.4us +9*1.6us = 28.8us. Figure 21 shows a graphical view of the FIFO operation

scheme.

GROUP A

Chnls 0-39

GROUP B

Chnls 40-79

GROUP C

Chnls 80-119

GROUP D

Chnls 120-159

GROUP E

Chnls 160-199

GROUP F

Chnls 200-239

GROUP H

Chnls 280-319

GROUP G

Chnls 240-279

GROUP I

Chnls 320-359

Time to Update 400 Channels = 28.8us

GROUP J

Chnls 360-399

1.6us

14.4us

FIFO DATA LOAD

Group B

1.6us

FIFO DATA LOAD

Group A

Output Update

Time for Group A

Output Update

Time for Group B

14.4us

FIFO DATA LOAD

Group J

1.6us

Output Update

Time for Group J

14.4us

Figure 21. Using FIFO mode 400 Channels Updated in under 30us.