AD5381BSTZ-5 Datasheet, PDF (35/40 Pages) Analog Devices – 40-Channel, 3 V/5 V, Single-Supply 12-Bit, denseDAC

Data Sheet
AD5381
DATA
REGISTER
A
DAC
REGISTER
12-BIT DAC
VOUT
INPUT INPUT
DATA REGISTER
DATA
REGISTER
B
A/B
LDAC
CONTROL INPUT
Figure 42. Toggle Mode Function
OPTICAL ATTENUATORS
Based on its high channel count, high resolution, monotonic
behavior, and high level of integration,the AD5381 is ideally
targeted at optical attenuation applications used in dynamic
gain equalizers, variable optical attenuators (VOAs), and optical
add-drop multiplexers(OADMs). In these applications, each
wavelength is individually extracted using an arrayed wave
guide; its power is monitoredusing a photodiode, transimped-
ance amplifier and ADC in a closed-loop control system. The
AD5381 controls the optical attenuator for each wavelength,
ensuring that the power is equalized in all wavelengthsbefore
being multiplexed onto the fiber. This preventsinformation loss
and saturation from occurring at amplification stages further
along the fiber.
UTILIZING FIFO
The AD5381 FIFO mode optimizes total system update rates
in applications where a large number of channels needto be
updated. FIFO mode is only available when parallel interface
mode is selected. The FIFO EN pin is used to enable the FIFO.
The status of FIFO EN is sampled during the initialization
sequence. Therefore,the FIFO statuscan only be changed by
resetting the device.
In a telescope that provides for the cancel-lation of atmospheric
distortion, for example, a large numberof channels need to be
updated in a short period of time. In such systems, as manyas
400 channels need to be updated within 40 µs. Four-hundred
channels require the use of 10 AD5381s. With FIFO mode
enabled, the data write cycle time is 40 ns; therefore, each group
consisting of 40 channels can be fully loaded in 1.6 µs. In FIFO
mode, a complete groupof 40 chan-nels will update in 14.4 µs.
The time taken to update all 400 channels is
14.4 µs + 9 × 1.6 µs = 28.8 µs.
Figure 44 shows the FIFO operation scheme.
ADD
PORTS
DROP
PORTS
11
DWDM
12
IN
FIBRE _AWG
1n–1
1n
OPTICAL
SWITCH
PHOTODIODES
ATTENUATOR
ATTENUATOR
DWDM
OUT
AWG FIBRE
ATTENUATOR
ATTENUATOR
AD5381,
40-CHANNEL,
12-BIT DAC
TIA/LOG AMP
(AD8304/AD8305)
N:1 MULTIPLEXER
ADG731
(40:1 MUX)
CONTROLLER
16-BIT ADC
AD7671
(0V TO 5V, 1MSPS)
Figure 43. OADM Using the AD5381 as Part of an Optical Attenuator
Rev. D | Page 35 of 40