AD9786-EB Analog Devices Inc, AD9786-EB Datasheet - Page 42

• Manufacturer Part Number: AD9786-EB
• Description: BOARD EVALUATION FOR AD9786
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9786-EB

• Number Of Dac's: 1
• Number Of Bits: 16
• Outputs And Type: 1, Differential
• Sampling Rate (per Second): 500M
• Data Interface: Parallel
• Dac Type: Current
• Voltage Supply Source: Single
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9786
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD9786
Master/Slave, Modulator/DATACLK Master Modes
In applications where two or more AD9786s are used to synthe-
size several digital data paths, it might be necessary to ensure
that the digital inputs to each device are latched synchronously.
In complex data processing applications, digital modulator phase
alignment might be required between two AD9786s. To allow
data synchronization and phase alignment, only one AD9786
should be configured as a master device, providing a reference
clock for another slave-configured AD9786.
With synchronization enabled, a reference clock signal is
generated on the DATACLK pin of the master. The DATACLK
pins on the slave devices act as inputs for the reference clock
generated by the master. The DATACLK pin on the master and
all slaves must be directly connected. All master and slave devices
must have the same clock source connected to their respective
CLK+/CLK– pins.
When configured as a master, the reference clock generated can
take one of two forms. In modulator master mode, the reference
clock is a square wave with a period equal to 16 cycles of the
DAC update clock. Internal to the AD9786 is a 16-state, finite
state machine, running at the DAC update rate. This state machine
generates all internal and external synchronization clocks and
modulator phasings. The rising edge of the master reference clock
is time aligned to state zero of the internal state machine. Slave
devices use the master reference clock to synchronize data latching
and align modulator phase by aligning state zero of the local
state machine to the master.
STATE MACHINE
CHANNEL DATA
CYCLE CLOCK
COEFFICIENT
MODULATOR
RATE CLOCK
MACHINE
MODADJ
CLOCK
STATE
DAC
0
1
1
0
–1
2
3
0
4
1
5
0
000
–1
6
Figure 81. Synchronous Serial Modulator Phase Alignment
7
0
8
1
9
0
10 11 12 13 14 15
–1
0
Rev. B | Page 42 of 56
1
0
–1
0
The second master mode, DATACLK master mode, generates a
reference clock that is at the channel data rate. In this mode, the
slave devices align their internal channel data rate clock to the
master. If modulator phase alignment is needed, a concurrent
serial write to all slave devices is necessary. To achieve this, the
CSB pin on all slaves must be connected together, and a group
serial write to the MODADJ register bits must be performed.
Following a successful serial write, the modulator coefficient
alignment is updated upon the next rising edge of the internal
state machine (see Figure 81). Modulator master mode does not
need a concurrent serial write, because slaves lock to the master
phase automatically.
In a slave device, the local channel data rate clock and the
digital modulator clock are created from the internal state
machine. The local channel data rate clock is used by the slave
to latch digital input data. At high data rates, the delay inherent
in the signal path from master to slave can cause the slave to lag
the master when acquiring synchronization. To accommodate
for this, an integer number of the DAC update clock cycles can
be programmed into the slave device as an offset. The value in
DATAADJ allows the local channel data rate clock in the slave
device to advance by up to eight cycles of the DAC clock, or to
be delayed by up to seven cycles (see Figure 82).
The digital modulator coefficients are updated at the DAC clock
rate and decoded in sequential order from the state machine
according to Figure 83. The MODADJ bits can be used to align
a different coefficient to the finite state machine’s zero state, as
shown in Figure 84.
–1
0
1
0
2
1
3
0
–1
4
5
0
000
6
1
7
0
–1
8
9
0
10 11 12 13 14 15
1
0
–1
0
1
0