AD9146 Analog Devices, AD9146 Datasheet - Page 44

• Manufacturer Part Number: AD9146
• Description: Dual, 16-Bit, 1230 MSPS, TxDAC+® Digital-to-Analog Converter
• Manufacturer: Analog Devices

Specifications of AD9146

• Resolution (bits): 16bit
• Dac Update Rate: 1.23GSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): +3.47V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: Byte,LVDS,Nibble

AD9146
The Tx enable feature also allows for an extended delay from
when the TXENABLE pin is brought high to when the DAC
outputs begin transmitting the data present in the FIFO and
datapath. Two different delay lengths are available. These delays
allow the part to be set up properly during the delay time with-
out transmitting false data and to begin receiving correct data
after the datapath is flushed. The amount of delay time to be
allotted for various wake-up times depends on the delay setting
used, as well as which portions of the DAC are powered down
and need to be reinitialized.
Table 23 lists the minimum wait time required for the DAC to
begin transmitting again after the TXENABLE pin is brought
high. Regardless of the delay setting, there is an inherent fixed
delay of 10 DAC clock cycles for all the options listed in Table 23
before the DAC begins transmitting. Additionally, because the
Tx enable logic is timed from a divided-down rate of the DAC
clock—specifically, DAC/64—the number of edges that the part
waits for before allowing data to be transmitted from the DAC can
vary. Because the synchronization between the DAC/64 clock and
the Tx enable logic trigger is unknown, the number of DAC/64
clock edges that must be waited for before the outputs are released
can vary by up to one cycle.
Table 23. Wake-Up Time for Various Tx Enable Delay Settings
Register 0x02
No extended
delay (0x00)
Extended
Delay 0 (0x20)
Extended
Delay 1 (0x60)
1
2
For timing purposes and to ensure that incorrect data is flushed,
the minimum wake-up time must be considered. This constraint
determines how soon the datapath must begin to be flushed.
Depending on which portions of the DAC are powered down
using the Tx enable feature, the amount of time required to start
setting up the part and flushing the datapaths must be adjusted.
An appropriate delay setting is required to accommodate the
earliest possible wake-up time needed for flushing before the
outputs are enabled.
In addition to the delays listed in Table 23, specific wake-up
times for individual powered-down portions of the AD9146
must be accounted for during the preparation time.
Values may vary by up to one DAC/64 cycle for the amount of wake-up time
of each delay setting.
Values based on 737.28 MHz DAC rate condition; uses (number of DAC/64 +
10 DAC clocks) for calculation.
Number of
DAC/64 Edges
to Wait
1
12
19
1
Additional
DAC Edges
to Wait
10
10
10
Minimum
Wait Time
360.82 ns
4.18 µs
6.611 µs
Rev. A | Page 44 of 56
2
The following example provides a typical configuration that
uses the Tx enable feature to power down the interpolation
filters. This example provides guidelines for how to determine
the amount of wake-up time to design in a system.
•
•
•
•
•
•
•
•
The minimum wake-up time with no delay setting is 360.82 ns
(see Table 23). In this example, the time required to flush the
datapath is only 238 ns. Therefore, if datapath flushing is done
simultaneous to the TXENABLE pin being brought high, there
is enough time for the flush to complete before the minimum
possible time that the outputs can begin transmitting. For each
individual case, the amount of time needed to flush the data-
path must be accounted for when calculating the minimum
time after which the DACs can begin transmitting data.
The TXENABLE pin must be held high while the part is being
powered up. After the part is powered up, the pin can be brought
low to clamp the outputs, when desired. Note that the pin
cannot be held low during power-up because the circuit logic is
transition sensitive and the part must see a falling edge before it
clamps the outputs.
TEMPERATURE SENSOR
The AD9146 has a band gap temperature sensor for monitoring
the temperature change of the AD9146. The temperature must
be calibrated against a known temperature to remove the part-
to-part variation on the band gap circuit used to sense the
temperature. The DACCLK must be running at a minimum
of 100 MHz to obtain a reliable temperature measurement.
To monitor temperature change, the user must take a reading
at a known ambient temperature for a single-point calibration
of each AD9146 device.
where:
Code_x is the readback code at the unknown temperature, Tx.
Code_ref is the readback code at the calibrated temperature, T
To use the temperature sensor, it must be enabled by setting
Register 0x01, Bit 4, to 0. In addition, to obtain accurate read-
ings, the die temperature range control register (Register 0x48)
should be set to 0x02.
f
f
Interpolation = 4×
Inverse sinc on
Tx enable filter power-down option selected
Datapath flush time = 175 DAC clocks
t
t
Tx = T
DATA
DAC
DAC
DPFLUSH
= 737.28 MHz
= 1.36 ns
= 184.32 MHz
REF
= 238 ns
+ 7.7 × (Code_x − Code_ref)/1000 + 1
Data Sheet
REF
.