AD9747 Analog Devices, AD9747 Datasheet - Page 22

• Manufacturer Part Number: AD9747
• Description: Dual 16-Bit 250 MSPS Digital-to-Analog Converters
• Manufacturer: Analog Devices

Specifications of AD9747

• Resolution (bits): 16bit
• Dac Update Rate: 250MSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): +3.47V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: Par

AD9741/AD9743/AD9745/AD9746/AD9747
DIGITAL INPUTS AND OUTPUTS
The AD9741/AD9743/AD9745/AD9746/AD9747 can operate
in two data input modes: dual-port mode and single-port mode.
For the default dual-port mode (ONEPORT = 0), each DAC
receives data from a dedicated input port. In single-port mode
(ONEPORT = 1), however, both DACs receive data from Port 1.
In single-port mode, DAC1 and DAC2 data is interleaved and
the IQSEL input is used to steer data to the correct DAC.
In single-port mode, when the IQSEL input is high, Port 1
data is delivered to DAC1 and when IQSEL is low, Port 1 data
is delivered to DAC2. The IQSEL input should always coincide
and be time-aligned with the other data bus signals. In single-
port mode, minimum setup and hold times apply to the IQSEL
input as well as to the input data signals. In dual-port mode, the
IQSEL input is ignored.
In dual-port mode, the data must be delivered at the sample rate
(up to 250 MSPS). In single-port mode, data must be delivered
at twice the sample rate. Because the data inputs function only
up to 250 MSPS, it is only practical to operate the DAC clock at
up to 125 MHz in single-port mode.
In both dual-port and single-port modes, a data clock output
(DCO) signal is available as a fixed time base with which to
stimulate data from an FPGA. This output signal always
operates at the sample rate. It may be inverted by asserting
the INVDCO bit.
INPUT DATA TIMING
With most DACs, signal-to-noise ratio (SNR) is a function of
the relationship between the position of the clock edges and the
point in time at which the input data changes. The AD9741/
AD9743/AD9745/AD9746/AD9747 are rising edge triggered
and thus exhibit greater SNR sensitivity when the data tran-
sition is close to this edge.
The specified minimum setup and hold times define a window
of time, within each data period, where the data is sampled
correctly. Generally, users should position data to arrive
relative to the DAC clock and well beyond the minimum
setup and minimum hold times. This becomes increasingly
more important at increasingly higher sample rates.
DUAL-PORT MODE TIMING
The timing diagram for the dual-port mode is shown in
Figure 27.
CLKP/CLKN
P1D<15:0>
P2D<15:0>
DCO
Figure 27. Data Interface Timing, Dual-Port Mode
t
DBS
Q1
I1
t
DBH
t
DCO
Q2
I2
Q3
I3
Q4
I4
Rev. 0 | Page 22 of 28
In Figure 27, data samples for DAC1 are labeled Ix and data
samples for DAC2 are labeled Qx. Note that the differential
DAC clock input is shown in a logical sense (CLKP/CLKN).
The data clock output is labeled DCO.
Setup and hold times are referenced to the positive transition of
the DAC clock. Data should arrive at the input pins such that
the minimum setup and hold times are met. Note that the data
clock output has a fixed time delay from the DAC clock and
may be a more convenient signal to use to confirm timing.
SINGLE-PORT MODE TIMING
The single-port mode timing diagram is shown in Figure 28.
CLKP/CLKN
In single-port mode, data for both DACs is received on the
Port 1 input bus. Ix and Qx data samples are interleaved and
arrive twice as fast as in dual-port mode. Accompanying the
data is the IQSEL input signal, which steers incoming data to its
respective DAC. When IQSEL is high, data is steered to DAC1
and when IQSEL is low, data is steered to DAC2. IQSEL should
coincide as well as be time-aligned with incoming data.
SPI PORT, RESET, AND PIN MODE
In general, when the AD9741/AD9743/AD9745/AD9746/
AD9747 are powered up, an active high pulse applied to the
RESET pin should follow. This insures the default state of all
control register bits. In addition, once the RESET pin goes low,
the SPI port can be activated, so CSB should be held high.
For applications without a controller, the AD9741/AD9743/
AD9745/AD9746/AD9747 also support pin mode operation,
which allows some functional options to be pin, selected with-
out the use of the SPI port. Pin mode is enabled anytime the
RESET pin is held high. In pin mode, the four SPI port pins
take on secondary functions, as shown in Table 16.
Table 16. SPI Pin Functions (Pin Mode)
Pin Name
SCLK
SDIO
CSB
SDO
P1D<15:0>
IQSEL
DCO
Figure 28. Data Interface Timing, Single-Port Mode
Pin Mode Description
ONEPORT (Register 0x02, Bit 6), bit value (1/0)
equals pin state (high/low)
DATTYPE (Register 0x02, Bit 7), bit value (1/0)
equals pin state (high/low)
Enable Mix Mode, if CSB is high, Register 0x0A
is set to 0x05 putting both DAC1 and DAC2 into
mix mode
Enable full power-down, if SDO is high, Register
0x03 is set to 0xFF
t
DBS
t
I1
DBH
t
DCO
Q1
I2
Q2