14-Bit, 210 MSPS TxDAC®
D/A Converter
AD9744
Data Sheet
FEATURES
APPLICATIONS
High performance member of pin-compatible
TxDAC product family
Excellent spurious-free dynamic range performance
SFDR to Nyquist
83 dBc at 5 MHz output
80 dBc at 10 MHz output
73 dBc at 20 MHz output
SNR at 5 MHz output, 125 MSPS: 77 dB
Twos complement or straight binary data format
Differential current outputs: 2 mA to 20 mA
Power dissipation: 135 mW at 3.3 V
Power-down mode: 15 mW at 3.3 V
On-chip 1.2 V reference
CMOS-compatible digital interface
28-lead SOIC, 28-lead TSSOP, and 32-lead LFCSP packages
Edge-triggered latches
Wideband communication transmit channel
Direct IFs
Base stations
Wireless local loops
Digital radio links
Direct digital synthesis (DDS)
Instrumentation
FUNCTIONAL BLOCK DIAGRAM
3.3V
REFLO
1.2V REF
REFIO
FS ADJ
RSET
3.3V
CURRENT
SOURCE
ARRAY
DVDD
DCOM
CLOCK
AVDD
150pF
ACOM
AD9744
IOUTA
SEGMENTED
SWITCHES
CLOCK
LSB
SWITCHES
IOUTB
LATCHES
DIGITAL DATA INPUTS (DB13–DB0)
SLEEP
MODE
02913-001
0.1µF
Figure 1.
GENERAL DESCRIPTION
The AD9744 1 is a 14-bit resolution, wideband, third generation
member of the TxDAC series of high performance, low power
CMOS digital-to-analog converters (DACs). The TxDAC family,
consisting of pin-compatible 8-, 10-, 12-, and 14-bit DACs, is
specifically optimized for the transmit signal path of communication systems. All of the devices share the same interface options,
small outline package, and pinout, providing an upward or
downward component selection path based on performance,
resolution, and cost. The AD9744 offers exceptional ac and dc
performance while supporting update rates up to 210 MSPS.
The AD9744’s low power dissipation makes it well suited for
portable and low power applications. Its power dissipation can
be further reduced to a mere 60 mW with a slight degradation
in performance by lowering the full-scale current output. Also,
a power-down mode reduces the standby power dissipation to
approximately 15 mW. A segmented current source architecture
is combined with a proprietary switching technique to reduce
spurious components and enhance dynamic performance.
Edge-triggered input latches and a 1.2 V temperature compensated
band gap reference have been integrated to provide a complete
monolithic DAC solution. The digital inputs support 3 V
CMOS logic families.
PRODUCT HIGHLIGHTS
1. The AD9744 is the 14-bit member of the pin compatible TxDAC
family, which offers excellent INL and DNL performance.
2. Data input supports twos complement or straight binary data
coding.
3. High speed, single-ended CMOS clock input supports
210 MSPS conversion rate.
4. Low power: Complete CMOS DAC function operates on
135 mW from a 2.7 V to 3.6 V single supply. The DAC fullscale current can be reduced for lower power operation, and a
sleep mode is provided for low power idle periods.
5. On-chip voltage reference: The AD9744 includes a 1.2 V
temperature compensated band gap voltage reference.
6. Industry-standard 28-lead SOIC, 28-lead TSSOP, and 32-lead
LFCSP packages.
Protected by U.S. Patent Numbers 5568145, 5689257, and 5703519.
1
Rev. C
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AD9744
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Reference Control Amplifier .................................................... 13
Applications ....................................................................................... 1
DAC Transfer Function ............................................................. 14
Functional Block Diagram .............................................................. 1
Analog Outputs .......................................................................... 14
General Description ......................................................................... 1
Digital Inputs .............................................................................. 15
Product Highlights ........................................................................... 1
Clock Input.................................................................................. 15
Revision History ............................................................................... 2
DAC Timing................................................................................ 16
Specifications..................................................................................... 3
Power Dissipation....................................................................... 16
DC Specifications ......................................................................... 3
Applying the AD9744 ................................................................ 17
Dynamic Specifications ............................................................... 4
Differential Coupling Using a Transformer............................ 17
Digital Specifications ................................................................... 5
Differential Coupling Using an Op Amp ................................ 17
Absolute Maximum Ratings............................................................ 6
Single-Ended Unbuffered Voltage Output .............................. 18
Thermal Characteristics .............................................................. 6
Single-Ended, Buffered Voltage Output Configuration ........ 18
ESD Caution .................................................................................. 6
Pin Configurations and Function Descriptions ........................... 7
Power and Grounding Considerations, Power Supply
Rejection ...................................................................................... 18
Typical Performance Characteristics ............................................. 8
Evaluation Board ............................................................................ 20
Terminology .................................................................................... 12
General Description ................................................................... 20
Functional Description .................................................................. 13
Outline Dimensions ....................................................................... 30
Reference Operation .................................................................. 13
Ordering Guide............................................................................... 31
REVISION HISTORY
12/13—Rev. B to Rev. C
Added Table 5; Renumbered Sequentially .................................... 6
Added Exposed Pad Note to Figure 4 and Table 6, Pin
Configurations and Function Descriptions Section .................... 7
Moved Terminology Section ......................................................... 12
Updated Outline Dimensions ....................................................... 30
Changes to Ordering Guide .......................................................... 31
4/05—Rev. A to Rev. B
Updated Format .................................................................. Universal
Changes to General Description .................................................... 1
Changes to Product Highlights....................................................... 1
Changes to DC Specifications ......................................................... 3
Changes to Dynamic Specifications ............................................... 4
Changes to Pin Function Description ........................................... 7
Changes to Figure 6 and Figure 9 ................................................... 9
Inserted New Figure 10; Renumbered Sequentially .................... 9
Changes to Figure 12, Figure 13, Figure 14, and Figure 15 ...... 10
Changes to Figure 22 Caption ...................................................... 11
Inserted New Figure 23; Renumbered Sequentially .................. 11
Changes to Functional Description ............................................. 13
Changes to Reference Operation Section .................................... 13
Added Figure 25; Renumbered Sequentially .............................. 13
Changes to Digital Inputs Section ................................................ 15
Changes to Figure 31 and Figure 32............................................. 16
Updated Outline Dimensions ....................................................... 30
Changes to Ordering Guide .......................................................... 31
5/03—Rev. 0 to Rev. A
Added 32-Lead LFCSP Package ....................................... Universal
Edits to Features.................................................................................1
Edits to Product Highlights..............................................................1
Edits to DC Specifications ................................................................2
Edits to Dynamic Specifications ......................................................3
Edits to Digital Specifications ..........................................................4
Edits to Absolute Maximum Ratings ..............................................5
Edits to Thermal Characteristics .....................................................5
Edits to Ordering Guide ...................................................................5
Edits to Pin Configuration ...............................................................6
Edits to Pin Function Descriptions .................................................6
Edits to Figure 2 .................................................................................7
Replaced TPCs 1, 4, 7, and 8 ............................................................8
Edits to Figure 3 .............................................................................. 10
Edits to Functional Description ................................................... 10
Added Clock Input Section ........................................................... 12
Added Figure 7 ............................................................................... 12
Edits to DAC Timing Section ....................................................... 12
Edits to Sleep Mode Operation Section....................................... 13
Edits to Power Dissipation Section .............................................. 13
Renumbered Figures 8 to Figure 26 ............................................. 13
Added Figure 11 ............................................................................. 13
Added Figure 27 to Figure 35 ....................................................... 21
Updated Outline Dimensions ....................................................... 26
Rev. C | Page 2 of 32
Data Sheet
AD9744
SPECIFICATIONS
DC SPECIFICATIONS
TMIN to TMAX, AVDD = 3.3 V, DVDD = 3.3 V, CLKVDD = 3.3 V, IOUTFS = 20 mA, unless otherwise noted.
Table 1.
Parameter
RESOLUTION
DC ACCURACY 1
Integral Linearity Error (INL)
Differential Nonlinearity (DNL)
ANALOG OUTPUT
Offset Error
Gain Error (Without Internal Reference)
Gain Error (With Internal Reference)
Full-Scale Output Current 2
Output Compliance Range
Output Resistance
Output Capacitance
REFERENCE OUTPUT
Reference Voltage
Reference Output Current 3
REFERENCE INPUT
Input Compliance Range
Reference Input Resistance (External Reference)
Small Signal Bandwidth
TEMPERATURE COEFFICIENTS
Offset Drift
Gain Drift (Without Internal Reference)
Gain Drift (With Internal Reference)
Reference Voltage Drift
POWER SUPPLY
Supply Voltages
AVDD
DVDD
CLKVDD
Analog Supply Current (IAVDD)
Digital Supply Current (IDVDD) 4
Clock Supply Current (ICLKVDD)
Supply Current Sleep Mode (IAVDD)
Power Dissipation4
Power Dissipation 5
Power Supply Rejection Ratio—AVDD 6
Power Supply Rejection Ratio—DVDD6
OPERATING RANGE
Min
14
Typ
Max
Unit
Bits
−5
−3
±0.8
±0.5
+5
+3
LSB
LSB
+0.02
+0.5
+0.5
20
+1.25
% of FSR
% of FSR
% of FSR
mA
V
kΩ
pF
1.26
V
nA
1.25
7
0.5
V
kΩ
MHz
0
±50
±100
±50
ppm of FSR/°C
ppm of FSR/°C
ppm of FSR/°C
ppm/°C
−0.02
−0.5
−0.5
2
−1
±0.1
±0.1
100
5
1.14
1.20
100
0.1
2.7
2.7
2.7
−1
−0.04
−40
3.3
3.3
3.3
33
8
5
5
135
145
3.6
3.6
3.6
36
9
6
6
145
+1
+0.04
+85
Measured at IOUTA, driving a virtual ground.
Nominal full-scale current, IOUTFS, is 32 times the IREF current.
3
An external buffer amplifier with input bias current 100 kΩ).
Figure 27. External Reference Configuration
REFERENCE CONTROL AMPLIFIER
The AD9744 contains a control amplifier that is used to regulate
the full-scale output current, IOUTFS. The control amplifier is
configured as a V-I converter, as shown in Figure 26, so that its
current output, IREF, is determined by the ratio of the VREFIO and
an external resistor, RSET, as stated in Equation 4. IREF is copied
to the segmented current sources with the proper scale factor to
set IOUTFS, as stated in Equation 3.
Rev. C | Page 13 of 32
AD9744
Data Sheet
The control amplifier allows a wide (10:1) adjustment span of
IOUTFS over a 2 mA to 20 mA range by setting IREF between 62.5 µA
and 625 µA. The wide adjustment span of IOUTFS provides several
benefits. The first relates directly to the power dissipation of the
AD9744, which is proportional to IOUTFS (refer to the Power
Dissipation section). The second relates to the 20 dB adjustment,
which is useful for system gain control purposes.
Equation 7 and Equation 8 highlight some of the advantages of
operating the AD9744 differentially. First, the differential operation
helps cancel common-mode error sources associated with IOUTA
and IOUTB, such as noise, distortion, and dc offsets. Second, the
differential code dependent current and subsequent voltage, VDIFF,
is twice the value of the single-ended voltage output (that is, VOUTA
or VOUTB), thus providing twice the signal power to the load.
The small signal bandwidth of the reference control amplifier is
approximately 500 kHz and can be used for low frequency small
signal multiplying applications.
Note that the gain drift temperature performance for a singleended (VOUTA and VOUTB) or differential output (VDIFF) of the
AD9744 can be enhanced by selecting temperature tracking
resistors for RLOAD and RSET due to their ratiometric relationship,
as shown in Equation 8.
DAC TRANSFER FUNCTION
Both DACs in the AD9744 provide complementary current
outputs, IOUTA and IOUTB. IOUTA provides a near full-scale
current output, IOUTFS, when all bits are high (that is, DAC
CODE = 16383), while IOUTB, the complementary output,
provides no current. The current output appearing at IOUTA
and IOUTB is a function of both the input code and IOUTFS and
can be expressed as
IOUTA = (DAC CODE /16384 ) × I OUTFS
(1)
IOUTB = (16383 − DAC CODE )/16384 × I OUTFS
(2)
where DAC CODE = 0 to 16383 (that is, decimal representation).
As mentioned previously, IOUTFS is a function of the reference
current IREF, which is nominally set by a reference voltage,
VREFIO, and external resistor, RSET. It can be expressed as
I OUTFS = 32 × I REF
(3)
where
I REF = VREFIO / RSET
(4)
The two current outputs will typically drive a resistive load
directly or via a transformer. If dc coupling is required, IOUTA
and IOUTB should be directly connected to matching resistive
loads, RLOAD, that are tied to analog common, ACOM. Note that
RLOAD may represent the equivalent load resistance seen by
IOUTA or IOUTB as would be the case in a doubly terminated
50 Ω or 75 Ω cable. The single-ended voltage output appearing
at the IOUTA and IOUTB nodes is simply
VOUTA = IOUTA × RLOAD
(5)
VOUTB = IOUTB × RLOAD
(6)
Note that the full-scale value of VOUTA and VOUTB should not
exceed the specified output compliance range to maintain
specified distortion and linearity performance.
VDIFF
= (IOUTA − IOUTB ) × RLOAD
(7)
Substituting the values of IOUTA, IOUTB, IREF, and VDIFF can be
expressed as
[
V DIFF = (2 × DAC CODE − 16383 )/16384
(32 × RLOAD / RSET )× VREFIO
]
(8)
ANALOG OUTPUTS
The complementary current outputs in each DAC, IOUTA, and
IOUTB may be configured for single-ended or differential operation. IOUTA and IOUTB can be converted into complementary
single-ended voltage outputs, VOUTA and VOUTB, via a load resistor,
RLOAD, as described in the DAC Transfer Function section by
Equation 5 through Equation 8. The differential voltage, VDIFF,
existing between VOUTA and VOUTB, can also be converted to a
single-ended voltage via a transformer or differential amplifier
configuration. The ac performance of the AD9744 is optimum
and specified using a differential transformer-coupled output in
which the voltage swing at IOUTA and IOUTB is limited to ±0.5 V.
The distortion and noise performance of the AD9744 can be
enhanced when it is configured for differential operation. The
common-mode error sources of both IOUTA and IOUTB can
be significantly reduced by the common-mode rejection of a
transformer or differential amplifier. These common-mode
error sources include even-order distortion products and noise.
The enhancement in distortion performance becomes more
significant as the frequency content of the reconstructed
waveform increases and/or its amplitude decreases. This is due
to the first-order cancellation of various dynamic commonmode distortion mechanisms, digital feedthrough, and noise.
Performing a differential-to-single-ended conversion via a
transformer also provides the ability to deliver twice the
reconstructed signal power to the load (assuming no source
termination). Since the output currents of IOUTA and IOUTB
are complementary, they become additive when processed
differentially. A properly selected transformer will allow the
AD9744 to provide the required power and voltage levels to
different loads.
The output impedance of IOUTA and IOUTB is determined by
the equivalent parallel combination of the PMOS switches
associated with the current sources and is typically 100 kΩ in
parallel with 5 pF. It is also slightly dependent on the output
voltage (that is, VOUTA and VOUTB) due to the nature of a PMOS
device. As a result, maintaining IOUTA and/or IOUTB at a
virtual ground via an I-V op amp configuration will result in
the optimum dc linearity. Note that the INL/DNL specifications
Rev. C | Page 14 of 32
Data Sheet
AD9744
for the AD9744 are measured with IOUTA maintained at a
virtual ground via an op amp.
CLOCK INPUT
IOUTA and IOUTB also have a negative and positive voltage
compliance range that must be adhered to in order to achieve
optimum performance. The negative output compliance range
of −1 V is set by the breakdown limits of the CMOS process.
Operation beyond this maximum limit may result in a breakdown
of the output stage and affect the reliability of the AD9744.
The 28-lead package options have a single-ended clock input
(CLOCK) that must be driven to rail-to-rail CMOS levels. The
quality of the DAC output is directly related to the clock quality,
and jitter is a key concern. Any noise or jitter in the clock will
translate directly into the DAC output. Optimal performance
will be achieved if the CLOCK input has a sharp rising edge,
since the DAC latches are positive edge triggered.
SOIC/TSSOP Packages
The positive output compliance range is slightly dependent on
the full-scale output current, IOUTFS. It degrades slightly from its
nominal 1.2 V for an IOUTFS = 20 mA to 1 V for an IOUTFS = 2 mA.
The optimum distortion performance for a single-ended or
differential output is achieved when the maximum full-scale
signal at IOUTA and IOUTB does not exceed 0.5 V.
DIGITAL INPUTS
The AD9744 digital section consists of 14 input bit channels
and a clock input. The 14-bit parallel data inputs follow
standard positive binary coding, where DB13 is the most
significant bit (MSB) and DB0 is the least significant bit (LSB).
IOUTA produces a full-scale output current when all data bits
are at Logic 1. IOUTB produces a complementary output with
the full-scale current split between the two outputs as a
function of the input code.
DVDD
LFCSP Package
A configurable clock input is available in the LFCSP package,
which allows for one single-ended and two differential modes.
The mode selection is controlled by the CMODE input, as
summarized in Table 7. Connecting CMODE to CLKCOM
selects the single-ended clock input. In this mode, the CLK+
input is driven with rail-to-rail swings and the CLK– input is
left floating. If CMODE is connected to CLKVDD, the differential
receiver mode is selected. In this mode, both inputs are high
impedance. The final mode is selected by floating CMODE. This
mode is also differential, but internal terminations for positive
emitter-coupled logic (PECL) are activated. There is no significant
performance difference among any of the three clock input modes.
Table 7. Clock Mode Selection
CMODE Pin
CLKCOM
CLKVDD
Float
02913-025
DIGITAL
INPUT
Clock Input Mode
Single-Ended
Differential
PECL
The single-ended input mode operates in the same way as the
CLOCK input in the 28-lead packages, as previously described.
Figure 28. Equivalent Digital Input
The digital interface is implemented using an edge-triggered
master/slave latch. The DAC output updates on the rising edge
of the clock and is designed to support a clock rate as high as
210 MSPS. The clock can be operated at any duty cycle that
meets the specified latch pulse width. The setup and hold
times can also be varied within the clock cycle as long as the
specified minimum times are met, although the location of
these transition edges may affect digital feedthrough and
distortion performance. Best performance is typically achieved
when the input data transitions on the falling edge of a 50%
duty cycle clock.
In the differential input mode, the clock input functions as a
high impedance differential pair. The common-mode level of
the CLK+ and CLK− inputs can vary from 0.75 V to 2.25 V, and
the differential voltage can be as low as 0.5 V p-p. This mode
can be used to drive the clock with a differential sine wave since
the high gain bandwidth of the differential inputs will convert
the sine wave into a single-ended square wave internally.
The final clock mode allows for a reduced external component
count when the DAC clock is distributed on the board using
PECL logic. The internal termination configuration is shown in
Figure 29. These termination resistors are untrimmed and can
vary up to ±20%. However, matching between the resistors
should generally be better than ±1%.
Rev. C | Page 15 of 32
AD9744
Data Sheet
POWER DISSIPATION
AD9744
The power dissipation, PD, of the AD9744 is dependent on
several factors that include:
CLOCK
RECEIVER
CLK–
•
50Ω
02913-026
50Ω
TO DAC CORE
VTT = 1.3V NOM
•
•
•
Figure 29. Clock Termination in PECL Mode
DAC TIMING
Input Clock and Data Timing Relationship
Dynamic performance in a DAC is dependent on the relationship
between the position of the clock edges and the time at which
the input data changes. The AD9744 is rising edge triggered,
and so exhibits dynamic performance sensitivity when the data
transition is close to this edge. In general, the goal when applying
the AD9744 is to make the data transition close to the falling
clock edge. This becomes more important as the sample rate
increases. Figure 30 shows the relationship of SFDR to clock
placement with different sample rates. Note that at the lower
sample rates, more tolerance is allowed in clock placement,
while at higher rates, more care must be taken.
The power supply voltages (AVDD, CLKVDD, and
DVDD)
The full-scale current output IOUTFS
The update rate fCLOCK
The reconstructed digital input waveform
The power dissipation is directly proportional to the analog supply
current, IAVDD, and the digital supply current, IDVDD. IAVDD is
directly proportional to IOUTFS, as shown in Figure 31, and is
insensitive to fCLOCK. Conversely, IDVDD is dependent on both the
digital input waveform, fCLOCK, and digital supply DVDD. Figure 32
shows IDVDD as a function of full-scale sine wave output ratios
(fOUT/fCLOCK) for various update rates with DVDD = 3.3 V.
75
70
35
30
25
IAVDD (mA)
CLK+
20
15
65
0
50MHz SFDR
2
50
6
8
10
12
IOUTFS (mA)
14
16
18
20
Figure 31. IAVDD vs. IOUTFS
45
20
40
50MHz SFDR
–2
18
–1
0
ns
1
2
3
210MSPS
02913-027
35
–3
4
02913-028
55
16
Sleep Mode Operation
The AD9744 has a power-down function that turns off the output
current and reduces the supply current to less than 6 mA over
the specified supply range of 2.7 V to 3.6 V and temperature
range. This mode can be activated by applying a logic level 1 to
the SLEEP pin. The SLEEP pin logic threshold is equal to 0.5 Ω
AVDD. This digital input also contains an active pull-down
circuit that ensures that the AD9744 remains enabled if this
input is left disconnected. The AD9744 takes less than 50 ns to
power down and approximately 5 µs to power back up.
Rev. C | Page 16 of 32
IDVDD (mA)
14
Figure 30. SFDR vs. Clock Placement at fOUT = 20 MHz and 50 MHz
165MSPS
12
10
125MSPS
8
6
65MSPS
4
2
0
0.01
0.1
RATIO (fOUT/fCLOCK)
Figure 32. IDVDD vs. Ratio at DVDD = 3.3 V
1
02913-029
dB
10
20MHz SFDR
60
Data Sheet
AD9744
11
for impedance matching purposes. Note that the transformer
provides ac coupling only.
10
9
MINI-CIRCUITS
T1-1T
IOUTA 22
7
DIFF
RLOAD
AD9744
PECL
IOUTB 21
5
OPTIONAL RDIFF
4
SE
Figure 34. Differential Output Using a Transformer
3
2
0
0
50
100
150
fCLOCK (MSPS)
200
250
02913-030
1
Figure 33. ICLKVDD vs. fCLOCK and Clock Mode
APPLYING THE AD9744
Output Configurations
The following sections illustrate some typical output configurations
for the AD9744. Unless otherwise noted, it is assumed that IOUTFS
is set to a nominal 20 mA. For applications requiring the optimum
dynamic performance, a differential output configuration is
suggested. A differential output configuration may consist of
either an RF transformer or a differential op amp configuration.
The transformer configuration provides the optimum high
frequency performance and is recommended for any application
that allows ac coupling. The differential op amp configuration is
suitable for applications requiring dc coupling, a bipolar output,
signal gain, and/or level shifting within the bandwidth of the
chosen op amp.
A single-ended output is suitable for applications requiring a
unipolar voltage output. A positive unipolar output voltage
results if IOUTA and/or IOUTB are connected to an appropriately sized load resistor, RLOAD, referred to ACOM. This
configuration may be more suitable for a single-supply system
requiring a dc-coupled, ground referred output voltage. Alternatively, an amplifier could be configured as an I-V converter,
thus converting IOUTA or IOUTB into a negative unipolar
voltage. This configuration provides the best dc linearity since
IOUTA or IOUTB is maintained at a virtual ground.
The center tap on the primary side of the transformer must be
connected to ACOM to provide the necessary dc current path
for both IOUTA and IOUTB. The complementary voltages
appearing at IOUTA and IOUTB (that is, VOUTA and VOUTB)
swing symmetrically around ACOM and should be maintained
with the specified output compliance range of the AD9744. A
differential resistor, RDIFF, may be inserted in applications where
the output of the transformer is connected to the load, RLOAD,
via a passive reconstruction filter or cable. RDIFF is determined
by the transformer’s impedance ratio and provides the proper
source termination that results in a low VSWR. Note that approximately half the signal power will be dissipated across RDIFF.
DIFFERENTIAL COUPLING USING AN OP AMP
An op amp can also be used to perform a differential-to-singleended conversion, as shown in Figure 35. The AD9744 is
configured with two equal load resistors, RLOAD, of 25 Ω. The
differential voltage developed across IOUTA and IOUTB is
converted to a single-ended signal via the differential op amp
configuration. An optional capacitor can be installed across
IOUTA and IOUTB, forming a real pole in a low-pass filter. The
addition of this capacitor also enhances the op amp’s distortion
performance by preventing the DAC’s high slewing output from
overloading the op amp’s input.
500
AD9744
225
IOUTA 22
225
IOUTB 21
AD8047
COPT
500
25
DIFFERENTIAL COUPLING USING A
TRANSFORMER
25
02913-032
6
02913-031
ICLKVDD (mA)
8
Figure 35. DC Differential Coupling Using an Op Amp
An RF transformer can be used to perform a differential-to-singleended signal conversion, as shown in Figure 34. A differentially
coupled transformer output provides the optimum distortion
performance for output signals whose spectral content lies
within the transformer’s pass band. An RF transformer, such as
the Mini-Circuits T1–1T, provides excellent rejection of
common-mode distortion (that is, even-order harmonics) and
noise over a wide frequency range. It also provides electrical
isolation and the ability to deliver twice the power to the load.
Transformers with different impedance ratios may also be used
The common-mode rejection of this configuration is typically
determined by the resistor matching. In this circuit, the differential
op amp circuit using the AD8047 is configured to provide some
additional signal gain. The op amp must operate off a dual supply
since its output is approximately ±1 V. A high speed amplifier
capable of preserving the differential performance of the AD9744
while meeting other system level objectives (such as cost or
power) should be selected. The op amp’s differential gain, gain
setting resistor values, and full-scale output swing capabilities
should all be considered when optimizing this circuit.
Rev. C | Page 17 of 32
AD9744
Data Sheet
The differential circuit shown in Figure 36 provides the necessary
level shifting required in a single-supply system. In this case,
AVDD, which is the positive analog supply for both the AD9744
and the op amp, is also used to level-shift the differential output
of the AD9744 to midsupply (that is, AVDD/2). The AD8041 is
a suitable op amp for this application.
COPT
RFB
200Ω
IOUTFS = 10mA
AD9744
IOUTA 22
U1
500Ω
200Ω
02913-035
AD9744
VOUT = IOUTFS × RFB
IOUTB 21
225Ω
IOUTA 22
1kΩ
AVDD
1kΩ
25Ω
25Ω
POWER AND GROUNDING CONSIDERATIONS,
POWER SUPPLY REJECTION
Figure 36. Single-Supply DC Differential Coupled Circuit
SINGLE-ENDED UNBUFFERED VOLTAGE OUTPUT
Figure 37 shows the AD9744 configured to provide a unipolar
output range of approximately 0 V to 0.5 V for a doubly terminated
50 Ω cable since the nominal full-scale current, IOUTFS, of 20 mA
flows through the equivalent RLOAD of 25 Ω. In this case, RLOAD
represents the equivalent load resistance seen by IOUTA or
IOUTB. The unused output (IOUTA or IOUTB) can be connected
to ACOM directly or via a matching RLOAD. Different values of
IOUTFS and RLOAD can be selected as long as the positive compliance
range is adhered to. One additional consideration in this mode
is the integral nonlinearity (INL), discussed in the Analog
Outputs section. For optimum INL performance, the singleended, buffered voltage output configuration is suggested.
AD9744
IOUTFS = 20mA
VOUTA = 0V TO 0.5V
IOUTA 22
50Ω
50Ω
25Ω
02913-034
IOUTB 21
Many applications seek high speed and high performance under
less than ideal operating conditions. In these application circuits,
the implementation and construction of the printed circuit
board is as important as the circuit design. Proper RF techniques
must be used for device selection, placement, and routing as
well as power supply bypassing and grounding to ensure
optimum performance. Figure 43 to Figure 46 illustrate the
recommended printed circuit board ground, power, and signal
plane layouts implemented on the AD9744 evaluation board.
One factor that can measurably affect system performance is
the ability of the DAC output to reject dc variations or ac noise
superimposed on the analog or digital dc power distribution.
This is referred to as the power supply rejection ratio (PSRR).
For dc variations of the power supply, the resulting performance
of the DAC directly corresponds to a gain error associated with
the DAC’s full-scale current, IOUTFS. AC noise on the dc supplies
is common in applications where the power distribution is
generated by a switching power supply. Typically, switching
power supply noise will occur over the spectrum from tens of
kHz to several MHz. The PSRR vs. frequency of the AD9744
AVDD supply over this frequency range is shown in Figure 39.
85
Figure 37. 0 V to 0.5 V Unbuffered Voltage Output
80
SINGLE-ENDED, BUFFERED VOLTAGE OUTPUT
CONFIGURATION
75
Figure 38 shows a buffered single-ended output configuration
in which the op amp U1 performs an I-V conversion on the
AD9744 output current. U1 maintains IOUTA (or IOUTB) at a
virtual ground, minimizing the nonlinear output impedance
effect on the DAC’s INL performance as described in the Analog
Outputs section. Although this single-ended configuration
typically provides the best dc linearity performance, its ac
distortion performance at higher DAC update rates may be
limited by U1’s slew rate capabilities. U1 provides a negative
unipolar output voltage, and its full-scale output voltage is
simply the product of RFB and IOUTFS. The full-scale output
should be set within U1’s voltage output swing capabilities by
scaling IOUTFS and/or RFB. An improvement in ac distortion
performance may result with a reduced IOUTFS since the signal
current U1 will be required to sink less signal current.
PSRR (dB)
70
65
60
55
50
45
40
0
2
4
6
8
FREQUENCY (MHz)
10
12
02913-036
COPT
02913-033
IOUTB 21
Figure 38. Unipolar Buffered Voltage Output
AD8041
225Ω
Figure 39. Power Supply Rejection Ratio (PSRR) vs. Frequency
Note that the ratio in Figure 39 is calculated as amps out/volts
in. Noise on the analog power supply has the effect of modulating
the internal switches, and therefore the output current. The
voltage noise on AVDD, therefore, will be added in a nonlinear
manner to the desired IOUT. Due to the relative different size of
Rev. C | Page 18 of 32
Data Sheet
AD9744
An example serves to illustrate the effect of supply noise on the
analog supply. Suppose a switching regulator with a switching
frequency of 250 kHz produces 10 mV of noise and, for
simplicity’s sake (ignoring harmonics), all of this noise is
concentrated at 250 kHz. To calculate how much of this
undesired noise will appear as current noise superimposed on
the DAC’s full-scale current, IOUTFS, one must determine the
PSRR in dB using Figure 39 at 250 kHz. To calculate the PSRR
for a given RLOAD, such that the units of PSRR are converted
from A/V to V/V, adjust the curve in Figure 39 by the scaling
factor 20 Ω log (RLOAD). For instance, if RLOAD is 50 Ω, the PSRR
is reduced by 34 dB (that is, PSRR of the DAC at 250 kHz,
which is 85 dB in Figure 39, becomes 51 dB VOUT/VIN).
AD9744 features separate analog and digital supplies and
ground pins to optimize the management of analog and digital
ground currents in a system. In general, AVDD, the analog
supply, should be decoupled to ACOM, the analog common, as
close to the chip as physically possible. Similarly, DVDD, the
digital supply, should be decoupled to DCOM as close to the
chip as physically possible.
For those applications that require a single 3.3 V supply for both
the analog and digital supplies, a clean analog supply may be
generated using the circuit shown in Figure 40. The circuit
consists of a differential LC filter with separate power supply
and return lines. Lower noise can be attained by using low ESR
type electrolytic and tantalum capacitors.
FERRITE
BEADS
TTL/CMOS
LOGIC
CIRCUITS
AVDD
100µF
ELECT.
10µF–22µF
TANT.
0.1µF
CER.
ACOM
3.3V
POWER SUPPLY
Figure 40. Differential LC Filter for Single 3.3 V Applications
Proper grounding and decoupling should be a primary
objective in any high speed, high resolution system. The
Rev. C | Page 19 of 32
02913-037
these switches, the PSRR is very code dependent. This can produce
a mixing effect that can modulate low frequency power supply
noise to higher frequencies. Worst-case PSRR for either one of
the differential DAC outputs will occur when the full-scale current
is directed toward that output. As a result, the PSRR measurement
in Figure 39 represents a worst-case condition in which the
digital inputs remain static and the full-scale output current of
20 mA is directed to the DAC output being measured.
AD9744
Data Sheet
EVALUATION BOARD
GENERAL DESCRIPTION
The TxDAC family evaluation boards allow for easy setup and
testing of any TxDAC product in the SOIC and LFCSP packages.
Careful attention to layout and circuit design, combined with a
prototyping area, allows the user to evaluate the AD9744 easily
and effectively in any application where high resolution, high
speed conversion is required.
This board allows the user the flexibility to operate the AD9744
in various configurations. Possible output configurations include
transformer coupled, resistor terminated, and single and
differential outputs. The digital inputs are designed to be driven
from various word generators, with the on-board option to add
a resistor network for proper load termination. Provisions are
also made to operate the AD9744 with either the internal or
external reference or to exercise the power-down feature.
JP3
CKEXTX
L2
BEAD
RED
TP2
DVDD
TB1 1
C7
0.1µF
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
DB13X
DB12X
DB11X
DB10X
DB9X
DB8X
DB7X
DB6X
DB5X
DB4X
DB3X
DB2X
DB1X
DB0X
BLK
TP4
+ C4
10µF
25V
C6
0.1µF
BLK
TP7
1 DCOM
2 R1
3 R2
4 R3
5 R4
6 R5
7 R6
8 R7
9 R8
10 R9
RP3
RP3
RP3
RP3
RP3
RP3
RP3
RP3
RP4
RP4
RP4
RP4
RP4
RP4
RP4
8 RP4
CKEXTX
RIBBON
RP5
OPT
RP1
OPT
22Ω 16
22Ω 15
22Ω 14
22Ω 13
22Ω 12
22Ω 11
22Ω 10
22Ω 9
22Ω 16
22Ω 15
22Ω 14
22Ω 13
22Ω 12
22Ω 11
22Ω 10
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
22Ω 9
RP6
OPT
CKEXT
DCOM 1
R1 2
R2 3
R3 4
R4 5
R5 6
R6 7
R7 8
R8 9
R9 10
DB13X
DB12X
DB11X
DB10X
DB9X
DB8X
DB7X
DB6X
DB5X
DB4X
DB3X
DB2X
DB1X
DB0X
1
2
3
4
5
6
7
8
9
10
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
DCOM 1
R1 2
R2 3
R3 4
R4 5
R5 6
R6 7
R7 8
R8 9
R9 10
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
DCOM
R1
R2
R3
R4
R5
R6
R7
R8
R9
J1
RP2
OPT
BLK
TP8
TB1 2
L3
BEAD
RED
TP5
C9
0.1µF
BLK
TP6
+ C5
10µF
25V
C8
0.1µF
BLK
TP10
BLK
TP9
TB1 4
Figure 41. SOIC Evaluation Board—Power Supply and Digital Inputs
Rev. C | Page 20 of 32
02913-038
AVDD
TB1 3
Data Sheet
AD9744
AVDD
+ C14
10µF
16V
C16
0.1µF
CUT
UNDER DUT
C17
0.1µF
JP6
DVDD
C18
0.1µF
DVDD
C19
0.1µF
R5
OPT
CKEXT
3
R11
50Ω
S5
JP4
AVDD
JP10
A B
2
S2
IOUTA
CLOCK
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
1
IX
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
CLOCK
DVDD
DCOM
MODE
AVDD
RESERVED
IOUTA
U1
AD9742 IOUTB
ACOM
NC
FS ADJ
REFIO
REFLO
SLEEP
2
A B
3
1
EXT JP5 INT
REF
28
27
26
25
24
23
22
21
20
19
18
17
16
15
CLOCK
TP1
WHT
DVDD
R4
50Ω
R2
10kΩ
C13
OPT
DVDD
JP8
JP2
IOUT
MODE
AVDD
3
T1
5
2
R6
OPT
4
S3
6
1
T1-1T
REF
R1
2kΩ
TP3
WHT
C11
0.1µF
C1
0.1µF
C2
0.1µF
C12
OPT
JP9
AVDD
SLEEP
TP11
WHT
R10
50Ω
S1
IOUTB
R3
10kΩ
IY
Figure 42. SOIC Evaluation Board—Output Signal Conditioning
Rev. C | Page 21 of 32
1
2
A B
3
JP11
02913-039
+ C15
10µF
16V
Data Sheet
02913-040
AD9744
02913-041
Figure 43. SOIC Evaluation Board—Primary Side
Figure 44. SOIC Evaluation Board—Secondary Side
Rev. C | Page 22 of 32
AD9744
02913-042
Data Sheet
02913-043
Figure 45. SOIC Evaluation Board—Ground Plane
Figure 46. SOIC Evaluation Board—Power Plane
Rev. C | Page 23 of 32
Data Sheet
02913-044
AD9744
02913-045
Figure 47. SOIC Evaluation Board Assembly—Primary Side
Figure 48. SOIC Evaluation Board Assembly—Secondary Side
Rev. C | Page 24 of 32
Data Sheet
AD9744
RED
TP12
TB1
CVDD
1
C3
0.1µF
TB1
BLK
C10
0.1µF
C2
10µF
6.3V
TP2
2
2
4
1
3
6
5
8
7
DB10X
10
9
DB9X
11
DB8X
13
DB7X
15
DB6X
17
DB5X
19
DB4X
21
DB3X
23
DB2X
25
DB1X
27
DB0X
12
L2 BEAD
TB3
16
DVDD
1
C7
0.1µF
TB3
14
RED
TP13
18
20
BLK
C6
0.1µF
C4
10µF
6.3V
TP4
22
24
26
2
28
RED
TP5
L3 BEAD
C9
0.1µF
TB4
32
AVDD
1
BLK
36
C8
0.1µF
C5
10µF
6.3V
TP6
34
DB12X
DB11X
29
31
33
35
JP3
CKEXTX
37
39
38
40
2
DB13X
J1
R3
100Ω
R4
100Ω
R15
100Ω
R16
100Ω
R17
100Ω
R18
100Ω
R19
100Ω
DB13X
DB12X
DB11X
DB10X
DB9X
DB8X
DB7X
DB6X
DB5X
DB4X
DB3X
DB2X
DB1X
DB0X
CKEXTX
R21
100Ω
R24
100Ω
R25
100Ω
R26
100Ω
R27
100Ω
R20
100Ω
1 RP3
22Ω 16
2 RP3
22Ω 15
3 RP3
22Ω 14
4 RP3
22Ω 13
5 RP3
22Ω 12
6 RP3
22Ω 11
7 RP3
22Ω 10
8 RP3
22Ω 9
1 RP4
22Ω 16
2 RP4
22Ω 15
3 RP4
22Ω 14
4 RP4
22Ω 13
5 RP4
22Ω 12
6 RP4
7 RP4
22Ω 11
22Ω 10
8 RP4
22Ω 9
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
CKEXT
R28
100Ω
02913-046
TB4
30
HEADER STRAIGHT UP MALE NO SHROUD
L1 BEAD
Figure 49. LFCSP Evaluation Board Schematic—Power Supply and Digital Inputs
Rev. C | Page 25 of 32
AD9744
Data Sheet
AVDD
DVDD
CVDD
C19
0.1µF
0.1
C17
0.1µF
C32
0.1µF
SLEEP
TP11
WHT
R29
10kΩ
DB7
DB6
DVDD
DB5
DB4
DB3
DB2
DB1
DB0
CVDD
CLK
CLKB
CMODE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DB7
DB6
DVDD
DB5
DB4
DB3
DB2
DB1
DB0
DCOM
U1
CVDD
CLK
CLKB
CCOM
CMODE
MODE
DB8
DB9
DB10
DB11
DB12
DB13
DCOM1
SLEEP
FS ADJ
REFIO
ACOM
IA
IB
ACOM1
AVDD
AVDD1
32
31
30
29
28
27
DB8
DB9
DB10
DB11
DB12
DB13
R11
50Ω
DNP
C13
26
25
24
23
22
TP3
TP1
WHT
WHT
JP8
IOUT
3
21
20
19
18
17
TP7
4
S3
AGND: 3, 4, 5
5
2
6
1
AVDD
T1 – 1T
C11
0.1µF
JP9
AD9744LFCSP
WHT
T1
DNP
C12
R30
10kΩ
R10
50Ω
CVDD
R1
2kΩ
0.1%
JP1
02913-047
MODE
Figure 50. LFCSP Evaluation Board Schematic—Output Signal Conditioning
CVDD
1
7
U4
C35
0.1µF
C20
10µF
16V
2
AGND: 5
CVDD: 8
CVDD
R5
120Ω
3
JP2
CKEXT
CLK
U4
6
S5
AGND: 3, 4, 5
4
AGND: 5
CVDD: 8
R2
120Ω
C34
0.1µF
R6
50Ω
02913-048
CLKB
Figure 51. LFCSP Evaluation Board Schematic—Clock Input
Rev. C | Page 26 of 32
AD9744
02913-049
Data Sheet
02913-050
Figure 52. LFCSP Evaluation Board Layout—Primary Side
Figure 53. LFCSP Evaluation Board Layout—Secondary Side
Rev. C | Page 27 of 32
Data Sheet
02913-051
AD9744
02913-052
Figure 54. LFCSP Evaluation Board Layout—Ground Plane
Figure 55. LFCSP Evaluation Board Layout—Power Plane
Rev. C | Page 28 of 32
AD9744
02913-053
Data Sheet
02913-054
Figure 56. LFCSP Evaluation Board Layout Assembly—Primary Side
Figure 57. LFCSP Evaluation Board Layout Assembly—Secondary Side
Rev. C | Page 29 of 32
AD9744
Data Sheet
OUTLINE DIMENSIONS
9.80
9.70
9.60
28
15
4.50
4.40
4.30
6.40 BSC
1
14
PIN 1
0.65
BSC
1.20 MAX
0.15
0.05
COPLANARITY
0.10
0.30
0.19
SEATING
PLANE
8°
0°
0.20
0.09
0.75
0.60
0.45
COMPLIANT TO JEDEC STANDARDS MO-153-AE
Figure 58. 28-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-28)
Dimensions shown in millimeters
18.10 (0.7126)
17.70 (0.6969)
15
28
7.60 (0.2992)
7.40 (0.2913)
14
2.65 (0.1043)
2.35 (0.0925)
0.30 (0.0118)
0.10 (0.0039)
COPLANARITY
0.10
10.65 (0.4193)
10.00 (0.3937)
1.27 (0.0500)
BSC
0.51 (0.0201)
0.31 (0.0122)
SEATING
PLANE
0.75 (0.0295)
45°
0.25 (0.0098)
8°
0°
0.33 (0.0130)
0.20 (0.0079)
COMPLIANT TO JEDEC STANDARDS MS-013-AE
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 59. 28-Lead Standard Small Outline Package [SOIC_W]
Wide Body (RW-28)
Dimensions shown in millimeters and (inches)
Rev. C | Page 30 of 32
1.27 (0.0500)
0.40 (0.0157)
06-07-2006-A
1
Data Sheet
AD9744
0.30
0.25
0.18
32
25
0.50
BSC
TOP VIEW
0.80
0.75
0.70
8
16
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF
SEATING
PLANE
3.25
3.10 SQ
2.95
EXPOSED
PAD
17
0.50
0.40
0.30
PIN 1
INDICATOR
1
24
9
BOTTOM VIEW
0.25 MIN
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-220-WHHD.
112408-A
PIN 1
INDICATOR
5.10
5.00 SQ
4.90
Figure 60. 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
5 mm × 5 mm Body, Very Very Thin Quad
(CP-32-7)
Dimensions shown in millimeters
ORDERING GUIDE
Model 1
AD9744AR
AD9744ARZ
AD9744ARZRL
AD9744ARU
AD9744ARURL7
AD9744ARUZ
AD9744ARUZRL7
AD9744ACPZ
AD9744ACPZRL7
AD9744-EBZ
AD9744ACP-PCBZ
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
28-Lead, 300-Mil SOIC_W
28-Lead, 300-Mil SOIC_W
28-Lead, 300-Mil SOIC_W
28-Lead TSSOP
28-Lead TSSOP
28-Lead TSSOP
28-Lead TSSOP
32-Lead LFCSP_WQ
32-Lead LFCSP_WQ
Evaluation Board (SOIC)
Evaluation Board (LFCSP)
Z = RoHS Compliant Part.
Rev. C | Page 31 of 32
Package Options
RW-28
RW-28
RW-28
RU-28
RU-28
RU-28
RU-28
CP-32-7
CP-32-7
AD9744
Data Sheet
NOTES
©2003–2013 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D02913-0-12/13(C)
Rev. C | Page 32 of 32
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