12-Bit, 210 MSPS
TxDAC Digital-to-Analog Converter
AD9742
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
3.3V
0.1µF
REFLO
1.2V REF
REFIO
FS ADJ
RSET
3.3V
CURRENT
SOURCE
ARRAY
DVDD
DCOM
CLOCK
AVDD
150pF
ACOM
AD9742
IOUTA
SEGMENTED
SWITCHES
CLOCK
LSB
SWITCHES
IOUTB
LATCHES
DIGITAL DATA INPUTS (DB11–DB0)
SLEEP
MODE
02913-B-001
High performance member of pin-compatible TxDAC
product family
Excellent spurious-free dynamic range performance
SNR at 5 MHz output, 125 MSPS: 70 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
Edge-triggered latches
Figure 1.
APPLICATIONS
Wideband communication transmit channel:
Direct IF
Base stations
Wireless local loops
Digital radio links
Direct digital synthesis (DDS)
Instrumentation
GENERAL DESCRIPTION
The AD97421 is a 12-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 AD9742 offers exceptional ac and dc
performance while supporting update rates up to 210 MSPS.
The AD9742’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.
2.
3.
4.
5.
6.
1
The AD9742 is the 12-bit member of the pin-compatible
TxDAC family, which offers excellent INL and DNL
performance.
Data input supports twos complement or straight binary
data coding.
High speed, single-ended CMOS clock input supports
210 MSPS conversion rate.
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.
On-chip voltage reference: The AD9742 includes a 1.2 V
temperature compensated band gap voltage reference.
Industry-standard 28-lead SOIC, 28-lead TSSOP, and
32-lead LFCSP packages.
Protected by U.S. Patent Numbers: 5,568,145; 5,689,257; and 5,703,519.
Rev. C
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AD9742
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Reference Control Amplifier .................................................... 13
Applications ....................................................................................... 1
DAC Transfer Function ............................................................. 13
Functional Block Diagram .............................................................. 1
Analog Outputs .......................................................................... 13
General Description ......................................................................... 1
Digital Inputs .............................................................................. 14
Product Highlights ........................................................................... 1
Clock Input.................................................................................. 14
Revision History ............................................................................... 2
DAC Timing................................................................................ 15
Specifications..................................................................................... 3
Power Dissipation....................................................................... 15
DC Specifications ......................................................................... 3
Applying the AD9742 ................................................................ 16
Dynamic Specifications ............................................................... 4
Differential Coupling Using a Transformer ............................... 16
Digital Specifications ................................................................... 5
Differential Coupling Using an Op Amp ................................ 16
Absolute Maximum Ratings ............................................................ 6
Single-Ended, Unbuffered Voltage Output ............................. 17
Thermal Resistance ...................................................................... 6
Single-Ended, Buffered Voltage Output Configuration ........ 17
ESD Caution .................................................................................. 6
Pin Configurations and Function Descriptions ........................... 7
Power and Grounding Considerations, Power Supply
Rejection ...................................................................................... 17
Typical Performance Characteristics ............................................. 8
Evaluation Board ............................................................................ 19
Terminology .................................................................................... 11
General Description ................................................................... 19
Functional Description .................................................................. 12
Outline Dimensions ....................................................................... 29
Reference Operation .................................................................. 12
Ordering Guide .......................................................................... 30
REVISION HISTORY
2/13—Rev. B to Rev. C
Updated Format .................................................................. Universal
Changes to Figure 4 and Table 6 ..................................................... 7
Moved Terminology Section ......................................................... 11
Updated Outline Dimensions ....................................................... 29
Changes to Ordering Guide .......................................................... 30
6/04—Rev. A to Rev. B
Changes to the Title, General Description, and Product
Highlights .......................................................................................... 1
Changes to Dynamic Specifications ............................................... 4
Changes to Figure 6 and Figure 10 ................................................. 9
Changes to Figure 12 to Figure 15 ................................................ 10
Changes to the Functional Description Section ......................... 12
Changes to the Digital Inputs Section ......................................... 14
Changes to Figure 29 ...................................................................... 15
Changes to Figure 30 ...................................................................... 16
5/03—Rev. 0 to Rev. A
Added 32-Lead LFCSP Package ....................................... Universal
Edits to Features and Product Highlights ......................................1
Edits to DC Specifications ................................................................2
Edits to Dynamic Specifications ......................................................3
Edits to Digital Specifications ..........................................................4
Edits to Absolute Maximum Ratings, Thermal Characteristics,
and Ordering Guide ..........................................................................5
Edits to Pin Configuration and Pin Function Descriptions ........6
Edits to Figure 2 .................................................................................7
Replaced TPCs 1, 4, 7, and 8 ............................................................8
Edits to Figure 3 and Functional Description Section .............. 10
Added Clock Input Section and Figure 7 .................................... 12
Edits to DAC Timing Section ....................................................... 12
Edits to Sleep Mode Operation Section and Power Dissipation
Section .............................................................................................. 13
Renumbered Figure 8 to Figure 26............................................... 13
Added Figure 11 ............................................................................. 13
Added Figure 27 to Figure 35 ....................................................... 21
Updated Outline Dimensions ....................................................... 26
5/02—Revision 0: Initial Version
Rev. C | Page 2 of 32
Data Sheet
AD9742
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 (Ext. 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
12
Typ
Max
Unit
Bits
−2.5
−1.3
±0.5
±0.4
+2.5
+1.3
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
1
0.5
V
MΩ
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).
Data Sheet
AD9742
VDIFF = (IOUTA − IOUTB ) × RLOAD
REFERENCE CONTROL AMPLIFIER
The AD9742 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 24, 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.
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 AD9742, which is proportional to IOUTFS (see
the Power Dissipation section). The second relates to the 20 dB
adjustment, which is useful for system gain control purposes.
(7)
Substituting the values of IOUTA, IOUTB, IREF, and VDIFF can be
expressed as:
V DIFF = {(2 × DAC CODE − 4095)/ 4096}
(32 × RLOAD / RSET )× VREFIO
(8)
Equations 7 and 8 highlight some of the advantages of operating
the AD9742 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 (i.e.,
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
AD9742 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
ANALOG OUTPUTS
Both DACs in the AD9742 provide complementary current
outputs, IOUTA and IOUTB. IOUTA provides a near full-scale
current output, IOUTFS, when all bits are high (i.e., DAC CODE =
4095), 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:
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 Equations 5 through 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 AD9742 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.
IOUTA = (DAC CODE / 4096 )× I OUTFS
(1)
IOUTB = (4095 − DAC CODE )/4096 × I OUTFS
(2)
where DAC CODE = 0 to 4095 (i.e., 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)
The distortion and noise performance of the AD9742 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
AD9742 to provide the required power and voltage levels to
different loads.
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.
Rev. C | Page 13 of 32
AD9742
Data Sheet
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 (i.e., 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
for the AD9742 are measured with IOUTA maintained at a
virtual ground via an op amp.
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 AD9742.
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 AD9742 digital section consists of 12 input bit channels
and a clock input. The 12-bit parallel data inputs follow standard
positive binary coding, where DB11 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.
CLOCK INPUT
SOIC/TSSOP Packages
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.
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 between any of the three clock input modes.
Table 7. Clock Mode Selection
CMODE Pin
CLKCOM
CLKVDD
Float
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 described previously.
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.
02912-B-024
DIGITAL
INPUT
Figure 25. 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.
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 26. These termination resistors are untrimmed and can
vary up to ±20%. However, matching between the resistors
should generally be better than ±1%.
AD9742
CLK+
CLOCK
RECEIVER
CLK–
50Ω
TO DAC CORE
50Ω
VTT = 1.3V NOM
Figure 26. Clock Termination in PECL Mode\
Rev. C | Page 14 of 32
02912-B-025
DVDD
Data Sheet
AD9742
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 AD9742 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 AD9742 is to make the data transition close to the falling
clock edge. This becomes more important as the sample rate
increases. Figure 27 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 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 28, and is insensitive to
fCLOCK. Conversely, IDVDD is dependent on both the digital input
waveform, fCLOCK, and digital supply DVDD. Figure 29 shows
IDVDD as a function of full-scale sine wave output ratios
(fOUT/fCLOCK) for various update rates with DVDD = 3.3 V.
75
35
30
25
IAVDD (mA)
DAC TIMING
15
70
65
10
0
55
2
4
6
50MHz SFDR
14
16
18
20
20
45
18
40
50MHz SFDR
2
3
210MSPS
14
Sleep Mode Operation
The AD9742 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 AD9742 remains enabled if this input is
left disconnected. The AD9742 takes less than 50 ns to power
down and approximately 5 µs to power back up.
12
165MSPS
10
125MSPS
8
6
4
65MSPS
2
0
0.01
0.1
RATIO (fOUT/fCLOCK)
1
02912-B-028
ns
1
Figure 29. IDVDD vs. Ratio @ DVDD = 3.3 V
12
POWER DISSIPATION
10
The power supply voltages (AVDD, CLKVDD, and DVDD)
The full-scale current output IOUTFS
The update rate fCLOCK
The reconstructed digital input waveform
DIFF
ICLKVDD (mA)
The power dissipation, PD, of the AD9742 is dependent on several
factors that include:
8
PECL
6
4
SE
2
0
0
50
100
150
200
fCLOCK (MSPS)
Figure 30. ICLKVDD vs. fCLOCK and Clock Mode
Rev. C | Page 15 of 32
250
02912-B-029
0
IDVDD (mA)
–1
02912-B-026
–2
16
Figure 27. SFDR vs. Clock Placement @ fOUT = 20 MHz and 50 MHz
•
•
•
•
10
12
IOUTFS (mA)
Figure 28. IAVDD vs. IOUTFS
50
35
–3
8
02912-B-027
20MHz SFDR
60
dB
20
AD9742
Data Sheet
APPLYING THE AD9742
termination that results in a low VSWR. Note that approximately
half the signal power will be dissipated across RDIFF.
The following sections illustrate some typical output configurations
for the AD9742. 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 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 will
result 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.
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-singleended signal conversion, as shown in Figure 31. 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 commonmode 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 for impedance matching
purposes. Note that the transformer provides ac coupling only.
MINI-CIRCUITS
T1-1T
IOUTA 22
DIFFERENTIAL COUPLING USING AN OP AMP
An op amp can also be used to perform a differential-to-singleended conversion, as shown in Figure 32. The AD9742 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.
500Ω
AD9742
225Ω
IOUTA 22
AD8047
225Ω
IOUTB 21
COPT
500Ω
25Ω
02912-B-031
Output Configurations
25Ω
Figure 32. DC Differential Coupling Using an Op Amp
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 AD9742 while meeting other system level objectives (e.g.,
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.
The differential circuit shown in Figure 33 provides the necessary
level shifting required in a single-supply system. In this case,
AVDD, which is the positive analog supply for both the AD9742
and the op amp, is also used to level shift the differential output
of the AD9742 to midsupply (i.e., AVDD/2). The AD8041 is a
suitable op amp for this application.
500Ω
RLOAD
IOUTB 21
OPTIONAL RDIFF
02912-B-030
AD9742
225Ω
IOUTA 22
AD8041
225Ω
IOUTB 21
Figure 31. Differential Output Using a Transformer
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 (i.e., VOUTA and VOUTB) swing
symmetrically around ACOM and should be maintained with the
specified output compliance range of the AD9742. 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
Rev. C | Page 16 of 32
COPT
25Ω
1kΩ
25Ω
1kΩ
Figure 33. Single-Supply DC Differential Coupled Circuit
AVDD
02912-B-032
AD9742
Data Sheet
AD9742
IOUTFS = 20mA
AD9742
VOUTA = 0V TO 0.5V
IOUTA 22
50Ω
50Ω
02912-B-033
IOUTB 21
25Ω
Figure 34. 0 V to 0.5 V Unbuffered Voltage Output
SINGLE-ENDED, BUFFERED VOLTAGE OUTPUT
CONFIGURATION
Figure 35 shows a buffered single-ended output configuration
in which the op amp U1 performs an I-V conversion on the
AD9742 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 U1 will be required to sink less signal current.
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 versus frequency of the AD9742
AVDD supply over this frequency range is shown in Figure 36.
85
80
75
70
65
60
55
50
45
40
0
2
4
6
8
FREQUENCY (MHz)
10
12
COPT
Figure 36. Power Supply Rejection Ratio (PSRR)
RFB
200Ω
Note that the ratio in Figure 36 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
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 36 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.
IOUTFS = 10mA
AD9742
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 40 to Figure 43 illustrate the
recommended printed circuit board ground, power, and signal
plane layouts implemented on the AD9742 evaluation board.
02912-B-035
Figure 34 shows the AD9742 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 single-ended, buffered
voltage output configuration is suggested.
POWER AND GROUNDING CONSIDERATIONS,
POWER SUPPLY REJECTION
PSRR (dB)
SINGLE-ENDED, UNBUFFERED VOLTAGE OUTPUT
IOUTA 22
U1
VOUT = IOUTFS × RFB
200Ω
Figure 35. Unipolar Buffered Voltage Output
02912-B-034
IOUTB 21
Rev. C | Page 17 of 32
AD9742
Data Sheet
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 37. 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
Proper grounding and decoupling should be a primary objective in
any high speed, high resolution system. The AD9742 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
Rev. C | Page 18 of 32
AVDD
100µF
ELECT.
10µF–22µF
TANT.
0.1µF
CER.
ACOM
3.3V
POWER SUPPLY
Figure 37. Differential LC Filter for Single 3.3 V Applications
02912-B-036
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 36
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 36 by the scaling factor 20 Ω log (RLOAD). For instance, if
RLOAD is 50 Ω, the PSRR is reduced by 34 dB (i.e., PSRR of the DAC
at 250 kHz, which is 85 dB in Figure 36, becomes 51 dB VOUT/VIN).
Data Sheet
AD9742
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 AD9742 easily
and effectively in any application where high resolution, high
speed conversion is required.
This board allows the user the flexibility to operate the AD9742
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 AD9742 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 38. SOIC Evaluation Board—Power Supply and Digital Inputs
Rev. C | Page 19 of 32
02912-B-037
AVDD
TB1 3
AD9742
Data Sheet
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
JP5
INT
EXT
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
2
R6
OPT
4
5
1
S3
6
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 39. SOIC Evaluation Board—Output Signal Conditioning
Rev. C | Page 20 of 32
1
2
A B
3
JP11
02912-B-038
+ C15
10µF
16V
AD9742
02912-B-039
Data Sheet
02912-B-040
Figure 40. SOIC Evaluation Board—Primary Side
Figure 41. SOIC Evaluation Board—Secondary Side
Rev. C | Page 21 of 32
Data Sheet
02912-B-041
AD9742
02912-B-042
Figure 42. SOIC Evaluation Board—Ground Plane
Figure 43. SOIC Evaluation Board—Power Plane
Rev. C | Page 22 of 32
AD9742
02912-B-043
Data Sheet
02912-B-044
Figure 44. SOIC Evaluation Board Assembly—Primary Side
Figure 45. SOIC Evaluation Board Assembly—Secondary Side
Rev. C | Page 23 of 32
AD9742
Data Sheet
RED
TP12
TB1
CVDD
1
C3
0.1µF
TB1
BLK
C2
10µF
6.3V
TP2
C10
0.1µF
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
38
40
2
DB13X
DB12X
DB11X
29
31
33
35
JP3
CKEXTX
37
39
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
7 RP3
22Ω 11
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
02912-B-045
TB4
30
HEADER STRAIGHT UP MALE NO SHROUD
L1 BEAD
Figure 46. LFCSP Evaluation Board Schematic—Power Supply and Digital Inputs
Rev. C | Page 24 of 32
Data Sheet
AD9742
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
02912-B-046
MODE
Figure 47. LFCSP Evaluation Board Schematic—Output Signal Conditioning
CVDD
1
7
U4
C20
10µF
16V
2
AGND: 5
CVDD: 8
C35
0.1µF
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
02912-B-047
CLKB
Figure 48. LFCSP Evaluation Board Schematic—Clock Input
Rev. C | Page 25 of 32
Data Sheet
02912-B-048
AD9742
02912-B-049
Figure 49. LFCSP Evaluation Board Layout—Primary Side
Figure 50. LFCSP Evaluation Board Layout—Secondary Side
Rev. C | Page 26 of 32
AD9742
02912-B-050
Data Sheet
02912-B-051
Figure 51. LFCSP Evaluation Board Layout—Ground Plane
Figure 52. LFCSP Evaluation Board Layout—Power Plane
Rev. C | Page 27 of 32
Data Sheet
02912-B-052
AD9742
02912-B-053
Figure 53. LFCSP Evaluation Board Layout Assembly—Primary Side
Figure 54. LFCSP Evaluation Board Layout Assembly—Secondary Side
Rev. C | Page 28 of 32
Data Sheet
AD9742
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 55. 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 56. 28-Lead Standard Small Outline Package [SOIC_W]
Wide Body (RW-28)
Dimensions shown in millimeters and (inches)
Rev. C | Page 29 of 32
1.27 (0.0500)
0.40 (0.0157)
06-07-2006-A
1
AD9742
Data Sheet
5.10
5.00 SQ
4.90
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
0.30
0.25
0.18
Figure 57. 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
AD9742AR
AD9742ARZ
AD9742ARZRL
AD9742ARU
AD9742ARURL7
AD9742ARUZ
AD9742ARUZRL7
AD9742ACPZ
AD9742ACPZRL7
AD9742-EBZ
AD9742ACP-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 Standard Small Outline Package [SOIC]
28-Lead Standard Small Outline Package [SOIC]
28-Lead Standard Small Outline Package [SOIC]
28-Lead Thin Shrink Small Outline Package [TSSOP]
28-Lead Thin Shrink Small Outline Package [TSSOP]
28-Lead Thin Shrink Small Outline Package [TSSOP]
28-Lead Thin Shrink Small Outline Package [TSSOP]
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
Evaluation Board [SOIC]
Evaluation Board [LFCSP]
Z = RoHS Compliant Part.
Rev. C | Page 30 of 32
Package Option
RW-28
RW-28
RW-28
RU-28
RU-28
RU-28
RU-28
CP-32-7
CP-32-7
Data Sheet
AD9742
NOTES
Rev. C | Page 31 of 32
AD9742
Data Sheet
NOTES
©2002–2013 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D02912-0-2/13(C)
Rev. C | Page 32 of 32
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