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PDF DAC908E Data sheet ( Hoja de datos )

Número de pieza DAC908E
Descripción 8-Bit/ 165MSPS DIGITAL-TO-ANALOG CONVERTER
Fabricantes Burr-Brown Corporation 
Logotipo Burr-Brown Corporation Logotipo



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®
DAC908
DAC908
For most current data sheet and other product
information, visit www.burr-brown.com
DAC908
TM 8-Bit, 165MSPS
DIGITAL-TO-ANALOG CONVERTER
FEATURES
q SINGLE +5V OR +3V OPERATION
q HIGH SFDR: 5.04MHz Output at 100MSPS: 67dBc
q LOW GLITCH: 3pV-s
q LOW POWER: 170mW at +5V
q INTERNAL REFERENCE:
Optional Ext. Reference
Adjustable Full-Scale Range
Multiplying Option
APPLICATIONS
q MEDICAL INSTRUMENTATION
Ultrasound (DBF)
q VIDEO, DIGITAL TV
q WAVEFORM GENERATION
Direct Digital Synthesis (DDS)
Arbitrary Waveform Generation (ARB)
q TEST INSTRUMENTATION
q COMMUNICATIONS
DESCRIPTION
The DAC908 is a high-speed, digital-to-analog converter (DAC)
offering an 8-bit resolution option within the SpeedPlus family
of high-performance converters. Featuring pin compatibility
among family members, the DAC900, DAC902, and DAC904
provide a component selection option to an 10-, 12-, and 14-bit
resolution, respectively. All models within this family of D/A
converters support update rates in excess of 165MSPS with
excellent dynamic performance, and are especially suited to
fulfill the demands of a variety of applications.
The advanced segmentation architecture of the DAC908 is
optimized to provide a high Spurious-Free Dynamic Range
(SFDR) for single-tone, as well as for multi-tone signals—
essential when used for the transmit signal path of communica-
tion systems.
The DAC908 has a high impedance (200k) current output with
a nominal range of 20mA and an output compliance of up to
1.25V. The differential outputs allow for both a differential, or
single-ended analog signal interface. The close matching of the
current outputs ensures superior dynamic performance in the
differential configuration, which can be implemented with a
transformer.
Utilizing a small geometry CMOS process, the monolithic
DAC908 can be operated on a wide, single-supply range of
+2.7V to +5.5V. Its low power consumption allows for use in
portable and battery operated systems. Further optimization can
be realized by lowering the output current with the adjustable
full-scale option.
For noncontinuous operation of the DAC908, a power-down
mode results in only 45mW of standby power.
The DAC908 comes with an integrated 1.24V bandgap refer-
ence and edge-triggered input latches, offering a complete
converter solution. Both +3V and +5V CMOS logic families
can be interfaced to the DAC908.
The reference structure of the DAC908 allows for additional
flexibility by utilizing the on-chip reference, or applying an
external reference. The full-scale output current can be adjusted
over a span of 2mA to 20mA, with one external resistor, while
maintaining the specified dynamic performance.
The DAC908 is available in the SO-28 and TSSOP-28 pack-
ages.
+VA
DAC908
FSA
REFIN
INT/EXT
BW +VD
Current
Sources
LSB
Switches
Segmented
Switches
IOUT
IOUT
BYP
+1.24V Ref.
AGND
CLK
Latches
PD
8-Bit Data Input
D7...D0
DGND
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111
Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1999 Burr-Brown Corporation
PDS-11507B
DAC908Printed in U.S.A. April, 2000
®

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DAC908E pdf
TIMING DIAGRAM
CLK
D7- D0
t1
tS tH
t2
IOUT
tPD
tSET
SYMBOL
t1
t2
tS
tH
tPD
tSET
DESCRIPTION
Clock Pulse High Time
Clock Pulse Low Time
Data Setup Time
Data Hold Time
Propagation Delay Time
Output Settling Time to 0.1%
MIN TYP MAX UNITS
6.25
6.25
2
2
(t1+t2)+1
25
ns
ns
ns
ns
ns
ns
®
5 DAC908

5 Page





DAC908E arduino
The value of the load resistance is limited by the output
compliance specification of the DAC908. To maintain speci-
fied linearity performance, the voltage for IOUT and IOUT
should not exceed the maximum allowable compliance range.
The two single-ended output voltages can be combined to
find the total differential output swing:
VOUTDIFF
=
VOUT
VOUT
=
(2
Code –
256
255)
I OUTFS
R LOAD
(7)
ANALOG OUTPUTS
The DAC908 provides two complementary current outputs,
IOUT and IOUT. The simplified circuit of the analog output
stage representing the differential topology is shown in
Figure 2. The output impedance of 200k|| 12pF for IOUT
and IOUT results from the parallel combination of the differ-
ential switches, along with the current sources and associ-
ated parasitic capacitances.
IOUT and IOUT. Furthermore, using the differential output
configuration in combination with a transformer will be
instrumental for achieving excellent distortion performance.
Common-mode errors, such as even-order harmonics or
noise, can be substantially reduced. This is particularly the
case with high output frequencies and/or output amplitudes
below full-scale.
For those applications requiring the optimum distortion and
noise performance, it is recommended to select a full-scale
output of 20mA. A lower full-scale range down to 2mA may
be considered for applications that require a low power
consumption, but can tolerate a reduced performance level.
INPUT CODE (D7 - D0)
1111 1111
1000 0000
0000 0000
IOUT
20mA
10mA
0mA
IOUT
0mA
10mA
20mA
Table I. Input Coding vs Analog Output Current.
+VA
DAC908
IOUT
RL
IOUT
RL
FIGURE 2. Equivalent Analog Output.
OUTPUT CONFIGURATIONS
The current output of the DAC908 allows for a variety of
configurations, some of which are illustrated below. As
mentioned previously, utilizing the converter’s differential
outputs will yield the best dynamic performance. Such a
differential output circuit may consist of an RF transformer
(see Figure 3) or a differential amplifier configuration (see
Figure 4). The transformer configuration is ideal for most
applications with ac coupling, while op amps will be suitable
for a dc-coupled configuration.
The single-ended configuration (see Figure 6) may be con-
sidered for applications requiring a unipolar output voltage.
Connecting a resistor from either one of the outputs to
ground will convert the output current into a ground-refer-
enced voltage signal. To improve on the dc linearity an I to
V converter can be used instead. This will result in a
negative signal excursion and, therefore, requires a dual
supply amplifier.
The signal voltage swing that may develop at the two
outputs, IOUT and IOUT, is limited by a negative and positive
compliance. The negative limit of –1V is given by the
breakdown voltage of the CMOS process, and exceeding it
will compromise the reliability of the DAC908, or even
cause permanent damage. With the full-scale output set to
20mA, the positive compliance equals 1.25V, operating with
+VD = 5V. Note that the compliance range decreases to
about 1V for a selected output current of IOUTFS = 2mA.
Care should be taken that the configuration of DAC908 does
not exceed the compliance range to avoid degradation of the
distortion performance and integral linearity.
Best distortion performance is typically achieved with the
maximum full-scale output signal limited to approximately
0.5V. This is the case for a 50doubly terminated load and
a 20mA full-scale output current. A variety of loads can be
adapted to the output of the DAC908 by selecting a suitable
transformer while maintaining optimum voltage levels at
DIFFERENTIAL WITH TRANSFORMER
Using an RF transformer provides a convenient way of
converting the differential output signal into a single-ended
signal while achieving excellent dynamic performance (see
Figure 3). The appropriate transformer should be carefully
selected based on the output frequency spectrum and imped-
ance requirements. The differential transformer configura-
tion has the benefit of significantly reducing common-mode
signals, thus improving the dynamic performance over a
wide range of frequencies. Furthermore, by selecting a
suitable impedance ratio (winding ratio), the transformer can
be used to provide optimum impedance matching while
controlling the compliance voltage for the converter outputs.
The model shown, ADT1-1WT (by Mini-Circuits), has a 1:1
ratio and may be used to interface the DAC908 to a 50
load. This results in a 25load for each of the outputs, IOUT
and IOUT. The output signals are ac coupled and inherently
isolated because of the transformer's magnetic coupling .
®
11 DAC908

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