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PDF AD9751 Data sheet ( Hoja de datos )
| Número de pieza | AD9751 | |
| Descripción | 10-Bit 300 MSPS High-Speed TxDAC+ D/A Converter | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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FEATURES
10-Bit Dual Muxed Port DAC
300 MSPS Output Update Rate
Excellent SFDR and IMD Performance
SFDR to Nyquist @ 25 MHz Output: 64 dB
Internal Clock Doubling PLL
Differential or Single-Ended Clock Input
On-Chip 1.2 V Reference
Single 3.3 V Supply Operation
Power Dissipation: 155 mW @ 3.3 V
48-Lead LQFP
APPLICATIONS
Communications: LMDS, LMCS, MMDS
Base Stations
Digital Synthesis
QAM and OFDM
10-Bit, 300 MSPS
High Speed TxDAC+® D/A Converter
AD9751*
FUNCTIONAL BLOCK DIAGRAM
DVDD DCOM
AVDD ACOM
PORT1
LATCH
PORT2
LATCH
MUX
DAC
IOUTA
IOUTB
CLK+
CLK–
CLKVDD
PLLVDD
CLKCOM
PLL
CLOCK
MULTIPLIER
REFERENCE
AD9751
RESET LPF DIV0 DIV1 PLLLOCK
REFIO
FSADJ
PRODUCT DESCRIPTION
The AD9751 is a dual muxed port, ultrahigh speed, single-
channel, 10-bit CMOS DAC. It integrates a high quality 10-bit
TxDAC+ core, a voltage reference, and digital interface circuitry
into a small 48-lead LQFP package. The AD9751 offers excep-
tional ac and dc performance while supporting update rates up
to 300 MSPS.
The AD9751 has been optimized for ultrahigh speed applica-
tions up to 300 MSPS where data rates exceed those possible on
a single data interface port DAC. The digital interface consists
of two buffered latches as well as control logic. These latches
can be time multiplexed to the high speed DAC in several ways.
This PLL drives the DAC latch at twice the speed of the exter-
nally applied clock and is able to interleave the data from the
two input channels. The resulting output data rate is twice that
of the two input channels. With the PLL disabled, an external
2× clock may be supplied and divided by two internally.
The CLK inputs (CLK+/CLK–) can be driven either differen-
tially or single-ended, with a signal swing as low as 1 V p-p.
The DAC utilizes a segmented current source architecture com-
bined with a proprietary switching technique to reduce glitch
energy and maximize dynamic accuracy. Differential current
outputs support single-ended or differential applications. The
differential outputs each provide a nominal full-scale current
from 2 mA to 20 mA.
The AD9751 is manufactured on an advanced low cost 0.35 µm
CMOS process. It operates from a single supply of 3.0 V to 3.6 V
and consumes 155 mW of power.
PRODUCT HIGHLIGHTS
1. The AD9751 is a member of a pin compatible family of high
speed TxDAC+s, providing 10-, 12-, and 14-bit resolution.
2. Ultrahigh Speed 300 MSPS Conversion Rate.
3. Dual 10-Bit Latched, Multiplexed Input Ports. The AD9751
features a flexible digital interface allowing high speed data
conversion through either a single or dual port input.
4. Low Power. Complete CMOS DAC function operates on
155 mW from a 3.0 V to 3.6 V single supply. The DAC full-
scale current can be reduced for lower power operation.
5. On-Chip Voltage Reference. The AD9751 includes a 1.20 V
temperature compensated band gap voltage reference.
*Protected by U.S. Patent numbers 5450084, 5568145, 5689257, and 5703519.
REV. C
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703 © 2003 Analog Devices, Inc. All rights reserved.
1 page  
AD9751
DIGITAL SPECIFICATIONS (TMIN to TMAX, AVDD = DVDD = PLLVDD = CLKVDD = 3.3 V, IOUTFS = 20 mA, unless otherwise noted.)
Parameter
Min Typ Max
Unit
DIGITAL INPUTS
Logic 1
2.1 3
Logic 0
0 0.9
Logic 1 Current
–10 +10
Logic 0 Current
–10 +10
Input Capacitance
5
Input Setup Time (tS), TA = 25°C
1.0 0.5
Input Hold Time (tH), TA = 25°C
1.0 0.5
Latch Pulsewidth (tLPW), TA = 25°C
1.5
Input Setup Time (tS, PLLVDD = 0 V), TA = 25°C
–1.0 –1.5
Input Hold Time (tH, PLLVDD = 0 V), TA = 25°C
2.5 1.7
CLK to PLLLOCK Delay (tD, PLLVDD = 0 V), TA = 25°C
3.5
4.0
Latch Pulsewidth (tLPW PLLVDD = 0 V), TA = 25°C
1.5
PLLOCK (VOH)
3.0
PLLOCK (VOL)
0.3
CLK INPUTS
Input Voltage Range
Common-Mode Voltage
Differential Voltage
Min CLK Frequency*
03
0.75 1.5
2.25
0.5 1.5
6.25
V
V
µA
µA
pF
ns
ns
ns
ns
ns
ns
ns
V
V
V
V
V
MHz
*Min CLK Frequency applies only when using internal PLL. When PLL is disabled, there is no minimum CLK frequency.
Specifications subject to change without notice.
–4– REV. C
5 Page 
AD9751
FUNCTIONAL DESCRIPTION
Figure 3 shows a simplified block diagram of the AD9751. The
AD9751 consists of a PMOS current source array capable of
providing up to 20 mA of full-scale current, IOUTFS. The array is
divided into 31 equal sources that make up the five most signifi-
cant bits (MSBs). The next four bits, or middle bits, consist of
15 equal current sources whose value is 1/16th of an MSB cur-
rent source. The remaining LSB is a binary weighted fraction of
the middle bit current sources. Implementing the middle and
lower bits with current sources, instead of an R-2R ladder,
enhances dynamic performance for multitone or low amplitude
signals and helps maintain the DAC’s high output impedance
(i.e., >100 kΩ).
All of the current sources are switched to one or the other of the
two outputs (i.e., IOUTA or IOUTB) via PMOS differential current
switches. The switches are based on a new architecture that
significantly improves distortion performance. This new switch
architecture reduces various timing errors and provides match-
ing complementary drive signals to the inputs of the differential
current switches.
The analog and digital sections of the AD9751 have separate
power supply inputs (i.e., AVDD and DVDD) that can operate
independently over a 3.0 V to 3.6 V range. The digital section,
which is capable of operating at a 300 MSPS clock rate, consists
of edge-triggered latches and segment decoding logic circuitry.
The analog section includes the PMOS current sources, the
associated differential switches, a 1.20 V band gap voltage refer-
ence, and a reference control amplifier.
The full-scale output current is regulated by the reference
control amplifier and can be set from 2 mA to 20 mA via an
external resistor, RSET. The external resistor, in combination
with both the reference control amplifier and voltage reference
VREFIO, sets the reference current IREF, which is replicated to the
segmented current sources with the proper scaling factor. The
full-scale current, IOUTFS, is 32 times the value of IREF.
REFERENCE OPERATION
The AD9751 contains an internal 1.20 V band gap reference.
This can easily be overdriven by an external reference with no
effect on performance. REFIO serves as either an input or output,
depending on whether the internal or an external reference is
used. To use the internal reference, simply decouple the REFIO
pin to ACOM with a 0.1 µF capacitor. The internal reference
voltage will be present at REFIO. If the voltage at REFIO is to
be used elsewhere in the circuit, an external buffer amplifier with
an input bias current less than 100 nA should be used. An example
of the use of the internal reference is shown in Figure 4.
A low impedance external reference can be applied to REFIO,
as shown in Figure 5. The external reference may provide either
a fixed reference voltage to enhance accuracy and drift perfor-
mance or a varying reference voltage for gain control. Note that
the 0.1 µF compensation capacitor is not required since the inter-
nal reference is overdriven, and the relatively high input impedance
of REFIO minimizes any loading of the external reference.
REFERENCE CONTROL AMPLIFIER
The AD9751 also contains an internal control amplifier that is
used to regulate the DAC’s full-scale output current, IOUTFS.
The control amplifier is configured as a voltage-to-current con-
verter as shown in Figure 4, so that its current output, IREF, is
determined by the ratio of VREFIO and an external resistor, RSET,
as stated in Equation 4. IREF is applied to the segmented current
sources with the proper scaling 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 application benefits. The first benefit relates directly to
the power dissipation of the AD9751, which is proportional to
IOUTFS (refer to the Power Dissipation section). The second
benefit relates to the 20 dB adjustment, which is useful for sys-
tem gain control purposes.
The small signal bandwidth of the reference control amplifier is
approximately 500 kHz and can be used for low frequency, small
signal multiplying applications.
0.1F
RSET
2k⍀
3.0V TO 3.6V
1.2V REF
REFIO
DVDD AVDD
PMOS CURRENT
SOURCE ARRAY
FSADJ
SEGMENTED
SWITCHES FOR
DB0 TO DB9
DAC
DAC LATCH
AD9751
DCOM
ACOM
2 –1 MUX
PORT 1 LATCH
PORT 2 LATCH
DB0 – DB9
DB0 – DB9
DIGITAL DATA INPUTS
PLL
CIRCUITRY
VDIFF = VOUTA – VOUTB
IOUTA
IOUTB
PLLVDD
CLKVDD
CLK+
CLK–
CLKCOM
RESET
LPF
VOUT B
RLOAD
50⍀
VOUT A
RLOAD
50⍀
DIV0 DIV1 PLLLOCK
Figure 3. Simplified Block Diagram
–10–
REV. C
11 Page | ||
| Páginas | Total 29 Páginas | |
| PDF Descargar | [ Datasheet AD9751.PDF ] | |
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