參數(shù)資料
型號(hào)： AD9744ARZ
廠商： Analog Devices Inc
文件頁(yè)數(shù)： 5/32頁(yè)
文件大?。?/td> 0K
描述： IC DAC 14BIT 210MSPS 28-SOIC
產(chǎn)品培訓(xùn)模塊： Data Converter Fundamentals
DAC Architectures
標(biāo)準(zhǔn)包裝： 27
系列： TxDAC®
設(shè)置時(shí)間： 11ns
位數(shù)： 14
數(shù)據(jù)接口： 并聯(lián)
轉(zhuǎn)換器數(shù)目： 1
電壓電源： 模擬和數(shù)字
功率耗散（最大）： 145mW
工作溫度： -40°C ~ 85°C
安裝類型： 表面貼裝
封裝/外殼： 28-SOIC（0.295"，7.50mm 寬）
供應(yīng)商設(shè)備封裝： 28-SOIC W
包裝： 管件
輸出數(shù)目和類型： 2 電流，單極；2 電流，雙極
采樣率（每秒）： 210M
產(chǎn)品目錄頁(yè)面： 785 (CN2011-ZH PDF)
配用： AD9744ACP-PCBZ-ND - BOARD EVAL FOR AD9744ACP
Data Sheet
AD9744
Rev. C | Page 13 of 32
FUNCTIONAL DESCRIPTION
Figure 23 shows a simplified block diagram of the AD9744. The
AD9744 consists of a DAC, digital control logic, and full-scale
output current control. The DAC contains a PMOS current
source array capable of providing up to 20 mA of full-scale
current (IOUTFS). The array is divided into 31 equal currents that
make up the five most significant bits (MSBs). The next four
bits, or middle bits, consist of 15 equal current sources whose
value is 1/16th of an MSB current source. The remaining LSBs
are binary weighted fractions of the middle bits current sources.
Implementing the middle and lower bits with current sources,
instead of an R-2R ladder, enhances its dynamic performance
for multitone or low amplitude signals and helps maintain the
DAC’s high output impedance (that is, >100 k).
All of these current sources are switched to one or the other of
the two output nodes, that is, IOUTA or IOUTB, via PMOS
differential current switches. The switches are based on the
architecture that was pioneered in the AD9764 family, with
further refinements to reduce distortion contributed by the
switching transient. This switch architecture also reduces
various timing errors and provides matching complementary
drive signals to the inputs of the differential current switches.
The analog and digital sections of the AD9744 have separate
power supply inputs, that is, AVDD and DVDD, that can operate
independently over a 2.7 V to 3.6 V range. The digital section,
which is capable of operating at a rate of up to 210 MSPS,
consists of edge-triggered latches and segment decoding logic
circuitry. The analog section includes the PMOS current
sources, the associated differential switches, a 1.2 V band gap
voltage reference, and a reference control amplifier.
The DAC 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, connected to the full-scale adjust
(FS ADJ) pin. 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 IREF.
REFERENCE OPERATION
The AD9744 contains an internal 1.2 V band gap reference. The
internal reference cannot be disabled, but can be easily overridden
by an external reference with no effect on performance. Figure 25
shows an equivalent circuit of the band gap reference. REFIO
serves as either an output or an input 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 F capacitor and connect REFLO to ACOM via a resistance
less than 5 . The internal reference voltage will be present at
REFIO. If the voltage at REFIO is to be used anywhere else in
the circuit, an external buffer amplifier with an input bias
current of less than 100 nA should be used. An example of the
use of the internal reference is shown in Figure 26.
Figure 25. Equivalent Circuit of Internal Reference
Figure 26. Internal Reference Configuration
An external reference can be applied to REFIO, as shown in
Figure 27. The external reference may provide either a fixed
reference voltage to enhance accuracy and drift performance or
a varying reference voltage for gain control. Note that the 0.1 F
compensation capacitor is not required since the internal reference
is overridden, and the relatively high input impedance of REFIO
minimizes any loading of the external reference.
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.
AVDD
REFIO
REFLO
84
A
7k
02913-057
150pF
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
3.3V
REFIO
FS ADJ
2k
0.1
F
AD9744
ADDITIONAL
LOAD
OPTIONAL
EXTERNAL
REF BUFFER
02913-023
150pF
+1.2V REF
AVDD
REFLO
CURRENT
SOURCE
ARRAY
3.3V
REFIO
FS ADJ
RSET
AD9744
EXTERNAL
REF
IREF =
VREFIO/RSET
AVDD
REFERENCE
CONTROL
AMPLIFIER
VREFIO
02913-024
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