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參數(shù)資料
| 型號： | AD768AR |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | DAC |
| 英文描述： | 16-Bit, 30 MSPS D/A Converter |
| 中文描述： | PARALLEL, WORD INPUT LOADING, 0.025 us SETTLING TIME, 16-BIT DAC, PDSO28 |
| 封裝： | 0.300 INCH, SOIC-28 |
| 文件頁數(shù)： | 11/20頁 |
| 文件大?。?/td> | 334K |
| 代理商： | AD768AR |
AD768
REV. B
–11–
For the values given in Figure 24, I
3
equals 4 mA, which results
in a nominal unipolar output swing of 0 V to 2 V. Note, since
A1 has an inverting gain of approximately –4 and a noise gain of
+5, A1’s distortion and noise performance should be considered.
1
27
28
AD768
R
FB
500
IOUTA
LADCOM
IOUTB
R
FF
100
R
L
24.9
R
P
20
I
1
I
2
I
3
A1
Figure 24. 0 V to 2 V Buffered Unipolar Output Using a
Current Divider
Bipolar Configuration
Bipolar mode is accomplished by providing an offset current,
I
BIPOLAR
, to the I/V amplifier’s (A1) summing junction. By set-
ting I
BIPOLAR
to exactly half the full-scale current flowing
through R
FB
, the resulting output voltage will be symmetrical
about the summing junction voltage, typically ground. Figure 25
shows the implementation for a bipolar
±
2.5 V buffered voltage
output. T he resistor divider sets the full-scale current for I
DAC
to
5 mA. T he internal 2.5 V reference generates a 2.5 mA I
BIPOLAR
current across R
BIP
. An output voltage of 0 V is produced when
the DAC is set to half scale (100. . .0) such that the 2.5 mA cur-
rent, I
DAC
, is exactly offset by I
BIPOLAR
. As the DAC is varied
from zero to full-scale, the output voltage swings from –2.5 V to
+2.5 V. Note, in configurations that require more than 15 mA
of total current from REFOUT , an external buffer is required.
Op amps such as the AD811, AD8001, and AD9631 are good
selections for superior dynamic performance. In dc applications,
op amps such as the AD845 or AD797 may be more appropriate.
27
AD768
REFOUT
R
FB
1k
IOUTA
LADCOM
IOUTB
75
24.9
R
P
20
A1
C
3
I
BIPOLAR
R
BIP
1k
I
DAC
28
1
Figure 25. Bipolar
±
2.5 V Buffered Voltage Output
DIFFE RE NT IAL OUT PUT CONFIGURAT IONS
AC Coupling via a T ransformer
Applications that do not require baseband operation typically
use transformer coupling. T ransformer coupling the comple-
mentary outputs of the AD768 to a load has the inherent benefit
of providing electrical isolation while consuming no additional
power. Also, a properly applied transformer should not degrade
the AD768’s output signal with respect to noise and distortion,
since the transformer is a passive device. Figure 26 shows a
center-tapped output transformer that provides the necessary dc
load conditions at the outputs IOUT A and IOUT B to drive a
±
0.5 V signal into a 50
load. In this particular circuit, the cen-
ter-tapped transformer has an impedance ratio of 4 that corre-
sponds to a turns ratio of 2. Hence, any load, R
L
, referred to the
primary side is multiplied by a factor of 4 (i.e., in this case
200
). T o avoid dc current from flowing into the R-2R ladder
of the DAC, the center tap of the transformer should be con-
nected to LADCOM.
In order to comply with the minimum voltage compliance of
–1.2 V, the maximum differential resistance seen between
IOUT A and IOUT B should not exceed 240
. Note that the
differential resistance consists of the load R
L
, referred to the
primary side of the transformer in parallel with any added differ-
ential resistance, R
DIFF
, across the two outputs. R
DIFF
is typically
added to the primary side of the transformer to match the effec-
tive primary source impedance to the load (i.e., in this case
200
).
1
27
AD768
IOUTA
LADCOM
IOUTB
R
DIFF
200
T1
R
L
50
4:1 IMPEDANCE
RATIO
T1 = MINI-CIRCUITS T4-6T
28
Figure 26. Differential Output Using a Transformer
DC COUPLING VIA AN AMPLIFIE R
A dc differential to single-ended conversion can be easily ac-
complished using the circuit shown in Figure 27. T his circuit
will attenuate both ac and dc common-mode error sources due
to the differential nature of the circuit. T hus, common-mode
noise (i.e., clock feedthrough) as well as dc unipolar offset errors
will be significantly reduced. Also, excellent temperature stabil-
ity can be obtained by using temperature tracking, thin film
resistors for R and R
REF
. T he design equations for the circuit are
provided such that the voltage output swing and IREF can be
optimized for a given application.
1
27
28
AD768
R*
IOUTA
LADCOM
IOUTB
R
REF
*
I
REF
A1
R*
6
3
REFOUT
REFIN
V
OUT
V
OUT
=
±
4 I
REF
R
WHERE I
REF
=R
REF
V
OUT
±
2V
R = 200
R
REF
= 5 x 200
*OHMTEK TDP-1403
Figure 27. DC Differential to Single-Ended Conversion
POWE R AND GROUNDING CONSIDE RAT IONS
In systems seeking to simultaneously achieve high speed and
high accuracy, the implementation and construction of the
printed circuit board design is often as important as the circuit
design. Proper RF techniques must be used in device selection,
placement and routing, and supply bypassing and grounding.
Maintaining low noise on power supplies and ground is critical
to obtaining optimum results from the AD768. Figure 28 pro-
vides an illustration of the recommended printed circuit board
ground plane layout which is implemented on the AD768 evalu-
ation board.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD768AR-REEL | 制造商:Analog Devices 功能描述:DAC 1-CH R-2R/Current Steering 16-bit 28-Pin SOIC W T/R |
| AD768ARZ | 功能描述:IC DAC 16BIT 30MSPS 28-SOIC RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 數(shù)模轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 設(shè)置時間:4.5µs 位數(shù):12 數(shù)據(jù)接口:串行，SPI? 轉(zhuǎn)換器數(shù)目:1 電壓電源:單電源 功率耗散（最大）:- 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應(yīng)商設(shè)備封裝:8-SOICN 包裝:剪切帶 (CT) 輸出數(shù)目和類型:1 電壓，單極；1 電壓，雙極 采樣率（每秒）:* 其它名稱:MCP4921T-E/SNCTMCP4921T-E/SNRCTMCP4921T-E/SNRCT-ND |
| AD768ARZ-REEL | 功能描述:IC DAC 16BIT 30MSPS 28-SOIC RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 數(shù)模轉(zhuǎn)換器 系列:- 產(chǎn)品培訓(xùn)模塊:Data Converter Fundamentals DAC Architectures 標(biāo)準(zhǔn)包裝:750 系列:- 設(shè)置時間:7µs 位數(shù):16 數(shù)據(jù)接口:并聯(lián) 轉(zhuǎn)換器數(shù)目:1 電壓電源:雙 ± 功率耗散（最大）:100mW 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:28-LCC（J 形引線） 供應(yīng)商設(shè)備封裝:28-PLCC（11.51x11.51） 包裝:帶卷 (TR) 輸出數(shù)目和類型:1 電壓，單極；1 電壓，雙極 采樣率（每秒）:143k |
| AD768-EB | 制造商:Analog Devices 功能描述:IC, 16-BIT 32 MSPS DAC - Bulk |
| AD768-EBZ | 制造商:Analog Devices 功能描述:EVAL BOARD - Boxed Product (Development Kits) |
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