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參數資料
| 型號： | AD9709AST |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | DAC |
| 英文描述： | RES 0.01 OHM MAX 25 AMP AXIAL |
| 中文描述： | PARALLEL, 8 BITS INPUT LOADING, 0.035 us SETTLING TIME, 8-BIT DAC, PQFP48 |
| 封裝： | PLASTIC, LQFP-48 |
| 文件頁數： | 15/27頁 |
| 文件大小： | 466K |
| 代理商： | AD9709AST |
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REV. 0
AD9709
–15–
SINGLE-ENDED, BUFFERED VOLTAGE OUTPUT
CONFIGURATION
Figure 37 shows a buffered single-ended output configuration
in which the op amp U1 performs an I-V conversion on the
AD9709 output current. U1 maintains I
OUTA
(or I
OUTB
) at a
virtual ground, thus minimizing the nonlinear output imped-
ance effect on the DAC’s INL performance as discussed in
the Analog Output section. Although this single-ended configu-
ration typically provides the best dc linearity performance, its ac
distortion performance at higher DAC update rates may be
limited by U1’s slewing capabilities. U1 provides a negative
unipolar output voltage and its full-scale output voltage is simply
the product of R
FB
and I
OUTFS
. The full-scale output should be
set within U1’s voltage output swing capabilities by scaling I
OUTFS
and/or R
FB
. An improvement in ac distortion performance may
result with a reduced I
OUTFS
since the signal current U1 will be
required to sink will be subsequently reduced.
I
OUTA
I
OUTB
AD9709
200
U1
V
OUT
= I
OUTFS
R
FB
R
FB
200
Figure 37. Unipolar Buffered Voltage Output
FREQUENCY
–
MHz
P
–
90
70
0.2
85
80
75
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Figure 38. AVDD Power Supply Rejection Ratio
POWER AND GROUNDING CONSIDERATIONS, POWER
SUPPLY REJECTION
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.
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. 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, I
OUTFS
. AC noise on the DC supplies
is common in applications where the power distribution is gen-
erated by a switching power supply. Typically, switching power
supply noise will occur over the spectrum from tens of kHz to
several MHz. The PSRR vs. frequency of the AD9709 AVDD
supply over this frequency range is shown in Figure 38.
Note that the units in Figure 38 are given in units of (amps out/
volts in). Noise on the analog power supply has the effect of
modulating the internal current sources, and therefore the
output current. The voltage noise on AVDD, therefore, will be
added in a nonlinear manner to the desired I
OUT
. PSRR is very
code dependent, thus producing mixing effects which can
modulate low-frequency power supply noise to higher frequen-
cies. Worst case PSRR for either one of the differential DAC
outputs will occur when the full-scale current is directed to-
wards that output. As a result, the PSRR measurement in Fig-
ure 38 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.
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 simplic-
ity sake (i.e., ignore 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 dc’s full-scale
current, I
OUTFS
, one must determine the PSRR in dB using
Figure 38 at 250 kHz. To calculate the PSRR for a given R
LOAD
,
such that the units of PSRR are converted from A/V to V/V,
adjust the curve in Figure 38 by the scaling factor 20
×
Log
(R
LOAD
). For instance, if R
LOAD
is the PSRR is reduced by
34 dB (i.e., PSRR of the DAC at 250 kHz which is 85 dB in
Figure 38 becomes 51 dB V
OUT
/V
IN
).
Proper grounding and decoupling should be a primary objective
in any high-speed, high-resolution system. The AD9709 fea-
tures separate analog and digital supply 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 possible. Similarly, DVDD, the digital supply, should
be decoupled to DCOM as close to the chip as physically possible.
100 F
10 F
–
22 F
0.1 F
TTL/CMOS
LOGIC
CIRCUITS
+5V
POWER SUPPLY
FERRITE
BEADS
AVDD
ACOM
ELECTROLYTIC
TANTALUM
CERAMIC
Figure 39. Differential LC Filter for Single 5 V and 3 V
Applications
For those applications that require a single 5 V or 3 V supply for
both the analog and digital supplies, a clean analog supply may
be generated using the circuit shown in Figure 39. 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.
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PDF描述 |
|---|---|
| AD9709-EB | 8-Bit, 125 MSPS Dual TxDAC D/A Converter |
| AD9712B | RES,0.0,0.25W,METAL FILM,0% |
| AD9712BAN | RES,0.0,0.25W,METAL FILM,0% |
| AD9712BAP | TEST POINT, WHITE, 0.040 HOLE, 0.062 PCB |
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9709ASTRL | 制造商:Analog Devices 功能描述:DAC 2-CH Segment 8-bit 48-Pin LQFP T/R 制造商:Rochester Electronics LLC 功能描述:8-BIT 125 MSPS DUAL TXDAC+ D/A CONVERTER - Tape and Reel |
| AD9709ASTZ | 功能描述:IC DAC 8BIT DUAL 125MSPS 48-LQFP RoHS:是 類別:集成電路 (IC) >> 數據采集 - 數模轉換器 系列:TxDAC+® 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:50 系列:- 設置時間:4µs 位數:12 數據接口:串行 轉換器數目:2 電壓電源:單電源 功率耗散（最大）:- 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-TSSOP，8-MSOP（0.118"，3.00mm 寬） 供應商設備封裝:8-uMAX 包裝:管件 輸出數目和類型:2 電壓，單極 采樣率（每秒）:* 產品目錄頁面:1398 (CN2011-ZH PDF) |
| AD9709ASTZ1 | 制造商:AD 制造商全稱:Analog Devices 功能描述:8-Bit, 125 MSPS, Dual TxDAC Digital-to-Analog Converter |
| AD9709ASTZKL1 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Analog Devices 功能描述: |
| AD9709ASTZRL | 功能描述:IC DAC 8BIT DUAL 125MSPS 48LQFP RoHS:是 類別:集成電路 (IC) >> 數據采集 - 數模轉換器 系列:TxDAC+® 產品培訓模塊:LTC263x 12-, 10-, and 8-Bit VOUT DAC Family 特色產品:LTC2636 - Octal 12-/10-/8-Bit SPI VOUT DACs with 10ppm/°C Reference 標準包裝:91 系列:- 設置時間:4µs 位數:10 數據接口:MICROWIRE?，串行，SPI? 轉換器數目:8 電壓電源:單電源 功率耗散（最大）:2.7mW 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:14-WFDFN 裸露焊盤 供應商設備封裝:14-DFN-EP（4x3） 包裝:管件 輸出數目和類型:8 電壓，單極 采樣率（每秒）:* |
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