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參數資料
| 型號： | AD9243* |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | 14-Bit Rail-to-Rail DACs with I2C Interface; Package: DFN; No of Pins: 10; Temperature Range: 0°C to +70°C |
| 中文描述： | 完整的14位。 3.0 MSPS的單片A / D轉換 |
| 文件頁數： | 14/24頁 |
| 文件大小： | 545K |
AD9243
REV. A
–14–
If the application requires the largest single-ended input range
(i.e., 0 V to 5 V) of the AD9243, the op amp will require larger
supplies to drive it. Various high speed amplifiers in the
“
Op
Amp Selection Guide” of this data sheet can be selected to
accommodate a wide range of supply options. Once again,
clamping the output of the amplifier should be considered for
these applications. Alternatively, a single-ended to differential
op amp driver circuit using the AD8042 could be used to
achieve the 5 V input span while operating from a single +5 V
supply.
Two dc coupled op amp circuits using a noninverting and inverting
topology are discussed below. Although not shown, the nonin-
verting and inverting topologies can be easily configured as part
of an antialiasing filter by using a Sallen-Key or Multiple-Feed-
back topology, respectively. An additional R-C network can be
inserted between the op amp’s output and the AD9243 input to
provide a real pole.
Simple Op Amp Buffer
In the simplest case, the input signal to the AD9243 will already
be biased at levels in accordance with the selected input range.
It is simply necessary to provide an adequately low source im-
pedance for the VINA and VINB analog input pins of the A/D.
Figure 32 shows the recommended configuration for a single-
ended drive using an op amp. In this case, the op amp is shown
in a noninverting unity gain configuration driving the VINA pin.
The internal reference drives the VINB pin. Note that the
addition of a small series resistor of 30
to 50
connected to
VINA and VINB will be beneficial in nearly all cases. Refer to
section “Analog Input Operation” for a discussion on resistor
selection. Figure 32 shows the proper connection for a 0V to 5 V
input range. Alternative single ended input ranges of 0V to 2
×
VREF can also be realized with the proper configuration of VREF
(refer to the section “Using the Internal Reference”).
10
m
F
VINA
VINB
SENSE
AD9243
0.1
m
F
R
S
+V
–V
R
S
VREF
5V
0V
U1
2.5V
Figure 32. Single-Ended AD9243 Op Amp Drive Circuit
Op Amp with DC Level Shifting
Figure 33 shows a dc-coupled level shifting circuit employing an
op amp, A1, to sum the input signal with the desired dc offset.
Configuring the op amp in the inverting mode with the given
resistor values results in an ac signal gain of –1. If the signal
inversion is undesirable, interchange the VINA and VINB con-
nections to reestablish the original signal polarity. The dc volt-
age at VREF sets the common-mode voltage of the AD9243. For
example, when VREF = 2.5 V, the output level from the op amp
will also be centered around 2.5 V. The use of ratio matched,
thin-film resistor networks will minimize gain and offset errors.
Also, an optional pull-up resistor, R
P
, may be used to reduce the
output load on VREF to
±
1 mA.
0V
DC
+VREF
–VREF
VINA
VINB
AD9243
0.1
m
F
500
V
*
0.1
m
F
500
V
*
7
1
2
3
4
5
A1
6
NC
NC
+V
CC
500
V
*
R
S
VREF
500
V
*
R
S
AVDD
R
P
**
*OPTIONAL RESISTOR NETWORK-OHMTEK ORNA500D
**OPTIONAL PULL-UP RESISTOR WHEN USING INTERNAL REFERENCE
NC = NO CONNECT
Figure 33. Single-Ended Input With DC-Coupled Level Shift
AC COUPLING AND INTERFACE ISSUES
For applications where ac coupling is appropriate, the op amp’s
output can be easily level shifted to the common-mode voltage,
V
CM
, of the AD9243 via a coupling capacitor. This has the
advantage of allowing the op amps common-mode level to be
symmetrically biased to its midsupply level (i.e., (V
CC
+ V
EE
)/2).
Op amps which operate symmetrically with respect to their
power supplies typically provide the best ac performance as well
as greatest input/output span. Hence, various high speed/perfor-
mance amplifiers which are restricted to +5 V/–5 V operation
and/or specified for +5 V single-supply operation can be easily
configured for the 5 V or 2 V input span of the AD9243, respec-
tively. The best ac distortion performance is achieved when the
A/D is configured for a 2 V input span and common-mode
voltage of 2.5 V. Note that differential transformer coupling,
which is another form of ac coupling, should be considered for
optimum ac performance.
Simple AC Interface
Figure 34 shows a typical example of an ac-coupled, single-
ended configuration. The bias voltage shifts the bipolar, ground-
referenced input signal to approximately VREF. The value for
C1 and C2
will depend on the size of the resistor, R. The ca-
pacitors, C1 and C2, are typically a 0.1
μ
F ceramic and 10
μ
F
tantalum capacitor in parallel to achieve a low cutoff frequency
while maintaining a low impedance over a wide frequency range.
The combination of the capacitor and the resistor form a high-
pass filter with a high-pass –3 dB frequency determined by the
equation,
f
–3
dB
= 1/(2
×
π
×
R
×
(C1 + C2))
The low impedance VREF voltage source biases both the VINB
input and provides the bias voltage for the VINA input. Figure
34 shows the VREF configured for 2.5 V. Thus the input range
C2
VINA
VINB
SENSE
AD9243
C1
R
+5V
–5V
R
S
VREF
+VREF
0V
–VREF
V
IN
C2
C1
R
S
Figure 34. AC-Coupled Input
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD9243AS | 制造商:Analog Devices 功能描述:ADC Single Pipelined 3Msps 14-bit Parallel 44-Pin MQFP 制造商:Analog Devices 功能描述:IC 14-BIT ADC |
| AD9243ASRL | 制造商:Analog Devices 功能描述:ADC Single Pipelined 3Msps 14-bit Parallel 44-Pin MQFP T/R |
| AD9243ASZ | 功能描述:IC ADC 14BIT 3MSPS 44-MQFP RoHS:是 類別:集成電路 (IC) >> 數據采集 - 模數轉換器 系列:- 標準包裝:1 系列:microPOWER™ 位數:8 采樣率（每秒）:1M 數據接口:串行，SPI? 轉換器數目:1 功率耗散（最大）:- 電壓電源:模擬和數字 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應商設備封裝:24-VQFN 裸露焊盤（4x4） 包裝:Digi-Reel® 輸入數目和類型:8 個單端，單極 產品目錄頁面:892 (CN2011-ZH PDF) 其它名稱:296-25851-6 |
| AD9243ASZRL | 功能描述:IC ADC 14BIT SGL 3MSPS 44MQFP RoHS:是 類別:集成電路 (IC) >> 數據采集 - 模數轉換器 系列:- 標準包裝:1,000 系列:- 位數:12 采樣率（每秒）:300k 數據接口:并聯 轉換器數目:1 功率耗散（最大）:75mW 電壓電源:單電源 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:24-SOIC（0.295"，7.50mm 寬） 供應商設備封裝:24-SOIC 包裝:帶卷 (TR) 輸入數目和類型:1 個單端，單極；1 個單端，雙極 |
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