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參數(shù)資料
| 型號(hào)： | ADS821E |
| 英文描述： | 10-Bit, 40MHz Sampling ANALOG-TO-DIGITAL CONVERTER |
| 中文描述： | 10位，40MHz的采樣模擬數(shù)字轉(zhuǎn)換器 |
| 文件頁(yè)數(shù)： | 12/18頁(yè) |
| 文件大?。?/td> | 384K |
| 代理商： | ADS821E |
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ADS821
SBAS040B
12
so that the current does not exceed 1mA. Although the circuit
in Figure 7 uses two resistors of equal value so that the
common-mode voltage is centered between the top and bot-
tom reference (+2.25V), it is not necessary to do so. In all
cases the center point, V
CM
, should be bypassed to ground in
order to provide a low-impedance AC ground.
If the signal needs to be DC-coupled to the input of the
ADS821, an operational amplifier input circuit is required. In
the differential input mode, any single-ended signal must be
modified to create a differential signal. This can be accom-
plished by using two operational amplifiers, one in the
noninverting mode for the input and the other amplifier in the
inverting mode for the complementary input. The low-distor-
tion circuit in Figure 8 will provide the necessary input shifting
required for signals centered around ground. It also employs
a diode for output level shifting to ensure a low-distortion
+3.25V output swing. See Figure 9 for another DC-coupled
circuit. Other amplifiers can be used in place of the OPA860
if the lowest distortion is not necessary. If output level shifting
circuits are not used, care must be taken to select opera-
tional amplifiers that give the necessary performance when
swinging to +3.25V with a
±
5V supply operational amplifier.
The OPA620 and OPA621, or the lower power OPA650 or
OPA820 can be used in place of the OPA860 in Figure 8. In
that configuration, the OPA820 will typically swing to within
100mV of positive full scale.
The ADS821 can also be configured with a single-ended input
full-scale range of +0.25V to +4.25V by tying the complemen-
tary input to the common-mode reference voltage, see Figure 10.
This configuration will result in increased even-order harmon-
ics, especially at higher input frequencies. This tradeoff,
however, may be quite acceptable for time-domain applica-
tions. The driving amplifier must give adequate performance
with a +0.25V to +4.25V output swing in this case.
EXTERNAL REFERENCES AND ADJUSTMENT OF
FULL-SCALE RANGE
The internal-reference buffers are limited to approximately
1mA of output current. As a result, these internal +1.25V and
+3.25V references may be overridden by external references
that have at least 18mA (at room temperature) of output drive
capability. In this instance, the common-mode voltage will be
set halfway between the two references. This feature can be
used to adjust the gain error, improve gain drift, or to change
the full-scale input range of the ADS821. Changing the full-
scale range to a lower value has the benefit of easing the
swing requirements of external input amplifiers. The external
references can vary as long as the value of the external top
reference (REFT
EXT
) is less than or equal to +3.4V, the value
of the external bottom reference (REFB
EXT
) is greater than or
equal to +1.1V, and the difference between the external
references are greater than or equal to 800mV.
For the differential configuration, the full-scale input range
will be set to the external reference values that are
selected. For the single-ended mode, the input range is
2
(REFT
EXT
–
REFB
EXT
), with the common-mode being
centered at (REFT
EXT
+ REFB
EXT
)/2. Refer to the Typical
Characteristics for expected performance versus full-scale
input range.
The circuit in Figure 11 works completely on a single +5V
supply. As a reference element, it uses the microPower
reference REF1004-2.5, which is set to a quiescent current
of 0.1mA. Amplifier A
2
is configured as a follower to buffer the
+1.25V generated from the resistor divider. To provide the
necessary current drive, a pull-down resistor (R
P
) is added.
Amplifier A
1
is configured as an adjustable gain stage, with
a range of approximately 1 to 1.32. The pull-up resistor again
relieves the op amp from providing the full current drive. The
value of the pull-up, pull-down resistors is not critical and can
be varied to optimize power consumption. The need for pull-
up, pull-down resistors depends only on the drive capability
of the selected drive amplifier and thus can be omitted.
FIGURE 7. AC-Coupled Differential Input Circuit.
ADS8xx
R
SER1(1)
49.9
R
3
1k
R
2
(6k
)
R
1
(6k
)
C
2
0.1
μ
F
C
22pF
C
22pF
C
3
0.1
μ
F
C
1
0.1
μ
F
C
IN
0.1
μ
F
V
CM
C
IN
0.1
μ
F
R
IN1
25
R
IN2
25
R
SER2(1)
49.9
+3.25V
Top Reference
+1.25V
Bottom Reference
IN
NOTE: (1) indicates optional component.
IN
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PDF描述 |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADS821E/1K | 制造商:BB 制造商全稱:BB 功能描述:10-Bit, 40MHz Sampling ANALOG-TO-DIGITAL CONVERTER |
| ADS821U | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 10-Bit 40 MSPS SE/ Diff Input RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 結(jié)構(gòu):Sigma-Delta 轉(zhuǎn)換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類型:Differential 信噪比:107 dB 接口類型:SPI 工作電源電壓:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-32 |
| ADS821U | 制造商:Texas Instruments 功能描述:10 bit sampling analog/digital converter |
| ADS821U | 制造商:Texas Instruments 功能描述:IC 10BIT ADC 40SPS 28-SOIC |
| ADS821U-1 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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