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參數(shù)資料
| 型號(hào)： | ADS800 |
| 英文描述： | 12-Bit, 40MHz Sampling ANALOG-TO-DIGITAL CONVERTER |
| 中文描述： | 12位，40MHz的采樣模擬數(shù)字轉(zhuǎn)換器 |
| 文件頁數(shù)： | 11/17頁 |
| 文件大?。?/td> | 368K |
| 代理商： | ADS800 |
ADS800
SBAS035B
11
www.ti.com
APPLICATIONS
DRIVING THE ADS800
The ADS800 has a differential input with a common-mode of
+2.25V. For AC-coupled applications, the simplest way to
create this differential input is to drive the primary winding of
a transformer with a single-ended input. A differential output
is created on the secondary if the center tap is tied to the
common-mode voltage of +2.25V, as per Figure 5. This
transformer-coupled input arrangement provides good high-
frequency AC performance. It is important to select a trans-
former that gives low distortion and does not exhibit core
saturation at full-scale voltage levels. Since the transformer
does not appreciably load the ladder, there is no need to
buffer the Common-Mode (CM) output in this instance. In
general, it is advisable to keep the current draw from the CM
output pin below 0.5
μ
A to avoid nonlinearity in the internal
reference ladder. A FET input operational amplifier such as
the OPA130 can provide a buffered reference for driving
external circuitry. The analog IN and
IN
inputs should be
bypassed with 22pF capacitors to minimize track-and-hold
glitches and to improve high input frequency performance.
Figure 6 illustrates another possible low-cost interface circuit
which utilizes resistors and capacitors in place of a trans-
former. Depending on the signal bandwidth, the component
values should be carefully selected in order to maintain the
FIGURE 6. AC-Coupled Differential Input Circuit.
product performance. The input capacitors, C
IN
, and the input
resistors, R
IN
, create a high-pass filter with the lower corner
frequency at f
C
= 1/(2pR
IN
C
IN
). The corner frequency can be
reduced by either increasing the value of R
IN
or C
IN
. If the
circuit operates with a 50
or 75
impedance level, the
resistors are fixed and only the value of the capacitor can be
increased. Usually, AC-coupling capacitors are electrolytic or
tantalum capacitors with values of 1
μ
F or higher. It should be
noted that these large capacitors become inductive with
increased input frequency, which could lead to signal ampli-
tude errors or oscillation. To maintain a low AC-coupling
impedance throughout the signal band, a small value (e.g.
1
μ
F) ceramic capacitor could be added in parallel with the
polarized capacitor.
Capacitors C
SH1
and C
SH2
are used to minimize current
glitches resulting from the switching in the input track-and-
hold stage and to improve signal-to-noise performance. These
capacitors can also be used to establish a low-pass filter and
effectively reduce the noise bandwidth. In order to create a
real pole, resistors R
SER1
and R
SER2
were added in series
with each input. The cutoff frequency of the filter is deter-
mined by f
C
= 1/(2pR
SER
(C
SH
+ C
ADC
)) where R
SER
is the
resistor in series with the input, C
SH
is the external capacitor
from the input to ground, and C
ADC
is the internal input
capacitance of the A/D converter (typically 4pF).
Resistors R
1
and R
2
are used to derive the necessary
common-mode voltage from the buffered top and bottom
references. The total load of the resistor string should be
selected so that the current does not exceed 1mA. Although
the circuit in Figure 6 uses two resistors of equal value so
that the common-mode voltage is centered between the top
and bottom 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
ADS800, an operational amplifier input circuit is required. In the
differential input mode, any single-ended signal must be modi-
fied to create a differential signal. This can be accomplished by
FIGURE 5. AC-Coupled Single-Ended to Differential Drive
Circuit Using a Transformer.
Mini-Circuits
TT1-6-KK81
or equivalent
22
26
27
CM
IN
IN
ADS800
AC Input
Signal
22pF
22pF
0.1
μ
F
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
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ADS800U | 12-Bit, 40MHz Sampling ANALOG-TO-DIGITAL CONVERTER |
| ADS826E(1) | 10-Bit, 60MHz Sampling ANALOG-TO-DIGITAL CONVERTER |
| ADS823 | IC,PERIPHERAL DRIVER,1 DRIVER,TSSOP,6PIN,PLASTIC |
| ADS823E | 10-Bit, 60MHz Sampling ANALOG-TO-DIGITAL CONVERTER |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADS800E | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ADS800E/1K | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ADS800U | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 40 MSPS SE/Diff inputs 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 |
| ADS800U/1K | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 40 MSPS SE/Diff inputs 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 |
| ADS800U/1KG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 40 MSPS SE/Diff inputs 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 |
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