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參數(shù)資料
| 型號： | ADS809 |
| 英文描述： | 12-Bit, 80MHz Sampling ANALOG-TO-DIGITAL CONVERTER |
| 中文描述： | 12位，80MHz的采樣模擬數(shù)字轉(zhuǎn)換器 |
| 文件頁數(shù)： | 11/20頁 |
| 文件大?。?/td> | 437K |
| 代理商： | ADS809 |
ADS809
SBAS170C
11
www.ti.com
for input frequencies from DC to approximately 10MHz, for
which the part maintains good distortion performance pro-
viding a 2Vp-p (max) output swing on
±
5V supplies. Com-
bining a differential driver circuit with a step-up transformer
can lead to significant improvement of the distortion perfor-
mance (see Figure 6).
Transformer Coupled Interface Circuits
If the application allows for AC-coupling, but requires a
signal conversion from a single-ended source to drive the
ADS809 differentially, using a transformer offers a number
of advantages. As a passive component, it does not add to
the total noise, plus using a step-up transformer, further
signal amplification can be realized. As a result, the signal
swing out of the amplifier driving the transformer can be
reduced, leading to more headroom for the amplifier and
improved distortion performance.
One possible interface solution that uses a transformer is
given in Figure 4. The input signal is assumed to be an
Intermediate Frequency (IF) and bandpass filtered prior to
the IF amplifier. Dedicated IF amplifiers, for example the
RF2312 or MAR-6, are fixed-gain broadband amplifiers and
feature a very high bandwidth, a low-noise figure, and a high
intercept point at the expense of high quiescent currents of
50-120mA. The IF amplifier may be AC-coupled or directly
connected to the primary side of the transformer.
A variety of miniature RF transformers are readily available
from different manufacturers, i.e.: Mini-Circuits, Coilcraft, or
Trak. For the selection, it is important to carefully examine
the application requirements and determine the correct model,
the desired impedance ratio, and frequency characteristics.
Furthermore, the appropriate model must support the tar-
geted distortion level and should not exhibit any core satura-
tion at full-scale voltage levels. Since the transformer does
not appreciably load the ladder, its center tap can be directly
tied to the CM pin of the converter, as shown in Figure 4. The
value of termination resistor (R
T
) should be chosen to satisfy
the termination requirements of the source impedance (R
S
).
It can be calculated using the equation R
T
= n
2
R
S
to ensure
proper impedance matching.
Transformer-Coupled, Single-Ended to
Differential Configuration
For applications in which the input frequency is limited to about
40MHz (i.e.: baseband), the wideband, current-feedback, op-
erational amplifier OPA685 may be used. As shown in Figure
5, the OPA685 configured for the noninverting mode amplifies
the single-ended input signal, and drives the primary of an RF
transformer. To maintain the very low-distortion performance
of the OPA685, it may be advantageous to reduce the full-
scale input range (FSR) of the ADS809 from 2Vp-p to 1.5Vp-
p or 1Vp-p (refer to the paragraph
“
Reference
”
for details on
selecting the converter
’
s full-scale range).
The circuit also shows the use of an additional RC low-pass
filter placed in series with each converter input. This optional
filter can be used to set a defined corner frequency and
attenuate some of the wideband noise. The actual compo-
nent values would need to be tuned for the individual appli-
cation requirements. As a guideline, resistor values are
typically in the range of 10
to 100
, capacitors in the range
of 10pF to 200pF. In any case, the R
IN
and C
IN
values should
have a low tolerance. This will ensure that the ADS809 sees
closely matched source impedances.
FIGURE 4. Driving the ADS809 with a Low-Distortion RF Amplifier and a Transformer Suited for IF Sampling Applications.
R
IN
R
IN
C
IN
C
IN
4.7
μ
F
0.1
μ
F
R
T
0.1
μ
F
1:n
XFMR
R
S
IF
Amp
Optional
Bandpass
Filter
V
IN
(IF)
+
ADS809
IN
IN
CM
+5V
+V
S
–
V
S
V
CM
+2.5V
R
IN
R
IN
C
IN
C
IN
2.2
μ
F
0.1
μ
F
R
T
0.1
μ
F
1:n
XFMR
R
S
R
G
OPA685
R
1
R
2
V
IN
+
ADS809
IN
IN
CM
+5V
–
V
+V
V
CM
+2.5V
FIGURE 5. Converting a Single-Ended Input Signal into a Differential Signal Using an RF Transformer.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADS809Y/250 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 80MHz Sampling ADC 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-32 |
| ADS809Y/250G4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 80MHz Sampling ADC 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-32 |
| ADS809Y/2K | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 80MHz Sampling ADC 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-32 |
| ADS809Y/2K5 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:A/D CONVERTER |
| ADS809Y/2KG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 80MHz Sampling ADC 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 安裝風格:SMD/SMT 封裝 / 箱體:VQFN-32 |
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