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參數(shù)資料
| 型號(hào)： | ADS5521IPAPR |
| 英文描述： | 12-Bit, 105MSPS Analog-toDigital Converter |
| 中文描述： | 12位，105Msps模數(shù)轉(zhuǎn)換器toDigital轉(zhuǎn)換器 |
| 文件頁數(shù)： | 13/20頁 |
| 文件大?。?/td> | 261K |
| 代理商： | ADS5521IPAPR |
SBAS309 MAY 2004
www.ti.com
13
This differential input topology produces a high level of
AC performance for high sampling rates. It also results
in a very high usable input bandwidth, especially
important for high intermediate-frequency (IF) or
undersampling applications. The ADS5521 requires
each of the analog inputs (INP, INM) to be externally
biased around the common-mode level of the internal
circuitry (CM, pin 17). For a full-scale differential input,
each of the differential lines of the input signal (pins 19
and 20) swings symmetrically between CM + 0.575V
and CM – 0.575V. This means that each input is driven
with a signal of up to CM
±
0.575V, so that each input
has a maximum differential signal of 1.15V
PP
for a total
differential input signal swing of 2.3V
PP
. The maximum
swing is determined by the two reference voltages, the
top reference (REFP, pin 29), and the bottom reference
(REFM, pin 30).
The ADS5521 obtains optimum performance when the
analog inputs are driven differentially. The circuit shown
in Figure 5 shows one possible configuration using an
RF transformer.
R
0
50
Z
0
50
1:1
INP
ADS5521
INM
CM
ADT11WT
R
50
1nF
0.1
μ
F
AC Signal
Source
10
Figure 5. Transformer Input to Convert
Single-Ended Signal to Differential Signal
The single-ended signal is fed to the primary winding of
an RF transformer. Since the input signal must be
biased around the common-mode voltage of the
internal circuitry, the common-mode voltage (V
CM
) from
the ADS5521 is connected to the center-tap of the
secondary winding. To ensure a steady low-noise V
CM
reference, best performance is obtained when the CM
(pin 17) output is filtered to ground with 0.1
μ
F and
0.01
μ
F low-inductance capacitors.
Output V
CM
(pin 17) is designed to directly drive the
ADC input. When providing a custom CM level, be
aware that the input structure of the ADC sinks a
common-mode current in the order of 4mA (2mA per
input). Equation (1) describes the dependency of the
common-mode current and the sampling frequency:
4mA
125MSPS
f
s
Where:
f
S
> 60MSPS.
This equation helps to design the output capability and
impedance of the driving circuit accordingly.
When it is necessary to buffer or apply a gain to the
incoming analog signal, it is possible to combine
single-ended operational amplifiers with an RF
transformer, or to use a differential input/output
amplifier without a transformer, to drive the input of the
ADS5521. TI offers a wide selection of single-ended
operational amplifiers (including the THS3201,
THS3202, OPA847, and OPA695) that can be selected
depending on the application. An RF gain block
amplifier, such as TI’s THS9001, can also be used with
an RF transformer for very high input frequency
applications. The THS4503 is a recommended
differential input/output amplifier. Table 4 lists the
recommended amplifiers.
When using single-ended operational amplifiers (such
as the THS3201, THS3202, OPA847, or OPA695) to
provide gain, a three-amplifier circuit is recommended
with one amplifier driving the primary of an RF
transformer and one amplifier in each of the legs of the
secondary driving the two differential inputs of the
ADS5521. These three amplifier circuits minimize
even-order harmonics. For very high frequency inputs,
an RF gain block amplifier can be used to drive a
transformer primary; in this case, the transformer
secondary connections can drive the input of the
ADS5521 directly, as shown in Figure 5, or with the
addition of the filter circuit shown in Figure 6.
Figure 6 illustrates how R
IN
and C
IN
can be placed to
isolate the signal source from the switching inputs of the
ADC and to implement a low-pass RC filter to limit the
input noise in the ADC. It is recommended that these
components be included in the ADS5521 circuit layout
when any of the amplifier circuits discussed previously
are used. The components allow fine-tuning of the
circuit performance. Any mismatch between the
differential lines of the ADS5521 input produces a
degradation in performance at high input frequencies,
mainly characterized by an increase in the even-order
harmonics. In this case, special care should be taken to
keep as much electrical symmetry as possible between
both inputs.
Another possible configuration for lower-frequency sig-
nals is the use of differential input/output amplifiers that
can simplify the driver circuit for applications requiring
DC coupling of the input. Flexible in their configurations
(see Figure 7), such amplifiers can be used for single-
ended-to-differential conversion, signal amplification.
P
(1)
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADS5521IPAPRG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 105MSPS 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 |
| ADS5522 | 制造商:BB 制造商全稱:BB 功能描述:14-Bit, 80MSPS Analog-to-Digital Converter |
| ADS5522EVM | 功能描述:數(shù)據(jù)轉(zhuǎn)換 IC 開發(fā)工具 ADS5522 Eval Mod RoHS:否 制造商:Texas Instruments 產(chǎn)品:Demonstration Kits 類型:ADC 工具用于評(píng)估:ADS130E08 接口類型:SPI 工作電源電壓:- 6 V to + 6 V |
| ADS5522IPAP | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 80MSPS 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 |
| ADS5522IPAPG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit 80MSPS 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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