參數(shù)資料
型號(hào)： ADS8481IBRGZRG4
英文描述： 18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
中文描述： 18位，1 MSPS的，偽差分單極輸入，微采樣模擬到數(shù)字轉(zhuǎn)換并行接口和參考
文件頁(yè)數(shù)： 21/31頁(yè)
文件大?。?/td> 717K
代理商： ADS8481IBRGZRG4
www.ti.com
ANALOG INPUT
When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs is captured on
the internal capacitor array. The voltage on the -IN input is limited between –0.2 V and 0.2 V, allowing the input
to reject small signals which are common to both the +IN and –IN inputs. The +IN input has a range of –0.2 V to
V
ref
+ 0.2 V. The input span [+IN – (–IN)] is limited to 0 V to V
ref
.
The input current on the analog inputs depends upon a number of factors: sample rate, input voltage, and
source impedance. Essentially, the current into the ADS8481 charges the internal capacitor array during the
sample period. After this capacitance has been fully charged, there is no further input current. The source of the
analog input voltage must be able to charge the input capacitance (65 pF) to an 18-bit settling level within the
acquisition time (250 ns) of the device. When the converter goes into the hold mode, the input impedance is
greater than 1 G
.
Care must be taken regarding the absolute analog input voltage. To maintain the linearity of the converter, the
+IN and –IN inputs and the span [+IN – (–IN)] must be within the limits specified. Outside of these ranges, the
converter's linearity may not meet specifications. To minimize noise, low bandwidth input signals with low-pass
filters are used.
ADS8481
_
+
20
W
680 pF
Low-Pass Filter
THS4031
V
IN
50
W
INP
INM
ADS8481
SLAS385A–FEBRUARY 2006–REVISED MARCH 2006
PRINCIPLES OF OPERATION (continued)
Care must be taken to ensure that the output impedance of the sources driving the +IN and –IN inputs are
matched. If this is not observed, the two inputs could have different settling times. This may result in offset error,
gain error, and linearity error which varies with temperature and input voltage.
The analog input to the converter needs to be driven with a low noise, high-speed op-amp like the THS4031. An
RC filter is recommended at the input pins to low-pass filter the noise from the source. A series resistor of 20
and a decoupling capacitor of 680 pF is recommended. The input to the converter is a uni-polar input voltage in
the range 0 to V
ref
. The THS4031 can be used in the source follower configuration to drive the converter.
Figure 40. Input Circuit
In systems, where the input is bi-polar, the THS4031 can be used in the inverting configuration with an
additional DC bias applied to its + input so as to keep the input to the ADS8481 within its rated operating voltage
range. This configuration is also recommended when the ADS8481 is used in signal processing applications
where good SNR and THD performance is required. The DC bias can be derived from the REF3220 or the
REF3240 reference voltage ICs. The input configuration shown below is capable of delivering better than 92dB
SNR and -100db THD at an input frequency of 100 kHz. In case band-pass filters are used to filter the input,
care should be taken to ensure that the signal swing at the input of the band-pass filter is small so as to keep
the distortion introduced by the filter minimal. In such cases, the gain of the circuit shown below can be
increased to keep the input to the ADS8481 large to keep the SNR of the system high. Note that the gain of the
system from the + input to the output of the THS4031 in such a configuration is a function of the gain of the AC
signal. A resistor divider can be used to scale the output of the REF3220 or REF3240 to reduce the voltage at
the DC input to THS4031 to keep the voltage at the input of the converter within its rated operating range.
21
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PDF描述
ADS8481IBRGZT 18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
ADS8481IBRGZTG4 18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
ADS8481IPFBR 18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
ADS8481IPFBT 18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
ADS8481IRGZR 18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
ADS8481IBRGZT 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 18-Bit 1-MSPS Pseudo Diff Unipolar 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
ADS8481IBRGZTG4 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 18-Bit 1-MSPS Pseudo Diff Unipolar 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
ADS8481IPFBR 制造商:BB 制造商全稱:BB 功能描述:18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
ADS8481IPFBT 制造商:BB 制造商全稱:BB 功能描述:18-BIT, 1-MSPS, PSEUDO-DIFFERENTIAL UNIPOLAR INPUT, MICROPOWER SAMPLING ANALOG-TO-DIGITAL CONVERTER WITH PARALLEL INTERFACE AND REFERENCE
ADS8481IRGZR 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 18-Bit 1MSPS Parall ADC w/Ref 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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