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參數(shù)資料
| 型號： | ADS5270 |
| 英文描述： | 8-Channel, 12-Bit, 40MSPS ADC with Serial LVDS Interface |
| 中文描述： | 8通道，12位，40MSPS的ADC的串行LVDS接口 |
| 文件頁數(shù)： | 15/18頁 |
| 文件大?。?/td> | 439K |
| 代理商： | ADS5270 |
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SBAS293D JANUARY 2004 REVISED MAY 2004
www.ti.com
15
clock paths for all the channels are matched from the
source point all the way to the sample-and-hold. This
ensures that the performance and timing for all the
channels are identical. The use of the clock tree for
matching introduces an aperture delay, which is defined as
the delay between the rising edge of ADCLK and the actual
instant of sampling. The aperture delays for all the
channels are matched, and vary between 2.5ns to 4.5ns
across devices. Another critical spec is the aperture jitter
that is defined as the uncertainty of the sampling instant.
The gates in the clock path are designed so as to give an
rms jitter of about 1ps.
The input ADCLK should ideally have a 50% duty cycle.
However, while routing ADCLK to different components on
board, the duty cycle of the ADCLK reaching the ADS5270
could deviate from 50%. A smaller (or larger) duty cycle
eats into the time available for sample or hold phases of
each circuit, and is therefore not optimal. For this reason,
the internal PLL is used to generate an internal clock that
has 50% duty cycle.
The use of the PLL automatically dictates the lower
frequency of operation to be about 20MHz.
LVDS BUFFERS
The LVDS buffer has two current sources, as shown in
Figure 4. OUT
P
and OUT
N
are loaded externally by a
resistive load that is ideally about 100
. Depending on the
data being 0 or 1, the currents are directed in one or the
other direction through the resistor. The LVDS buffer has
four current settings. The default current setting is 3.5mA,
and gives a differential drop of about
±
350mV across the
100
resistor.
External
Termination
Resistor
OUT
P
High
Low
OUT
N
Low
High
Figure 4. LVDS Buffer
The LVDS buffer gets data from a serializer that takes the
output data from each channel and serializes it into a
single data stream. For a clock frequency of 40MHz, the
data rate output by the serializer is 480 MBPS. The data
comes out LSB first, with a register programmability to
revert to MSB first. The serializer also gives out a 1X clock
and a 6X clock. The 6X clock (denoted as LCLK
P
/ LCLK
N
)
is meant to synchronize the capture of the LVDS data. The
deskew mode can be enabled as well, using a register
setting. This mode gives out a data stream of alternate 0s
and 1s and can be used determine the relative delay
between the 6X clock and the output data for optimum
capture. A 1X clock is also generated by the serializer and
transmitted by the LVDS buffer. The 1X clock (referred to
as ADCLK
P
/ADCLK
N
) is used to determine the start of the
12-bit data frame. The sync mode (enabled through a
register setting) gives out a data of six 0s followed by six
1s. Using this mode, the 1X clock can be used to determine
the start of the data frame. In addition to the deskew mode
pattern and the sync pattern, a custom pattern can be
defined by the user and output from the LVDS buffer.
NOISE COUPLING ISSUES
High-speed mixed signals are sensitive to various types of
noise coupling. One of the main sources of noise is the
switching noise from the serializer and the output buffers.
Maximum care is taken to isolate these noise sources from
the sensitive analog blocks. As a starting point, the analog
and digital domains of the chip are clearly demarcated.
AVDD and AVSS are used to denote the supplies for the
analog sections, while LVDD and LVSS are used to denote
the digital supplies. Care is taken to ensure that there is
minimal interaction between the supply sets within the
device. The extent of noise coupled and transmitted from
the digital to the analog sections depends on the following:
1.
The effective inductances of each of the supply/ground
sets.
2.
The isolation between the digital and analog
supply/ground sets.
Smaller effective inductance of the supply/ground pins
leads to better suppression of the noise. For this reason,
multiple pins are used to drive each supply/ground. It is
also critical to ensure that the impedances of the supply
and ground lines on board are kept to the minimum
possible values. Use of ground planes in the board as well
as large decoupling capacitors between the supply and
ground lines are necessary to get the best possible SNR
from the device.
It is recommended that the isolation be maintained on
board by using separate supplies to drive AVDD and
LVDD, as well as separate ground planes for AVSS and
LVSS.
The use of LVDS buffers reduces the injected noise
considerably, compared to CMOS buffers. The current in
the LVDS buffer is independent of the direction of
switching. Also, the low output swing as well as the
differential nature of the LVDS buffer results in low-noise
coupling.
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| ADS5270EVM | 功能描述:數(shù)據(jù)轉(zhuǎn)換 IC 開發(fā)工具 ADS5270 Eval Mod RoHS:否 制造商:Texas Instruments 產(chǎn)品:Demonstration Kits 類型:ADC 工具用于評估:ADS130E08 接口類型:SPI 工作電源電壓:- 6 V to + 6 V |
| ADS5270IPFP | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 8-Ch Anlg-to-Dig Converter 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 |
| ADS5270IPFPG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 8-Ch Anlg-to-Dig Converter 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 |
| ADS5270IPFPT | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 8-Ch Anlg-to-Dig Converter 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 |
| ADS5270IPFPTG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 8-Ch Anlg-to-Dig Converter 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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