参数资料
型号: DC570A
厂商: Linear Technology
文件页数: 19/28页
文件大小: 0K
描述: BOARD DELTA SIGMA ADC LTC2440
软件下载: QuikEval System
设计资源: DC570A Design File
DC570A Schematic
标准包装: 1
系列: QuikEval™
ADC 的数量: 2
位数: 24
采样率(每秒): 3.5k
数据接口: MICROWIRE?,串行,SPI?
工作温度: 0°C ~ 70°C
已用 IC / 零件: LTC2440
已供物品:
相关产品: LTC2440CGN#TRPBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP
LTC2440IGN#TRPBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP
LTC2440IGN#PBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP
LTC2440CGN#PBF-ND - IC ADC DIFFER 24-BIT HS 16-SSOP
LTC2440IGN#TR-ND - IC CONV A/D 24-BIT DIFF 16-SSOP
LTC2440CGN#TR-ND - IC CONV A/D 24-BIT DIFF 16-SSOP
LTC2440IGN-ND - IC ADC DIFFER 24-BIT HS 16-SSOP
LTC2440CGN-ND - IC ADC DIFFER 24-BIT HS 16-SSOP
LTC2440
26
2440fd
Example:
If an amplier (e.g. LT1219) driving the input of an LTC2440
has wideband noise of 33nV/√Hz, band-limited to 1.8MHz,
the total noise entering the ADC input is:
33nV/√Hz √1.8MHz = 44.3μV.
When the ADC digitizes the input, its digital lter lters
out the wideband noise from the input signal. The noise
reduction depends on the oversample ratio which denes
the effective bandwidth of the digital lter.
At an oversample of 256, the noise bandwidth of the ADC
is 787Hz which reduces the total amplier noise to:
33nV/√Hz √787Hz = 0.93μV.
The total noise is the RMS sum of this noise with the 2μV
noise of the ADC at OSR=256.
√0.93μ/V2 + 2μV2 = 2.2μV.
Increasing the oversampling ratio to 32768 reduces the
noise bandwidth of the ADC to 6.2Hz which reduces the
total amplier noise to:
33nV/√Hz √6.2Hz = 82nV.
The total noise is the RMS sum of this noise with the
200nV noise of the ADC at OSR = 32768.
√82nV2 + 2μV2 = 216nV.
In this way, the digital lter with its variable oversampling
ratio can greatly reduce the effects of external noise
sources.
Using Non-Autozeroed Ampliers for Lowest Noise
Applications
Ultralow noise applications may require the use of low
noise bipolar ampliers that are not autozeroed. Because
the LTC2440 has such exceptionally low offset, offset drift
and 1/f noise, the offset drift and 1/f noise in the ampli-
ers may need to be compensated for to retain the system
performance of which the ADC is capable.
The circuit of Figure 23 uses low noise bipolar ampliers
and correlated double sampling to achieve a resolution of
14nV, or 19 effective bits over a 10mV span. Each measure-
ment is the difference between two ADC readings taken
with opposite polarity bridge excitation. This cancels 1/f
noise below 3.4Hz and eliminates errors due to parasitic
thermocouples. Allow 750μs settling time after switching
excitation polarity.
APPLICATIONS INFORMATION
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