aydali 发表于 2013-11-17 17:06:22

ADS1245 DIY5.5位电压电阻表合适吗？

进坛一段时间，模电菜鸟也有DIY5.5位电压电阻表的发烧想法。哪款ADC更合适，性价比更高呢？求推荐。
ADS1245行吗？下面摘录DATASHEET部分参数。

FEATURES
 20-Bit Effective Resolution
 High-Impedance Buffered Input
 ±2.5V Differential Input Range
 Pin-Compatible with ADS1244
 0.0006% INL (typ), 0.0015% INL (max)
 Simple Two-Wire Serial Interface
 Simultaneous 50Hz and 60Hz Rejection
 Single Conversions with Sleep Mode
 Single-Cycle Settling
 Self-Calibration
 Well Suited for Multi-Channel Systems
 Easily Connects to the MSP430
 Current Consumption: 158μA
 Analog Supply: 2.5V to 5.25V
 Digital Supply: 1.8V to 3.6V

ELECTRICAL CHARACTERISTICS
All specifications at TA = −40°C to +85°C, AVDD = +5V, DVDD = +3V, fCLK = 2.4576MHz, and VREF = +1.25V, unless otherwise noted.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Analog Input
Full-scale input voltage range AINP − AINN ±2VREF V
Absolute input range AINP, AINN with respect to GND GND + 0.1 AVDD − 1.25 V
Differential input impedance fCLK = 2.4576MHz 3 GΩ
System Performance
Resolution No missing codes 24 Bits
Data rate fCLK = 2.4576MHz 15 SPS(1)
Integral nonlinearity (INL) Differential input signal, end point fit ±0.0006 ±0.0015 %FSR(2)
Offset error 1 14 ppm of FSR
Offset error drift(3) 0.01 ppm of FSR/°C
Gain error(4) 0.005 0.1 %
Gain error drift(3) 0.5 ppm/°C
At DC 90 100 dB
Common-mode rejection fCM(5) = 50 ± 1Hz, fCLK = 2.4576MHz 100 dB
fCM = 60 ± 1Hz, fCLK = 2.4576MHz 100 dB
Normal-mode rejection
fSIG(6) = 50 ± 1Hz, fCLK = 2.4576MHz 60 dB
fSIG = 60 ± 1Hz, fCLK = 2.4576MHz 70 dB
Input referred noise          2          ppm of FSR,RMS
Analog power-supply rejection At DC, ΔAVDD = 5% 100 dB
Digital power-supply rejection At DC, ΔAVDD = 5% 100 dB

〆﹏熋訷悪鎩 发表于 2013-11-18 10:48:24

5.5D 100mV或 200mV档四线短路至少跳20μV~40μV 而且不好校准回来

参考rigol 6.5DMM dm3061

aydali 发表于 2013-11-19 21:55:33

100mV或 200mV档最末位已是1μV，不加引入噪声的ADC已是难事。在2.5V参考电压下测这种小信号，整体电路环境噪声+放大电路噪声+ADC本身噪声，跳20μV~40μV很正常了吧。

〆﹏熋訷悪鎩 发表于 2013-11-20 10:57:11

问题 还有有上百μV 和上mV的趋势

〆﹏熋訷悪鎩 发表于 2013-11-20 11:01:19

5.5D 感觉还是双斜积分好些

aydali 发表于 2013-11-20 15:12:12

双积分型ADC除了常见的4位半7135，还有哪些可以做5位半的？
现在Sigma-Delta型ADC便宜易用，要比分立元件自己搭建双斜积分电路要简单很多。双斜积分方式在噪声抑制方面为什么比Sigma-Delta型要好呢？

〆﹏熋訷悪鎩 发表于 2013-11-20 20:17:14

aydali 发表于 2013-11-20 15:12
双积分型ADC除了常见的4位半7135，还有哪些可以做5位半的？
现在Sigma-Delta型ADC便宜易用，要比分立元件 ...

5.5D肯定是自己搭的 我的就是 没公开 自用
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