仪表放大器桥接电路误差分析

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MT-066 指南
仪表放大器桥接电路误差预算分析
在典型应用中，有必要了解仪表放大器的误差源。下图1所示为一个350 的称重传感器， 当用10 V源激励时，其满量程输出为100 mV。用外部499 增益设置电阻，将AD620的增 益设为100。表中列出了每种误差源对2145 ppm的总非调整误差的贡献。但需要注意的是， 增益、失调和CMR误差都可以通过系统校准消除。其余误差——增益非线性度和0.1 Hz至 10 Hz噪声——无法通过校准消除，最终使系统分辨率限制为42.8 ppm(大约相当于14位精 度)。当然，本例只是用于说明，但对于解决增益非线性度、LF噪声等性能限制性误差问 题具有重要意义。
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+10V VCM = 5V + 499Ω RG AD620B – REF G = 100 350Ω, 100mV FS LOAD CELL AD620B SPECS @ +25°C, ±15V VOSI + VOSO/G = 55µV max IOS = 0.5nA max Gain Error = 0.15% Gain Nonlinearity = 40ppm 0.1Hz to 10Hz Noise = 280nVp-p CMR = 120dB @ 60Hz MAXIMUM ERROR CONTRIBUTION, +25°C FULLSCALE: VIN = 100mV, VOUT = 10V VOS IOS Gain Error Gain Nonlinearity CMR Error 0.1Hz to 10Hz 1/f Noise Total Unadjusted Error Resolution Error 55µV ÷ 100mV 350Ω × 0.5nA ÷ 100mV 0.15% 40ppm 120dB 1ppm × 5V ÷ 100mV 280nV ÷ 100mV ≈ 9 Bits Accurate ≈ 14 Bits Accurate 550ppm 1.8ppm 1500ppm 40ppm
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MT-066
参考文献
1. Hank Zumbahlen, Basic Linear Design, Analog Devices, 2006, ISBN:0-915550-28-1.另见Linear Circuit Design Handbook, Elsevier-Newnes, 2008, ISBN-10:0750687037, ISBN-13:978-0750687034。Chapter 2. 2. Walter G. Jung, Op Amp Applications, Analog Devices, 2002, ISBN 0-916550-26-5, 另见Op Amp Applications Handbook, Elsevier/Newnes, 2005, ISBN 0-7506-7844-5.Chapter 2. 3. Charles Kitchin and Lew Counts, A Designer's Guide to Instrumentation Amplifiers, 3rd Edition, Analog Devices, 2006.
50ppm 2.8ppm 2145ppm 42.8ppm
图1：AD620B 桥接放大器直流误差预算
ADI网 站 上 提 供 了 一 种 通 用百度文库型 放 大 器 ( 包 括 仪 表 放 大 器 ) 误 差 预 算 分 析 工 具 和 Analog Bridge Wizard™ 以协助桥接电路的设计。
Rev.0, 10/08, WK