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电路笔记
CN-0038
连接/参考器件
利用 ADI 公司产品进行电路设计
放心运用这些配套产品迅速完成设计。
欲获得更多信息和技术支持，请拨打 4006-100-006
或访问 www.analog.com/zh/circuits 。
AD5426/AD5432/
AD5443
8/10/12 位乘法 DAC
AD8065
高性能 FastFET™ 放大器
采用 AD5426/AD5432/AD5443 电流输出 DAC 的可编程增益元件
电路功能与优势
配解决增益温度系数误差问题。外部电阻的温度系数需要彼
本电路利用乘法 DAC 和运算放大器提供可编程增益功能。最
此匹配，但不必与 DAC 内部梯形电阻的温度系数相匹配。
大增益值和温度系数由外部电阻设置，可编程增益的分辨率
由 DAC 的分辨率设置。
之所以需要电阻 R1，是因为 R1 加上 DAC 的输入阻抗必须
等于总反馈电阻，即 RFB + R2||R3。DAC 的输入阻抗为 RFB，
电路描述
因此
图 1所示电路就是推荐用来提高电路增益的方法。R1、R2 和
R3 应具有相似的温度系数，但不必与DAC的温度系数相匹
配。在要求增益大于 1 的电路中，推荐使用这种方法。增益
为：
R1 和 R2 的值必须适当选择，这样对于给定的电源电压，输
出电压才不会超过运算放大器的输出范围。另外还应注意，
VOUT = –增益×VIN×(D/2N)
运算放大器的偏置电流乘以总反馈电阻(RFB + R2||R3)，即可
其中 D 为载入 DAC 的数字字，N 为位数：D = 0 至 255（8
产生相应的失调电压。因此，R1 和 R2 的值不能太大，否则
位 AD5426）；D = 0 至 1023（10 位 AD5432）；D= 0 至 4095
将对总输出失调电压产生显著影响。
（12 位 AD5443）。该电路的主要优势就是能够利用电阻匹
图 1. 采用电流输出 DAC 的可编程增益电路（原理示意图）
Rev.A
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电路笔记
CN-0038
运算放大器的输入失调电压要乘以电路的可变增益（由于存
MT-031 Tutorial, Grounding Data Converters and Solving the
在 DAC 的代码相关输出阻抗）。由于放大器的输入电压出现
Mystery of AGND and DGND. Analog Devices.
失调，因而两个相邻数字小数之间的噪声增益变化会使输出
MT-033 Tutorial, Voltage Feedback Op Amp Gain and
电压产生步进变化。此输出电压变化与两个代码间所需的输
Bandwidth. Analog Devices.
出变化相叠加，引起差分线性误差；如果该误差足够大，可
MT-035 Tutorial, Op Amp Inputs, Outputs, Single-Supply, and
能会导致 DAC 非单调。AD8065 借助其低输入失调电压和低
Rail-to-Rail Issues. Analog Devices.
偏置电流特性可解决这一问题。
MT-101 Tutorial, Decoupling Techniques. Analog Devices.
Voltage Reference Wizard Design Tool. Analog Devices.
常见变化
OP1177是另一款适合该电流电压转换电路的优秀运算放大
器，它同样具有低失调电压和超低偏置电流特性。至于基准
电压源的选择，输入电压会受所选运算放大器的轨到轨电压
限制，增益则同样由电阻R2 和R3 设置。
数据手册和评估板
AD5426 Data Sheet.
AD5432 Data Sheet.
AD5443 Data Sheet.
进一步阅读
AD8065 Data Sheet.
ADIsimPower Design Tool. Analog Devices.
OP1177 Data Sheet.
Kester, Walt. 2005.The Data Conversion Handbook. Analog
Devices. Chapters 3 and 7.
修订历史
MT-015 Tutorial, Basic DAC Architectures II: Binary DACs.
7/09—Rev. 0 to Rev. A
Analog Devices.
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