电路笔记 CN-0049 双中频增益模块

电路笔记 CN-0049  双中频增益模块
电路笔记
CN-0049
利用 ADI 公司产品进行电路设计
连接/参考器件
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 。
ADL5534
20 MHz 至 500 MHz 双中频放大器
AD9640
14 位、80/105/125/150 MSPS 双模数转
换器
双中频增益模块 ADL5534 与高速 ADC AD9640 的接口
电路功能与优势
差分输入阻抗设置为 100 Ω。
本电路利用中频放大器ADL5534,为 14 位、150 MSPS双通
当用作准差分放大器时,ADL5534的两个放大器可提供 100
道ADC AD9640提供双中频增益模块。ADL5534是一款高线
Ω差分输入和输出阻抗。利用一个 2:1 阻抗比磁通耦合变压
性度、双通道、20 dB固定增益放大器,可以用作高性能中频
器,可以将 50 Ω RF信号源输入转换为差分信号,从而使 50 Ω
采样ADC的驱动器。该器件为高速ADC的 200 mVpp至 2 Vpp
信号源与ADL5534的 100 Ω差分负载相匹配。ADL5534输出
满量程RFIN信号电平实现接口提供了一种简便的途径。
端与AD9640输入端之间采用三阶低通滤波器,可为信号源和
ADL5534的低噪声(70 MHz下 2.5 dB NF)和低失真(70 MHz
负载提供 100 Ω差分阻抗。
下 40 dBm IP3)特性确保ADC性能不受影响。
由于ADL5534和AD9640要求不同的共模电平,因此ADL5534
电路描述
必须交流耦合至AD9640。为降低来自ADL5534的任何低频噪
在图 1所示的应用电路中,ADL5534驱动一个 150 MSPS、14
声并提供直流阻隔,选用了 100 pF的电容。
位ADC AD9640。两个 49.9 Ω电阻与AD9640 CML输出相连,
并将AD9640
可为AD9640 CML输入建立 0.9 V直流偏置电压,
图 1. 利用CML的 50 Ω电阻实现ADL5534 与AD9640 的接口,以便为AD9640 输入建立 0.9 V直流偏置电压,
并将AD9640 差分阻抗设置为 100 Ω(原理示意图:未显示去耦及所有连接)
Rev.A
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电路笔记
CN-0049
图 2. LC 滤波器的频率响应测量结果
图 4. 输入音为 93 MHz 和 92 MHz、采样速率为
此滤波器的测量结果显示,对于以 92 MHz为中心的 20 MHz
122.8MSPS 时测得的双音性能
带宽,插入损耗为 0.5 dB。图 2显示了该滤波器的宽带响应测
常见变化
量结果。
本应用电路可以针对ADL5534 和 AD9640 工作范围内的任何
图 3为约 93MHz输入信号的单音FET结果,显示SNR为 69.3
dB,SFDR为 82 dBc。注意,因为存在混叠,FET的基带频率
中频频率进行修改。数字可编程差分可变增益放大器AD8375
可用来代替ADL5534。
或者,也可以用电阻可编程差分放大器AD8352进行单端至差
为 122.8 MHz – 93 MHz = 31.8 MHz。
分转换,而且无需使用外部巴伦。AD8352、AD8375和AD8376
(AD8375的双通道版本)均为真差分放大器,可在输入端提
供共模信号抑制功能。
该电路必须构建在具有较大面积接地层的多层电路板上。为
实现最佳性能,必须采用适当的布局、接地和去耦技术(请
参考“教程MT-031”、“ 教程MT-101”、ADL5534评估板
布局以及AD9640 评估板布局)。ADL5534和AD9640的裸露
焊盘均应直接焊接到低阻抗接地层。
图 3. 输入频率为 93MHz、采样速率为
122.8MSPS 时测得的单音性能
图 4为 91 MHz和 93 MHz的双音结果,显示IMD3 为−80.5
dBc,SFDR为 78 dBc。AD9640针对单音和双音测试的采样时
钟速率均为 122.8 MSPS。
Rev. A | Page 2 of 3
电路笔记
CN-0049
进一步阅读
数据手册和评估板
AN-742 Application Note, Frequency Domain Response of
ADL5534 Data Sheet
Switched Capacitor ADCs. Analog Devices.
ADL5534 Evaluation Board
AN-827 Application Note, A Resonant Approach to Interfacing
AD9640 Data Sheet
Amplifiers to Switched-Capacitor ADCs. Analog Devices.
AD9640 Evaluation Board
Kester, Walt. 2006. High Speed System Applications. Analog
AD8352 Data Sheet
Devices. Chapter 2, “Optimizing Data Converter Interfaces.”
AD8375 Data Sheet
MT-031 Tutorial, Grounding Data Converters and Solving the
Mystery of "AGND" and "DGND." Analog Devices.
修订历史
MT-073 Tutorial, High Speed Variable Gain Amplifiers. Analog
2/10—Rev. 0 to Rev. A
Devices.
Updated Format ................................................................ Universal
MT-101 Tutorial, Decoupling Techniques. Analog Devices.
Changes to Circuit Function and Benefits ...................................... 1
Changes to Circuit Description ....................................................... 1
Changes to Common Variations ..................................................... 2
8/08—Revision 0: Initial Version
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CN08537sc-0-2/10(A)
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Rev. A | Page 3 of 3
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