电路笔记 CN-0156 Circuits from the Lab™ reference circuits are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support visit www.analog.com/CN0281. 连接/参考器件 AD9834 75 MHz完整低功耗DDS AD5620 12位电压输出nanoDAC® 用于AD9834波形发生器(DDS)的幅度控制电路 电路功能与优势 电阻驱动AD9834的FS ADJUST引脚，从而决定满量程DAC 图1所示电路提供一种简单的方法，可控制75 MHz低功耗 电流的幅度。 (20 mW)波形发生器(DDS) AD9834的输出波形幅度。 本例所用的DAC为nanoDAC系列的12位AD5620。它内置 DDS(直接数字频率合成器)器件能够产生正弦波、方波和 一个5 ppm/°C片内基准电压源，配有SPI接口，采用8引脚 三角输出波形，因此可以用作波形发生器。 SOT-23或MSOP封装。低功耗(3.3 V电源时为2.2 mW)和小尺 AD9834内置相位调制和频率调制功能。不过，为了调制输 寸(8引脚SOT-23)的特点，使得AD5620非常适合从AD9834 产生幅度调制输出。 出信号的幅度，需要一个低功耗DAC或数字电位计来设置 满量程电流。可以利用一个电压输出DAC，通过一个串联 +3.3V VDD GND VFB AD5620 VDAC VOUT SYNC SCLK DIN RSET = 6.8kΩ +3.3V +3.3V AVDD DVDD FS ADJUST ADJUST PEAK-TO-PEAK USING AD5620 MICRO FSYNC SCLK IOUT 200Ω AD9834 IOUTB SDATA 200Ω MCLK 09019-001 DGND AGND 图1. 用于AD9834 DDS的低功耗幅度控制电路(原理示意图： 未显示所有连接和去耦) Rev. A Circuits from the Lab™ circuits from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2010–2013 Analog Devices, Inc. All rights reserved. CN-0156 电路描述 提高AD5620的电压输出将降低AD9834的满量程输出电 该电路采用3 V至5 V单电源供电。DAC和DDS均采用SPI接 口工作。许多DDS器件的片内DAC都能为AD9834 DDS提供 流。当AD5620的输出电压等于VREF或1.20 V时，达到最小满 互补电流输出IOUT和IOUTB。 量程电流。 DAC的基准电流是内部基准电压VREF和外部电阻RSET的函 图3显示半量程输出电流对应的AD9834输出电压，其中 VDAC = 0.5 × VREF或0.6 V。 数，该电阻一般从DAC FS ADJUST引脚接地。基准电流等 于VREF/RSET，其中VREF是AD9834的内部基准电压，典型值 为1.20 V。RSET电阻的典型值为6.8 kΩ。 DAC的满量程电流是基准电流的倍数。例如，AD9834的 满量程电流为： I FULLSCALE = 18 × (VREF / RSET ) 如果FS ADJUST连接到一个可变电压VDAC，则满量程电流为： I FULLSCALE = 18 × (VREF − VDAC ) / RSET 改变VDAC将改变满量程电流，从而改变DDS器件的电压输 09019-003 出。可以利用一个电压输出DAC提供该可变电压。 AD5620是一种适用的低功耗、小尺寸、高性价比解决方 案。它属于nanoDAC系列，内置一个5 ppm/°C片内基准电压 图3. 幅度控制DAC设为0.6 V时的DDS输出 (此时产生半量程DDS输出) 源，采用8引脚SOT-23或MSOP封装，输出电压为0 V至+2.5 V。 本电路必须构建在具有较大面积接地层的多层电路板上。 当VDAC = 0 V(零电平)时，达到最大满量程输出电流，AD9834 为实现最佳性能，必须采用适当的布局、接地和去耦技术 的电流在约0.16 mA至约3.12 mA之间变化。负载电阻为200 Ω 时，AD9834的输出电压在约0.032 V至约0.624 V之间变化。 (请参考指南MT-031和指南MT-101)。 AD9834 IOUT引脚上的输出电压如图2所示，其中DDS输出 常见变化 频率设为1 MHz。 AD5640和AD5660分别是AD5620的14位和16位版本，适合 需要较高分辨率的应用。AD9833可提供与AD9834相同的 功能，但不具有幅度调制能力。 了解详情 ADIsimDDS Design and Evaluation Tool. Kester, Walt. The Data Conversion Handbook . 2005. Chapters 3, 7, and 8. Analog Devices. MT-015 Tutorial, Basic DAC Architectures II: Binary DACs. Analog Devices. 09019-002 MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of AGND and DGND. Analog Devices. 图2. 幅度控制DAC设为0 V时的DDS输出 (此时产生DDS最大满量程输出) MT-085 Tutorial, Fundamentals of Direct Digital Synthesis (DDS). Analog Devices. MT-101 Tutorial, Decoupling Techniques. Analog Devices. Riordan, Liam. AN-1070 Application Note, Programming the AD9833/AD9834. Analog Devices. Rev. A | Page 2 of 3 CN-0156 数据手册和评估板 AD9834 Data Sheet AD9834 Evaluation Board AD5620 Data Sheet AD5620 Evaluation Board 修订历史 2013年7月—修订版0至修订版A 更改“电路描述”部分和图3标题 ....................................................2 2010年6月—修订版0： 初始版 (Continued from first page) Circuits from the Lab circuits are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the Circuits from the Lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the Circuits from the Lab circuits. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the Lab circuits are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab circuits at any time without notice but is under no obligation to do so. ©2010–2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN09019sc-0-7/13(A) Rev. A | Page 3 of 3