PDF《ADI 技术指南合集》

不使用时,电流被释放掉,而 不是器件被使能或关断.其中涉及到的技术非常复杂,在此无法详加讨论,有兴趣的读者 可以查阅参考文献4. 对于这种DAC的普通(线性)版本,所有电流的标称值相等.如果将其用于高速重构,则可 以通过动态改变递增代码切换电流的顺序来提高线性度.一般情况下,代码001始终开启 电流A,代码010始终开启电流A和B,代码011始终开启电流A、B和C,依此类推.但为了 提高线性度,对于每个新的数据点,递增代码的电流开启顺序可以不同.只要在解码器中 增添少量逻辑,就能轻松做到这一点.最简单的实现方法是使用一个计数器,每经过一个 时钟周期,计数器便递增1,电流开启顺序随之改变:ABCDEFG、BCDEFGA、CDEFGAB ……但这种算法可能会在DAC输出中产生杂散音.更好的办法是对每个时钟周期设置一个

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6 MT-014 参考文献: 1. Peter I. Wold, Signal-Receiving System, U.S. Patent 1,514,753, filed November 19, 1920, issued November 11, 1924. (thermometer DAC using relays and vacuum tubes). 2. Clarence A. Sprague, Selective System, U.S. Patent 1,593,993, filed November 10, 1921, issued July 27, 1926. (thermometer DAC using relays and vacuum tubes). 3. Leland K. Swart, Gas-Filled Tube and Circuit Therefor, U.S. Patent 2,032,514, filed June 1, 1935, issued March 3, 1936. (a thermometer DAC based on vacuum tube switches). 4. Robert Adams, Khiem Nguyen, and Karl Sweetland, A

113 dB SNR Oversampling DAC with Segmented Noise-Shaped Scrambling, ISSCC Digest of Technical Papers, vol. 41, 1998, pp. 62, 63, 413. (describes a segmented audio DAC with data scrambling). 5. Robert W. Adams and Tom W. Kwan, Data-directed Scrambler for Multi-bit Noise-shaping D/A Converters, U.S. Patent 5,404,142, filed August 5, 1993, issued April 4, 1995. (describes a segmented audio DAC with data scrambling). 6. Walt Kester, Analog-Digital Conversion, Analog Devices, 2004, ISBN 0-916550-27-3, Chapter 3. Also available as The Data Conversion Handbook, Elsevier/Newnes, 2005, ISBN 0-7506-7841-0, Chapter 3. Copyright 2009, Analog Devices, Inc. All rights reserved. Analog Devices assumes no responsibility for customer product design or the use or application of customers'

products or for any infringements of patents or rights of others which may result from Analog Devices assistance. All trademarks and logos are property of their respective holders. Information furnished by Analog Devices applications and development tools engineers is believed to be accurate and reliable, however no responsibility is assumed by Analog Devices regarding technical accuracy and topicality of the content provided in Analog Devices Tutorials. 但新的伪随机顺序,这需要更多的逻辑,但正如我们所说的,即使复杂的逻辑现在也已变 得非常便宜,而且很容易利用CMOS工艺实现.还有其它更复杂的技术,使用数据本身来 选择各位,从而将电流不匹配转化为整形噪声.同样,这些技术太过复杂,不适合在此类 指南中进行讨论.(详细讨论见参考文献4和5)

7 图1:电压模式二进制加权电阻DAC 作者:Walt Kester DAC基本架构II:二进制DAC 指南 MT-015 R/8 R/4 R/2 R V V REF OUT MSB LSB Adapted from: B. D. Smith, Coding by Feedback Methods, Proceedings of the I. R. E., Vol. 41, August 1953, pp. 1053-1058 Rev.A, 10/08, WK Page

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10 简介 虽然串DAC和温度计DAC是迄今最为简单的DAC架构,但需要高分辨率时,它们绝不是 最有效的.二进制加权DAC每位使用一个开关,首创于1920年代(参见参考文献