AC耦合放大器无需直流偏置-AC-Coupled Ampli

2011-05-26 17:53:41来源: 互联网 关键字:放大器
Abstract: Unity gain op amp buffers capacitive transducer and other high-impedance signal sources without the need for bias resistors.

Capacitive transducers and other high-impedance signal sources usually require AC coupling and a buffer amplifier to condition the signal. Buffers take many forms, but most of them compromise signal quality through external resistors which provide a DC path for the input bias current. Fortunately, recent improvements in op amp technology allow AC-coupled inputs without the need for bias resistors.

These new op amps have inputs that operate over the entire supply voltage range. Some are CMOS, but many are implemented with complementary bipolar transistors. For these, each input connects to both an NPN difference pair and a PNP difference pair. By combining these parallel input stages, the second stage ensures a wide input common-mode range.

Some op amps exhibit an input-voltage level for which bias current to the NPN pair exactly equals that from the opposite-polarity PNP pair, causing the input bias current to go to zero, as in Figure 1. For the amplifier shown, this effect self-biases the inputs at a level consistently close to 2VCC/3. This voltage can range between 0.5V and VCC-0.5V, however.


Figure 1. This self-biasing op amp buffers a high-impedance AC signal without the use of bias-current resistors.

To avoid the distortion effects that increase with signal deviation from 2VCC/3, you should limit the input signal swings to 500mVP-P. If necessary, downstream circuitry can remove the DC offset while providing gain and filtering. Even with small, low-cost coupling capacitors, this circuit's ultra-high input impedance and absence of bias resistors enables operation well below 1Hz.

A similar version of this article appeared in the March 16, 2000 issue of EDN magazine.

关键字:放大器

编辑:神话 引用地址:http://www.eeworld.com.cn/mndz/2011/0526/article_9172.html
本网站转载的所有的文章、图片、音频视频文件等资料的版权归版权所有人所有,本站采用的非本站原创文章及图片等内容无法一一联系确认版权者。如果本网所选内容的文章作者及编辑认为其作品不宜公开自由传播,或不应无偿使用,请及时通过电子邮件或电话通知我们,以迅速采取适当措施,避免给双方造成不必要的经济损失。

上一篇:单电源运算放大器的设计考虑
下一篇:运算放大器的输入-Operational Amplifier

关注eeworld公众号 快捷获取更多信息
关注eeworld公众号
快捷获取更多信息
关注eeworld服务号 享受更多官方福利
关注eeworld服务号
享受更多官方福利
推荐阅读
全部
放大器

小广播

独家专题更多

2017东芝PCIM在线展会
2017东芝PCIM在线展会
TI车载信息娱乐系统的音视频解决方案
TI车载信息娱乐系统的音视频解决方案
汇总了TI汽车信息娱乐系统方案、优质音频解决方案、汽车娱乐系统和仪表盘参考设计相关的文档、视频等资源
迎接创新的黄金时代 无创想,不奇迹
迎接创新的黄金时代 无创想,不奇迹
​TE工程师帮助将不可能变成可能,通过技术突破,使世界更加清洁、安全和美好。
电子工程世界版权所有 京ICP证060456号 京ICP备10001474号 电信业务审批[2006]字第258号函 京公海网安备110108001534 Copyright © 2005-2017 EEWORLD.com.cn, Inc. All rights reserved