描述
高采样速率模数转换器(ADC)通常用在现代无线接收器设计中,以中频(IF)采样速率采集复数调制的信号。这类设计通常都选用基于CMOS开关电容的ADC,因为它们的低成本和低功耗特点很吸引人。但这类ADC采用一种直接连接到采样网络的无缓冲器的前端,这样就会出现驱动ADC的放大器的输入跟踪和保持阻抗随时间变化的问题。为了有效地驱动ADC,使噪声最低和有用信号失真最小,必须设计一种无源网络接口帮助抑制宽带噪声,并对跟踪阻抗和保持阻抗进行变换以便为驱动放大器提供更好的负载阻抗。针对几种常见的IF频率,本文中提出了一种谐振匹配方法,用于将跟踪和保持阻抗转换为比较容易计算的负载,从而实现抗锯齿滤波器的精密设计。
开关电容ADC
开关电容ADC不带缓冲器,以便能降低功耗。这种ADC的采样保持放大器电路(SHA)主要包括一个输入开关、一个输入采样电容器、一个采样开关和一个放大器。如图1所示,输入开关直接连接驱动器和采样电容器。输入开关闭合时(跟踪模式),驱动器电路驱动输入电容器,当此模式结束时,输入电容器开始对输入信号进行采样(捕获)。而当输入开关断开时(保持模式),驱动器被输入电容器隔离。ADC的跟踪模式周期和保持模式周期大约相等。
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主营:世界知名品牌的PLC、DCS系统备件模块
①Allen-Bradley(美国AB)系列产品》
②Schneider(施耐德电气)系列产品》
③General electric(通用电气)系列产品》
④Westinghouse(美国西屋)系列产品》
⑤SIEMENS(西门子系列产品)》
⑥销售ABB Robots.FANUC Robots、YASKAWA Robots、KUKA Robots、Mitsubishi Robots、OTC Robots、PanasonicRobots、MOTOMAN Robots。
⑦estinghouse(西屋):OVATION系统、WDPF系统、MAX1000系统备件。
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顺序控制、梯形逻辑控制、事故追忆处理、数模转换、输入/输出信号处理、数
据通信及处理等。Invensys Triconex:冗余容错控制系统、基于三重模件冗余(TMR)
结构的zui现代化的容错控制器。
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◆Motorola(摩托罗拉):MVME 162、MVME 167、MVME1772、MVME177等系列。
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