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七郎 / Seven Liu

科学与艺术,恰如人生中的红颜知己。 本博内容保留所有权利.

 
 
 

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PLL 锁相环  

2012-06-18 14:22:03|  分类: 读点英文 |  标签: |举报 |字号 订阅

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Short for phase-locked Loop, an electronic circuit that controls an oscillator so that it maintains a constant phase angle (i.e., lock) on the frequency of an input, or reference, signal.

Phase-Locked Loop的缩写。用来控制示波仪(振荡器),使其相位角度保持与某一频率的输入或参考信号相一致。

 

A PLL ensures that a communication signal is locked on a specific frequency and can also be used to generate, modulate and demodulate a signal and divide a frequency.

锁相环可使通讯信号锁定于特定频率,还可用于生成、调制和解调一个信号以及进行分频。

 

PLL is used often in wireless communications where the oscillator is usually at the receiver and the input signal is extracted from the signal received from the remote transmitter.

锁相环常用于无线通信,振荡器通常位于接收器,而其输入信号是从远程传输系统接收信号中提取的。

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A phase-locked loop (PLL) is an electronic circuit with a voltage- or current-driven oscillator that is constantly adjusted to match in phase (and thus lock on) the frequency of an input signal. In addition to stabilizing a particular communications channel (keeping it set to a particular frequency), a PLL can be used to generate a signal, modulate or demodulate a signal, reconstitute a signal with less noise, or multiply or divide a frequency. PLLs are frequently used in wireless communication, particularly where signals are carried using frequency modulation (FM) or phase modulation (PM). PLLs can also be used in amplitude modulation (AM). PLLs are more commonly used for digital data transmission, but can also be designed for analog information. Phase-locked loop devices are more commonly manufactured as integrated circuits (ICs) although discrete circuits are used for microwave.

锁相环是电路,其中包含一个由电流或电压驱动的振荡器,该振荡器被持续调整,以保持与输入信号频率之相位相匹配(并锁定到该频率)。另外,为使特定信道保持稳定(保持其设定于特定频率),锁相环可用于生成、调制或解调信号、重构低噪音信号、按比例放大或分割某频率。锁相环常用于无线电通信,尤其是调频(FM)载波信号或调相(PM)载波信号。也可用于调幅(AM)。尽管锁相环在数字化数据传输中应用非常普遍,但它也可以被设计用于模拟信号处理中。虽然分立电路用于微波,锁相环设备仍通常被制造成集成电路(ICs)形式。

 

A PLL consists of a voltage-controlled oscillator (VCO) that is tuned using a special semiconductor diode called a varactor. The VCO is initially tuned to a frequency close to the desired receiving or transmitting frequency. A circuit called a phase comparator causes the VCO to seek and lock onto the desired frequency, based on the output of a crystal-controlled reference oscillator. This works by means of a feedback scheme. If the VCO frequency departs from the selected crystal reference frequency, the phase comparator produces an error voltage that is applied to the varactor, bringing the VCO back to the reference frequency. The PLL, VCO, reference oscillator, and phase comparator together comprise a frequency synthesizer. Wireless equipment that uses this type of frequency control is said to be frequency-synthesized.

锁相环中包括一个压控振荡器(VCO),用称为变容二极管的特殊的半导体二极管对VCO进行调整。VCO首先被调整到和期望的接收或传输频率相接近的频率。基于参考晶振的输出,称为相位比较器的电路使VCO的寻找并锁定到期望频率。这是通过反馈机制实现的。如果VCO的频率背离了参考晶振的频率,相位比较器就会向变容二极管输出一个误差电压,使VCO返回到参考频率。锁相环PLL、压控振荡器VCO和参考晶振,以及相位比较器构成一个频率合成器。无线设备的这种频率控制方式被称为合成频率。

 

Since a PLL requires a certain amount of time to lock on the frequency of an incoming signal, the intelligence on the signal (voice, video, or data) can be obtained directly from the waveform of the measured error voltage, which will reflect exactly the modulated information on the signal.

因为锁相环锁定到某输入信号的频率需要一定的时间,可从测量误差电压的波形中直接获得(音频、视频或数据)智能信号,这将使调制信息精确的反应到信号上。


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