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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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3.4 HF parameters 高频参数  

2012-07-20 10:31:15|  分类: 读点英文 |  标签: |举报 |字号 订阅

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The Data area contains the user data (recorded or pre-mastered). The information is stored as pits and lands called "symbols". The symbols used are all a full multiple of the channel bit clock, T. The user data is stored using the symbols 2T, 3T, 4T, 5T, 6T, 7T and 8T. This comes from the channel bit-stream (RLL: 1, 7). There is additional symbol, 9T, which along with some of the symbols mentioned above creates a unique synchronization pattern, needed for demodulation.

数据区中包含的是用户数据(刻录的或预录的)。信息以称为"符号"的"坑"或"台"的形式进行存储。符号都和通道比特时钟周期T的呈倍数关系。存储用户数据用到了2T, 3T, 4T, 5T, 6T, 7T 和8T 共七种符号,这是由通道比特流(RLL:1,7 )决定的。除此之外,还有符号9T用于和前述七种符号一起构成一种独特的同步模式,以便于进行解调制。

Most of the parameters in this chapter describe the characteristics of the signals generated by the pits and lands in the Data area. The HF-parameters are measured on the sum of outputs from all four photo detectors (called "HF read signal" in Figure 3.32). The resulting signal is DC-connected to through an ADC(analogue to digital conversion) through an extremely linear pre-sampling filter with a crossover frequency of 30MHz. The amplitude of the 2T, 3T and 8T symbols is measured.

本章中大多数参数都是用于描述数据区内由"坑"和"台"生成的信号的特性。高频参数测量的是四象限探测器输出信号的总和(图3.32中称为"高频读取信号")。得到的信号通过一个截止频率为30MHz的非常敏感的线性预采样滤波器然后直接连接到模-数转换器中。其中,2T, 3T和8T三种符号的信号幅度被重点测量。

 

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Deliberate astigmatism in optical systems

光学系统中对散光的应用

Compact Disc players use an astigmatic lens for focusing. When one axis is more in focus than the other, dot-like features on the disc project to oval shapes. The orientation of the oval indicates which axis is more in focus, and thus which direction the lens needs to move. A square arrangement of only four sensors can observe this bias and use it to bring the read lens to best focus, without being fooled by oblong pits or other features on the disc surface.

光盘播放时使用一个散光片进行聚焦。在聚焦时如果一个轴比别的轴长,聚焦光斑就变成了椭圆形。椭圆形的方向指出了哪个轴过长,因而哪个方向上的镜头需要移动。四象限光电探测器可观测到这种偏移并根据偏移量使读取镜头获得最好的聚焦状态。

 

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