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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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4.14 HF signal, equalizer, slicer, PLL & Channel bits 高频信号、均衡器、切片器、锁相环和信道位  

2012-07-02 14:23:48|  分类: 读点英文 |  标签: |举报 |字号 订阅

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To be able to extract the user data stored on the disc, the durations of the pits/marks and lands/spaces must be determined. When reading the disc the read spot travels along the track passing pits and lands after each other. The pits and lands are designed to reflect different amount of light back to the photo detectors. The differences in light intensity are called the analogue HF-signal.

为了能从光盘上提取存储于其中的数据,必须确定"坑/标记"和"台/间隔"的持续时间。读取盘片时,光斑沿着轨道依次经过交替的坑和台。坑和台的设计目的是反射不同的光量反射到光点探测器上。光强的差异被称为模拟高频信号

For the symbol-pair where both the pit and the land are at least as long as the read spots diameter, maximum HF-signal amplitude can be achieved. Shorter symbols create lower HF-signal amplitude. For the shortest symbol pair on a Blu-ray Disc (that of 2T-pit and 2T-land) the HF-signal amplitude is considerably lower than the signal from the shortest symbols on a DVD. The amplitude of the HF-signal as a result of the 2T-pits and 2T-lands is called I2.

对于符号来说,无论"坑"还是"台"的长度都应至少相当于读取光斑的直径,这样才能达到最大的高频信号幅度。较短的符号形成较低的高频信号幅度。BD光盘上最短的符号对(由2T的坑和2T的台形成)与DVD比较,其高频信号幅度相当低。由2T的坑和2T的台形成的高频信号幅度称为I2.

To increase the reliability of data retrieval, the HF-signal amplitude of the shortest and most frequently occurring symbols need to increase. The traditional way of doing this is to apply a linear equalizer that boosts the signals from the shorter symbols thus improving the signal to noise ratio. However, excessive boost creates inter symbol interference which increased the Jitter during playback. Due to the low signal amplitude of the I2-component, a conventional equalizer is of limited use for the Blu-ray Disc format. Instead of a conventional equalizer, a limiting equalizer is used. The limiting equalizer boosts the amplitude of the HF-components, but has a limiter that restricts the signal amplitude to around the amplitude of the boosted I2-component.

为了提高数据再生的可靠性,需要提高最短的和出现最多的符号对的高频信号幅度。传统的办法是使用线性均衡器来提高最短符号的幅度以改善信噪比。但过分提高符号的幅度会形成码间干扰,增加了了播放中的Jitter。因为I2的幅度太低,传统的均衡器无法满足BD格式的要求,取而代之的是限幅均衡器。限幅均衡器提高各高频成分的幅度,但其中的限制器会将信号幅度约束在增强后的I2的周围。

After equalizing the analogue HF-signal it is converted to a digital HF-signal (with only two levels, high and low) by applying a slicer. All parts of the analogue HF-signal above the slicing level will be set to high on the digital HF-signal and all parts of analogue HF-signal below the slicing level will be set to low. The slicer thus determines where the transition from low to high will occur. The slicer works by adjusting itself to a level where there is a 50% duty cycle in the digital HF-signal (i.e. dc-free).

高频模拟信号经均衡后,被切片器转换为数字高频信号(只包含"高"和"低"两种电平)。所有高于切片电平的模拟高频信号被设为数字高频信号中的高电平,繁殖被设为低电平。在何处进行高低电平转换由切片器决定。切片器将自己调整到数字高频信号占空比(duty to cycle ratio)为50%的电平进行工作(即没有直流。)。

The durations of the components of the digital HF-signal (i.e. channel bits stream) is determined by using a PLL-clock with a clock length of one time unit (i.e. 1T). The channel bits stream is generated by comparing the time between two transitions in the digital HF-signal with the transitions of the PLL-clock.

数字高频信号(即信道比特流)通过时钟周期为一个时间单位(即1T)的锁相环时钟确定数字高频信号各成分的持续时间。通过将信道比特流中两种状态转换的时间和PLL时钟进行比较,进而生成通道比特流。

The PLL-frequency is regenerated from the digital HF-signal.

锁相环频率是从数字高频信号中再生的。

 

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Key Words:

·symbol-pair 符号对

·analogue n. 类似物;类似情况;对等的人 adj. 类似的;相似物的;模拟计算机的

·analog n. [自] 模拟;类似物 adj. [自] 模拟的;有长短针的

·component 成分、组件、原件;adj. 组成的,构成的

·regenerate 再生

·restrict 限制、约束、限定

·extract 提取、摘录、榨取

·retract 缩回、缩进

·considerably 相当地

·determine 确定

·boost 增压、提高、促进

·inter symbol interference 码间干扰

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