《专业英语A篇翻译.docVIP

Unit3 A In its simplest form, a conventional op-amp consists of a differential amplifier (bipolar or FFT) followed by offset compensation and output stages, as shown in Figure 3.3. All of those elements are integrated on a single chip and housed in an IC package. The differential amplifier has a high-impedance (constant-current)“tail” to give it a high input impedance and a high degree of common-mode signal rejection. It also has a highimpedance collector (or drain) load, to give it a large amount of signal-voltage gain (typicallyabout 100 dB).. 在最简单的常规运放里，包括差动放大级和失调补偿级以及输出级，如图3.3（图略）所示，所有的器件都组合在一块芯片上，装在集成组件内。差动放大级有一个高阻抗的“尾巴”（恒流源）以提供高输入阻抗和对共模信号的深度抑制，同时，它还具有一个高阻抗的集电极或漏极负载以提供高的信号电压增益（典型数据约为100dB）。 Unit6 A The signal-processing block at the transmitter conditions the source for more efficient transmission.For example, in an analog system, the signal processor may be an analog low-pass filter that is used to restrict the bandwidth of m(t). In a hybrid system, the signal processor may be an analog-to-digital converter (ADC). This produces a “digital word” that represents samples of the analog input signal. In this case, the ADC in the signal processor is providing source coding of the input signal. In addition, the signal processor may also add parity bits to the digital word to provide channel coding so that error detection and correction can be used by the signal processor in the receiver to reduce or eliminate bit errors that are caused by noise in the channel.The signal at the output of the transmitter signal processor is a baseband signal because it has concentrated nearf =0. consequently, they are said to be baseband signals. 发送机中的信号处理单元对信源进行调理，以便更有效地传送。譬如说，在模拟系统中，信号处理器可以是一个模拟低通滤波器，以限制m(t)的带宽。在混合系统中，信号处理器可以是一个模-数变换器（ADC）,他用数字来表示模拟输入信号的样本值。也就是说，ADC对输入信号进行源编码。此外，信号处理器还可以给数码字加入奇偶校验码位，即提供信道编码，使得接收机的信号处理器可以进行误码检测和纠错，以减少或消除由信道噪声所引起的误码。发送机中信号处理器的输出信号仍是基带信号，因为它的频谱也集中在f=0附近。 In 1948, C. E. Shannon (also of Bell Telephone Laboratories) published a paper in the Bell Sys