试分析时基发生器工作原理。
参考答案：
时基发生器由时基闸门、扫描发生器、电压比较器和释抑电路组成。时基闸门电路是一个典型的施密特触发器，它是双稳态电路。扫描电压产生器是一个积分器，他能产生高线性的锯齿波。当开关断开时，电源E通过电阻R对电容C充电，产生负向锯齿波U0，此电压送至水平放大器，另一路送至电压比较器。当U0大于Ur时时基闸门翻转，扫描发生器放电，形成锯齿波。释抑电路的作用是保证每次扫描锯齿波的起点一致，以确保同步。
| 阅读短文，然后从Ⅱ栏中选择恰当的选项完成Ⅰ栏各题目。 | ||
| Mr. White worked in London. He was a famous scientist. He was interested in nothing except his work. He forgot everything else when he was working. One afternoon he received a telephone call: his only son had been knocked down by a car in Paris. The young man's leg was seriously hurt and he had to be taken to hospital. Mrs. White was worried and asked her husband to go there with her to see him at once. The scientist was busy with his work, so he made quite a few excuses, but it only made her angry. Finally he agreed to leave for Paris with her. Their flight number was BA 347. They arrived at the hospital in the evening. A friend of their son's asked, "When did you start your journey, Mr. White?" "At half past five," answered Mr. White. "Today or yesterday?" "What's the date today?" "July 3." "Oh, I remember," said Mr. White, "We started out this afternoon." "How did you come here, by air or by sea?" "I don't know," answered Mr. White."You'd better ask my wife. She always arranges (安排) these things." | ||
|