问题 问答题 简答题

什么叫运算放大器?理想运算放大器应具有哪些理想参数?

答案

参考答案:

运算放大器是一种具有高增益(放大倍数),并带深度负反馈的直接耦合放大器。它通过线性或非线性元件组成的输入网络和反馈网络,可以对输入信号进行多种数字运算和处理。

理想运算放大器应具有的理想参数如下:

⑴开环电压增益Avo=∞;

⑵输入电阻ri=∞;

⑶输出电阻ro=0;

⑷开环带宽BW=∞;

⑸当同相端的电压UP和反相端的电压UN相等时,即UP=UN,Uo=0;

⑹没有温度漂移;

阅读理解

  Does your pet have a slim figure? According to the Association of Pet Obesity Prevention (APOP), about half of all dogs and nearly 60% of all indoor cats are overweight. Larry Kornegay, president of the American Veterinary Medical Association, says he sees an overweight pet nearly every day, and unusually the owner is overweight. So talking about the topic can be touchy. “I talk about their pet’s health. Still, some clients take it personally.”

Here are some tips for pet weight loss:

See the vet(兽医). Have your vet put together a plan and treat any existing medical problems. Pain relief and diet changes may be required for arthritic(患关节炎的) pets, which will allow for exercise to at least begin.

Skip the crash diet (an attempt to lose weight quickly by strictly limiting the diet). A special weight-loss diet may be suggested. For example, look for the supplement which burns fat and builds muscle mass in foods. Never place any pet on a crash diet, especially cats, which can suffer a potentially fatal liver disease as a result. There’s a safe weight-loss drug for dogs you can ask your vet about.

Dine alone. “Cut out treats and resist temptation by keeping pets out of the room you’re dining in,” says Chicago vet Sheldon Rubin. You can buy low-calorie treats for dogs and cats. Rubin also recommends mini carrots, small apple slices or blueberries for dogs. What’s important is finding other ways, aside from food, to show your love. Play with your cat using an interactive toy, and take your dog for walks. Walks are great for bonding, and good for you. Studies show people are actually more willing to lose weight themselves if it also will help their pet.

Feed pets at special times. Pre-measure food carefully—don’t give them a larger meal than ever—and leave it in various places, so pets sniff it out and use the stairs. It’s fun, and it’s good exercise.

小题1:. The underlined word “touchy” in Paragraph 1 probably means__________

A.sensitive

B.exciting

C.moving

D.pleasant小题2:. What can be inferred from the passage?

A.Overweight people usually like overweight pets.

B.Pets’ weight is easier to lose than humans’.

C.Cats have a greater chance of serious liver disease.

D.Overweight people often ignore their pets’ weight.小题3: Which of the following methods is healthy for your pets?

A.Providing them with mini carrots or blueberries.

B.Keeping them with you when you’re dining.

C.Supplying them with larger meals or drinks.

D.Leaving the food in a fixed place for your pets.小题4:. What does the passage mainly tell us?

A.How to feed pets without a crash diet.

B.The importance of pet weight loss.

C.How to help pets lose weight.

D.The problems that pets will meet.

单项选择题