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1、Analog and Digital,模拟电子和数字电子,Ideal Operational Amplifiers and Practical Limitations,In order to discuss the ideal parameters of operational amplifiers, we must first define the terms, and then go on to describe what we regard as the ideal values for those terms. At first sight, the specification she
2、et for an operational amplifier seems to list a large number of values, some in strange units, some interrelated, and often confusing to those unfamiliar with the subject. The approach to such a situation is to be methodical, and take the necessary time to read and understand each definition in the
3、order that it is listed. Without a real appreciation of what each means, the designer is doomed to failure. The objective is to be able to design a circuit from the basis of the published data, and know that it will function as predicted when the prototype is constructed.1 It is all too easy with li
4、near circuits, which appear relatively simple when compared with todays complex logic arrangements, to ignore detailed performance parameters which can drastically reduce the expected performance.,理想运算放大器和实践的局限性,为了讨论理想运算放大器的参数，我们必须首先定义，然后去描述什么我们视为理想值的那些条款。乍一看，一个运算放大器的规格表似乎列出大量的值，一些奇怪的单位，相关的，并常常混淆了那些
5、不熟悉的题目。这种情况的办法是要有条理，并以阅读和理解每个定义它列出的顺序在必要的时间。没有什么每个方法的实际升值，设计者是注定要失败的。目标是要能够从公布的数据的基础上的电路设计，并知道它将函数作为预测当原型的构建。1很容易与线性电路相对简单，这似乎与今天的复杂逻辑的安排相比，忽略详细的性能参数可以大大减少预期的性能。,Let us take a very simple but striking example. Consider a requirement for an amplifier having a voltage gain of 10 at 50 kHz driving into
6、 a 10 k load. A common low-cost, internally frequency-compensated op amp is chosen; it has the required bandwidth at a closed-loop gain of 10, and it would seem to meet the bill. The device is connected, and it is found to have the correct gain. But it will only produce a few volts output swing when
7、 the data clearly shows that the output should be capable of driving to within two or three volts of the supply rails. The designer has forgotten that the maximum output voltage swing is severely limited by frequency, and that the maximum low-frequency output swing becomes limited at about 10 kHz. O
8、f course, the information is in fact on the data sheet, but its relevance has not been appreciated. This sort of problem occurs regularly for the inexperienced designer. So the moral is clear: always take the necessary time to write down the full operating requirements before attempting a design. At
9、tention to the detail of the performance specification will always be beneficial. It is suggested the following list of performance details be considered:,让我们以一个非常简单而惊人的例子。考虑一个在50 千赫驱动为10 K负荷具有10电压增益的一种放大器的要求。一个常见的低成本，内部频率补偿运算放大器的选择；它所需要的带宽闭环增益为10，并且看起来符合比尔。设备连接，并发现有正确的增益。它只能产生几伏的电压输出摆幅时，数据清楚地表明，输出可
10、以驱动两到三伏的供电轨。设计师忘记了最大输出电压摆幅是极为有限的频率，和最大的低频输出摆幅被限制在大约10千赫的 。当然，这些信息实际上是对数据表，但其相关性没有得到欣赏。这样的问题经常发生在没有经验的设计师。道德是如此清晰：总是要写出完整的操作要求之前，设计必要的时间。注意的性能规范细节永远是有益的。这是建议下列性能的细节被认为：,1. Closed loop gain accuracy, stability with temperature, time and supply voltage 2. Power supply requirements, source and load impe
11、dances, power dissipation 3. Input error voltages and bias currents. Input and output resistance, drift with time and temperature 4. Frequency response, phase shift, output swing, transient response, slew rate, frequency stability, capacitive load driving, overload recovery 5. Linearity, distortion
12、and noise 6. Input, output or supply protection required. Input voltage range, common-mode rejection 7. External offset trimming requirement Not all of these terms will be relevant, but it is useful to remember that it is better to consider them initially rather than to be forced into retrospective
13、modifications.,1。闭环增益精度，稳定性，温度，时间，和电源电压 2。电源要求，源阻抗和负载阻抗，功率消耗 3输入误差电压和偏置电流。输入和输出电阻，随时间和温度漂移 4。频率响应，相移，输出摆幅，瞬态响应，转换率，频率稳定度，电容性负载的驱动，过载恢复 5的线性度，失真和噪声 6。输入，输出或电源保护要求。输入电压范围的共模抑制 7外部偏置微调的要求并不是所有这些条款将是相关的，但值得注意的是，它是更好地考虑他们最初的而不是被迫修改有用性。,All parameters are subject to wide variations,Never forget this fact.
14、 How many times has a circuit been designed using typical values, only to find that the circuit does not work because the device used is not typical? The above statement thus poses a tricky question: when should typical values and when should worst-case values be used in the design? This is where th
15、e judgment of the experienced designer must be brought to bear. Clearly, if certain performance requirements are mandatory, then worst-case values must be used. In many cases, however, the desirability of a certain defined performance will be a compromise between ease of implementation, degree of importance, and economic considerations.,所有的参数都是很大的变化,不要忘记这一点。有多少次电路是根据典型值设计，却发现电路不工作因为使用的器件不典型的？以上的陈述，从而构成一个棘手的问题：当典型值应该在什么时候最坏情况下的值是用于设计？这是在有经验的设计者必须承受判决。显然，如果一定的性能要求是强制性的，那么必须使用最坏情况下的值。然而，在许多情况下，某一规定性能的愿望将易于实现之间的一种折衷，重要程度，和经济上的考虑。,谢谢,