## Small Signal Circuits

The Small Signal Circuit View:

• We can derive small circuit equivalent models for our devices, and thereby conduct small signal analysis directly on circuits.
• We can replace large signal models with small signal circuit models.
• KVL和KCL只是电路的不同表达方式而已，因为它们其实都表达了这个电路的拓扑结构。记住任何一个KVL等式都代表了一个回路，任意一个KCL表示节点的连接方式。
• Foundations:

Small Signal Circuit Analysis:

• Find operating point using DC bias inputs using large signal model.
• Develop small signal (linearized) models for elements.
• Replace original elements with small signal models.

Analyze resulting linearized circuit…

Key: Can use superposition and other linear circuit tools with linearized circuit!

breeze 轻而易举的事

rinky-dink

pull rug out

## State and Memory

Notice that the capacitor voltage for $$t \geq 0$$ is independent of the form of the input voltage before $$t=0$$. Instead, it depends only on the capacitor voltage at $$t=0$$, and the input voltage for $$t \geq 0$$

State : summary of past inputs relevant to predicting the future

One application of STATE——DIGITAL MEMORY
Why memory? Or, why is combinational logic insufficient? 比如计算1+2+....，在labview中就是用移位寄存器，每次存放上一次加和的数据，相当于只需要一个加法器(adder)就能完成所有的计算。

• Memory Abstraction图中，有一个隐含的假设(implicit assumption)，也就是存储脉冲宽度要远远大于$$R_{ON}C$$，其中$$R_{ON}$$是MOSFET的电阻，显然只有上述前提才能保证电容充满了，即准确反映出input的状态；
• MOSFET的导通电阻$$R_{ON}$$远小于$$R_L$$；
• 方案B的问题在于：In practice, capacitors will leak their charge over time due to parasitic resistances.
• 方案C，最上面那个开关(store上面一条横线)是store那个开关的状态取反，注意那个开关是和一个电源连接的，这样只要持续供电，电容里面的状态就可以保持，这就是【static memory】。图A和B都是【dynamic memory】。

The one-bit memory element that we have discussed thus far is called a dynamic one-bit memory element or a dynamic D-latch. It is dynamic in the sense that it stores a value written into it only for a finite amount of time (due to nonzero parasitic resistances in practical implementations). The static one-bit memory element or a static D-latch is another type of memory element that has the same logic properties as the dynamic D-latch, but can store a value written into it indefinitely. Figure 10.61 shows one possible circuit for a static memory element. In this circuit, a non-ideal switch with a very high ON resistance is connected between the power supply and the storage node of the memory element. When the output of the memory element is a logical 1, this switch is turned on and introduces a small stream of charge into the storage node to offset any leakage. Because it trickles charges into the node, this switch is called a trickle switch. The ON resistance of the trickle switch is made very large compared to the ON resistance of the store switch, so that the trickle input can be overridden easily by the input dIN

• 方案D对比方案C，是为了提升dOUT引脚的抗干扰能力，这样external value cannot influence storage node from dOUT node.

## Damped Second-Order Systems

EECS真正酷的地方在于，专家们用的方法其实是非常简单的，但前提是你需要建立一些直觉。

xx

xxxxxxx

xx

meander

slosh back and forth

switch flick

parasitic resistance 寄生电阻

5句话总结6.002课程的主要特点：

• 一个器件MOSFET
• 两个过程(非线性电路通过小信号分析转换为线性电路，常系数微分方程转换为复系数代数方程)
• 三个模块(直流电路、动态电路、正弦交流稳态电路)
• 四种手段(大课、复习课、答疑课、实验)
• 五种设备(反相器、放大器、存储器、运算放大器、二极管)

EECS必修课：

• 6.001 计算机程序结构与编译
• 6.002 电路与电子学
• 6.003 信号与系统
• 6.004 计算结构