Good morning, nice to meet you here. my name is xxx. I’m a senior student in xxx university. My major is Electronic Information Engineering.I like making or controlling machines.That’s why I choose my major. my objective is obtain a master of degree hardware design and development in German.
I want to apply for the universities such as Karlsruher Institut für Technologie,which has a good academic reputation and excellent professors.Also university of stuttgart and Technical University of Munich are included. They are all very good universities.
German universities have advanced equipments and good study enviroment, which can help me learn my professional knowledge better. At the same time, I want to experience international cross-culture. As you konw, word is becoming samller and closer due to the quickly developing technology.
My parents will pay the tuition for me. And they have already prepared enough money for my aboard study.
In this course, I mainly learned the basic components of the circuit and some laws and theorems of the circuit analysic.
在电压和电流取关联参考方向时，在任何时刻其两端的电压和电流服从欧姆定律。欧姆定律指出通过电阻的电流跟电阻两端的电压成正比，和电阻成反比。U = R*i
When the voltage and current take the correlation reference direction,the voltage and current at both of resistor obey Ohm’s laws at any given moment. Ohm’s law states that the current across the resistor is directly proportional to the voltage at the both ends of resistor and inversely proportional to the resistor.
R是电阻元件的参数，是一个正常的实数，单位是欧姆。电阻的倒数称为电导，i = G*u，电导的单位是西门子，R和G都是电阻元件的参数。
R is the parameter of resistor and it’s a positive constant real number. The unit of resistance is ohm. The reciprocal of resistance is conductance and the conductance is simens. R and G are both the parameter of resistor.
The characteristics of resistor is called volt-ampere characteristics . The characteristics curve is a straight line passing through the origin the slope of the line is related to the resistance of component.
When the terminal voltage of a linear resistance element is no matter any value,the current flows through it is always zreo. So the circuit opens.
when the current of a liner resistance element is no matter any value,the terminal voltage of it is always zero. So the circuit is short out.
Correlation reference direction: The reference direction of the current flows the positive end of the voltage into the circuit and flows out from the negative end. Then the reference direction of the two are the same, so the reference direction is related. The reference direction is specified artificially.Because the actual direction of the current or voltage is unknown, after setting the reference direction, the actual direction direction of the current can be reflected by the plus and minus of the value.
A capacitor consists of two metal plates spaced apart in different mediums(such as mica or air). When the voltage is added to the two polar plate, the same number of positive and negative charges are accumulated on the two polar and an electric field is established in the medium, which has the electric field energy. After the power is removed, the charge can remain concentrated on the plate and the electric field continues to exist. Thus, a capacitor is an energy storage component that can hold charges.
电容器储存电荷的能力称之为电容，电容等于电容器所带所带的电荷量q与电容器两极板上电压u的比值。C = q/u, 电容的单位是法拉F。
The capacity of a capacitor store charges is called capacitance. The capacitance is equal to the ration of the amount of charges carried by the capacitor to the voltage on the two plates of the capatior. The unit of capacitance is Farad.
If the current and voltage of the capacitor component take the correlation reference direction, the relation between the current and the voltage can be obtained, which indicates that the current is directly proportional to the rate of the voltage. When the voltage does not change with time, the current is zero. Therefore, when the capacitor is under the circumstance of DC , the voltage at both ends is constant, which is equivalent to open circuit. That is to say, the capacitor has the function of blocking the direct current.
The capacitors in series are similar to resistors in parallel. The paraller connection of capation is similar to the series of risistors.
When the capacitor is connected to the DC power supply, there is current flowing through the circuit. Two pieces of metal plates produce repectively equal but opposite charges. When the capacitor is charging, an equal number but opposite charges will be produced on the two plates. The voltage at the two ends of the capacitor increases gradually. Once the voltage increases to equal the supply voltage, the capacitor is charged and there is no current flowing through the circuit.
The image of capacitor charging is consistent with the zero-state response of the RC first-order circuit. Zero-state response is the response that caused by the input signal when the inital state is zero.
When the connection between the capacitor an the power source is cut off, the capacitor is discharged through a resistor. The voltage between the metal plates will gradually drop to zreo. (Under the action of electric field, the positive and negative charges on the two metal plates are constantly nertralized, so the voltage drops continuously.)
An inductor is a device that converts electrical energy into magnetic energy and stores it. For example, a winding coil with an iron core. After the coil is charged with electricity, the magnetic flux will be generated inside the coil. The ration of the coil’s magnetic flux to the current is the inductance. The unit of inductance is Henry.
The indutors in series are similar to the serices of resistors and the shunt of inductance is similar to that of resistors in parallel.
When the inductor is connected to the DC source, the sudden increacse in the current will cause the inductor to generate a induced electromotive force that is opposite to the power supply. The induced electromotive fotce hinders the changes of the current and the slowed current will cause the decrease of voltage . When the current is stable, there is no induced electromotive force generated. The voltage drops to zero volt and the energy storage of inductor is finished. VL is zero volt, so in the DC circuit. the inductor flows through the inductor can’t mutate.
When the inductor is disconnected from the power source, the voltage drops to a negative value instantaneously. But at the same time the current remains the same flow direction and size. Inductors release energy through resistors and VL increases gradually to zero while iL gradually decreased to zero.
For any node in the circuit, the sum of currents flowing into the node at any time equals to the sum of currents flows out the node.
Along any closed loop, the algebraic sum of all branch voltage at any time is identically vanishing. Before in summing of voltages, we need to specify a circuitous direction of the circuit,the voltage is positive. Othewise, the voltage is negative.
Superposition theorem states that in the linear resistance circuit, a voltage or current is the supersition of valtage or current produced by individual independent power separately applied to the circuit. The superposition theorem applies only to linear circuit, but not to nonliear circuits. In the subcircuit of superimposed circuit, the non-working voltage source is set to zero and replaced by the short circuit and replaced by the short circuit. The non-working current source is set to zero and replaced by the open circuit.
A port with independent sources and linear resistors can be equivalent replaced by a series combinations of valtage source ande resistors or parallel combination of current source and resistor for extermal circuits. The voltage of voltage source equal to the open-circuit voltage of prot. The resistor equals to the input resistors, when all the indepent sources ant the port are set to zero. The current of current source equal to the short-circuit current of the port.
电压源是一个理想的元器件，电压源的电压U(t)与通过元件的电流无关，总保持给定的时间函数U(t) = Us(t)。当Us(t)为恒定值时，这种电压源称为直流电压源，用Us表示。
Voltage source is an ideal circuit compnent, the voltage of the voltage source is independent of the current through the componet and always keep a given time function. When it is a constant value, this voltage source is called a DC voltage source and is represented by Us.
电流源也是一个理想的电路元件，电流源的电流i(t)与元件的端电压无关，总能保持为给定的时间函数i(t) = is(t)。电流源在伏安特性曲线上是一条不通过原点且与电压轴平行的直线。当is(t)随时间变化时，这条直线将随之平移。
The current source is also an ideal circuit element. The current of the current source is indepent of the component’s terminal voltage and can always be maintained as a given time function. current source in the volt-ampere characteristic curve is a line that does not pass through the origin and is paralled to the voltage axis. When is(t) changes with the time, the line will move along.
When i(t)=0，the current source is equivalent to open-circuit. It is pointless to open the current source, which is not equal to zero.
In experimental course, we verified the superposition theorem and Norton theorem and observed the response waveform of RC first-order circuit.