Chapter 2 Basic knowledge of computer circuits

(1) course Introduction

Chapter	Content	Requirements	Analogy (building a house)
Chapter 1	Basic knowledge of Circuit Analysis	Master	Cement, water, sand
Chapter 2	Basic Semiconductor Devices	Master	Cement, water, sand
Chapter 3	Basic Switch Theory	Master	Cement, water, sand
Chapter 4	Door Circuit	Basic Circuit	Cement, water, sand
Chapter 5	Combined Logic Circuit	Key points (analysis methods and design)	Wall
Chapter 6	Time series logic circuit	Key points (analysis method)	Wall
Chapter 7	Knowledge Extension		House
Chapter 8	Knowledge Extension		House

 

(2) learning methods

1. Learn any course. Pay attention to the following two points:

① Basic Knowledge: they have been valid and basic concepts for decades. Be familiar with them and remember them.

② Capability: ability to analyze and solve problems. Including the ability to read books, new devices, and new technologies are constantly emerging. These capabilities did not appear out of thin air, but were learned purposefully and targeted based on the accumulation of basic knowledge.

 

Chapter 1 Basic knowledge of computer circuits

(1) Summary

1. Basic Physical Quantity of the circuit: ① current ② voltage ③ power

2. Two types of constraints of the circuit: ① the volt-ampere relationship of the component ② kierhov's law (related to the circuit and independent from the component)

3. Three Important Methods: ① equivalent variation ② venveni's theorem ③ superposition Theorem

4. concept: ① circuit diagram (composed of circuit components) ② Voltage Source Element ③ Current Source Element ④ circuit branch (composed of circuit components) ⑤ connection point (a point on the circuit diagram is used to link more than three branches) ⑥ circuit loop (composed of closed circuit branches) VII reference point (any hypothetical point, recorded as O) ✓ Circuit Analysis (calculate the current of a branch)

(2) content subject

I. Basic Physical Quantity of a circuit:

1. CurrentI, I (uppercase I indicates the DC current) has the size and direction (① reference direction (any hypothetical direction) ② true direction (Direction of positive charge Movement )) in a circuit diagram with an ampersand, the reference direction of current is defined as + pole to-pole inside the ampersand.

2. VoltageU, u (Capital U represents the DC voltage) physical quantities with size and direction are related to the two nodes in the circuit in the V direction (also known as polarity, divided into ① reference limit (any hypothetical direction), ② true polarity (moving the positive charge from A to B, when the electric field loses energy, then the polarity is A to B) ).

3. Potential(The voltage of some nodes in the circuit for the reference point ).

4. Link reference: The voltage reference direction is consistent with the current reference direction. (Otherwise, it is called a non-correlated reference direction ).

5. Absorbed Power(Product of voltage and current) Unit: Watt (w) formula p = + u * I; (Reference direction) P =-u * I; (Reference direction not associated) when P> 0 (indicating that the absorption power is assumed to be true, that is, the element in the circuit absorbs power) when P <0 (the current flow through the component generates power ).

Appendix: EWB Simulation and Digital Circuit Simulation Platform

 

Ii. basic components of the circuit and the voltammetry relationship

1. Resistance R (ideal model for actual resistors) Unit: ohm u = r * I (associated) u =-R * I (not associated)

P = u * I = (R * I) * I = r * I2 P = u * I = u2/R, which indicates that the resistance is a component that absorbs power.

2. capacitor C (ideal model for actual capacitors) I = C * du/dt has the characteristics of the component that stores Electric Field Energy:

① The voltage on the capacitor cannot change suddenly.

② In the DC circuit, u = U (constant), I = 0, and the capacitor is equivalent to an open circuit (directly separated ).

3. inductance L unit: Heng (h) u = L * di/dt has the characteristics of the component that stores magnetic field energy:

① The current on the inductor generally cannot change.

② In the DC circuit, I = I (constant), u = 0, so the inductance is equivalent to a short circuit.

4. The (ideal) voltage source u = us; I is jointly determined by us and the external circuit. When US = 0, a zero-value voltage source) is equivalent to a short-circuit wire.

5. (ideal) Current Source I = is; U is jointly determined by is and the external circuit. When is = 0, (zero-value current source) is equivalent to an open-circuit wire. At the same time, pay attention to their painting method, the direction of the inside of the circle.

6. Controlled Source (useful for transistor and amplifier)

Iii. kikhov's Law

1. Key points: unrelated to the circuit structure and circuit components

2. Current Law (KCl) Σ I = 0 (the algebra of the current flowing into a node and the algebraic sum of the current flowing out of the node ).

3. Voltage Law (kvl) Σ u = 0 (the voltage algebra of all branches along a closed branch is 0 ).

Iv. Analysis Method of simple resistance circuit

1. Equivalent Transformation: if the two circuits are equivalent, their ports have the same voltammetry relationship.

① Equivalent transformation between the actual voltage source and the actual current source (a combination of the voltammetry relationship and kikhov's law)

② Merge between current sources (based on KCl)

③ Merge voltage sources (based on kvl)

④ Formula for series, parallel, partial pressure, and shunt; Series: r = R1 + R2; parallel: r = R1 * R2/(R1 + R2) This formula is suitable for only two parallel connections.

⑤ Note: The two circuits obtain the same ur, but the internal power consumption is different. This indicates that the equivalent conversion analysis object is an external circuit.

2. David's Theorem

I applicable conditions: only suitable for Linear Circuits, that is, circuits composed of linear components. The above components are linear components.

II solution steps:

① Calculate the open circuit part and the open circuit voltage UOC

② Calculate thevenam equivalent resistance Ro, short-circuit the voltage source, open the current source, and then use the series or parallel formula to obtain

③ Recover the open circuit part and find the voltage or current with the circuit.

3. superposition theorem u = U' + u''

I applicable conditions: only suitable for Linear Circuits, that is, circuits composed of linear components, non-linear components such as diodes.

II solution steps:

① The voltage source does not function as a 0-value Voltage Source: Short Circuit to find U'

② The current source does not function as a 0-value current source: open circuit to find u''

③ Obtain the obtained voltage U = U' + u''

V. Transition Process of simple RC Circuit

1. Simple RC Circuit definition: A circuit consisting of only one R, C, and a voltage source is sometimes called a first-order RC Circuit because it has only one capacitor.

2. Three elements of the first-order circuit:

① UC (0): initial capacitor voltage during transition

② UC (∞): capacitor voltage at the end of the transition process

③ RC: Time Constant (r: The davenam equivalent resistance at both ends of the capacitor)