Summary of review knowledge points for electronic information engineering professional courses: (2) Analog electronics

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Preface

Chapter One Introduction

1. Signal

Devices that convert various types of non-electrical signals into electrical signals are called sensors.

The circuit can be equivalent to: an ideal voltage source and a resistor in series (Thevenin) or an ideal current source and a resistor in parallel (Norton).

2. Spectrum of the signal

1. Realize the transformation of the signal from the time domain to the frequency domain through Fourier transform.

2. Any periodic function can be expanded into a Fourier series as long as it satisfies the Dilihli condition.
For a linear time-invariant system, if the real parts of all poles of its transfer function (including real and imaginary parts) are less than zero, the system is stable. This condition can be judged by the Dilihli condition.

3. The amplitude of the signal frequency component that changes with the angular frequency is called the amplitude spectrum, and the phase that changes with the angular frequency is called the phase spectrum.

3. Analog signals and digital signals

An analog signal is a continuously changing signal whose value can take on any value within a certain time range. Analog signals can be represented by continuous functions, such as sound, light intensity, etc. Analog signals are characterized by infinite granularity and continuity.

Digital signals are discretely changing signals, and their values ​​can only take on limited discrete values. Digital signals can be represented by discrete numerical sequences, such as binary signals in computers. Digital signals are characterized by limited precision and discreteness.

Analog signals can be converted into digital signals through the process of sampling and quantization. Sampling is to sample a continuous analog signal within a certain time interval to obtain a series of discrete values. Quantization is the mapping of sampled values ​​to finite discrete values, usually represented by a fixed number of bits.

Digital signals can be converted into analog signals through the process of restoration and filtering. Reduction is the conversion of discrete values ​​of digital signals into continuous analog signals. Filtering is to filter the restored signal to eliminate the noise and distortion introduced during the digitization process.

4. Amplification circuit model

1. The purpose of amplification is to amplify weak electrical signals to the range we need.

2. Amplification refers to linear amplification, that is, the information contained in the signal before and after amplification is exactly the same, and only the amplitude and power of the signal change. Deformation of the waveform is considered distortion.

3. Classification of amplifier circuits: voltage amplifier circuit, current amplifier circuit, transimpedance amplifier circuit (input voltage, amplified output voltage), transconductance amplifier circuit (input voltage, amplified output current)

4. The main gain indicators of the amplifier circuit
① Input resistance: determines how much signal the circuit can obtain from the signal source

②Output resistance: determines the load capacity. When the load changes, if the output changes very little, the load capacity is strong. What is important is that the output should remain stable even if the load changes.

③Gain : Such as voltage gain, transimpedance gain, etc., which actually reflects the ability of the amplifier circuit to convert energy supply into output signal energy.

④ Frequency response: Simply put, changes in the frequency of the input sinusoidal signal will also affect changes in the output.

Looking at this picture,
the middle section is flat with stable gain, which is the mid-frequency zone. The gain drops by 3db at 20hz and 20Khz, and the output power is half of the mid-frequency zone, which is called the half-power point.
The frequency difference between the high and low half-power points of the amplitude-frequency response is defined as the bandwidth (passband)

⑤ Nonlinear distortion
Linear distortion means that the changes in signal amplitude and phase during signal transmission or signal processing are linear, that is, the amplitude and phase of each frequency component of the input signal in the output change in the same proportion . Linear distortion can be caused by the frequency response of the transmission medium, non-ideal characteristics of circuit components, system delay, etc. Linear distortion can be corrected through correction or compensation methods, such as using equalizers, pre-emphasis filters, etc.

Nonlinear distortion means that the changes in signal amplitude and phase during signal transmission or signal processing are nonlinear, that is, the amplitude and phase of each frequency component of the input signal in the output do not change in the same proportion . Nonlinear distortion can be caused by nonlinear characteristics of electronic components, saturation effects of circuits, nonlinear responses of nonlinear systems, etc. Nonlinear distortion causes signal distortion, spectrum spreading, intermodulation interference and other problems, and is often more difficult to correct.

Chapter 2 Operational Amplifier

1. Integrated Circuit-OPA

The integrated circuit operational amplifier (Op-Amp for short) is a high-gain, differential input, single-ended output amplifier circuit that is commonly used in various analog signal processing and amplification applications. It usually consists of a large number of transistors and other electronic components integrated onto a single chip.

The main characteristics of operational amplifiers include:
High gain: The open-loop gain of operational amplifiers is very high, usually between 10 ^{5 and 10} 6, and can amplify weak input signals to larger output signals.
Differential input: The operational amplifier has two input terminals, namely the non-inverting input terminal (+IN) and the inverting input terminal (-IN), which are used to receive differential input signals.
Single-ended output: The output terminal (OUT) of the operational amplifier is a single-ended output, and the amplitude of the output signal can be amplified in proportion to the amplitude of the input signal.
Wide voltage range: Op amps can usually operate over a wide supply voltage range to accommodate different application requirements.
High Input Impedance: Op amps have high input impedance, allowing them to receive input signals from external circuits without affecting them.

2. Basic linear op amp circuit

① Non-inverting amplifier circuit

A non-inverting amplifier circuit is an amplification circuit using an operational amplifier (Op-Amp) in which the input signal has the same phase as the output signal.
The basic structure of the non-inverting amplifier circuit is to connect the non-inverting input terminal (+IN) and the inverting input terminal (-IN) of the operational amplifier through a feedback resistor, and at the same time connect the input signal to the non-inverting input terminal. This way the output signal will have the same phase as the input signal and will be amplified.

②Virtual short and virtual break
Virtual short refers to treating two circuit nodes as a short-circuit connection, that is, treating the voltage difference between them as zero. In real circuits, when the resistance between two nodes is very small, or the value of the resistance can be ignored, the virtual short approximation can be used to simplify circuit analysis. By directly connecting two nodes, the calculation process of the circuit can be simplified and the complexity can be reduced. The appearance of virtual short is actually the result of negative feedback in the op amp circuit. Deep negative feedback makes the input differential signal Vp-Vn close to 0, and the voltages at the two input terminals are equal.

Virtual Open refers to treating two circuit nodes as open circuits, that is, treating the current between them as zero. In real circuits, when the resistance between two nodes is very large, or the value of the resistance is negligible, the virtual break approximation can be used to simplify circuit analysis. By disconnecting two nodes, the calculation process of the circuit can be simplified and the complexity can be reduced. If the input resistance of the op amp is extremely large, it will cause I=U/R, U is small and R is extremely large, and I approaches 0, causing a virtual break.

③Integral circuit and differential circuit
The integral circuit is a circuit that performs an integral operation on the input signal. It usually consists of an operational amplifier (Op-Amp) and a capacitor. The input signal is connected to the inverting input terminal (-IN) of the op-amp through a capacitor, while the output signal is taken from the output terminal (OUT) of the op-amp. By choosing an appropriate capacitor value, the input signal can be integrated and produce a corresponding integrated result at the output . Integrating circuits are commonly used in signal processing, filtering, and control systems.

A differential circuit is a circuit that performs differential operations on input signals. It usually consists of an op amp and a resistor. The input signal is connected to the non-inverting input (+IN) of the op amp through a resistor, while the output signal is taken from the output of the op amp. By choosing appropriate resistor values, the input signal can be differentiated and produce a corresponding differentiated result at the output . Differential circuits are commonly used in signal processing, filtering, and control systems.

Chapter 3 Diodes and Their Circuits

1. Semiconductor concept-covalent bond structure

(1) Intrinsic semiconductor - a semiconductor with pure chemical composition. It is in the form of a single crystal in physical structure.
(2) Hole - when the electron breaks away from the covalent bond, a vacancy is formed in the covalent bond.
(3) Electron-hole pairs - free electron and hole pairs generated by thermal excitation.
(4) Movement of holes - The movement of holes is achieved by filling the holes with valence electrons in adjacent covalent bonds in turn.
(5) N-type semiconductor - a semiconductor doped with pentavalent impurity elements (such as phosphorus).
In N-type semiconductors, free electrons are majority carriers, which are mainly provided by impurity atoms; holes are minority carriers, formed by thermal excitation.
(6) P-type semiconductor - a semiconductor doped with trivalent impurity elements (such as boron).
In P-type semiconductors, holes are majority carriers, which are mainly formed by doping; free electrons are minority carriers, which are formed by thermal excitation.
(7) Drift motion - The motion of carriers caused by the action of an electric field is called drift motion.
(8) Diffusion motion - The motion of carriers caused by the difference in carrier concentration is called diffusion motion.

2. Formation of PN junction

This paragraph is more troublesome to explain, so I try to describe the process in the most understandable terms.
First, we need to know that free electrons are the majority carriers in N-type semiconductors, while holes are the majority carriers in P-type semiconductors. When we combine N-type semiconductor and P-type semiconductor, both electrons and holes need to diffuse from the high concentration area to the low concentration area, that is, the free electrons in the N-type semiconductor run to the P-type semiconductor, and the P-type semiconductor The holes in the semiconductor run to the N-type semiconductor, thus forming a space charge region (PN junction) at the original interface, in which the N zone close to the N-type semiconductor has a + charge, and the P zone close to the P-type semiconductor has a - charge. Electricity, it can be seen that an internal electric field is formed to prevent carrier diffusion. The internal electric field promotes the drift of minority carriers and prevents the diffusion of majority carriers. Finally, the diffusion of majority carriers and the drift of minority carriers reach a dynamic balance, forming a balanced PN junction. In the space charge region, due to the lack of multiple carriers, it is also called a depletion layer.

A simpler explanation: P-type semiconductor is doped with 3-valent elements, resulting in more holes inside; N-type semiconductor is doped with 5-valent elements, resulting in more electrons inside. When the two are combined, holes and electrons attract and diffuse each other. An internal electric field is formed in the middle, and then gradually prevents diffusion movement, and finally reaches an equilibrium state, that is, PN junction .

3. Characteristics of PN junction

1. Unidirectional conductivity of the PN junction.
When an external voltage makes the potential of the P region in the PN junction higher than the potential of the N region, it is called the application of forward voltage, referred to as forward bias; otherwise, it is called the application of reverse voltage, referred to as reverse bias.
(1) When a forward voltage is applied to the PN junction: low resistance and large forward diffusion current. The PN junction behaves as a resistor with a small resistance and is turned on .
(2) When a reverse voltage is applied to the PN junction: high resistance, small reverse drift current. At this time, the PN junction resistance is very large and cuts off .
From this it can be concluded that the PN junction has unidirectional conductivity .

2.Reverse breakdown of PN junction

3. Capacitance effect of PN junction
Diffusion capacitance:
When the PN junction is in forward bias, diffusion movement causes the majority of carriers to pass through the PN junction, and there is a higher than normal charge accumulation near the PN junction in the opposite area. The amount of stored charge depends on the forward voltage applied to the PN junction. The further away from the junction, the concentration will decrease due to the recombination of holes and electrons.
If there is an increment of △V in the external forward voltage, the corresponding diffusion movement of holes (electrons) generates an increment of charge △Q near the junction. The ratio of the two, △Q/△V, is the diffusion capacitance Cd.

4. Diode

1. Structure of diode
Point contact diode: small PN junction area and small junction capacitance, used in high-frequency circuits such as detection and frequency conversion.
Surface contact diode: large PN junction area, used in power frequency high current rectification circuits.

2. Characteristics of diode:
A diode is an electronic device with two electrodes, which has forward characteristics and reverse characteristics.

Forward Characteristics:
A diode is forward biased when its anode is connected to a positive voltage (relative to the cathode) and its cathode is connected to a negative voltage.
In the forward biased state, the diode exhibits a lower resistance, called forward resistance (forward conduction).
When the forward voltage exceeds the forward voltage drop of the diode (generally 0.6-0.7V), the diode begins to conduct and current can flow through the diode.
The forward characteristic allows the diode to be used as a rectifier, converting AC signals into DC signals.

Reverse Characteristic:
When the anode of a diode is connected to a negative voltage (relative to the cathode) and the cathode is connected to a positive voltage, the diode is in a reverse biased state.
In the reverse biased state, the diode exhibits a very high resistance, called reverse resistance (reverse blocking).
When the reverse voltage exceeds the reverse breakdown voltage of the diode, the diode will break down and the current will suddenly increase.
The reverse characteristic allows diodes to be used as protection circuits to prevent voltages from exceeding a certain range.

2. Main parameters of diode

Forward conduction voltage, maximum rectified current IF, reverse breakdown voltage Vbr, reverse current Ir, inter-electrode capacitance Cd, reverse recovery time.

5. Basic circuit analysis methods of diodes and their applications

The diode is a nonlinear device, so its circuit generally requires the analysis method of a nonlinear circuit.
(1) Graphical analysis method
The graphical analysis method is relatively simple, but the prerequisite is that the V-I characteristic curve of the diode is known. Just find the intersection of their work.

(2) Simplified model analysis method:
Linearize the exponential model piecewise to obtain an equivalent model of the diode characteristics, such as using the small signal analysis method. When vs =0, point Q is called the static operating point, which reflects the working state of DC. When vs =Vmsinωt (Vm<<VDD), linearize the VI characteristics in a small range near the Q point to obtain a small signal model, that is, a straight line with the Q point as the tangent point. For specific methods, see "[Summary of Knowledge Points] Lecture 2 on Circuit Principles"

Including ideal model, constant voltage drop model, polyline model

Simple diode model (Ideal Model):
The simple diode model assumes that the diode is completely conducting when conducting in the forward direction and completely blocking when conducting in the reverse direction.
When conducting forward, the simple diode model treats the diode as an ideal wire without any voltage drop.
In reverse cutoff, the simple diode model treats the diode as a completely disconnected open circuit.

Constant Voltage Drop Model: The
constant voltage drop model assumes that the diode has a fixed voltage drop (generally 0.6-0.7V) when the diode is forward-conducting.
This model more closely approximates the characteristics of actual diodes and is widely used in many circuit analyses.
The constant voltage drop model treats the diode as an ideal voltage source with a fixed voltage drop when conducting forward.

Piecewise-linear Model:
The Piecewise-linear Model is a more accurate model that describes the forward characteristics of the diode by approximating it as a polyline.
The polyline model usually uses two linear segments to approximately describe the characteristics of the diode.
The broken line model treats the diode as a voltage source with a fixed voltage drop when conducting in the forward direction, but unlike the constant voltage drop model, the broken line model takes into account the dynamic resistance of the diode.

(3) Application: rectifier circuit, limiting circuit, switching circuit.

Rectifier circuit:
A rectifier circuit is used to convert AC signals into DC signals.
The most common rectifier circuit is a single-phase rectifier circuit using diodes. It conducts the AC signal in the positive half cycle and cuts off the AC signal in the negative half cycle, so that the output signal remains a unidirectional DC signal .
Rectifier circuits are commonly used in fields such as power converters, motor drives, and communications equipment.

Limiting circuit:
The limiting circuit is used to limit the amplitude of the input signal to ensure that the output signal is within a certain range.
The most common limiting circuit uses the forward cutoff and reverse cutoff characteristics of a diode to limit the signal amplitude .
Limiting circuits are commonly used in audio amplifiers, communications equipment, and sensor signal processing.

Switching circuit:
Switching circuit is used to control the switching state of current or signal to achieve switching between on and off .
Switching circuits can be implemented using components such as transistors, relays, or integrated circuits.
Switching circuits are commonly used in areas such as digital circuits, motor control, automation systems, and communications equipment.

6.Special diode

Specialty diodes are diodes with special functions or characteristics that allow them to be used in a wider range of specific applications than ordinary diodes. The following are several common special diodes:

Zener Diode:
A Zener diode is a special type of diode used in voltage stabilization and voltage reference applications.
It operates at reverse breakdown voltage, and when the reverse voltage reaches a specific value, the Zener diode starts conducting, keeping the reverse voltage stable at that value.
Zener diodes are commonly used in voltage regulators, power supply regulation, and voltage reference circuits.

Photodiode: Photodiode
is a photoelectric sensor used to convert light signals into electrical signals.
It produces a current response to light irradiation. The greater the light intensity, the greater the current.
Photodiodes are commonly used in applications such as photoelectric measurement, optical communications, and optoelectronic control.

Rectifier diode (Schottky Diode):
The rectifier diode is a diode with fast switching characteristics and low forward voltage drop.
Its forward voltage drop is lower than that of ordinary diodes and its switching speed is faster.
Rectifier diodes are commonly used in applications such as high frequency circuits, power switches, power conversion and mixers.

Variable capacitance diode (Varactor Diode):
A variable capacitance diode is a diode with adjustable capacitance characteristics.
Its capacitance value can be adjusted by reverse voltage for frequency tuning and oscillation circuits.
Variable capacitance diodes are commonly used in applications such as RF tuners, oscillators, and filters.

led

The principle of one-way conductivity of diode

The PN junction is composed of a combination of P-type semiconductor and N-type semiconductor materials. Impurity atoms in P-type semiconductors are usually trivalent, such as boron (B) or aluminum (Al), which create holes (positive charges) in the crystal lattice. Impurity atoms in N-type semiconductors are usually pentavalent, such as phosphorus (P) or arsenic (As), which create additional free electrons (negative charges) in the crystal lattice.

When P-type and N-type semiconductor materials come into contact, diffusion occurs between holes in the P region and free electrons in the N region. This diffusion process causes holes in the P region to move to the N region, and free electrons in the N region to move to the P region.

During the diffusion process, when holes and free electrons meet, they recombine to form a charge-neutral region between positive and negative charges, called a depletion region. The charge distribution inside the depletion layer forms a barrier that prevents further diffusion.

When the diode is under the forward bias voltage, that is, the anode is connected to the P region and the cathode is connected to the N region, the potential barrier decreases and the charge neutral region becomes narrower. Electrons and holes can move to each other through the PN junction to form a current. passage through. In this case, the diode is said to be conducting.

When the diode is under the reverse bias voltage, that is, when the anode is connected to the N region and the cathode is connected to the P region, the potential barrier increases, the depletion layer becomes thicker, and electrons and holes are blocked by the potential barrier and cannot pass through the PN junction. moves, forming a high-resistance state. In this case, the diode is considered to be blocking.

Chapter 4 BJT three-stage tube

1. Internal principles: ① Current conduction ② Current amplification

The functions of the BJT transistor are: ① current conduction ② current amplification.
The base, collector, and emitter of a triode are essentially semiconductors doped with different impurities. The N-type shows negative polarity to the outside, indicating that there are more free electrons inside and is doped with +5-valent elements; the P-type shows positive polarity to the outside, indicating that there are more holes inside and is doped with +3-valent elements. In the NPN transistor, two PN junctions are formed, called the emitter junction and the collector junction.

Prerequisite: The emitter is forward biased and the collector is reverse biased.

Principle of current (conduction) transmission: When there is no current at the base, the transistor is turned off, and when current is input to the base, it is conductive.

Understand the principle: Each part in NPN is doped with impurities, but at different concentrations. There are more emitters and collectors, and the least base. When our power supply is connected to the positive side, so that the emitter is forward biased, the electrons deflect and move to the emitter junction under the action of the electric field, and a small number of holes in the base reach the emitter junction, forming an emitter current, and the emitter junction is turned on.
When the collector is reverse biased, most of the electrons on the collector follow the electric field in the same direction, forming a collector current, causing the collector to conduct.

Principle of current amplification (small current controls large current):

When the base current increases, more electrons from the corresponding emitter will be deflected to the base, and more free electrons will flow to the collector, causing the current to amplify.

The reason why the base is made very thin (low doping concentration)

The base is made very thin, so that electrons from the emitter can flow to the base more easily. Because the base is thin, it cannot carry a large number of electrons, causing more free electrons to move toward the collector.

Can two diodes put together replace a triode?

Answer: No. First of all, the P and N regions of the two diodes have fixed thicknesses and fixed doping element concentrations. The combined triode does not meet the requirements for the thickness and concentration of the base, emitter, and collector. Second, assuming it is an NPN type, the P areas of the two diodes need to be connected together. The P area will most likely not be very thin. Then when an electric field is applied, it is difficult for electrons to go from the base to the collector, resulting in no conduction. .

The direction of current flow and the direction of electron flow

BJT's NPN transistor essentially has the base as the valve, the emitter as the water tank, and the collector as the faucet. After a forward bias voltage is applied to the emitter, the electrons diffuse to the base. Because the base is thin, the electron concentration difference is high and the electrons Continue to spread towards the collector.
Both the base and the emitter are connected to a power supply, which provides a continuous flow of electrons. The direction of the current is opposite to the direction of electron flow.

2. Several working states of BJT transistors

① Cut-off state: Vbb=0 that supplies power to the base, making the emitter junction unable to be forward biased

② Saturation state: At this time, both the emitter junction and the collector junction are forward biased, because Vce is too small, Vbb≠0, there is base power supply, but the emitter power supply is weak, which is equivalent to no water (electrons) in the water tank.

③ Amplification state: the emitter junction is forward biased and the collector junction is reverse biased. Continuously increase the Vcc voltage until Vce>0.7V, and then enter the amplification state. ib (base current) is a very small value, but it can affect ic (collector current) and amplify it to a large multiple. And it can remain stable.

Which application circuits are suitable for cutoff, saturation and amplification states?

Simply put, cutoff and saturation are suitable for switching circuits; amplification state is suitable for amplification circuits .

When the BJT is in the cut-off state, the switch can be turned off so that the current cannot pass.
The saturation state is suitable for switching circuits. When the BJT is in the saturation state, the switch can be closed to allow current to pass.
When the BJT is in the amplified state, larger current amplification can be achieved between the collector and emitter by controlling the base current.

3. Analysis of BJT amplifier circuit

① Graphical analysis method: static operating point and dynamic operating point of BJT amplifier circuit

The static operating point (Quiescent Point, Q point) and dynamic operating point of the BJT amplifier circuit refer to the working state of the BJT in the amplifier circuit.

There are two input power supplies for the base, one is a DC voltage source and the other is an AC voltage source. When the AC voltage source is 0, only the DC voltage source is used to supply energy to meet the amplification state conditions. The circuit working state at this time is called static. After adding the alternating voltage source, it becomes dynamic.

Static operating point: The static operating point refers to the stable operating state of the BJT when there is no input signal. At the static operating point, each voltage and current parameter of the BJT is at a fixed value and does not change with changes in the input signal. The selection of the static operating point has an important impact on the stability and linearity of the amplifier circuit.

The static operating point is determined by two key parameters:
Collector current (Ic): the value of the collector current at the static operating point.
Collector-emitter voltage (Vce): The voltage between the collector and emitter at the static operating point.

The selection of the static operating point usually requires consideration of the following factors:
Ensure that the BJT is in the amplification region (Active Region) to achieve linear amplification of the signal.
Make sure the BJT operates in a safe area and avoid over-saturation or over-cutoff to prevent damage.

Dynamic operating point: The dynamic operating point refers to the working state of the BJT when there is an input signal, also called the operating line (Operating Line). When an input signal is applied to the amplifier circuit, the current and voltage parameters of the BJT will change with the change of the signal. The dynamic operating point is the working state that describes this change.

The dynamic operating point can be represented by the AC load line, which is a straight line determined by the static operating point and the load resistance (or load current). At the dynamic operating point, the output voltage and output current of the BJT will change with the change of the input signal to achieve signal amplification.

The selection of dynamic operating point needs to consider the following factors:
Ensure that the BJT is in the amplification zone to achieve linear amplification of the signal.
Ensure that the dynamic operating point is on the AC load line to avoid over-saturation or over-cutoff to maintain signal linearity and reliability.

②H parameter small signal model analysis method

Solution steps:
Use the H parameter small signal model to analyze the basic common emitter amplifier circuit:
(1) Use the DC path to find the Q point;
(2) Draw the small signal equivalent circuit;
(3) Find the dynamic indicators of the amplifier circuit, such as voltage gain, Input resistance, output resistance.
Advantages and disadvantages of the small signal model analysis method:
**Advantages: **It is very convenient to analyze the dynamic performance indicators (Av, Ri and Ro, etc.) of the amplifier circuit, and is suitable for analysis at higher frequencies.
**Disadvantages:** In the small-signal equivalent circuit of the BJT and the amplifier circuit, the voltage, current and other electrical quantities as well as the H parameters of the BJT are based on the changing amount (AC amount) and cannot be used to analyze and calculate the static operating point. .

4. Three configurations of BJT amplifier circuit: common emitter, common base, and common collector

5. The difference between MOS tube and BJT transistor

Working principle of MOS tube (N-channel)

Let’s look at the principle first:

For a MOS tube, such as an N-channel MOS tube, it has a gate, a source, and a drain.
Structure: N-channel MOS tube is composed of P-type substrate and N-type channel. On the substrate, there is an insulating layer (usually silicon dioxide) and a metal gate (Gate).

Why is it called a field effect tube? Because a forward electric field is applied to the gate, the electrons in the P-type semiconductor approach the gate and the holes move away, causing an N-channel electronic conduction between the upper and lower N-type semiconductors and the gate. When the gate electric field is not applied, the P-type semiconductor recovers, causing the MOS to turn off.

Bias: When no external voltage is applied to the gate, the N-channel MOS tube is in the off state, and no conductive path is formed in the channel.
Off state: In the off state, there is no carrier flow in the channel, and the current between the drain and source of the NMOS tube is zero . Therefore, NMOS tubes have high input impedance.

Channel formation: When a forward bias voltage is applied to the gate, the electric field between the gate and the substrate attracts free electrons in the N-type channel region. When the electric field is strong enough, the free electrons in the channel form a conducting path.
On-state: In the on-state, the free electrons in the channel form a conductive channel from source to drain, and current can flow from the drain to the source. At this time, the current between the drain and source of the NMOS tube is controlled by the gate voltage.

Output characteristics: When the gate voltage increases, the conductive path in the channel widens, causing the drain-source resistance to decrease, thereby increasing the current flow. Therefore, the NMOS tube has current amplification characteristics in the on state.

So what is the difference between MOS and BJT?

①Obviously, structurally, the MOS tube does not have a PN junction. It is a structure made of metal, insulating layer, and semiconductor. There are N-type and P-type semiconductors, but there is no connection to form a PN junction. BJT is composed of two PN structures.
② In terms of working principle, the MOS tube is a field effect tube, so the external electric field is applied to the gate to form the N channel to conduct, while the BJT uses the characteristics of two PN junctions to apply forward bias and reverse bias conditions be able to conduct.
③Input impedance: MOS tubes have high input impedance and have little impact on the input signal. The input impedance of BJT is relatively low, and the input signal will have a greater impact on it.

Chapter 7 Analog Integrated Circuits

FET, BJT current sources and differential amplifier circuits manufactured with integrated technology

1.BJT current source circuit and FET current source

No more writing.

2. Differential amplifier circuit

①Circuit structure

A differential amplifier circuit is a common circuit configuration used to amplify differential-mode signals (i.e., the difference between two input signals) and suppress common-mode signals (i.e., the average of the two input signals). Differential amplifier circuits are commonly used in signal transmission, anti-interference, and measurement and control systems.

A differential amplifier circuit usually consists of a differential amplifier, which includes two input ports and one output port. Each input port is connected to an amplifier input pin, and the output port is connected to an amplifier output pin.

A differential amplifier produces an output signal by amplifying the difference between two input signals. When the two input signals are equal, the output signal of the differential amplifier is zero. When there is a difference between the two input signals, the differential amplifier will amplify the difference and output a corresponding differential voltage.

A differential amplifier typically amplifies the input signal differentially, meaning that the two input signals cancel each other and only amplify the difference between them. This makes the differential amplifier circuit suppressive for common-mode interference signals because the common-mode signal has the same amplitude and phase on both input ports and is therefore canceled at the output port of the differential amplifier.

Key points: two inputs, one output, using transistors, mirror symmetry,
amplifying differential mode signals and suppressing common mode signals.
When the two input signals are equal, the output signal of the differential amplifier is zero. When there is a difference between the two input signals, the differential amplifier will amplify the difference and output a corresponding differential voltage.

②Zero point drift:

(1) Concept: Ideally, when the input signal is zero, the output signal should remain zero. However, in actual situations, due to the influence of various factors, the output signal may be offset, that is, zero point drift.
(2) Influencing factors: The main reason why temperature affects transistor parameters
(3) Elimination methods: differential amplification circuit, introduction of DC negative feedback, temperature compensation

A differential amplifier circuit divides the input signal into two signals with opposite phases, and then amplifies and compares the two signals to obtain an output signal. Since the two input signals have the same zero drift, they are canceled out during the amplification and comparison processes, thereby reducing the impact of the zero drift.
DC negative feedback adjusts the input signal by using part of the output signal as a negative feedback input, thereby reducing the impact of zero point drift.
Temperature compensation can be achieved through the use of temperature sensors and compensation circuits. The temperature sensor can detect changes in ambient temperature and pass relevant information to the compensation circuit. The compensation circuit adjusts the output signal according to temperature changes to eliminate zero drift

③Temperature drift:

Temperature drift refers to the change in the signal output by a measuring instrument or sensor as the ambient temperature changes. Temperature drift is caused by changes in the characteristics of electronic components due to temperature changes.

In many electronic devices and sensors, temperature changes can affect the device's operating conditions, resulting in changes in the output signal. This is because temperature changes will affect the conductivity, resistance, capacitance and other characteristics of electronic components, thereby affecting the amplitude and offset of the output signal.

Chapter 8 Feedback Amplification Circuit

1. The concept of feedback

What is feedback?

Its basic principle is to control and regulate the system by feeding back part of the output signal to the input end. The purpose of the feedback system is to make the output of the system as close as possible to the desired reference signal, thereby achieving performance requirements such as stability, accuracy, and robustness.

What is the purpose of feedback?

In order to improve the static and dynamic performance of the amplifier circuit, the output terminal is used to react on the input.
DC feedback affects DC performance, such as the static operating point. AC feedback affects AC performance such as gain, input, output resistance, bandwidth, etc.

Negative feedback and positive feedback

Why should negative feedback be introduced in the amplifier circuit?

The main purpose of introducing negative feedback in an amplifier circuit is to improve the performance and stability of the circuit. Here are a few of the main reasons for introducing negative feedback:

Improve gain stability: Negative feedback can reduce the sensitivity of the gain of the amplifier circuit to changes in component parameters. When the gain of the amplifier is affected by fluctuations in component parameters or temperature, negative feedback can automatically adjust the gain of the amplifier by adjusting the difference between the input and output, making the entire circuit more stable.

Reduce nonlinear distortion: The amplifier is prone to nonlinear distortion under high gain conditions, that is, there is distortion between the output signal and the input signal. Negative feedback can reduce nonlinear distortion by reducing the gain of the amplifier, making the output signal closer to the linear change of the input signal.

suppress noise

Extended frequency response: Some amplifiers experience frequency attenuation at high frequencies, resulting in distortion or attenuation of the output signal. By introducing negative feedback, the frequency response range of the amplifier can be extended, allowing it to maintain stable gain over a wider frequency range.

Increase input and output impedance: Negative feedback can reduce the input and output impedance of the amplifier, allowing for a better match between the amplifier and other circuits or devices, resulting in better signal transmission and power delivery.

Discrimination method: instantaneous polarity method. That is, in the circuit, starting from the input terminal and along the signal flow direction, mark the slope of the voltage change of the relevant node at a certain moment (positive slope or negative slope, represented by "+" and "-" signs).

Types of feedback

Voltage feedback and current feedback

Voltage feedback and current feedback are determined by the sampling object of the feedback network at the output end of the amplifier circuit.
Voltage feedback: The feedback signal xf is proportional to the output voltage, that is, xf = Fvo. Voltage negative feedback stabilizes the output voltage.
Current feedback: The feedback signal xf is proportional to the output current, that is, xf = Fio, and current negative feedback stabilizes the output current.
Judgment method: load short circuit method - short circuit the load (the output is short-circuited to ground when no load is connected), the feedback amount is zero - voltage feedback; if the feedback amount still exists - current feedback.

Summary of the characteristics of the four configurations
(1) Series feedback: summation of input voltages (KVL)
(2) Parallel feedback: summation of input currents (KCL)
(3) Voltage negative feedback: stable output voltage, with constant voltage characteristics
( 4) Current negative feedback: stable output current, with constant current characteristics

Deep negative feedback, virtual short and virtual break

Deep Negative Feedback: Deep negative feedback refers to the situation where the feedback signal has a high degree of amplification in the circuit, that is, the feedback signal plays a major control role in the circuit. Under deep negative feedback, changes in the output signal are mainly determined by the feedback signal rather than changes in the input signal . Deep negative feedback can make the performance of the circuit more stable and controllable.

Virtual Short: Virtual short refers to the situation in a negative feedback circuit where the equivalent voltage between the feedback node (output node) and the input node is very small or approaches zero . This means that there is almost no voltage difference between the feedback node and the input node , so that the input signal has little effect on the voltage at the feedback node. The function of the virtual short is to isolate the feedback signal from the input signal, so that the feedback signal dominates the control of the circuit.

Virtual Open: Virtual Open refers to the situation in a negative feedback circuit where the equivalent current between the feedback node (output node) and the input node is very small or approaches zero . This means that almost no current flows between the feedback node and the input node , so that the input signal has little effect on the feedback node's current. The function of the virtual break is to isolate the feedback signal from the input signal, so that the feedback signal dominates the control of the circuit.

Stability of negative feedback amplifier circuit (conditions for self-oscillation and stable operation)

Self-oscillation phenomenon: Without any input signal, the amplifier circuit will still produce a signal output of a certain frequency.

1. Causes and conditions
: The additional phase shift generated by A and F in the high-frequency area or low-frequency area reaches 180, causing the negative feedback in the mid-frequency area to become positive feedback in the high-frequency area or low-frequency area. When the Under certain amplitude conditions, self-oscillation will occur .

The deeper the depth of feedback, the easier it is to self-excite.

Chapter 9 Power Amplifier Circuit

1.Power amplification

A power amplifier circuit is an amplifier circuit designed to output larger power. Therefore, it is required to output larger voltage and current at the same time. The tube works close to the limit state and is generally used to directly drive the load and has a strong load capacity.
According to the conduction status of the transistor during the entire cycle of the sinusoidal signal:
(1) Category A: conduction during one cycle
(2) Category B (complementary symmetry of dual power supplies): conduction angle equal to 180°
(3) Category A and B: conduction The conduction angle is greater than 180°
(4) Category C: The conduction angle is less than 180°

Work efficiency:
Category A: 50%
Category B: 78.5%

2. Main problems of Class B (complementary symmetrical power amplifier circuit)

①BJT has a dead zone voltage, so crossover distortion will occur.

② Crossover distortion refers to the distortion caused by the transistor being cut off when the input voltage is low due to the dead voltage of the BJT.

③The crossover distortion problem can be solved by using Class A and B complementary symmetrical circuits.

Chapter 10 Signal Processing Circuit

1. Voltage comparator

The basic working principle of a voltage comparator is to compare two input voltages and generate a high/low level output based on the comparison result. The output of the comparator is usually a digital signal, either high or low.
Through the analysis of the above voltage comparators, the following conclusions can be drawn:
(1) The op amp used for the voltage comparator usually works in the open loop or positive feedback state and nonlinear region, and its output voltage is only high-level VOH. and low level VOL.
(2) Voltage transmission characteristics are generally used to describe the functional relationship between output voltage and input voltage.
(3) Key elements of voltage transmission characteristics: high-level VOH and low-level VOL of the output voltage, threshold voltage, and jump direction of the output voltage.
The vI obtained by letting vP=vN is the threshold voltage. The output voltage jumps when vI is equal to the threshold voltage. The jumping direction depends on whether it is the non-inverting input mode or the inverting input mode.

2. Sine wave generation circuit

An oscillator circuit is a circuit that uses a feedback circuit to generate an oscillation signal. Among them, the most common are LC oscillators and crystal oscillators. The LC oscillator consists of an inductor and a capacitor, and the oscillation frequency is controlled by adjusting the values ​​of the inductor and capacitor. Crystal oscillators use piezoelectric crystals as oscillating elements and use the mechanical vibration of the crystal to generate a stable frequency.

3. Square wave generation circuit

The principle of capacitor charging and discharging is used. When the vc at the reverse input terminal is less than the voltage at the non-inverting input terminal, the output vo is a high level VOH. At the same time, it charges the capacitor along Rf, causing the vc potential at the reverse input terminal to increase. When When the vc at the reverse input terminal is greater than the voltage at the non-inverting input terminal, the output vo is a low level VOL, and the capacitor discharges along Rf, causing the potential of vc at the reverse input terminal to drop. When the vc at the reverse input terminal is less than the voltage at the non-inverting input terminal, Start the cycle again and repeat this to get a square wave at the voltage output. The function of the voltage regulator tube is to limit the voltage in both directions.
Square wave generation circuit with variable duty cycle: The principle is to add diodes, Rf1 and Rf2 to change the charge and discharge time and thereby change the duty cycle.

4. Filter circuit

(1) Filter - is an electronic device that allows useful frequency signals to pass while suppressing or attenuating unwanted frequency signals.
(2) Active filter - a filter composed of active components.
(3) Low pass, high pass, band pass, band stop filtering