introduction
Chapter 1 Introduction to Digital Logic
1. What are the advantages of digital integrated circuits compared to analog circuits?
① High stability and strong anti-interference ability
② Digital circuits only use 0 and 1 for logical operations, so it is easier to design the circuit.
③ Easy to integrate, small size, low cost
④ Strong programmability, encryption technology can be used to improve confidentiality
⑤ High speed, low power consumption
⑥ Strong scalability
2. What are the advantages and disadvantages of COMS and TTL circuits?
COMS field effect transistor circuit (Complementary Metal-Oxide-Semiconductor) and TTL transistor circuit (Transistor-Transistor Logic) are two common digital circuit families, which are widely used in the electronics industry.
Here are some of their advantages and disadvantages:
Advantages of CMOS circuits:
Low power consumption: The power consumption of CMOS circuits is very low, because there is transient power consumption only when the input signal changes, and there is basically no static power consumption at other times.
High integration: Due to the design flexibility of CMOS circuits, highly integrated chips can be achieved. This makes CMOS circuits play an important role in the field of integrated circuits.
Low Noise: CMOS circuits have lower noise levels, giving them an advantage in noise-sensitive applications.
Wide operating voltage range: CMOS circuits can operate within a wide voltage range and are therefore suitable for a variety of different application scenarios.
Disadvantages of CMOS circuits:
Slower speed: Compared with TTL circuits, CMOS circuits have slower switching speeds. This is because the transistors in the CMOS circuit need to undergo a charging and discharging process.
Sensitive to electromagnetic interference: CMOS circuits are more sensitive to electromagnetic interference, which may reduce the reliability of the circuit.
Higher cost: Because CMOS circuits require more transistors and additional manufacturing processes, the cost is higher than TTL circuits.
Advantages of TTL circuits:
High-speed operation: TTL circuits have faster switching speeds and are suitable for applications with higher speed requirements.
Strong anti-interference ability: TTL circuits have strong resistance to electromagnetic interference and can work stably in noisy environments.
Relatively low cost: Due to the simple design of TTL circuits, the manufacturing cost is relatively low.
Disadvantages of TTL circuits:
Higher power consumption: TTL circuits have higher power consumption because energy is continuously consumed when the input signal changes.
Limited operating voltage range: The operating voltage range of TTL circuits is narrow, and the stability of the power supply voltage needs to be strictly controlled.
Low integration: The design complexity and power consumption of TTL circuits are high, which limits its application in highly integrated chips.
3. Conversion between binary, octal, ten and hexadecimal
My idea is: uniformly convert to a familiar system as an intermediate quantity, and then convert to get the result.
For example, if you want to convert octal to hexadecimal, first convert octal to binary (convert each bit of octal to binary independently), and then convert this binary (convert every 4 digits into a segment and convert to hexadecimal)
In the same way, to convert hexadecimal to decimal, you must first convert hexadecimal to binary (each bit in hexadecimal is independently converted into binary), then multiply each bit in binary by the corresponding power of 2, and then compare them. Add to get decimal number)
4. Original code, complement code and complement code of binary numbers - for signed binary numbers
Use 0 to represent + and 1 to represent -
Rule: For a positive binary number, its complement and inverse code are the same as the original code.
For a negative binary number, the original code is itself, the complement code is the inversion of the numerical value of the original code bit by bit, and the complement code is the lowest bit + 1 after the complement code is found.
Note: There is no direct subtraction of binary numbers. It needs to be converted to two's complement operation first, and then the minuend and the complement of the subtrahend are added.
5. Reliability coding: remainder 3 code, Gray code
①Remaining 3 codes: The code is obtained by 8421 codes + 3.
② Remainder cyclic code: It has adjacency, and there is only one bit difference between any two adjacent codes.
③Gray code: The encoding method is: for binary numbers, the highest bit is reserved, and then starting from the highest bit of binary, XOR operation is performed with the next bit of binary. For example,
binary: 1 0 1 1
0Gray code: 1 1 1 0 1
6.AND or NOT, compound logic operations, bit operations
AND, OR, and NOT are the basic operators in logic and are used to combine and manipulate logical values (true or false).
AND operation (AND):
represented by the symbol "∧" or "&&".
The result is true when all inputs are true; otherwise, the result is false.
true ∧ true = true true ∧ false = false false ∧ true = false false ∧ false = false
Or operation (OR):
represented by the symbol "∨" or "||".
The result is true when at least one input is true; otherwise, the result is false.
true ∨ true = true true ∨ false = true false ∨ true = true false ∨ false = false
Not operation (NOT):
represented by the symbol "¬" or "!".
Negates the logical value of the input.
¬True = False ¬False = True
In addition to the AND, OR, and NOT operations, there are other compound logical operators that can combine multiple logical operations as needed:
Exclusive OR operation (XOR): When the input logical values are different, the result is true; otherwise, the result is false.
Exclusive OR operation (XNOR): When the input logical values are the same, the result is true; otherwise, the result is false.
NAND operation (NAND): The result of the AND operation is inverted.
NOR operation (NOR): The result of the OR operation is negated.
Bit operations: For binary numbers, shifting one bit to the left is equivalent to multiplying by 2 raised to the power of one; shifting n bits to the left is equivalent to multiplying by 2 raised to the nth power; shifting n bits to the right is equivalent to dividing by 2 raised to the nth power.
Chapter 2 Logical Algebra, Functions and Hardware Languages
1.Basic theorem:
① Substitution theorem: A function can replace the same variable A appearing on both sides of the equation, and the equation still holds.
② Inversion theorem: When finding the non-function of the original function L, interchange OR with, 01 interchange, and original non-interchange
③ Duality theorem: Dual form of L: interchange OR with interchange, 01
2. Minimum term
(AND) The form of a product that contains all n occurrences of variables, with each variable appearing only once in its original/informal form. For example: the minimum term of three variables A, B, C: ABC, A is not B, not C, etc.
3. Maximum term
The form of phase or (addition), similar to: A+B+C
4. The relationship between the maximum term and the minimum term
The two have a mutually inverse relationship.
5. Representation of logical functions:
①Truth table: a table composed of 0 and
1 ②Function expression:
③Waveform diagram
④Gate circuit logic diagram
6. Karnaugh map
Chapter 3 Logic Gate Circuit
Discuss NMOS, BiCMOS in CMOS circuits and bipolar junction BJT gate circuits in TTL.
1. Advantages and disadvantages of COMS and TTL
① The COMS circuit is small in size, so it has low production cost and low power consumption. The TTL circuit occupies a relatively large area.
②CMOS circuit has faster response speed, stronger anti-interference ability and strong load capacity.
③ At present, CMOS occupies a dominant position in the market and is more widely used.
2.What is BiCMOS integrated circuit?
Answer: It combines the high speed and high driveability of BJT with the advantages of low cost and low power consumption of COMS.
3.Characteristics of MOS tube
① N-channel enhancement mode means that the field effect transistor is in a closed state when there is no control voltage. When a forward voltage (called the gate-source voltage) is applied to the gate of a field effect transistor, an N-type channel is formed beneath the gate, causing current to flow through the tube . Therefore, N-channel enhancement mode requires a forward voltage to turn on.
② N-channel depletion mode means that the field effect transistor is in a conductive state when there is no control voltage. When a negative voltage (called gate-source voltage) is applied to the gate of a field effect transistor, an N-type channel is formed under the gate, causing current to flow through the tube. Therefore, N-channel depletion mode requires a negative voltage to turn off.
③P-channel enhancement mode (P-channel enhancement mode) means that the P-channel enhancement type field effect transistor is in a conductive state without a control voltage. When a negative voltage (called gate-source voltage) is applied to the gate of a field effect transistor, a P-type channel is formed under the gate, causing current to flow through the tube. Therefore, P-channel enhancement mode requires a negative voltage to turn on.
④P-channel depletion mode means that when there is no control voltage, the P-channel depletion field effect transistor is in a closed state. When a forward voltage (called gate-source voltage) is applied to the gate of a field effect transistor, a P-type channel is formed under the gate, causing current to flow through the tube. Therefore, P-channel depletion mode requires a forward voltage to turn off.
N-channel enhanced MOS tube output characteristics:
similar to BJT, the cut-off area is when Vds is less than the on-voltage, the N-channel is not formed, it can be considered that the gate is a resistor with extremely high resistance, and no current flows through it, so the MOS tube No power is consumed in static state and the power consumption is low.
When it is greater than the turn-on voltage, the MOS is made to work in the variable resistance region, and the output current is not affected by the applied electric field, but the circuit is turned on.
Therefore, the cut-off area and the variable resistance area can be used to implement the switching circuit.
4.COMS inverter
Looking at the picture, you can see that the principle is very simple. For example, when 0V is input, the lower N channel is in a cut-off state and is disconnected; the upper P channel is in a conductive state, connecting VDD to the output, making the output high level.
4. Logic gates composed of COMS: NAND gate, NOR gate, XOR gate
5. CMOS open-drain (OD) gate and three-state output gate circuit
① OD open-drain gate, as the name suggests, the drain is open, and the output circuit only has NMOS tubes, and the output end must be connected to a pull-up resistor to connect to the power supply.
② Line AND: Two output signals implement AND logic on a bus. A pull-up resistor should be added to prevent excessive current from burning out the circuit.
③Tri-state gate: The tri-state gate has three states, outputting high level, low level and high resistance state. When EN is enabled, input = output; when EN is disabled, it is in a high impedance state.
④ Specific values of logic levels: TTL is 0.3-3.6V, CMOS is 0, 5V, and 12V. For example, the power supply of a microcontroller is 3.3V. When connecting to the 5V port of a computer, you need to use USB to TTL, which is equivalent to converting from CMOS to TTL.
⑤ Fan-out coefficient: The maximum number of input terminals of a gate circuit that can be connected to the same series of gate circuits. The larger the fan-out coefficient, the stronger the load capacity.
Chapter 4 Combinational Logic Circuits
1. Competition in Combinational Logic Circuits – Adventure
① Concept: At the moment when the signal level changes, the circuit may be inconsistent with the logic function in the steady state, resulting in erroneous output.
② Competition: The input signal changes and the signal propagation path is different, causing the next-level gate circuit to change first and then later (with differences caused by delay), which is called competition.
③Risk: The phenomenon of interference pulses affecting output caused by competition.
2. Eliminate competition – a risky approach?
Answer: ① Eliminate the complementary terms in circuit design.
② Add a product term to avoid the addition of complementary terms
③ Connect a capacitor in parallel at the output: Connect a filter capacitor to the output port to weaken the amplitude of the interference pulse.
3. Encoder, decoder, data selector, data distributor, half adder and full adder
Encoder: An encoder is a combinational logic circuit used to encode multiple input signals into a smaller number of output signals . It maps different input modes to unique output encodings. Common encoders include binary encoders and priority encoders.
Decoder: A decoder is a combinational logic circuit used to convert input encoding patterns into corresponding output signals . It is the opposite of an encoder and decodes the encoded signal into multiple output signals. Decoders are often used to convert digital signals into corresponding control signals.
Data Selector: A data selector is a combinational logic circuit used to select a specific data output from multiple input data . Input signals to a data selector typically include multiple data inputs and a selection signal that specifies which data input to output.
Data Distributor: A data distributor is a combinational logic circuit used to distribute an input signal to multiple output signals . Its function is the opposite of a data selector, copying one input signal to multiple output signals.
Half Adder and Full Adder: A half adder is a combinational logic circuit used to perform the addition operation of two single-bit binary numbers. It can only process two input bits. The full adder is an extension of the half adder and can handle three input bits, two of which are the digital bits to be added, and the third input bit is the carry bit . Half adders and full adders are commonly used in digital adding circuits.
4. Application of decoder: digital tube
The application of the decoder in the digital tube display is to convert the digital signal into the corresponding control signal to realize the digital display function of the digital tube. Nixie tube is a commonly used digital display device, consisting of multiple LEDs (light-emitting diodes), each LED represents a number or character.
The digital tube usually consists of 7 or 8 segments of LEDs, with each segment corresponding to one LED. In order to control the display of the digital tube, the digital signal needs to be converted into the corresponding control signal to light up the corresponding LED segment to display the corresponding number or character.
This can be achieved using a decoder. The input signal of the decoder is a digital signal, and the output signal is the corresponding control signal. By connecting the output signal of the decoder to each LED segment of the digital tube, the decoder will generate a corresponding control signal according to the input signal, lighting up the corresponding LED segment of the digital tube, and realizing digital display.
Commonly used digital tube decoders include BCD decoders or 7-segment decoders. The BCD decoder converts the 4-bit binary code (BCD code) into the corresponding control signal, which can be used to display decimal numbers from 0 to 9. The 7-segment decoder converts the 4-bit binary code into the corresponding control signal, which can be used to display hexadecimal numbers or specific characters from 0-F.
Chapter 5 Latches and Flip-Flops (Circuits that implement storage functions)
1.Latch
1. What is a latch?
A latch is a combinational logic circuit used to store and maintain the state of input signals. It can change the output signal according to the level state of the input signal without the need for a clock signal, and keep the output signal in the new state until a new input signal arrives.
A latch is usually composed of a flip-flop (Flip-Flop), which is the basic component of a latch. The flip-flop has two stable states, namely "Set" and "Reset", and can switch between these two states according to changes in the input signal. Latches enable more complex storage and retention functions by connecting multiple flip-flops together.
A latch works like a memory cell that can store a certain number of bits of data. When the latch is in the "set" state, the output signal is high level or logic 1, indicating that the stored data is valid. When the latch is in the "reset" state, the output signal is low level or logic 0, indicating that the stored data is invalid.
2. What are the types of latches?
There are many different types of latches, some common ones include:
SR latch (Set-Reset Latch): The SR latch has two input terminals, namely Set and Reset inputs. It can change the output signal according to the state of the input signal and keep the output signal in the new state until a new input signal arrives.
D Latch: The D latch has a data (D) input and an enable (EN) input. It can change the output signal according to the state of the data input signal, and can control whether to store new data into the latch through the enable signal.
JK latch (JK Latch): The JK latch has two input terminals, namely J and K inputs. It can change the output signal according to the state of the input signal, and has some special functions, such as setting, reset and flip, etc.
T latch (T Latch): The T latch has an input terminal T, which is used to control the state of the latch. When the T input is 1, the latch's output will flip; when the T input is 0, the latch's output will remain unchanged.
2. Trigger
1. What is the trigger?
A flip-flop (Flip-Flop) is an electronic component used to store and control signals. It can change the output signal according to the edge change of the level of the input signal under the action of the clock signal, and keep the output signal at the new level. state until the next clock signal arrives.
The flip-flop evolved from the latch, which solves some problems of the latch, such as the inability to accurately control the change time of the output signal and the instability of the state. Flip-flops are usually composed of multiple logic gates, and common ones include RS flip-flops, D flip-flops, JK flip-flops, and T flip-flops.
Different types of flip-flops have different characteristics and functions, but they all have two stable states, namely "Set" and "Reset", and can switch between these two states according to changes in the input signal. switch between. Flip-flops generally have a clock input. When the edge (rising edge or falling edge) of the clock signal arrives, the flip-flop changes the output signal according to the current input signal state and keeps the output signal in the new state until the next The clock signal arrives.
2. Type of trigger?
There are many different types of triggers, some common ones include:
RS flip-flop (Set-Reset Flip-Flop): The RS flip-flop has two input terminals, namely Set and Reset inputs. It can change the output signal according to the state of the input signal, and has two stable states, namely set and reset.
D flip-flop (Data Flip-Flop): A D flip-flop has a data (D) input and a clock (CLK) input. It can store the input data into the flip-flop at the edge of the clock signal according to the state of the data input signal, and keep the stored data in the new state until the next clock signal arrives.
JK flip-flop (JK Flip-Flop): The JK flip-flop has two input terminals, namely J and K input. It can change the output signal according to the state of the input signal, and has some special functions, such as setting, reset and flip, etc., which can be used to implement various logic functions.
T flip-flop (Toggle Flip-Flop): The T flip-flop has an input terminal T, which is used to control the state of the flip-flop. When the T input is 1, the output of the flip-flop will flip; when the T input is 0, the output of the flip-flop will remain unchanged.
3. The difference between latches and flip-flops
Latches and flip-flops
have something in common: they have two stable states: 0 and 1. Once the state is determined, it can maintain itself. A latch or flip-flop can store one bit of binary code.
Differences:
(1) Latch - a memory circuit that is sensitive to pulse levels and changes state under the action of a specific input pulse level.
(2) Flip-flop - a memory circuit that is sensitive to pulse edges and changes state instantly when the rising edge or falling edge of the clock pulse changes.
4. Sequential logic circuit
Sequential logic circuit:
Working characteristics: The working characteristic of a sequential logic circuit is that the output state at any time is not only related to the current input signal, but also related to the previous state of the circuit.
Structural features: It is composed of combinational logic circuit and storage circuit, and there is feedback in the circuit. Latches and flip-flops are the basic logic units that constitute sequential logic circuits.
Chapter 6 Sequential Logic Circuit
1. Basic concepts
Structural characteristics of sequential circuits: The circuit consists of a combinational circuit and a storage circuit; there is feedback in the circuit.
Output equation: O=f(I, S) - expresses the relationship between the output signal, input signal and state variables.
Excitation equation: E=f(I, S) - expresses the relationship between the excitation signal, input signal and state variables.
State equation: Sn+1=f(E, Sn) - expresses the conversion relationship of the storage circuit from the current state to the secondary state.
Synchronization: All flip-flops in the storage circuit have a unified clock source, and their states are updated at the same time.
Asynchronous: There is no unified clock pulse or no clock pulse, and the status updates of the circuit do not occur simultaneously.
2. Register, shift register
1. Registers and shift registers
** (1) Register: ** is a logical component used to store code or data in a digital system. Its main component is a flip-flop.
A flip-flop can store 1-bit binary code, and a register that stores n-bit binary codes needs to be composed of n flip-flops. A register is actually a collection of flip-flops.
(2) Shift register: A shift register is a logical functional component that can not only store numbers, but also move numbers to high or low bits under the action of clock pulses . According to the movement mode, it is divided into unidirectional shift register and bidirectional shift register. Among them, unidirectional shift register can be divided into left shift and right shift . In a microcontroller, the value in the register can be shifted left and right to achieve certain purposes, which uses a shift register.
3. Counter
2. Counter
(1) Asynchronous binary counter - 4-bit asynchronous binary adding counter - asynchronous is reflected in the output of the previous stage being the clock source signal of the next stage, thus achieving asynchronous.
The function of the counter: not only can count but also can be used as a frequency divider.
(2) Binary synchronous up counter
Working principle: Q0 flips once at each CP, FF0 can use a T flip-flop with T=1;
Q1 only flips when the next CP after Q0 = 1 arrives, FF1 can use T= T flip-flop for Q0;
Q2 only flips when the next CP comes after Q0 = Q1 = 1, FF2 can adopt a flip-flop with T = Q0Q1T;
Q3 only flips when the next CP comes after Q0 = Q1 = Q2 = 1 Flip, FF3 can use flip-flop T = Q0Q1Q2T
Chapter 7 Semiconductor Memory
1. Read-only memory ROM
In normal working condition only information can be read out .
Non-volatile: Information will not be lost after power failure. It is often used to store fixed information (such as programs, constants, etc.).
2.RAM (random access memory)
Read or write operations can be performed at any time in the running state .
Volatility: The stored data must be powered by a power supply to be saved. Once the power is lost, all data will be lost.
Chapter 9 Transformation and Generation of Pulse Waveforms
Need to generate clock pulses, timing signals, etc.
1. Monostable circuit
The working characteristics of the monostable trigger: the circuit is in a stable state when there is no trigger signal; under the action of an external trigger signal, the circuit flips from a stable state to a temporary stable state; due to the role of the RC delay link in the circuit, the circuit temporarily The steady state cannot be maintained for a long time. After a period of time, the circuit will automatically return to the steady state. The duration of the transient steady state is only related to the value of the RC parameter.
2.Schmitt trigger
Schmitt trigger voltage transmission characteristics and working characteristics:
(1) Schmitt trigger is a level-triggered device. When the input signal reaches a certain voltage value, the output voltage will mutate; the circuit has two threshold voltages. When the input signal increases and decreases, the threshold voltage of the circuit is the positive threshold voltage (VT+) and the negative threshold voltage (VT-) respectively.
(2) Internal positive feedback accelerates level conversion
The functions of Schmitt trigger: ① Waveform transformation, which can transform sine waves, triangle waves, etc. into square waves. ②Waveform shaping and anti-interference,
3.Multivibrator circuit
A self-excited oscillation circuit can generate a rectangular wave of a certain frequency without the need for an external input signal.
4.555 timer
Function: Timing, timing, pulse generation, trigger control
5.AD and DA conversion
AD conversion is the process of converting continuously changing analog signals into discrete digital signals. AD converters sample analog input signals, then quantize and encode the sampled values, converting them into discrete signals in digital form . The output of the AD converter is a binary number that represents the size and amplitude of the analog input signal. AD converters are often used to convert analog sensor signals, audio signals, etc. into digital signals for processing and analysis of digital systems.
DA conversion is the process of converting discrete digital signals into continuously changing analog signals. The DA converter decodes and quantizes the digital signal, and then generates an analog output signal corresponding to the input signal through current, voltage or other methods based on the value and amplitude of the digital signal . DA converters are often used to output digital systems to analog devices or modules, such as converting digital audio signals into analog audio signals and outputting them to speakers.