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digital logic circuit

This is a mind map about digital logic circuits, including sequential logic circuits, digital-to-analog and analog-to-digital conversion, pulse signal generation and shaping, programmable logic devices, etc.

Edited at 2021-09-01 21:10:05

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digital logic circuit

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Outline

Analysis and design of combinational logic circuits
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digital logic circuit

sequential logic circuit

Latches

Basic RS latch (reset set) (two cross-coupled NOR gates used)

Gated RS latch (C control signal, respectively and RS AND operation first)

Gated D latch (when C=1, Q(n 1)=D)

trigger

Definition: Use a special timing control signal of a clock to limit the change time of the state of a memory unit

master-slave flip-flop

Master-slave RS flip-flop

Form: Two identical gated RS latches are connected. The control signal is provided by the external clock signal CLK. They are mutually inverted. The master-slave latches are alternately gated.

Keep, set to zero, set to 1, disable (RS are all 1)

Master-slave D flip-flop: Two identical D latches are connected, the control signal is provided by the external CLK, and they are opposite to each other.

Master-slave JK flip-flop

It is composed of a master-slave D flip-flop and several gate circuits.

Hold, set to 0, set to 1, flip (JK are both 1)

master-slave flip-flop

Advantages: It solves the somersault (multiple changes of the excitation signal) and oscillation of the latch (when the control signal is valid, which is equivalent to two combination circuits forming a feedback system that is a mutual feedback network, and the system may be affected by transient characteristics. unstable and oscillating)

Disadvantages: Requires the input data to remain constant during data reception by the main latch to avoid any interference

edge trigger

The flip-flop can only receive data when the clock transitions (rising or falling edge) (strictly speaking, within a very short period of time before and after the transition)

Maintain blocking edge trigger

CMOS edge trigger

Pulse operating characteristics

Setup time: The input signal arrives a period of time (Tset) before the edge of the clock pulse arrives.

Hold time: After the clock pulse arrives, the input signal must remain unchanged for a period of time (Th)

Transmission delay time: the time required from the edge of the time pulse until the new state of the flip-flop is stably established

Maximum clock frequency, pulse width, power consumption

Application examples

Anti-chatter switch: Eliminates a series of pulsating vibrations generated when a mechanical switch is turned off or turned on.

Asynchronous pulse synchronization

Single pulse generator: A circuit that converts an input pulse of arbitrary width into a single pulse with a defined width

Analysis and design of sequential logic circuits

analyze

Synchronization: output equation--driving equation--state equation--state table--state diagram--logic function

Asynchronous: pulse type/potential type

Synchronous timing design: state diagram--simplification and removal of redundant states--binary coding--flip-flop--drive output--self-starting characteristic check (when the number of states of the sequential circuit is not equal to the exponent of 2, there will be redundancy in the sequential circuit Invalid state, once the circuit enters the invalid state, it can automatically return to a certain valid state after a limited number of clocks)

Finite State Machine

Moore type: The output is only related to the current state of the finite state machine and has nothing to do with the input signal at the current time.

Mealy type: The output is not only related to the state at the current moment, but also related to the input signal at the current moment.

adventure

Asynchronous sequential logic circuit: It is difficult to determine the order in which the excitation signal and the clock signal arrive at the same flip-flop.

Synchronous sequential logic circuit: The gate has limited load capacity. In fact, one clock signal is used to drive several gate circuits, and then these gate circuits drive several flip-flops. However, due to the transmission delay time of each gate different

Elimination: Use synchronous instead of asynchronous to extend the signal transmission delay

counter

Asynchronous counter

Asynchronous binary counter: Each flip-flop is connected as a T' flip-flop, and the flip-flops are connected in series. The output of the low-order flip-flop is used as the clock input of the high-order flip-flop. The maximum operating frequency is f=1/nTpf

Asynchronous decimal counter: Based on the asynchronous binary adder, a NAND gate is added. The inputs of the NAND gate are Q3 and Q1. When both are 1, the NAND gate outputs low level and all flip-flops in the counter are cleared.

sync counter

Synchronous binary counter: composed of T flip-flop, T0=1; Ti=Q(i-1)Q(i-2)....Q1Q0; maximum frequency f=1/(Tpf Tpg)

Synchronized decimal counter

Reversible counter: can be added or subtracted

Universal sync integration

74163 (binary), 74160 (BCD), 74190 (reversible)

Arbitrary base counter

Feedback reset method: using the binary code of the corresponding state to generate an asynchronous clear signal through a combinational circuit

Feedback setting method (number setting): repeatedly placing a certain value into the counter to jump M-N states

application

Sequence signal generator: counter plus data selector

Keyboard scanning circuit

Sequential logic components that temporarily store secondary digital numbers

One type is a register composed of multi-bit D flip-flops in parallel. The data is stored when the effective edge of the clock arrives. The other type is composed of D latches. The data is stored at a certain agreed level of the clock. .

Shift Register

One-way shift register: serial in-serial/parallel out one-way shift register; serial/parallel in-serial out one-way shift register

bidirectional shift register

application

Programmable crossover

serial adder

serial accumulator

Sequence signal generator

shift register counter

ring counter

twisted ring counter

Digital-to-analog and analog-to-digital conversion

D/A converter

Classification

Inverted T-shaped resistor network D/A converter: only R and 2R,

Resistor network D/A converter: less resistance, but a big difference

Technical Parameters

Resolution: The ability to resolve the minimum output voltage

Conversion error: fluctuation of the reference voltage, zero point drift of the operational amplifier, on-resistance and on-voltage drop of the analog switch, deviation of the resistor resistance in the resistor network, half of the minimum output voltage

Conversion speed: Setup time, the time from the sudden change of the input digital quantity until the output voltage enters the range of -0.5LSB from the steady-state value

Accuracy: Comparing the actual output with the ideal value, it is determined by differential nonlinearity-integral nonlinearity

linearity, monotonicity

A/D converter

Basic principles: sampling, holding, quantization, encoding

Classification

Successive approximation A/D converter

Double integrating A/D converter: converts the input analog voltage signal into a time width signal proportional to it, and then counts clock pulses of a fixed frequency within this time width. The counting result is proportional to the input analog voltage. Digital signal

Technical Parameters

Resolution: Number of binary digits output

Conversion Error: Multiple of Least Significant Bit

Conversion speed: the time required to complete an AD converter conversion

Generation and shaping of pulse signals

555 integrated timer---basic structure: resistor divider, voltage comparator, RS latch, transistor discharge and lighting

Schmitt trigger circuit

Output characteristics: There are two stable states (high and low levels, but the stable state needs to be maintained by the input signal level); it has hysteretic voltage transmission characteristics

Using 555 timer to construct a Schmitt trigger circuit

Waveform transformation, pulse shaping, pulse amplitude identification

monostable trigger circuit

Composition and working principle: steady state, temporary steady state, temporary steady state duration t=RC, automatically returns to stable state

Pulse shaping, pulse delay, pulse timing

multivibrator

The self-excited oscillator can automatically generate a rectangular wave generator with a certain frequency and a certain pulse width after the power is turned on without the need for an external trigger signal.

Two transient stable states

programmable logic device

Basic structure: AND or array structure, lookup table structure (LUT)

PAL: Programmable vs Array, Fixed or Array

GAL: Programmable vs Array, Fixed or Array

CPLD: Programmable AND-OR array, output logic macrocell

FPGA: LUT, basic structure: IOB (programmable input and output module) CLB (configurable logic module) ICR (interconnect resource) SRAM (static memory)

Semiconductor storage device

ROM

Fixed ROM: address decoder plus storage array, information is stored during manufacturing

Programmable ROM

One-Time Programmable ROM (PROM)

Optically erasable programmable ROM (EPROM): avalanche injection write, bulk erase under UV

Electrically Erasable Programmable ROM (EEPROM): word erase and word rewrite functions under high voltage, tunnel effect

FLASH Memory

RAM

Address decoder memory matrix read and write control circuit

Bipolar RAM

Field effect transistor RAM

SRAM

DRAM: cyclic charging

combinational logic circuit

adventure

static adventure

Definition: Before and after the input changes, the steady-state output should not change, but during the input change process, glitches appear.

Classification

Functional adventure

Definition: When multiple input quantities change, the variables change at different speeds

Elimination: The strobe pulse appears after the changes in the circuit caused by input changes have stabilized, so that a risk-free steady-state output is obtained.

logical adventure

Definition: There is only one change in the input variable, which excludes functional hazards and actually represents the delay of the gate.

Elimination: Modify the logic design and add redundant terms (including product terms of the remaining invariant variables) to the simplest output; gated output

dynamic adventure

Definition: Before and after the input changes, the steady-state output should change, but during the process of the input changes, the output will briefly repeat

Elimination: It is generally caused by static risk in the front stage of the circuit. Therefore, static risk can be eliminated. Dynamic risk can also be eliminated.

Verilog language--FPGA implementation of DDS

Encoder

binary encoder

Mutually exclusive encoder, at the same time, only one of the N input terminals of the encoder is at a valid level

priority encoder

8-wire-3-wire priority encoder 74148

10-wire-4-wire priority encoder 74147

Decoder/data distributor

Two-line and four-line decoder, three-line and eight-line decoder, four-line and 16-line decoder

display decoder

data selector

N data input terminals, k address code input terminals, and one data output terminal

arithmetic operation circuit

basic adder

Half adder HA: only considers the addition of two one-bit binary numbers, regardless of the carry of the low bit.

Full adder FA: taking into account the low carry, it can be implemented with two half adders and an OR gate

serial carry adder

high speed adder

Fully parallel adder: The multi-bit adder output sum S and the highest carry signal can always be written as the simplest logical expression of the input signals A and B. Therefore, a two-level gate structure can be used to realize the circuit logic function, but when the number of bits is too large , the number of gate circuits will increase sharply, and the circuit structure will be too complex.

carry-ahead

Idea: The carry input signal added to each full adder is obtained in advance through the logic circuit

Carry-ahead circuit CLA: The carry signal can be expressed as a function of P and G, G=AB; P=A B; when P and G are known, the carry signal can be obtained as long as it goes through the delay of the two-level gate circuit .

The carry-lookahead adder usually uses a 4-bit adder as a basic module and implements an adder with a multiple of 4 bits in a hierarchical structure.

full subtractor

Numeric comparator

transcoder

logic gate circuit

Switching characteristics of transistors: semiconductor diodes, transistors, MOS tubes

Discrete component gate circuits: diode AND gate, diode OR gate, transistor NOT gate

TTL gate circuit

Voltage transfer characteristics of TTL NAND gate

digital logic basics

coding

BCD code: 8421 code, 5421 code, 2421 code, remaining 3 codes

Gray code: cyclic code. There is only one difference between two adjacent codes, and the remaining bits are the same.

parity check code

Alphanumeric code: ASCII (7 bits)

Basic laws and rules of logical algebra

Basic rules: substitution, inversion, duality

Commonly used formulas, basic laws, exclusive or identical or logical operations

Standard form of logical function

Minimum term

Standard AND or formula

Maximum term

standard OR and

Simplification of logical functions

formula method

Karnaugh map simplification