What Is a Digital Integrated Circuit?

Digital integrated circuits are digital logic circuits or systems made by integrating components and wires on the same semiconductor chip. According to the number of gate circuits or elements and devices included in digital integrated circuits, digital integrated circuits can be divided into small scale integrated (SSI) circuits, medium scale integrated MSI circuits, large scale integration (LSI) circuits, ultra large scale integrated VLSI circuits, and Ultra Large Scale Integration (ULSI) circuit.

Chinese name: Digital integrated circuit
Foreign name: digital integrated circuit

Key words: Information Science Components IC
Number of components: Between 100 and 1,000
Model composition: The three parts of prefix, number, and suffix

Basic introduction of digital integrated circuits

Digital integrated circuits are designed and operated based on digital logic (Boolean algebra), integrated circuits used to process digital signals. According to the definition of integrated circuits, digital integrated circuits can also be defined as: digital logic circuits or systems made by integrating components and wires on the same semiconductor chip. According to the number of gate circuits or elements and devices contained in digital integrated circuits, digital integrated circuits can be divided into small scale integrated (SSI) circuits, medium scale integrated MSI circuits, large scale integrated (LSI) circuits, ultra large scale integrated VLSI circuits, Ultra Large Scale Integration (ULSI) circuits and Giga Scale Integration (GSI).

Small-scale integrated circuits contain less than 10 gate circuits, or the number of components does not exceed 10; medium-scale integrated circuits contain 10 to 100 gate circuits, or between 100 to 1,000 components; Large-scale integrated circuits include more than 100 gate circuits, or the number of components is between 1,000 and 10,000; VLSI circuits include more than 10,000 gate circuits, or the number of components is 100. The number of gate circuits of ULSI is more than 100,000, or the number of components is between 1,000,000 and 100,000. With the advancement of microelectronics technology, the scale of integrated circuits is getting larger and larger. It simply does nt make much sense to simply divide the types by the number of integrated components. At present, the integrated scale integrated circuits are collectively referred to as integrated scales exceeding 100 million. Components of integrated circuits.

Digital integrated circuit model composition

The digital integrated circuit model is generally composed of a prefix, a number, and a suffix. The prefix represents the manufacturer, and the number includes the product serial number and the device serial number. The suffix generally indicates the temperature level and package type. As shown in Table 0-1, the composition of TTL 74 series digital integrated circuit models and the meaning of symbols.

Digital integrated circuit logic function

Digital logic circuits can be divided into two categories: combinational logic circuits and sequential logic circuits. In combinational logic circuits, the output at any time depends only on the input at that time, and has nothing to do with the previous working state of the circuit. The most commonly used combinational logic circuits are encoders, decoders, data selectors, demultiplexers, numerical comparators, full adders, parity checkers, and so on. In a sequential logic circuit, the output at any time depends not only on the input at that time, but also on the original state of the circuit. Therefore, the sequential logic circuit must have a memory function and must contain a memory cell circuit. The most commonly used sequential logic circuits are registers, shift registers, and counters.

The specific combinational logic circuits and sequential logic circuits are endless. Because they are widely used, they all have standardized and serialized integrated circuit products. These products are usually called general-purpose integrated circuits. Correspondingly, those integrated circuits designed and manufactured for special purposes are called application-specific integrated circuits (ASIC).

Digital IC Internal Design

The composition of the digital circuit: combined logic + register (flip-flop). Combinational logic is a function composed of basic gates, and its output will only be related to the current input. In the above example, the first diagram is combinational logic, which only completes logical operations. In addition to sequential circuits, which include basic gates, Contains storage element use cases to save past information. The steady-state output of a sequential circuit depends not only on the current input, but also on the state formed by past inputs. The second figure is the sequential circuit. While completing the logical operation, the processing result can be temporarily stored and used for the next operation.

From a functional point of view, a digital integrated circuit can be divided into two parts: a data path (also called a data path) and control logic. These two parts are integrated by a large number of sequential logic circuits, and most of them are synchronous sequential circuits, because sequential circuits are divided into several nodes by multiple flip-flops or registers, and these flip-flops are controlled by the clock Working at the same beat can simplify the design. In the long-term design process, many standard universal units have been accumulated, such as selectors (also called multiplexers, which can select one output from multiple input data), comparators (for comparing the size of two numbers), Adders, multipliers, shift registers, and so on. These unit circuits have a regular shape and are easy to integrate (this is why digital circuits have been better developed in integrated circuits). These units are connected together according to the design requirements to form a data path. The data to be processed passes from this input to this path to the output, and the processed result is obtained. At the same time, it is also necessary to control the various components of the data path by specially designed control logic, and work in accordance with their respective functional requirements and specific timing relationships.

Digital integrated circuit category description

There are many types of digital integrated circuit products. According to the circuit structure, they can be divided into two series: TTL and MOS.

TTL digital integrated circuits use two kinds of carriers, electrons and holes, to conduct electricity, so they are also called bipolar circuits. MOS digital integrated circuits are circuits that use only one type of carrier to conduct electricity. Among them, electrons that conduct electricity are called NMOS circuits; holes that conduct electricity are called PMOS circuits. It is a CMOS circuit.

Compared with TTL digital integrated circuits, CMOS digital integrated circuits have many advantages, such as a wide working power supply voltage range, low static power consumption, strong anti-interference ability, high input impedance, low cost, and so on. Therefore, CMOS digital integrated circuits have been widely used.

There are many kinds of digital integrated circuits, including hundreds of devices such as various gate circuits, flip-flops, counters, codecs, and memories. The series of digital integrated circuit products are shown in the table below.

The national standard model regulations are formulated with reference to the models commonly used in the world. In the national standard model, the first letter "C" represents China; the second letter "T" represents TTL, and "C" represents CMOS. CT is China's TTL digital integrated circuit, and CC is China's CMOS digital integrated circuit. Subsequent parts are completely consistent with international universal models. ^[1]

General characteristics of digital integrated circuits

TTL Digital integrated circuit TTL circuit

(1) Power supply voltage range

The working power supply voltage range of the TTL circuit is very narrow. S, LS, F series is 5V ± 5%; AS, ALS series is 5Y ± 10%.

(2) Frequency characteristics

The working frequency of TTL circuit is higher than 4000 series. The operating frequency of standard TTL circuits is less than 35MHz; the operating frequency of LS series TTL circuits is less than 40MHz; the operating frequency of ALS series circuits is less than 70MHz; the operating frequency of S series circuits is less than 125MHz; the operating frequency of AS series circuits is less than 200MHz.

(3) Voltage output characteristics of TTL circuit

When the working voltage is ten 5V, the output high level is greater than 2.4V, the input high level is greater than 2.0V; the output low level is less than 0.4V, and the input low level is less than 0.8V.

(4) Minimum output drive current

Standard TTL circuit is 16mA; LS-TTL circuit is 8mA; S-TTL circuit is 20mA; ALS-TfL circuit is 8mA; AS-TTL circuit is mA. High current output TTL circuit: standard TTL circuit is 48mA; LS-TTL circuit is 24mA; S-TTL circuit is 64mA; ALS-TTL circuit is 24 / 48mA; AS-TTL circuit is 48 / 64mA.

(5) Fan-out capability (taking the number of LS-TTL loads as an example)

Standard TTL circuit is 40; IS-TTL circuit is 20; S-TTL circuit is 50; ALS-TTL circuit is 20; AS-TTL circuit is 50. High current output TTL circuit: standard TTL circuit is 120; LS-TTL circuit is 60; S-TTL circuit is 160; ALS-TTL circuit is 60/120; AS-TTL circuit is 120/160.

For each series of TTL integrated circuits with the same function number, their pinouts and logic functions are exactly the same. For example, the pin diagrams of each integrated circuit such as 7404, 74LS04, 74A504, 74F04, 74ALS04 and logic functions are completely the same, but they have significant differences in circuit speed and power consumption.

CM0S Digital integrated circuit CM0S circuit

(1) Power supply voltage range

The operating power supply voltage range of the integrated circuit is 3 to 18V, and the 74HC series is 2 to 6V.

(2) Power consumption

When the power supply voltage VDD = 5V, the static power consumption of the CM0S circuit is: 2.5 to 5 W for gate circuits; 5 to 20 W for buffers and flip-flops; 25 to 100 W for medium-scale integrated circuits.

(3) Input impedance

The input impedance of the CM05 circuit only depends on the leakage current of the protection diode at the input end, so the input impedance is extremely high, which can reach more than 108 ~ 1011. Therefore, the CMOS circuit hardly consumes the power of the driving circuit.

(4) Anti-interference ability

Because their power supply voltage has a large allowable range, their output high and low level swings are also large, and their anti-interference ability is strong. The maximum noise tolerance is 45% VDD and the guaranteed value can reach 30% VDD. The larger the tolerance value.

(5) Logical swing

The logic high level 1 output by the CM0S circuit is very close to the power supply voltage. . Therefore, the CM0S circuit has the highest power utilization factor.

(6) Fan-out capability

In low frequency operation, one output can drive more than 50 CMOS devices.

(7) Radiation resistance

The CMOS tube is a majority carrier controlled conductive device, and the radiation has little effect on the majority carrier concentration. Therefore, the CMOS circuit is particularly suitable for devices operating under aerospace, satellite and nuclear test conditions.

The CM0S integrated circuit has low power consumption, low internal heat generation, and can greatly improve integration. Because of the complementary symmetrical structure of the circuit itself, when the ambient temperature changes, its parameters have a mutual compensation effect, so its temperature stability is good.

(8) Manufacturing process of CM0S integrated circuit

The manufacturing process of the CM0S integrated circuit is simpler than the manufacturing process of the TTL integrated circuit, and it also occupies a small silicon area, which is especially suitable for manufacturing large-scale and ultra-large-scale integrated circuits.

Digital integrated circuit considerations

It is not allowed to work under the condition of exceeding the limit parameters. If the circuit works under the limit parameters, it may work abnormally and easily cause damage. The TTL integrated circuit's power supply voltage allows a relatively narrow range of variation, generally between 4.5 and 5.5V, so a + 5V regulated power supply must be used; the CM0S integrated circuit's operating power supply voltage range is relatively wide, and there is a large choice. When selecting the power supply voltage, in addition to first taking into consideration that you must avoid exceeding the limit power supply voltage, you must also note that the level of the power supply voltage will affect the circuit's operating frequency and other performance. If the power supply voltage is low, the circuit operating frequency will decrease or increase the transmission delay time. For example, when the CM0S trigger drops from + 15V to ten 3V, its maximum operating frequency will drop from 10MHz to tens of kHz.

The polarity of the power supply voltage must not be reversed. The positive and negative poles of the power supply are reversed and connected incorrectly, which will cause damage to the device due to excessive current.

The CM0S circuit requires that the amplitude of the input signal cannot exceed VDD ~ VSS, that is, VSS = V1 = VDD is satisfied. When the voltage applied to the input of the CM0S circuit is too high (greater than the power supply voltage) or too low (less than 0V), or the power supply voltage changes suddenly, the circuit current may increase rapidly and the device is burned out. This phenomenon is called thyristor effect. The main measures to prevent the SCR effect are:

The input signal amplitude cannot be greater than VDD and less than 0V;

Eliminate interference on the power supply;

· When conditions permit, reduce the power supply voltage as much as possible. If the circuit operating frequency is relatively low, it is best to use + 5V power supply;

· Add current limiting measures to the power supply used, so that the power supply current is limited to 30mA.

Treatment of redundant input. For the CM0S circuit, the extra input terminals must not be left floating; otherwise, the high voltage generated by electrostatic induction is likely to cause damage to the device. These extra input terminals should be connected to yDD or yss, or connected in parallel with other active input terminals. These three methods of disposal should be determined according to the actual situation.

For the TTL circuit, the excess input terminal is allowed to float. When floating, the logic input state of this terminal is generally treated as "1". Although the floating is equivalent to a high level, it does not affect the logical relationship between the AND gate and the NAND gate. However, the floating is easy to be interfered, which may cause the circuit to malfunction. Therefore, the redundant input end should be properly handled according to actual needs. For example, the redundant input terminals of the AND gate and NAND gate can be directly connected to the power supply; different resistors can also be connected to the power supply through a common resistor; or the redundant input terminals can be used in parallel. The extra input terminals of the OR gate and NOR gate should be directly grounded.

The excess output terminals should be left floating and must not be directly connected to VDD or VSS, otherwise excessive short-circuit current will be generated and the device will be damaged. The output terminals of CM0S circuits with different logic functions cannot be directly connected together, otherwise the turned-on P-channel MOS field-effect transistor and the turned-on N-channel MOS field-effect transistor form a low-resistance path, causing a power short circuit and causing device damage . Except for tri-state gates and open-collector gates, the output terminals of TTL integrated circuits are not allowed to be used in parallel. If the output terminals of several open-collector gate circuits are connected in parallel to realize the "wire-and" function, a pull-up resistor should be connected between the output terminal and the power supply.

Due to the high impedance of the CM0S circuit, it is easy to be punctured by electrostatic induction. In addition to the protection circuit inside the circuit, attention should be paid to electrostatic shielding when using and storing it. When welding the CM0S circuit, the welding tool should be well grounded. The welding temperature should not be too high. It is also impossible to disassemble, unplug, and insert integrated circuits while the power is on.

Multiple models of digital circuits can be used directly interchangeably. For example, the domestic CC4000 series can be used directly with the CD4000 series and MC14000 series. However, for some ICs with the same pin function and package form, the electrical parameters are different. Pay attention when switching.

Pay attention to the design process and enhance anti-interference measures. When designing a printed circuit board, avoid long leads to prevent interference between signals and delays in signal transmission. In addition, the power cord should be designed to be wider, and the ground wire should be grounded in a large area, which can reduce ground noise interference. In the design of CM0S logic system, the capacitive load should be minimized. Capacitive load will reduce the operating speed and increase power consumption of the CM0S integrated circuit.