[basic] summary knowledge of logic gate circuit

Gate circuit knowledge point

changxuedianzi· 2016-11-24 23:19:10

1 logic gate overview of

implementation basic and common logic operation of electronic circuits, called logic gate circuit. In the digital circuit, the so-called "gate" is the only circuit to achieve the basic logic. The logical relationship is the most basic and, or, not, is the most basic logic gate and gate, or gate and gate. The realization of "and" operation of the call gate, to achieve "or" operation called "non operational" or gate, called the gate, also called inverter, etc.. A logic gate is a basic component in an integrated circuit (also known as an integrated circuit).

2, logic gate circuit composed of

logic gate can use a resistor and a capacitor diode, triode, separation of the original form, as discrete components door. Can the door circuit for all devices and connecting wires fabricated on the same semiconductor substrate, forming the integrated logic gate circuit. A simple logic gate can be made of a transistor. The combination of these transistors can produce a high or low level signal on behalf of two kinds of signals.

3, logic gate circuit

high and low level can represent the logic of the "true" and "false" or the binary 1 and 0, so as to realize the logic operation. Including the common logic gate and gate, or gate, not gate and XOR gate (also known as: exclusive or) etc.. Logic gates can be used in combination to achieve more complex logic operations.

4, logic gate circuit category

is the logic gate circuit in digital circuit the most basic logic element. The so-called door is a kind of switch, it can according to certain conditions to control the signal through or not through. There is a certain logic relation between the input and output of the gate circuit, so the gate circuit is also called the logic gate circuit. The basic logic relation is "with", "or", "non" three. The logic gate circuit can be divided into three categories according to the different internal active devices. The first kind is bipolar transistor logic gate circuit, including several TTL, ECL circuit and I2L circuit type; second is unipolar MOS logic gate circuit, including NMOS, PMOS, LDMOS, VDMOS, VVMOS, IGT and other types; the third category is the combination of the two BICMOS gate circuit. Commonly used is the CMOS logic gate circuit.

(1) TTL Transistor-Transistor Logic that is, BJT-BJT gate, is a commonly used logic gate circuit, digital electronic technology applications, technology is relatively mature. TTL mainly has BJT (Junction Transistor Bipolar that is, bipolar junction transistor, crystal transistor) and resistance, with the characteristics of fast speed. The earliest TTL gate circuit is the 74 series, and later appeared 74H series, 74L series, 74LS, 74AS, 74ALS and other series. However, due to the large power consumption and other shortcomings, TTL is gradually replaced by the CMOS circuit. TTL gate circuit has 74 (commercial) and 54 (military) two series, each series has a number of sub series. TTL level signal is used at most is usually because of data representation using binary rules, +5V is equivalent to logic "1", 0V is equivalent to logic "0", which is called TTL (transistor transistor logic level) signal system, this is the standard communication technology between computer processor control equipment parts.

TTL data signal processor for computer the internal control equipment is ideal, the first computer processor control data transmission equipment for power requirements is not high and the heat loss is low, the other TTL signal directly with the integrated circuit without the need for expensive line driver and receiver circuit; moreover, the internal device data transmission computer processor the control is carried out at high speed, and TTL interface operation can meet this requirement. In most cases, TTL communication is a parallel data transmission mode, and the parallel data transmission is not suitable for more than 10 feet. This is due to the reliability and cost of both sides. Because there are partial and asymmetric problems in the parallel interface, these problems have an impact on the reliability.

(2) CMOS logic gate circuit extremely low power consumption, low cost, wide range of power supply voltage, a logic high, strong anti-interference ability, high input impedance, fanout ability.

logic gate circuit according to the degree of integration it can be divided into: SSI (small scale integrated circuit, each component contains 10 to 20 equivalent gates). MAI (medium scale integrated circuits, each component contains 20 to 100 equivalent gates). LAI (large scale integrated circuit, each component contains 100 to 1000 equivalent gates). VLSI (ultra large scale integrated circuit, each component contains more than 1000 equivalent gate). Commonly used MOS gate circuit has NMOS, PMOS, CMOS, LDMOS, VDMOS and other 5 kinds of. Using N communication enhanced FET logic circuit called NMOS circuit; P channel field-effect transistor logic circuit called PMOS circuit; the CMOS circuit is complementary NMOS and PMOS circuit, logic circuit with lateral double diffused MOS tube called LDMOS logic circuit with vertical double circuit; the diffusion of MOS tube, called VDMOS circuit.

(3 ECL (Emitter Coupled) Logic) is also known as the emitter coupled logic circuit, current mode logic circuit. It is through the transistor gate circuit implementation is coupled to shoot the principle of using operational amplifiers. In all digital circuits, it speeds up, the average delay time can be as small as 1ns tpd. The ECL circuit is composed of a differential pair tube and a pair of radio, so the input impedance is large, the output impedance is small, the driving ability is strong, the signal detection ability is high, the difference output, the ability of anti common mode interference is strong. But because the switch tube of the unit door is in turn, the whole circuit is not "cut off", so the power consumption of the circuit is relatively large.

5, logic gate circuit considerations

two voltage supply voltage: rated voltage and limit the power supply voltage, rated supply voltage to allow the size of supply voltage during normal operation: TTL circuit for 5V. 5% (54 5V 10%); the CMOS circuit is 3 ~ 15V (4000B 3 18V). Extreme operating supply voltage means that the device will be permanently damaged beyond the supply voltage. The TTL circuit is 7V; the 4000 series CMOS circuit is 18V.

high level input voltage should be greater than VIHmin and less than the supply voltage; low level input voltage should be greater than 0V and less than VILmax. Input voltage less than 0V or greater than the supply voltage will be possible to damage the logic circuit.

load requirements 10px margin-bottom:; 10px; list-style-type: none; text-indent: 28px; color: RGB (73, 73, 73); font-family: font-size: 14px; Microsoft YaHei; line-height: 24px; white-space: normal; background-color: RGB (255, 255, 255); "> except OC gate and three state outside the common gate circuit can output and then, otherwise it may burn the device; the output gate number with similar doors shall not exceed the fanout coefficient or it may cause a state. Instability; load in high speed turns less; gate circuit output is connected with the normal load, the output current is less than IOLmax and IOHmax. 4, work and transportation environment problem: temperature, humidity, static electricity will affect the normal operation of the device. 74 series of TTL can work in 0 to 70 DEG C and 54 series of -40 to 125 DEG C, this is the difference between an ordinary military working temperature and working temperature in civilian work; should pay attention to the influence of electrostatic devices, usually by the following method to overcome the influence: the use of anti-static packaging during transportation; when in use, to ensure that equipment good grounding; test device is coupled with the signal should first boot, shutdown disconnect signal after power off.


6, logic gate circuit

(1) for CMOS integrated circuit to shield, usually placed in a metal container, or with a conductive material will pin short, don't put the static high pressure chemical materials or chemical fiber fabric in easy.

(2) welding CMOS circuit in general, 20W internal heating electric soldering iron, and iron have good grounding; can also be quickly welded with waste heat electric iron power; prohibited in the case of electricity welding circuit.

(3) in order to prevent input the protective diode reverse breakdown voltage, the input must be in VDD and Vss, Vdd = VI = Vss.

(4) CMOS test circuit if the signal power supply and power supply circuit, the use of 2 sets of power, in the boot should first turn on the power supply circuit, after the signal power supply. Shutdown, the signal power should be turned off, the power supply circuit, the CMOS circuit itself is not connected to the power supply, the input signal is not allowed to enter.

(5) absolute surplus input can not be vacant, otherwise easy to accept outside interference, destroy the logic relationship between normal, or even damage. The redundant input should be connected Vdd NAND gate and gate, or high level or with the use of input in parallel. For a gate, or gate redundant input should be grounded or low level or with the use of input in parallel.

(6) must be in the other components on the printed circuit board is installed, then installed CMOS circuit, CMOS input circuit to avoid dangling. When the CMOS circuit is pulled out from the printed circuit board, it must first cut off the power supply on the printed circuit board.

(7) input connection long when, due to the influence of distributed capacitance and inductance, easy to constitute LC oscillation or damage protection diodes must be at the end of the input series 1 10 ~ 20 K resistor R.

(8) method for preventing input CMOS the circuit terminal noise is: between the previous stage and CMOS trigger circuit access Schmidt shaping circuit, or join filter capacitor filter noise.


7, logic gate circuit problems of

16px; (1) TTL power supply circuit adopts +5V, when used, can not be reversed and the power supply can not take the wrong, also higher than 5.5V. Otherwise it will damage the device.

(2) input circuit can not the direct connection with low resistance power supply is higher than +5.5V or lower than 0.5V, because of the low resistance power supply larger current and burn out device.

(3) output is not allowed with the power supply or short circuit, must be connected with the power supply through a resistor, in order to improve the output level.

(4) insert or pull out integrated circuit, be sure to turn off the power, otherwise it will permanently damage caused by power supply shock.

(5) extra input terminal the allowable span. The grounding resistance is less than or equal to =500 R.

TTL CMOS" interface, interface circuit the circuit "is used between different types of logic gates or logic gate circuit and the external circuit, so that the two effective connection of the normal work of the intermediate circuit.

(6) CMOS driving circuit TTL circuit: TTL driver circuit with CMOS circuit, the problems need to be solved is the CMOS circuit can not provide enough large drive current. CMOS circuit allows the maximum filling current generally only about 0.4mA, while the TTL circuit input short circuit current Iis is about 1.4mA.

(7) TTL driving circuit CMOS circuit: CMOS circuit wide supply voltage range (3V ~ 18V), are often higher than the +5V power, the TTL circuit so CMOS driver circuit with TTL circuit, must output the high level of TTL increased. Through the interface circuit can reach this goal. 3, TTL and CMOS gate drive other load: on many occasions, often need to drive lights, LED with TTL or CMOS circuit (light emitting diode) or other display, optocoupler, relay, silicon controlled load

Chang electronic (changxuedianzi)

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