Generators and shapers of impulses. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Generators and shapers of impulses. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

Comments on the article

Based on the logic elements of digital devices, a variety of pulse generators can be designed. Here are some specific examples.

The generator according to the circuit in Figure 1 (open-collector 2I-NOT elements are used) generates pulses in a wide frequency range - from units of hertz to several kilohertz. The dependence of the frequency f (kHz) on the capacitance of the capacitor C1 (pF) is expressed by the approximate formula f"3*105/C1. The pulse voltage duty cycle is almost equal to 2. When the power supply voltage is reduced by 0,5 V, the frequency of the generated pulses decreases by 20%.

Generators and shapers of impulses. Generator
Fig. 1

In the generator according to the circuit in Figure 2, the pulse duration can be controlled by a variable resistor R2 (duty cycle varies from 1,5 to 3), and the frequency by resistor R1. For example, in a generator with C1 \u0,1d 2 μF, with the exception of resistor R1, only resistor R8, the frequency of the generated pulses can be changed from 125 to 1 kHz. To obtain a different frequency range, it is necessary to change the capacitance of the capacitor CXNUMX.

Generators and shapers of impulses. Generator circuit
Fig. 2

A wide change in the frequency of the generated pulses (about 50 thousand times) provides a device assembled according to the circuit in Figure 3. The minimum pulse frequency here is about 25 Hz. The duration of the pulses is regulated by the resistor R1. The repetition frequency can be determined by the formula:

f=1/(2R1C1)

f - frequency Hz, R1 - resistance Ohm, C1 - capacitance farad.

Generators and shapers of impulses. Generator circuit
Fig. 3

When implementing digital devices for various purposes, it is often necessary to form short pulses along the fronts of the input signal. In particular, such pulses are used to reset counters as synchronization pulses when writing information to registers, etc. Figure 4 shows the circuit and timing diagrams of a short negative pulse shaper based on a positive voltage drop at its input. When the voltage Uin changes from low to high, this difference without delay enters the input 13 of the element DD1.4. At the same time, at the input 12 of the element DD1.4, a high-level voltage is maintained during the signal propagation time through the elements DD1.1-DD1.3 (about 75 ns). As a result, the output of the device remains low during this time. Then, at the input 12, the voltage is set to a low level, and the output of the device is set to high. Thus, a short negative pulse is formed, the edge of which coincides with the front of the input voltage. In order to use such a device to form a negative pulse at the cutoff of the input signal, it must be supplemented with another inverter (Figure 4).

Pulse generators and shapers
Fig. 4

Figure 5 shows a diagram and a timing diagram of the operation of the pulse shaper along the front and edge of the input signal. The duration of each generated pulse is equal to

tи1=tи2=nt1,0зд.р.+(n+1)t0,1зд.р.

Here n is an even number of elements involved in signal delay. The principle of operation of this shaper is similar to the principle of operation of the previously described short pulse shapers.

The shaper of short pulses has become widespread, the circuit and timing diagram of which are shown in Figure 6. At a low-level voltage at the input of the device, capacitor C1 is charged through resistors R1 and R2. In this case, the output voltage of the device is low. When a high-level voltage appears at the input of the shaper, capacitor C1 begins to discharge through resistor R2. Until the voltage across the capacitor drops to a low level, both inputs of the DD1.2 element, and, consequently, at the output of the shaper, have high voltage levels. As soon as the voltage on the capacitor becomes less than 0,4 V, the level at the output of the shaper changes (Figure 6, b). The pulse duration is proportional to the capacitor discharge time constant and is equal to ti=3R2*С1.

Pulse generators and shapers
Fig. 5

Pulse generators and shapers
Fig. 6

Pulse shapers are also included in the K155 series microcircuits. So, the K155AG1 microcircuit is a single vibrator with three inputs, direct and inverse, outputs and leads for connecting external timing circuits, Figure 7. The single vibrator can be triggered by both positive and negative drops in input signals at a certain voltage, independent of the duration of the input pulses. The one-shot switch is switched by a negative edge of the input signal applied to one of the inputs A, while a high level voltage is applied to the input B, or a positive edge applied to the input B, if a low level voltage is present at one of the inputs A or A1.

Pulse generators and shapers

Pulse generators and shapers
Fig. 7

Pulse generators and shapers
Fig. 8

With the maximum resistance of the resistor Rin = 40 kOhm, the duration of the output pulse should not exceed 0,9T, where T is the repetition period of the input pulses. The duration of the output pulse depends on the resistance Rin=(0-40) kOhm and C=(0-1000) uF and is determined by the formula:

ti=RC1n2. Here R \u2d 2k + Rin, XNUMXk is the resistance of the internal resistor.

The K155 series also includes the K155AGZ chip. It contains two single vibrators in one housing. The options for connecting external timing elements and the timing diagram of the one-shot operation are shown in Figure 8. The one-shot is also triggered either by a negative (input signal drop at input A at a high level at inputs B and R), or positive by a positive voltage drop at input B at a low level at the input A and a high level at the input R. The pulse duration ti1 is determined by the time constant of the timing circuit, but can be reduced by applying a low-level voltage to the input R at ti2 ti1.

Author: -=GiG=-, gig@sibmail; Publication: cxem.net

See other articles Section Beginner radio amateur.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Alcohol content of warm beer 07.05.2024

Beer, as one of the most common alcoholic drinks, has its own unique taste, which can change depending on the temperature of consumption. A new study by an international team of scientists has found that beer temperature has a significant impact on the perception of alcoholic taste. The study, led by materials scientist Lei Jiang, found that at different temperatures, ethanol and water molecules form different types of clusters, which affects the perception of alcoholic taste. At low temperatures, more pyramid-like clusters form, which reduces the pungency of the "ethanol" taste and makes the drink taste less alcoholic. On the contrary, as the temperature increases, the clusters become more chain-like, resulting in a more pronounced alcoholic taste. This explains why the taste of some alcoholic drinks, such as baijiu, can change depending on temperature. The data obtained opens up new prospects for beverage manufacturers, ... >>

Major risk factor for gambling addiction 07.05.2024

Computer games are becoming an increasingly popular form of entertainment among teenagers, but the associated risk of gaming addiction remains a significant problem. American scientists conducted a study to determine the main factors contributing to this addiction and offer recommendations for its prevention. Over the course of six years, 385 teenagers were followed to find out what factors may predispose them to gambling addiction. The results showed that 90% of study participants were not at risk of addiction, while 10% became gambling addicts. It turned out that the key factor in the onset of gambling addiction is a low level of prosocial behavior. Teenagers with a low level of prosocial behavior do not show interest in the help and support of others, which can lead to a loss of contact with the real world and a deepening dependence on virtual reality offered by computer games. Based on these results, scientists ... >>

Traffic noise delays the growth of chicks 06.05.2024

The sounds that surround us in modern cities are becoming increasingly piercing. However, few people think about how this noise affects the animal world, especially such delicate creatures as chicks that have not yet hatched from their eggs. Recent research is shedding light on this issue, indicating serious consequences for their development and survival. Scientists have found that exposure of zebra diamondback chicks to traffic noise can cause serious disruption to their development. Experiments have shown that noise pollution can significantly delay their hatching, and those chicks that do emerge face a number of health-promoting problems. The researchers also found that the negative effects of noise pollution extend into the adult birds. Reduced chances of reproduction and decreased fertility indicate the long-term effects that traffic noise has on wildlife. The study results highlight the need ... >>

Random news from the Archive

Aircraft and climate 18.10.2002

After the terrorist attacks of September 11, 2001, the skies over the United States were closed to civil aviation for three days so that airports could increase security measures.

These three days have given climatologists a unique opportunity to study the effects of high-altitude flight on the weather. One aviation-related factor that can affect the weather is contrails. Such a trace in the form of a white track occurs due to the crystallization of atmospheric moisture in the form of ice on the smallest particles of unburned fuel flying out of the aircraft's turbines.

During the three days that flights were banned, the number of such white lanes in the sky over the United States dropped sharply. On the one hand, any clouds, including traces of aircraft, make it difficult for sunlight to reach the Earth's surface, that is, they must cool the planet. On the other hand, they should also reduce the dissipation of heat into space, delaying the infrared radiation of the Earth.

Based on data from 4000 US weather stations, three days without flights over the entire territory of the country, the usual gap between day and night air temperatures has increased by more than a degree. This happened mainly due to an increase in daytime temperatures, especially over those areas of the United States where air traffic is especially intense on ordinary days. That is, the warming effect of white footprints in the sky prevails over the cooling effect.

Airplane paths now occupy 0,1 percent of the sky above the planet, and by 2050 they will capture 0,5 percent.

Other interesting news:

▪ Non-volatile memory can be made using a virus

▪ Trains instead of planes

▪ Spatters to the rescue

▪ New image recognition processors from Toshiba

▪ Laboratory in a vest pocket

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Riddles for adults and children. Article selection

▪ article Song of the Triumphant Pig. Popular expression

▪ article Which animals showed a positive effect after receiving a placebo? Detailed answer

▪ Berek's article. Legends, cultivation, methods of application