What main types of signals do you know? Signal shapes. Main types of signals and their mathematical description

The purpose of radio-electronic devices, as is known, is to receive, transform, transmit and store information presented in the form of electrical signals. Signals operating in electronic devices, and accordingly the devices themselves, are divided into two large groups: analog and digital.

Analog signal- a signal that is continuous in level and in time, i.e. such a signal exists at any time and can take any level from a given range.

Quantized signal- a signal that can only take on certain quantized values ​​corresponding to quantization levels. The distance between two adjacent levels is the quantization step.

Sampled signal- a signal whose values ​​are specified only at moments of time, called sampling moments. The distance between adjacent sampling instants is the sampling step. At constant, Kotelnikov’s theorem is applicable: , where is the upper limit frequency of the signal spectrum.

Digital signal- a signal quantized in level and discretized in time. The quantized values ​​of a digital signal are usually encoded with some code, with each sample selected during the sampling process being replaced by the corresponding code word, the symbols of which have two meanings - 0 and 1 (Fig. 2.1).

Typical representatives of analog electronics devices are communications, radio broadcasting, and television devices. The general requirements for analog devices are minimal distortion. The desire to meet these requirements leads to more complex electrical circuits and device designs. Another problem of analog electronics is achieving the necessary noise immunity, because noise in an analog communication channel is fundamentally irreducible.

Digital signals are generated by electronic circuits, the transistors in which are either closed (the current is close to zero) or completely open (the voltage is close to zero), so they dissipate little power and the reliability of digital devices is higher than that of analogue ones.

Digital devices are more noise-resistant than analog devices, since small extraneous disturbances do not cause erroneous operation of the devices. Errors appear only with such disturbances that a low signal level is perceived as high, or vice versa. In digital devices, you can also use special codes to correct errors. Analogue devices do not have this option.

Digital devices are insensitive to the spread (within acceptable limits) of the parameters and characteristics of transistors and other circuit elements. Error-free digital devices require no configuration and are fully repeatable. All this is very important in the mass production of devices using integrated technology. The cost-effectiveness of production and operation of digital integrated circuits has led to the fact that in modern radio-electronic devices not only digital, but also analog signals are subject to digital processing. Digital filters, regulators, multipliers, etc. are common. Before digital processing, analog signals are converted to digital using analog-to-digital converters (ADCs). Inverse conversion - restoration of analog signals from digital ones - is performed using digital-to-analog converters (DACs).

With all the variety of problems solved by digital electronics devices, their functioning occurs in number systems that operate with only two digits: zero (0) and one (1).

The operation of digital devices is usually clocked a sufficiently high-frequency clock generator. During one clock cycle, the simplest microoperation is implemented - reading, shifting, logical command, etc. Information is presented in the form of a digital word. Two methods are used to transmit words - parallel and serial. Sequential coding is used when exchanging information between digital devices (for example, in computer networks, modem communications). Information processing in digital devices is implemented using parallel information coding, which ensures maximum performance.

The elemental base for building digital devices consists of integrated circuits (ICs), each of which is implemented using a certain number of logical elements - the simplest digital devices that perform elementary logical operations.

Analog signal is a continuous function of a continuous argument, i.e. defined for any value of the independent variable. Sources of analog signals, as a rule, are physical processes and phenomena that are continuous in their development (the dynamics of changes in the values ​​of certain properties) in time, in space or in any other independent variable, while the recorded signal is similar (analogous) to the process generating it. An example of a mathematical notation for a specific analog signal: y(t) = 4.8exp[-( t-4) 2 /2.8]. An example of a graphical display of this signal is shown in Fig. 2.2.1, while both the numerical values ​​of the function itself and its arguments can take on any values ​​within certain intervals y£1 y £ y 2,t£1 t £ t 2. If the intervals of signal values ​​or its independent variables are not limited, then by default they are assumed to be equal to -¥ to +¥. The set of possible signal values ​​forms a continuous space in which any point can be determined with infinite accuracy.

Rice. 2.2.1. Graphical display of the signal y(t) = 4.8 exp[-( t-4) 2 /2.8].

Discrete signal in its values ​​it is also a continuous function, but defined only by discrete values ​​of the argument. According to the set of its values, it is finite (countable) and is described by a discrete sequence y(n×D t), Where y£1 y £ y 2,D t- interval between samples (signal sampling interval), n = 0, 1, 2, ..., N– numbering of discrete reading values. If a discrete signal is obtained by sampling an analog signal, then it represents a sequence of samples, the values ​​of which are exactly equal to the values ​​of the original signal in coordinates n D t.

An example of sampling an analog signal shown in Fig. 2.2.1, is shown in Fig. 2.2.2. At D t= const (uniform data sampling) a discrete signal can be described by the abbreviated notation y(n).

When the signal is unevenly sampled, the designations of discrete sequences (in text descriptions) are usually enclosed in curly brackets - ( s(t i)), and the reading values ​​are given in the form of tables indicating the coordinate values t i. For short, uneven number sequences, the following numerical description is also used: s(t i) = {a 1 , a 2 , ..., a N}, t = t 1 , t 2 , ..., t N.

Digital signal quantized in its values ​​and discrete in its argument. It is described by a quantized lattice function y n = Q k[y(n D t)], Where Q k- quantization function with the number of quantization levels k, while the quantization intervals can be either uniform or uneven, for example, logarithmic. A digital signal is specified, usually in the form of a numeric array of successive values ​​of the argument at D t = const, but, in the general case, the signal can also be specified in the form of a table for arbitrary argument values.

Essentially, a digital signal is a formalized version of a discrete signal when the values ​​of the latter are rounded to a certain number of digits, as shown in Fig. 2.2.3. In digital systems and in computers, a signal is always represented with an accuracy of up to a certain number of bits and therefore is always digital. Taking these factors into account, when describing digital signals, the quantization function is usually omitted (implied uniform by default), and the rules for describing discrete signals are used to describe signals.

Rice. 2.2.2. Discrete signal Fig. 2.2.3. Digital signal

y(n D t) = 4.8 exp[-( n D t-4) 2 /2.8], D t= 1. y n = Q k,D t=1, k = 5.

In principle, an analog signal recorded by appropriate digital equipment can also be quantized in its values ​​(Fig. 2.2.4). But it makes no sense to separate these signals into a separate type - they remain analog piecewise continuous signals with a quantization step, which is determined by the permissible measurement error.

Most of the discrete and digital signals you deal with are sampled analog signals. But there are signals that initially belong to the discrete class, for example gamma rays.

Rice. 2.2.4. Quantized signal y(t)= Q k, k = 5.

Spectral representation of signals. In addition to the usual time (coordinate) representation of signals and functions, when analyzing and processing data, the description of signals by frequency functions is widely used, i.e. by arguments inverse to the arguments of the time (coordinate) representation. The possibility of such a description is determined by the fact that any signal, no matter how complex in its shape, can be represented as a sum of simpler signals, and, in particular, as a sum of the simplest harmonic oscillations, the totality of which is called the frequency spectrum of the signal. Mathematically, the signal spectrum is described by functions of the amplitude values ​​and initial phases of harmonic oscillations using a continuous or discrete argument - frequency. The amplitude spectrum is usually called amplitude-frequency response(frequency response) of the signal, spectrum of phase angles – phase-frequency response(FCHH). The description of the frequency spectrum displays the signal as unambiguously as the coordinate description.

In Fig. Figure 2.2.5 shows a segment of the signal function, which is obtained by summing the constant component (the frequency of the constant component is 0) and three harmonic oscillations. The mathematical description of the signal is determined by the formula:

Where A n= (5, 3, 6, 8) - amplitude; fn= (0, 40, 80, 120) - frequency (Hz); φ n= (0, -0.4, -0.6, -0.8) - initial phase angle (in radians) of oscillations; n = 0,1,2,3.

Rice. 2.2.5. Temporal representation of the signal.

The frequency representation of this signal (signal spectrum in the form of frequency response and phase response) is shown in Fig. 2.2.6. Please note that the frequency representation of a periodic signal s(t), limited in the number of harmonics of the spectrum, is only eight samples and is very compact compared to the continuous time representation, defined in the interval from -¥ to +¥.

Rice. 2.2.6. Frequency representation of the signal.

Graphic display analog signals (Fig. 2.2.1) do not require any special explanation. When graphically displaying discrete and digital signals, either the method of direct discrete segments of the corresponding scale length above the argument axis is used (Fig. 2.2.6), or the method of an envelope (smooth or broken) based on sample values ​​(dotted curve in Fig. 2.2.2). Due to the continuity of fields and, as a rule, the secondary nature of digital data obtained by sampling and quantization of analog signals, we will consider the second method of graphic display to be the main one.

What is an electrical signal and what is it used for? Let's discuss in this article.

A signal is something that can be transmitted through space and time. So, what conditions must exist to call a signal a “signal”?

Firstly, with The signal must be created (generated) by someone.

Secondly, the signal must be intended for whom.

Thirdly, someone must accept this signal and draw some conclusions for themselves, that is, interpret the signal correctly.

Let's plunge into the Wild West.

I think it's no secret that the Indians lit a fire, and the smoke from the fire was used to transmit a signal. This means that in our case the fire is a signal generator. So, the first point works).Who was the smoke from the fire intended for? For cowboys? Of course not! For our own Indians. So point two works. Okay, you saw two columns of smoke rising into the sky. Does this mean anything to you? Someone is probably grilling kebabs? May be. But if you approach these fires, then they will make a shashlik out of you). For the Indians, these two columns of smoke meant that their detachment had successfully hunted cowboys ;-). Well, the third rule has been fulfilled ;-).

But what is an electrical signal? I am tormented by vague doubts that somewhere there is an electric current involved :-). How is electric current characterized? Well, of course, voltage and current. The most remarkable thing is that electric current is very convenient to transmit through space using wires. In this case, its speed of propagation will be equal to the speed of light. Although the electrons in the conductor move at a speed of only a few millimeters per second, the electric field immediately covers the entire wire at the speed of light! And as you remember, the speed of light is 300,000 kilometers per second! Therefore, the electron at the other end of the wire will almost immediately begin to move.

Transmission of electrical signals

So, we will use wires to transmit a signal through space. A little higher we examined the conditions for the occurrence of a signal. So, first of all, we need a generator of these signals! That is, it could be some kind of battery or circuit that would generate electric current. Next, there must be someone who would receive this signal. This could be some kind of load, such as a light bulb, a heating element, or an entire circuit that would receive this signal. And thirdly, the load must somehow react to this signal. The light bulb must emit light, the heating element must warm up, and the circuit must perform some function.

As you understand from all of the above, the main trump card of a signal is its generator. So, as we have already discussed, two parameters of electric current can be transmitted through wires - this is voltage and current. That is, we can create a generator that would change either its voltage or current in the load, which would cling through the wires to this generator. Basically, in electronics it is the “voltage” parameter that is used, since the voltage is easy to obtain and change its value.

Time and electrical signal

As I said, the signal is transmitted in time and space. That is, time is an important parameter for an electrical signal. Now we will have to sweat a little and remember the mathematics and physics course for high school. Let's remember the Cartesian coordinate system. As you remember, we plotted the Y axis vertically and the X axis horizontally:

In electronics and electrical engineering, we plot time along X, let's call it t, and vertically we plot voltage, call it U. As a result, our coordinate system will look like this:

A device that shows us the change in voltage over time is called oscilloscope, and the graph of this voltage is called oscillogram. An oscilloscope can be:

or analog:

Types of electrical signals

D.C

What electrical signal is the simplest signal in electronics? I think it's DC signal. What does direct current mean? This is a current whose voltage value does not change over time. How does it look on our graph? Something like this:

Here we see a 3 volt DC signal.

Vertically we have voltage in volts, and horizontally – well, let’s say, in seconds. Direct current always has the same voltage value over time, so it doesn’t matter whether we count in seconds or in hours. The tension neither jumped nor fell. It was 3 Volts and remains so. That is, we can say that the direct current signal is a straight line parallel to the time axis t.

This is what a DC signal looks like on an analog oscilloscope

What kind of electric current generators can produce such a constant voltage signal?

These are, of course, different batteries

mobile phone batteries

for laptop

car batteries

and other chemical current sources.

In laboratory conditions, it is easier to obtain a constant voltage from an alternating voltage. A device that can do this is called a laboratory constant voltage power supply.

Noise signal or just noise

What will happen if the tension becomes chaotic? You'll get something like this:

This electrical signal is called noise.

I think this is the first time some of you are seeing a noise waveform, but I am 100% sure that everyone heard the sound of this signal ;-). Well, click on Play ;-)

The hiss of a radio receiver or an old TV that is not tuned to a station or any channel is noise ;-) No matter how strange it may sound, such a signal is also very often used in electronics. For example, you can assemble a frequency jammer circuit that would extinguish all television and radio receivers within a kilometer radius). That is, we generate a noise signal, amplify it and send it on the air ;-) As a result, we jam all the transceiver equipment.

Sine wave

The sine wave is the most favorite signal among electronics engineers.

Everyone loves to swing on a swing?

Here we see a girl happily swinging on them. But suppose she doesn’t know the trick that you can swing yourself by bending and straightening your legs in time. Therefore, the girl’s father came and pushed his daughter forward.

The graph below shows exactly this case.

As you can see, the girl's trajectory through time turned out to be very funny. This movement schedule is called “ sine wave“. In electronics, such a signal is called sinusoidal. It seems like a painfully simple graph, but you won’t believe it, it’s this simple sine wave that all electronics are built on.

Because sine wave repeats its shape throughout the entire time, then it can be called periodic. That is, you eat lunch periodically - in periods - equal periods of time. It's the same here. This signal periodically repeats itself. Important parameters of periodic signals are amplitude, period and frequency.

Amplitude (A) – maximum voltage deviation from zero to a certain value.

Period (T) – time during which the signal is repeated again. That is, if you have lunch today at 12:00, tomorrow also at the same time, at 12:00, and the day after tomorrow also at the same time, then your lunch takes place over a period of 24 hours. Everything is elementary and simple ;-)

Frequency (F) – it’s just a unit divided by a period, that is

Measured in Hertz. Explained as “so many vibrations per second.” Well, that's enough to start with for now ;-).

As I already said, the sine wave plays a very important role in electronics. You don't even have to go far. It is enough to stick the oscilloscope probes into your home outlet, and you can already observe a sinusoidal signal with a frequency of 50 Hertz and an amplitude of 310 Volts.

Square wave

Very often in electronics a rectangular signal is used:

The square wave in the figure below, where the pause time and the duration time of the signal are equal, is called meander.

Triangle signal

Close friends of the sine wave are triangle signal

The triangle signal has a very close sidekick - this sawtooth signal

Complex signal

Also used in electronics complex signals. Here, for example, is one of them (I drew it out of the blue):

All these signals refer to periodic signals, since for them you can specify period, frequency following and amplitude the signals themselves:

Bipolar signals

For signals that “break through the floor,” that is, they can have a negative voltage value, such as these signals

In addition to period and amplitude, they have one more parameter. It's called scope or double amplitude. In bourgeois language it sounds like amplitude Peak-to-peak, which literally translates as “amplitude from peak to peak.”

Here is the double amplitude for a sine wave (2A)

but for a triangular signal:

Most often it is designated as 2A, which tells us that this is a double amplitude signal.

Pulse signals

There are also signals that do not obey the periodic law, but also play an important role in electronics.

Impulses- these are the same signals, but they do not obey the periodic law, and change their meaning depending on the situation.

For example, here is a series of impulses:

Each pulse has a different duration in time, so we cannot talk about any periodicity of the signals.

Beep

There is also a sound signal

Although it looks like white noise, it carries information in the form of sound. If such an electrical signal is applied to the dynamic head, then you can hear some kind of recording.

Conclusion

Currently, electrical signals play a very important role in radio electronics. Without them, no electronics would exist, let alone digital ones. Currently, digital electronics has reached its zenith, thanks to digital signals and complex coding systems. The data transfer speed is simply stunning! This can be gigabytes of information per second. But it all once began with a simple telegraph...

A signal is a material carrier of information (data) that is transmitted from a source to a consumer. May represent physical signals or mathematical models.

Signals can be analog or discrete.

An analog (continuous) signal is reflected by some physical quantity that changes in a given time interval, for example, timbre or sound intensity.

Let's give an example of a continuous message. Human speech transmitted by a modulated sound wave; the signal parameter in this case is the pressure created by this wave at the location of the receiver - the human ear.

A discrete (digital) signal is composed of a countable set of information elements.

The signal parameter takes a finite number of values ​​sequential in time.

The set of the smallest elements of a discrete signal is called an alphabet, and the discrete signal itself is also called a message.

The message transmitted using such signals is discrete.

The information transmitted by the source is discrete.

An example of a discrete message could be the process of reading a book, the information in which is presented in text, i.e. a discrete sequence of individual icons (letters).

The analog signal can be converted to discrete. This process is called discretization.

A continuous message can be represented by a continuous function defined on a certain segment [a, b] (Fig. 2.1). A continuous message can be converted into a discrete message (this procedure is called sampling).

To do this, from the infinite set of values ​​of this function (signal parameter), a certain number is selected, which can approximately characterize the remaining values. The resulting sequence of function values ​​y 1, y 2, ... y n. is a discrete representation of a continuous function, the accuracy of which can be improved indefinitely by reducing the lengths of segments partitioning the range of values ​​of the argument.

Thus, any message can be represented as discrete, in other words, a sequence of characters of some alphabet.

The ability to sample a continuous signal with any desired accuracy (to increase the accuracy, it is enough to reduce the step) is fundamentally important from the point of view of computer science. A computer is a digital machine, that is, the internal representation of information in it is discrete. Discretization of the input information (if it is continuous) makes it suitable for computer processing.

Signal coding

To automate work with data belonging to different types, it is very important to unify their form of presentation - for this, coding is usually used, that is, expressing data of one type through data of another type.

Signal encoding means:

· its presentation in a certain form, convenient or suitable for subsequent use of the signal;

· a rule that describes the mapping from one set of characters to another set of characters.

Both individual characters of the original alphabet and their combinations are subject to coding.

Let's give an example.

A table of correspondences between natural numbers of three number systems is given.

This table can be considered as a certain rule that describes the mapping of a set of decimal number system characters into binary and hexadecimal. Then the original alphabet is the decimal digits from 0 to 9, and the code alphabets are 0 and 1 for the binary system; numbers from 0 to 9 and symbols (A, B, C, D, E, F) - for hexadecimal.

Types of coding depending on the purposes of coding.

1. Pattern coding is used whenever information is entered into a computer for its internal representation.

This type of coding is used to represent a discrete signal on a particular computer medium.

Most codes used in computer science for pattern encoding are uniform in length and use binary to represent the code (and possibly hexadecimal as a means of intermediate representation).

This type of coding uses:

a) direct codes.

They are used to represent numerical data in a computer and use the binary number system. Can be used to encode non-numeric data.

b) ASCII codes.

The most common is the ASCII code (American Standard Code for Information Interchange), which is used for the internal representation of symbolic information in the MS DOS operating system, in Notepad in the Windows’xx operating system, as well as for encoding text files on the Internet.

c) codes that take into account the frequency of symbols.

In some encoding systems, the value of the code is determined by the frequency of the symbol being encoded. As a rule, such frequencies are known for the letters of the alphabets of natural languages, for example, English or Russian, and have been used for a long time when placing keyboard keys: the most frequently used letters are located on the keys in the middle of the keyboard, the most rarely used ones are on the periphery, which creates ease of operation for person.

2. Cryptographic coding, or encryption, is used when it is necessary to protect information from unauthorized access.

3. Efficient, or optimal, coding is used to eliminate redundancy of information, i.e. reducing its volume, for example, in archivers.

To encode the symbols of the original alphabet, binary codes of variable length are used: the higher the frequency of the symbol, the shorter its code.
The efficiency of the code is determined by the average number of binary digits for encoding one character.

4. Noise-protective, or noise-resistant, coding is used to ensure a given reliability in the case when interference is imposed on the signal, for example, when transmitting information over communication channels.

A binary code of constant length is used as the base code that is subjected to anti-noise coding. Such source (base) code is called primary because it is subject to modification.

Data

The term "data"

Data means:

1) presentation of information in a formalized (encoded) form that allows it to be stored, transmitted or processed using technical means;

2) registered signals.

Data carriers can be:

· paper is the most common medium. Data is recorded by changing the optical characteristics of its surface;

· CD-ROM. Changes in optical properties are used in devices that record with a laser beam on plastic media with a reflective coating;

· magnetic tapes and disks – use changes in magnetic properties.

Data Operations

You can perform various operations with data:

· data collection – accumulation of data in order to ensure sufficient completeness of information for decision-making;

· formalization of data - bringing data coming from different sources to the same form in order to make them comparable to each other, that is, to increase their level of accessibility;

· data filtering – filtering out “extra” data that is not necessary for decision-making; at the same time, the level of “noise” should decrease, and the reliability and adequacy of the data should increase;

· data sorting – ordering data according to a given criterion for ease of use; increases the availability of information;

· data grouping – combining data according to a given characteristic in order to improve ease of use; increases the availability of information;

· data archiving – organizing data storage in a convenient and easily accessible form; serves to reduce the economic costs of data storage and increases the overall reliability of the information process as a whole;

· data protection – a set of measures aimed at preventing the loss, reproduction and modification of data;

· data transportation – reception and transmission (delivery and supply) of data between remote participants in the information process; in this case, the data source in computer science is usually called a server, and the consumer is called a client;

· data transformation – transferring data from one form to another or from one structure to another.

Signals - carriers information in automation tools can differ both in physical nature and parameters, and in the form of information presentation. Within the framework of the State Instrumentation System (GSP), the following types of signals are used in the serial production of automation equipment:

Electrical signal (voltage, strength or frequency of electrical current);

Pneumatic signal (compressed air pressure);

Hydraulic signal (pressure or differential pressure of fluid).

Accordingly, within the framework of the GSP, electrical, pneumatic and hydraulic branches of automation equipment are formed

According to the form of information presentation, the signal can be analog, pulse or code.

Analog signal characterized by current changes in any physical carrier parameter (for example, instantaneous values ​​of electrical voltage or current). Such a signal exists at almost any given moment in time and can take any value within a given range of parameter changes.

Pulse signal characterized by the presentation of information only at discrete moments in time, i.e. the presence of time quantization. In this case, information is presented in the form of a sequence of pulses of the same duration, but different amplitudes (pulse amplitude modulation of the signal) or the same amplitude, but different durations (pulse width modulation of the signal).

Code signal is a complex sequence of pulses used to transmit digital information. Moreover, each digit can be represented as a complex sequence of pulses, i.e. code, and the transmitted signal is discrete (quantized) both in time and in level.

Optical signal– a light wave that carries certain information. The peculiarity of a light wave in comparison with a radio wave is that, due to its short wavelength, it can practically carry out the transmission, reception and processing of signals modulated not only in time, but also in spatial coordinates. This allows you to significantly increase the amount of information introduced into the optical signal. The optical signal is a function of four variables (x,y,z,t) - 3 coordinates and time. An electromagnetic wave is a change in time and at each point in space of electric and magnetic fields, which are interconnected according to the law of induction. An electromagnetic wave is characterized by mutually perpendicular vectors of electric E and magnetic H fields, which change over time according to the same harmonic law.