In the case of an amplifier operating with its final, that is, already amplified signal, a direct effect on its output level is manifested. That is, there is a so-called feedback. In fact, for ease of understanding, such a connection can be compared with a train that moves along the ring road and all the cars are attached one after the other without breaking.
So, this feedback is positive when the train accelerates, and negative when it slows down. Of course, these are all conditional concepts, but to make everything clear and reliable, let's look at examples of POS and OOS, not on the example of a train, but in electronics, where they are found.

What is PIC positive feedback

Positive feedback is a type in which a change in the output of the system results in a change in the input signal that causes the output to deviate further from its original value, and in the case of negative feedback, the process is completely reversed.
Many of us have experienced an example of the feedback that occurs when operating a set of PA equipment for performances: when a speaker holds a microphone too close to the speakers, a high-pitched "howl" sound is produced, which is due to the fact that the audio amplifier picks up and amplifies its own noise. This phenomenon is an example of positive or regenerative feedback, as any sound entering the microphone is amplified and turned into an even louder sound from the loudspeaker, and thus a feedback loop is created in which the vibration sustains itself, increasing more and more, resulting in noise is produced at an ever-increasing volume until the system enters a "saturation" state and can no longer amplify the sound.
One might wonder what the possible benefits of feedback in amplifiers are, given such annoying manifestations as the “howling” sound of PA equipment for performances. If we introduce positive or regenerative feedback into the amplifier circuit, then a tendency will be created to generate and maintain oscillations, the frequency of which is determined by the values ​​of the components that feed the feedback signal from the output to the input. This is one way to make a generator, a circuit for getting alternating current from a direct current source. Oscillators are extremely useful circuits, and so feedback can have some practical use.

What is Negative Feedback

Negative feedback, on the other hand, has a “softening” effect on the amplifier: as the amplitude of the output signal increases, the feedback signal counteracts the change in the output signal. While positive feedback makes the system less stable, negative feedback works in the opposite way: the stability of the system only increases.
An amplifier with negative feedback is not only more stable, but it also distorts the input signal to a lesser degree and can generally amplify over a wider frequency range. The trade-off for these benefits (there must be disadvantages of negative feedback, right?) is a reduction in gain. If a portion of the amplifier's output signal "feeds back" to the input, and counteracts any changes in the output signal, then a higher amplitude input signal is required to provide the same output amplitude as before. This is what causes the reduced gain in the presence of negative feedback. In any case, the benefits such as stability, reduced distortion, and wider bandwidth are worth sacrificing some gain.
Consider a simple amplifier circuit and see how we could introduce negative feedback into it (see figure below).

Common emitter open loop amplifier

The diagram shows a common-emitter amplifier in which the bias resistor chain is formed by resistors R1 and R2. The capacitor couples Vin to the amplifier in such a way that the signal source does not have a DC voltage supplied by the voltage divider R1/R2. Resistor R3 serves to control the voltage gain. At maximum voltage gain, this resistor can be omitted, but since such base resistors are often used in common-emitter amplifier circuits, it is shown in the figure.
Like all common-emitter amplifiers, the amplifier shown inverts the amplified input signal. In other words, the rising voltage of the input signal leads to a drop in the output voltage and vice versa. The figure below shows the waveforms on an oscilloscope.

Common Emitter Open Loop Amplifier and Original Waveforms for Comparison

Since the output signal is a mirror image copy of the input signal, any connection between the output (collector) and the input (base) of the transistor (as shown in the figure below) will create negative feedback.

Negative feedback, collector feedback attenuates the output signal

Resistors R1, R2, R3 and Rfeed. together operate in such a way that the voltage at the base of the transistor (with respect to ground) is the average of the input voltage and the feedback voltage, which results in a lower amplitude signal being delivered to the transistor. So the amplifier circuit in the figure above will have a reduced voltage gain, but better linearity (less distortion) and a wider bandwidth.

Summing up about positive and negative feedback (PIC and NF)

Feedback - feeding the output signal of the amplifier to its input.
Positive or regenerative feedback causes the input signal to change in such a way that the output signal deviates from its original value and the system oscillates (AC). The frequency of these oscillations is largely determined by the selection of the components of the feedback circuit.
Negative feedback contributes to the stability of the amplifier, so that changes in the output signal are less for a given input signal than in the absence of feedback. This leads to a decrease in the gain, however, it also gives certain advantages: a decrease in distortion and an increase in the bandwidth (operating frequency range).
Negative feedback can be introduced into a common-emitter circuit by connecting the collector to the base, or by adding a resistor between the emitter and ground.
An emitter-to-ground "feedback" resistor is commonly used in common-emitter circuits as a preventive measure against temperature rise distortion.
Negative feedback also has the advantage that the voltage gain becomes more dependent on the resistor values ​​and less dependent on the characteristics of the transistors themselves.
Common-collector amplifiers have deeper negative feedback due to the presence of a load resistor between the emitter and ground. This feedback provides exceptionally stable gain as well as protection against distortion caused by the temperature rise of the transistors.
The gain of a common-emitter amplifier can be restored without sacrificing distortion immunity by connecting a shunt capacitor in parallel with the emitter "feedback resistor".
If the voltage gain is arbitrarily high (10000 and above), and negative feedback is used to reduce the gain to a reasonable level, then the gain will be approximately equal to Rfeedback. / Rin .. In the presence of feedback, changes in the gain of the transistor? or other component parameters will not have much effect on the voltage gain, resulting in a stable amplifier with a simple design.

Feedback - the impact of the output value of any system C (Fig. 1) on the input of the same system. In a broader sense, feedback is the impact of the results of the functioning of a certain system on the nature of this functioning.

A functioning system, in addition to the output value, can also be affected by external influences (x in Fig. 1). The circuit AB through which feedback is transmitted is called a circuit, line or feedback channel.

Rice. one.

The channel itself may contain some system (D, Fig. 2) that converts the output value in the process of its transmission. In this case, we say that the feedback from the output of the system to its input is carried out with the help of or through the system D.

Rice. 2.

Feedback is one of the most important concepts in electronics and automatic control theory. Specific examples of the implementation of systems containing feedback can be found when studying a wide variety of processes in automatic systems, living organisms, economic structures, etc.

Due to the universality of the concept applicable in various fields of science and technology, the terminology in this area has not been established, and each particular field of knowledge, as a rule, uses its own terminology.

For example, in automatic control systems widely applied concepts of negative and positive feedback, which determine the connection between the output of the system and its input through an amplifying link with a negative or positive gain, respectively.

In the theory of electronic amplifiers, the meaning of these terms is different: feedback is called negative, which reduces the absolute value of the total gain, and positive - increases it.

Depending on the implementation methods in the theory of electronic amplifiers, there are feedback on current, voltage and combined.

Automatic control systems often include additional feedback used to stabilize systems or improve transient processes in them. They are sometimes called corrective and among them are tough(carried out with the help of an amplifying link), flexible(implemented by a differentiating link), isodrome etc.

In various systems, one can always find closed chain of influences. For example, in fig. 2 part C of the system acts on part D, and the latter again on C. Therefore, such systems are also called systems with a closed chain of influences, systems with a closed cycle or a closed loop.

In complex systems, there can be many different feedback loops. In a multi-element system, the output of each element can, in general, affect the inputs of all other elements, including its own input.

Any impact can be considered from three main perspectives: metabolic, energetic and informational. The first is associated with changes in the location, shape and composition of matter, the second - with the transfer and transformation of energy, and the third - with the transfer and transformation of information.

In control theory, only the information side of influences is considered. Thus, feedback can be defined as the transfer of information about the output value of the system to its input, or as the flow of information converted by the feedback link from the output to the input of the system.

The principle of the device is based on the use of feedback automatic control systems (ACS). In them, the presence of feedback provides an increase in noise immunity due to a decrease in the influence of interference (z in Fig. 3) acting in the direct path of the system.

Rice. 3.

If in a linear system with links having transfer functions Kx(p) and K2(p) the feedback circuit is removed, then the image x of the output value x is determined by the following relationship:

If it is required that the output value x be exactly equal to the setting action x*, then the total system gain K(p) = K1(p)K2(p) should be equal to unity, and there should be no interference z. The presence of z and the deviation of K(p) from unity determine the occurrence of the error e, i.e., the difference

For K(p)=1 we have

If we now close the system with the help of feedback, as shown in Fig. 3, the image of the output value x will be determined by the following relationship:

It follows from the relation that for a sufficiently large gain Kx(p) in absolute value, the second term is negligibly small and, therefore, the influence of interference z is negligible. At the same time, the value of the output value x will differ very little from the value of the setting action.

In a closed system with feedback, it is possible to significantly reduce the effect of interference compared to an open system, since the latter does not respond to the actual state of the controlled object, is “blind” and “deaf” to a change in this state.

Let's take an airplane flight as an example. If the aircraft's rudders are set in advance with high accuracy so that it flies in a given direction, and if they are rigidly fixed, then gusts of wind and other random and previously unforeseen factors will knock the aircraft off the desired course.

Only a feedback system (autopilot) is able to correct the position, which is able to compare the given course x * with the actual x and, depending on the resulting mismatch, change the position of the rudders.

Feedback systems are often said to be driven by error e (mismatch). If the link Kx(p) is an amplifier with a sufficiently large gain, then under certain conditions imposed on the transfer function K2(p) of the rest of the path, the closed system remains stable.

In this case, the error e in the steady state can be made arbitrarily small. It is enough for it to appear at the input of the amplifier Kx (p) so that a sufficiently large voltage u is formed at its output, which automatically compensates for the interference and provides such a value of x at which the difference e \u003d x * -x would be sufficiently small. The slightest increase in e causes a disproportionate increase in u. Therefore, any (within practical limits) interference z can be compensated, and, moreover, with an arbitrarily small error value e, a shunting path with a large gain is often called deep.

Feedback in mixed systems also takes place during the functioning of complex systems consisting of objects of different nature, but acting purposefully. These are the systems: operator (human) and machine, teacher and student, lecturer and audience, human and learning device.

In all these examples we are dealing with a closed chain of influences. Through the feedback channels, the operator receives information about the nature of the functioning of the controlled machine, the trainer receives information about the student's behavior and learning outcomes, etc. In all these cases, in the process of functioning, both the content of the information transmitted through the channels and the channels themselves change significantly.

Feedback

Feedback- this is the feedback of the results of the process on its course or of the controlled process on the governing body. Feedback characterizes the systems of regulation and control in wildlife, society and technology. Distinguish positive and negative feedback. Feedback is also classified according to the nature of the bodies and media through which they are carried out. Feedback in complex systems is considered as the transfer of information about the course of the process, on the basis of which one or another control action is generated. In this case, the feedback is called informational. The concept of feedback as a form of interaction plays an important role in the analysis of the functioning and development of complex control systems in wildlife and society, in revealing the structure of the material unity of the world.

Common dual feedback theory, according to which feedback in natural systems is presented in two forms: informational and non-informational. It is believed that the non-informational type is common in inanimate nature, while the informational type appears starting from the organic level of matter. The organization of systems in the living world gives rise to a completely different, new type of development mechanisms, unknown in inanimate nature, containing feedback mechanisms. This is the main feature that distinguishes the living from the non-living.

Thus, an important aspect of control in living systems is the presence of feedback. The principle of feedback is one of the basic principles of self-government, self-regulation and self-organization. Without feedback, the process of self-management is impossible. With the help of feedback, the deviations of the object from the given state themselves form control actions that bring the state of the object to the given one.

Feedback in biology

Representations about regulation by the principle of feedbacks. appeared in biology a long time ago. Already the first hypothesis about reflex reactions (R. Descartes, 17th century, J. Prohaska, 18th century) contained the premises of this principle. In a clearer form, these ideas were developed in the works of C. Bell, I.M. Sechenov and I.P. Pavlov, and later - in the 30-40s. 20th century ON THE. Bernstein and P.K. Anokhin. In the most complete and closest to its modern understanding, the principle of feedback (negative) - as a general principle for all living systems - was formulated by the Russian physiologist N.A. Belov (1912–24) under the name of "parallel-cross interaction" and experimentally studied on endocrine organs by M.M. Zavadovsky, who called it "plus - minus interaction." Belov showed that negative Feedback is a general principle that ensures a tendency towards equilibrium in any (not only living) systems, but, like Zavadovsky, he believed that positive Feedback cannot exist in living systems. Soviet scientist A.A. Malinovsky showed the presence in living systems of all types of O. with. and formulated the differences in their adaptive value (1945–60). Abroad, feedback in biology began to be widely studied after the appearance in 1948 of N. Wiener's book Cybernetics. In the USSR in the 50-60s. 20th century I.I. Schmalhausen successfully applied the idea of ​​feedback in population genetics.

Thus, feedback is the feedback effect of the results of the process on its course. Feedback is a fundamental concept of cybernetics, especially control theory and information theory; Feedback allows you to control and take into account the actual state of the controlled system (ie, ultimately, the results of the control system) and make appropriate adjustments to its control algorithm. Feedback can be positive or negative.

The role of positive and negative feedbacks is different. Negative feedbacks ensure the stability of the functions of living systems, their resistance to external influences. They are the main mechanism of energy and metabolic balance in living systems, population control, self-regulation of the evolutionary process. Positive feedbacks play a positive role of enhancers of vital processes. They play a special role in growth and development. Consider them in more detail.

Negative feedback (NFB)– a type of feedback in which the input signal of the system is changed in such a way as to counteract the change in the output signal.

Negative feedback makes the system more resistant to random parameter changes.

negative feedback is widely used by living systems of different levels of organization - from cells to ecosystems - to maintain homeostasis. For example, in cells, on the principle of negative feedback, many mechanisms for regulating the work of genes are based, as well as the regulation of the work of enzymes (inhibition of the metabolic pathway by the end product). In the body, the system of hypothalamic-pituitary regulation of functions is based on the same principle, as well as many mechanisms of nervous regulation that support individual parameters of homeostasis (thermoregulation, maintaining a constant concentration of carbon dioxide and glucose in the blood, etc.). In populations, negative feedbacks provide abundance homeostasis. The physiological meaning of negative feedback lies in the fact that an increase in a regulated value (for example, the activity of an organ) above a certain limit causes a lowering effect on the part of the subsystem associated with it; a sharp decrease in the controlled value causes the opposite effect.

negative feedback also maintains human body temperature around 37°C.

Man and all living beings, being self-regulating homeostatic systems, live mainly due to negative feedback.

Positive Feedback (POS)– type of feedback in which a change in the output signal of the system leads to such a change in the input signal, which contributes to a further deviation of the output signal from the original value.

positive feedback speeds up the response of the system to a change in the input signal, so it is used in certain situations where a quick response is required in response to a change in external parameters. At the same time, positive feedback leads to instability and the emergence of qualitatively new systems called generators (producers).

Positive feedback mismatches the system, and, ultimately, the existing system is transformed into another system, which is more stable (that is, negative feedbacks begin to act in it).

The action of the non-linear positive feedback mechanism leads to the fact that the system begins to develop in the blow-up mode.

Positive feedback plays an important role in macroevolution. In general, in macroevolution, positive feedback leads to a hyperbolic acceleration of development rates, which creates the effect of a uniform distribution of events on a logarithmic time scale.

At the level of the simplest microorganisms, which do not yet have nerve cells, a feedback channel (perception - response) existed and exists directly on the border separating the external environment of the organism from the internal environment. Based on the now generally accepted theory of the origin of life, let's consider how the feedback worked at the prebiological level. For example: the simplest multimolecular systems - coacervates, already had the beginnings of feedback - the exchange of substances of their internal environment with the external one. Perhaps one of the defining moments in the emergence of life was the formation of a membrane with the rudiments of selective permeability and separating the system from the external environment.

In more detail, the effect of feedbacks can be considered on the example of the growth in the population of some species, for example, small fish, depending on the availability of food (plankton) and the presence of predatory fish. The more food, the more offspring of fish can feed and then give new offspring. With an unlimited amount of food and the absence of predators and diseases in fish, their numbers could increase indefinitely. There is a positive feedback here, which is expressed in the fact that the process of growth of the fish population leads to an even greater (in geometric progression) growth. In the case of the presence of predatory fish, another feedback arises: the number of predators will affect the amount of food for them (the number of small fish). This feedback will be negative. As a result of the action of feedbacks, the abundance in populations is undulating, and fluctuations in abundance will occur around a certain average level.

Bibliography

Danilova V.S. Kozhevnikov N.N. basic concepts of modern natural science: a textbook for universities / V.S. Danilova. - M.: ASPECT PRESS, 2000

Kuznetsov V.I., Idlis G.M., Gutina V.N. Natural science. – M.: Agar, 2001

Tulinov V.D., Nedelsky N.F., Oleinikov B.I. Concepts of modern natural science, M.: MUPC, 2005

Feedback- this is the provision of objective information to a specific employee or unit about the adequacy of their performance of their functions. Subjective feedback such as “You are doing a poor job” or “We appreciate your hard work” is not objective feedback. Adequate feedback should contain objective information about the results of the work of an employee or department: sales units, number of days of absence, quality control results, etc.

Tab. one. Why is it beneficial to use objective feedback?

1. Sufficient data - a typical organization produces a great deal of objective data through financial, accounting and other procedures, reports to higher authorities that can be used in feedback programs.
2. Small investment of time and money - research shows that feedback programs that save an average of $77,000 a year typically cost less than $1,000 to develop and run.
3. Natural Control Connections - Simply frankly providing objective performance data does not require the use of gimmicks such as lotteries or other motivational techniques.
4. Quick results - Immediate implementation of improvements in performance is a common feedback effect.
5. Suitable for any type of organization - Objective feedback can be used in non-profit or government organizations that have strict limits on incentives and rewards.
6. Complements other techniques to increase productivity, productivity - OS is an essential part of studies, management development programs and organizational development activities.

Feedback instructs and motivates, serves as a reward or promises it.

Figure 1 illustrates how feedback in conjunction with a standard and a mechanism for comparing actual performance against the standard can control virtually any system. Let's take a thermostat as an example. By monitoring the room temperature using sensors (similar to the mechanism for comparing the real with the standard), it maintains the optimal one you set (the standard for performing work).

Rice. 1. Functional feedback model

Hierarchy of standards. Feedback control becomes less mechanical when the manager understands that workers are sensitive to various combinations of three types of standards, from general to specific (Figure 1):

1. Fundamental Standards(conceptual or moral).
2. Software standards(decision rules based on the “if-then” principle).
3. Action standards(specific behavior).

Humans differ from machines in their unique ability to understand, formalize, and act on the basis of shared moral standards.

Model of feedback as a process of perception

The impact of feedback on work behavior is more complex than it might seem at first glance (see Figure 2).

Fig.2. Conceptual model of feedback as a process of perception

Feedback Sources

Employees receive feedback from others - colleagues, superiors, subordinates and from people outside the organization. Less obvious, however, is the fact that the task itself is a ready source of objective feedback. For example, some tasks, such as computer programs or flying an airplane, provide feedback to the performer about how well or poorly they perform it. Feedback from a task is effective only if it is perceived as having to do with the actions of the perceiver, and not as a result of technology or other people's actions.

The third source of feedback is the person himself, his Self, but conceit or other perception problems can pollute this source. People with high self-confidence tend to rely more (trust) on personal feedback than those with lower self-confidence. Although conditions vary, a worker can be bombarded from all three sources at the same time. This necessitates the protective functions of perception and cognitive evaluation to help sort out incoming feedback.

Feedback Barriers

As with other stimuli, people selectively perceive feedback. Personal characteristics, such as the need for achievement, may determine the desire for feedback. Researchers of organizational behavior note that workers in organizations of Eastern cultures are more focused on receiving feedback than Western ones. In unexpected situations, the need for feedback increases. Long-term employees are less eager to get feedback than younger professionals. Therefore, managers must consider individual readiness to receive feedback based on personality and situational variables. Feedback should be tailored to the specific recipient.

Feedback: American versus Japanese. In the spirit of harmony in the Japanese tradition, avoiding a direct "no" at almost any cost. They may ask a question, promise to answer some time later, change the subject, and even leave the room abruptly. Another common response is no response at all, dead silence. "It makes Americans feel like they've hit a wall," notes cross-cultural negotiator John Pfeiffer (1988).

feedback sign - characterization of the feedback content in the evaluative sense. Feedback can be positive or negative. In general, people tend to perceive and respond more accurately to positive feedback than negative feedback. Negative or threatening feedback causes the employee to react defensively.

People evaluate feedback factors such as its accuracy, the reliability of the source, the fairness of the performance appraisal system, their own expectations, and the validity of standards. Any feedback that does not overcome one or more of these barriers will be rejected or ignored. Personal experience to a large extent determines the significance of the influence of these factors. Feedback from a source that is not credible based on past relationship experience will be questioned.

Behavioral Outcomes of Feedback

Since feedback is associated with the process of forming the goals of the employee, it includes the following outcomes: direction, effort, perseverance. However, if the fourth outcome in the formation of goals is the formulation of a strategy for achieving the goal (action plan), then the fourth possible outcome of feedback is resistance. Feedback systems that smack of manipulation or fail to pass the test of perception and cognitive evaluation systems will elicit resistance.

Organizational feedback methods cannot be taken for granted, especially in situations of intercultural interactions.

The leader can significantly increase the effectiveness of his influence on subordinates if he follows the suggestions of management consultants on how to properly submit feedback (Table 2).

Tab. 2. How to give feedback correctly

1. Verbal feedback is desirable even when non-verbal feedback is positive.
2. For the formation of complete clarity and confidence of the employee in the correctness of his understanding of the meaning of the verbal message of the leader, non-verbal feedback must confirm the verbal one.
3. Immediate feedback is almost always more effective than delayed feedback.
4. Negative feedback may be better than no feedback, but positive feedback produces better results.
5. People tend to remember what they heard first and last in a feedback message longer.
6. If you want a subordinate to respond to your feedback, you must give it personally, and in many cases, privately to the subordinate.
7. A small amount (amount) of feedback is the cause of little trust and may result in hostility.
8. Lack of feedback is regarded as approval or agreement with existing ideas and behavior.

The last component of the motivation management system is the organizational rewards subsystem. A variety of rewards compensate employees for their costs (efforts, abilities, time, etc.) to achieve organizational goals, and therefore the effectiveness of the remaining components of the system will depend on the correct organization of this subsystem.