Electronic amplifiers

Electronic amplifiers are devices to increase the power of oscillations without changing their form using electronic lamps and semiconducting triodes (transistors). Electronic amplifiers are widely used in biological and medical research as an integral part of many measuring and recording devices to increase their sensitivity. Such a need arises, in particular, in the measurement and registration of bioelectric activity of organs and tissues on the oscilloscope. Oscilloscope call any device for registration of oscillatory processes in the coordinates of "deviation - time". Industrial devices for reception of electric processes are slavnye (electro-optical) oscilloscopes, containing as yoke of Slavny the galvanometer - loop ortopeediline thin wires with attached mirror between the poles of a powerful magnet. When current passes through a loop with mirror, rotate, and mirror reflected beam falls on a moving film. Common osmyslenie oscilloscopes N-102 have slavnye galvanometer with internal resistance 2-10 Ohm and sensitivity (without amplifiers) about 20 mm deviation of 1 mA current at frequencies up to 900 Hz. Similarly oscilloscopes N-105 write on a wide (120 mm) photo paper, and there is a possibility to use a special ultraviolet paper, giving directly visible record in daylight. Cathode-ray oscilloscopes different systems have as a main element oscillographic pipe - glass bulb, on the one hand with podogretyj cathode (source of free electrons), and on the other screen is coated with phosphor, shining at the point of the fall of the electron beam. Using the "scanner" ray makes the reciprocating motion along the horizontal line, while under the influence of the studied oscillations he rejected vertically. Cathode-ray oscilloscopes industrial types of amplifiers in widely used in medicine as oscilloscopes for visual observation of various oscillatory processes, and in the presence of fotopaslauga - for their registration. There are oscilloscopes ink recording and magnetometry (special recorders) for clinical and physiological studies.
Oscilloscopes are commonly used in clinical and physiological research, demand for full deflection values in tens and hundreds of volts voltage electron beam, electro-mechanical or chernilnikova oscilloscopes) or tens of milliamps of current (electro-optical, or slavnye)that in the thousands and hundreds of thousands of times exceeds the amount of bioelectric vibrations. This contradiction is eliminated by the use of electronic amplifiers.
In connection with the measuring converters of non-electric quantities electric (see Sensors) electronic amplifiers allow you to register different and very weak biophysical and biochemical reactions and processes in a living organism (pulse wave, the colours and the sounds of the heart, blood oxygenation, and others) and pass reinforced oscillations by radio or telephone (see Telemetry). Electronic amplifiers are also used in devices for the formation and strengthening of oscillations of different forms in order to influence on organs and tissues (pacemakers), and also to control the flow of light and sound stimuli (photopolarimeter).
The principle of operation of electronic amplifiers, and as amplifiers of any type, is that subject to strengthen weak vibrations are used to control the flow of energy received from special power source (battery batteries, rectifiers, and so on). As a controlled item (AC electrical resistance) is an electronic lamp, in which the three metal electrode - cathode, anode and managing the grid. For permanent heating of the cathode use an additional source of energy. The anode and cathode lamp is connected to an external circuit, containing the power source and the load. Amplified electrical power fluctuations are served at the input terminals between the grid and the cathode. When no signal is input through the lamp flows DC, and changing the capacity of the grid with respect to the cathode increases or decreases the flow of electrons (this is equivalent to changing the resistance of the lamp).
Depending on the type of load (oscilloscope) and the output values are distinguished cascades (stage) electronic amplifiers: voltage, current and power. With almost one cascade can be obtained gain up to 100 - 200. If you need to have more increased use of multi-stage amplifier in which the output terminals of the previous cascade connected to the input terminals later.
Spread electronic amplifiers on semiconductor triodes (transistors). In the simplest case, a circuit of the transistor similar scheme with electronic lamp. The external circuit include electrodes: the emitter (similar to the cathode) and header (similar to the anode), a control electrode is base (similar to the grid). Voltage gain can reach 100, and capacity - up to 1000 on one cascade. Advantages of semiconductor triodes are small dimensions, long term of operation, absence of power supply for heat (and therefore instant preparation for work), low power consumption, allowing, for example, manufacturing amplifiers and pacemakers the size of a few cubic centimeters for implantation into the chest cavity, sub-miniature transmitters for androdioecious (see) and other purposes.
The main characteristics of electronic amplifiers are: 1) the gain is equal to the product of their gain cascades; 2) frequency and phase response of a graphical or tabular job based amplification and phase shift vibrations from their frequencies; 3) transient response - form image enhanced curve in time supply to the input signal is a rectangular shape; 4) the amplitude characteristics of the dependence of the amplitude of oscillations at the output of the value of the amplitude of the input; 5) the nonlinearity coefficient - deviation amplitude characteristics (in percent) from a straight line; 6) noise level - the value of the effective voltage own noise referred to the input of the amplifier.