EMOS signal extraction device. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Audio equipment

 Comments on the article

The author of the article proposes a new version of the bridge circuit for extracting the EMOS signal for an active loudspeaker. A feature of this bridge is the compensation of the common-mode component in it due to two equal and anti-phase signal voltages acting on the shoulders of the bridge. For such a structure, it is not necessary to use an op-amp with high common-mode rejection.

Electromechanical feedback (EMOS) as a reserve for improving the quality of sound reproduction is still not widely used due to the need for constructive integration of the loudspeaker and amplifier, as well as the complex adjustment of the bridge.

In his article [1], S. Mitrofanov rightly notes the difficulties of balancing the bridge (Wheatstone bridge), where the back-EMF signal of the voice coil of the loudspeaker is emitted. Even when using modern microcircuits. The previously described EMOS amplifiers are prone to self-excitation due to the presence of a common-mode signal that is many times greater than the useful signal in the measuring diagonal of the bridge. The common-mode rejection ratio (CMRR) of the signal in some operational amplifiers reaches 120 dB (at frequencies below 100 Hz). For higher frequencies, it is lower and, in the presence of additional phase shifts of the amplified signal, can lead to self-excitation of the device. The self-excitation of the amplifier with EMOS can be combated by reducing the gain or increasing the depth of the OOS covering the bridge device, however, the efficiency of the EMOS also decreases.

In the version of the balanced bridge proposed by the author [2], it was possible to eliminate a significant drawback of the Wheatstone bridge - the presence of an in-phase component in the output signal. It should be noted that a galvanometer connected directly to the measuring diagonal of the bridge and therefore not sensitive to a common-mode signal served as an indicator of the equilibrium of the Wheatstone bridge. Amplification of the bridge unbalance signal using a differential amplifier connected to the measuring diagonal requires the use of an op-amp with a large common-mode signal suppression.

The bridge device proposed by the author is devoid of a common-mode signal at the output, which makes it possible to create an easily tuned UMZCH with a loudspeaker covered by EMOS. This bridge, like the Wheatstone bridge, consists of four resistances (active or complex), but has two voltage sources of opposite polarity (Fig. 1, a).

In case of equality of |U1| = |U2| the equilibrium condition has the form: R1R3 = R2(R4-R3-R1). If the current through the R1R2 arm is much greater than the current through the R3R4 arm, the signal extraction accuracy increases. If the bridge is used in an alternating current circuit, then the voltages U1 and U2 must change in amplitude synchronously and be antiphase; In this case, the circuit shown in Fig. 1b. The output signal of the inverting amplifier DA1 serves as the second power source of the bridge. When a sinusoidal signal U1 is applied as the bridge supply voltage, for example, the voltage at the output DA1 is phase-shifted relative to U1 by 180°. Thus, if the classical Wheatstone power supply bridge can be called in-phase, then the bridge proposed in [2, 3] should be called anti-phase.

When balancing such a bridge, for example, by selecting a resistor R3, the phase of the output voltage Uout can change relative to the voltage U1 - 0 or 180 °.

On fig. 2 shows a diagram of an experimental UMZCH with EMOS with the selection of a feedback signal in a modified bridge.

The amplifier based on the op-amp DA2 and elements VD1 - VD4, VT1, VT2 with a loudspeaker based on the 4GD-36 electrodynamic head included in the bridge is covered by feedback with the release of the back-emf of the head. The bridge is balanced by a two-stage variable resistor R3 (type SP5-35A) to a voltage at point A of not more than 5 ... 10 mV with a phase corresponding to negative OOS (the position of the moving contacts of the regulator according to the scheme is above the balance point of the bridge). If you go over the equilibrium position of the bridge (when moving the moving contacts below the balance point), the phase of the feedback circuit will change and a positive feedback will occur, as evidenced by the hum of the loudspeaker. It is convenient to set up the bridge using a sine wave generator and an oscilloscope. A sinusoidal signal is fed to the input of the amplifier, the input of the oscilloscope is connected to point A. When adjusting the resistance, it must be borne in mind that first the movable system of the fine resistive element (right according to the diagram) is rotated from stop to stop, and then the movable system of the coarse resistive element is rotated.

By balancing the EMOS signal extraction bridge by adjusting R3, it is necessary to achieve the maximum signal amplitude at point A. An increase in the signal indicates that the bridge is close to equilibrium and, as a result, a decrease in the NF depth. On this setting can be considered complete. Instead of a variable resistor, by measuring its resistance between the extreme terminals (1, 2) and the movable contact (3), you can install the closest constant resistors in terms of resistance. It should be noted that the inductive resistance of the coil of the electrodynamic head is compensated to some extent by the inductance of the wire variable resistor.

The correct operation of EMOS is verified as follows. In a tuned UMZCH with EMOS, connect the oscilloscope input to point B and apply light blows with a stick to the speaker cone. The waveform on the oscilloscope screen will be as shown in Fig. 3a. Then connect the oscilloscope to point A and do the same. The waveform will take the form shown in fig. 3b.

From these oscillograms it can be seen that the OOS signal at point A is in antiphase with the signal generated by the loudspeaker coil (point B).

Literature

1. Mitrofanov S. Amplifier with EMOS on integrated circuits. - Radio, 1976, No. 6, p. 32, 33.
2. RF patent No. 2138056 (author L. B. Mashkinov). - Bulletin "Discoveries, inventions,...", 1999, No. 26
3. Mashkinov L. Measuring bridge. - Devices and systems, 2001, No. 3, p. 35.

Author: L.Mashkinov, Chernogolovka, Moscow region

See other articles Section Audio equipment.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Walking is good for the brain 05.05.2017 Ernest Greene and colleagues at New Mexico Highland University have found that simply walking activates your brain - hitting your foot while walking sends pressure waves through your arteries that significantly alter and can increase blood flow to your brain. Until recently, it was believed that the blood supply to the brain (cerebral blood flow or CVD) is automatically regulated by the body and more or less independent of changes in blood pressure caused by exercise or stress. It has previously been determined that the impact of the foot during running (4-5 G) causes significant retrograde (reverse) waves through the arteries, which are synchronized with heart rate and stride speed to dynamically regulate blood flow to the brain. In this study, researchers used a non-invasive ultrasound method to measure carotid internal velocity waves and artery diameters to calculate cerebral blood flow in both hemispheres of the brain of 12 healthy young adults while standing still and walking uniformly at a speed of 1 m/sec. It turned out that while the pressure on the foot during walking is weaker than during running, walking still generates large pressure waves in the body, which significantly increase blood flow to the brain. Although the effect of walking on cerebral blood flow was less significant than that caused by running, it was more pronounced than that observed during cycling, which does not affect the foot at all. "New evidence now suggests that blood flow to the brain is highly dynamic and directly dependent on cyclic aortic pressures that interact with retrograde pressure impulses from exposure to the legs," the authors state. pressure on pedals, walking and running. It is hypothesized that these actions may optimize perfusion, function, and overall sense of well-being during exercise." "It's amazing that it took us so long to finally measure this apparent hydraulic effect on cerebral blood flow," explained Ernest Greene. rhythm (about 120 per minute) when we move vigorously.

Other interesting news:

▪ Ball lightning is modeled

▪ Neurostimulation helps with chronic pain

▪ Neurons learn new things without forgetting the old

▪ The Japanese are preparing new types of digital video recorders

▪ Mandatory disposal of satellites

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Reference materials. Article selection

▪ article God deliver us from such judges. Popular expression

▪ article Which country manufactures weapons with different rifling than the rest of the world? Detailed answer

▪ Article Head of Public Relations Department. Job description

▪ article Three-channel high temperature alarm. Encyclopedia of radio electronics and electrical engineering

▪ article Simple lathe. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024