What does vrm stand for: What Is a VRM? A Basic Definition

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Different types of motherboard VRM — what are the topologies and what to choose
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Published: 29 December 2021

We deal with processor power systems on motherboards

A long time ago, an additional power connector appeared on the motherboard, in addition to the large standard ATX. Next to the processor, you can see a small group of 4 to 8 pins, and sometimes even a couple of these. This is precisely the power for the VRM — the stabilization and power supply system for the processor. In modern motherboards, the components are not particularly considered: they are almost always hidden behind radiators. VRM is one of the most important components, because the processor’s power completely depends on it, and the stable operation of the entire system will depend on how high it is.
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How VRM works

The Voltage Regulator Module is a switching DC/DC converter, more commonly known as a DC-DC converter. Its main part is an inductor, the operation mode of which is regulated by two keys with a capacitor at the output to smooth out ripples.

The work can be divided into 2 cycles: first, one transistor opens, energizing the core of the inductor. On the second cycle, the inductor is disconnected from the input voltage and the core begins to give off energy, an electromotive force arises, which forms the desired reverse polarity voltage at the output of the inductor and is collected in the capacitor.
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A fairly simple circuit allows you to lower the voltage and increase the current strength, moreover, with high efficiency, 90-95%. The use of pulse technology allows you to make the circuit as miniature as possible.

There are usually several such single modules on the motherboard, the exact number is usually indicated in the documentation for the motherboard in terms of the number of phases of the processor power system. Moreover, these modules are really controlled by a special controller with a time shift. The more phases, the more stable the output voltage and the more current the VRM of the motherboard can provide, respectively, the more powerful processor can be used in the finished assembly. The maximum processor power is indicated in the documentation for the motherboard, but as we wrote earlier, it has little to do with the official one and may not correspond to the real one.
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Why such difficulties

The VRM is powered by 12 volts, which is usually the main indicator for computer power supplies. This is the highest voltage that a computer has. From school physics lessons, we know that power is the current multiplied by the voltage, and if the processor has a power of 120 W, then the final consumption along the 12 V line is at the level of 10 amperes, so quite thin wires can be used.

But the processor itself is already powered by voltages of about 1-1.4 volts, respectively, it consumes hundreds of amperes, and with such values ​​\u200b\u200bthe wires to it would look more like a kit for a welding machine. In fact, it is, only all this is done on the motherboard in the form of tracks, and in the processor socket several legs are designed specifically for power, creating the necessary area comparable to the conductor cross section of hundreds of amperes.
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How a large number of VRM phases is achieved

VRM controllers rarely have a different number of phases than 4, and the processor power system itself is a complex balanced device. Achieving high output values ​​by increasing the power of the components themselves is the simplest solution to the problem. But in this case, the VRM will be quite hot, and excess heat in the computer is an eternal headache. Therefore, motherboard manufacturers have learned to solve the shortage in the lines of the control controller in several ways.
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The easiest way is to amplify one phase with two modules, that is, from 4 lines we get 8 lines, but they are not entirely honest. In fact, this is still the same four-phase VRM, just each line now has more power due to an additional module with a choke. And some manufacturers do not even hesitate to give out such a solution as additional phases, but this is not so.

Another way to increase both the power and the number of phases is to install an intermediate frequency doubler chip between additional modules, and not directly, as in the previous example. In this case, we really get a system with an increased number of phases, even if these are not real controller outputs. But such a solution is honest and allows you to get a more linear voltage at the VRM output, besides, the heat dissipation of such a system will be lower: more throttle modules work in turn, and, accordingly, they will emit less heat.
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It will not be superfluous to study which transistors are used in tying the inductor. Often here manufacturers also try to save money. We remember that the inductor is charged with a higher voltage, respectively, with a lower current, and a small voltage is removed from it, but a larger current, so transistors can be of different capacities, this is a fairly common and effective solution. Sometimes the second more powerful transistor is replaced by two, and this does not even look like an attempt to save money. Nevertheless, 2 transistors will eventually heat up less, and not only because a current will flow through them, divided in half between them. The total resistance of two transistors will be less than one, that is, this is also one of the ways to deal with heat generation.
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The most powerful VRMs with their fine tuning are used by manufacturers in overclocking motherboards, designed specifically to meet all the needs of enthusiasts and overclockers. Naturally, to unlock the full potential of the system, you will need a processor with an unlocked multiplier.

Manufacturers themselves are interested in the quality of their products, of course, top gaming motherboards are equipped with better power systems that support overclocking, and when overclocked, the processor needs better and more stable power. This is not required from inexpensive budget boards, and the power supply systems on them are much more modest. In most cases, the motherboard documentation contains all the necessary information and lists of supported processors.
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How do smartwatches, sports trackers and other gadgets measure heart rate? Part 1 / Habr

Hello everyone!

It’s not long before our crowdfunded EMVIO stress watch campaign starts. There was a small respite and fingers were asked to the keyboard.

At the very initial stage of development, we conducted a small analytical review of methods for measuring the pulse in humans and periodically updated it with new projects. I wanted to share this information with the community. We hope that it will be of interest to a wide range of readers and will give an idea of ​​the state of technology in this area. nine0157
In this review, the emphasis is on the use of methods for measuring heart rate in gadgets such as «for fan». Some methods have already been implemented in ready-made mass products, others are waiting in the wings. But first, a few words about what we actually measure and why it is important.

A little about our heart

As you know, the heart is an autonomous muscular organ that performs a pumping function, ensuring a continuous flow of blood in the blood vessels through rhythmic contractions. In the heart there is a site in which impulses are generated responsible for the contraction of muscle fibers, the so-called pacemaker. In the normal state, in the absence of pathologies, this area completely determines the heart rate. As a result, a cardiac cycle is formed — a sequence of contractions (systole) and relaxation (diastole) of the heart muscles, starting from the atria and ending with the ventricles. In general, the pulse is understood as the frequency with which the cardiac cycle is repeated. However, there are nuances in how we register this frequency. nine0011

What do we consider a pulse

In those days when medicine did not have technical diagnostic tools, the pulse was measured in all known ways — by palpation, i.e. put a finger on a certain area of ​​the body and listened to their tactile sensations, and counted the number of pushes of the artery wall through the skin in a certain time — usually 30 seconds or one minute. Hence the Latin name for this effect appeared — pulsus, i.e. beat, respectively, the unit of measurement: beats per minute, beatsperminute (bpm). There are many methods of palpation, the most famous is the feeling of the pulse on the wrist and on the neck, in the area of ​​the carotid artery, which is so popular in the movies. nine0157
In electrocardiography, the pulse is calculated from the signal of the electrical activity of the heart — an electrocardiosignal (ECS) by measuring the duration of the interval (in seconds) between adjacent R teeth of the EXC, followed by conversion to beats per minute using a simple formula: BPM = 60 / (RR-interval) . Accordingly, you need to remember that this is a ventricular pulse, because. the atrial contraction period (PP interval) may vary slightly.

Attention!!! We would like to note an important point right away, which confuses terminology and is often found in comments to articles about gadgets with heart rate measurement. In fact, the pulse, which is measured by the contractions of the walls of blood vessels, and the pulse, which is measured by the electrical activity of the heart, have a different physiological nature, a different shape of the time curve, a different phase shift, and, accordingly, require different registration methods and processing algorithms. nine0172 Therefore, there can be no RR-intervals when measuring the pulse by modulating the volume of blood filling of arteries and capillaries and mechanical vibrations of their walls. And vice versa, it cannot be said that if you do not have RR intervals, then you cannot measure intervals similar in physiological significance to the pulse wave.

How do gadgets measure heart rate?

So, here is our version of an overview of the most common ways to measure heart rate and examples of gadgets that implement them. nine0011

1. Pulse measurement by electrocardiogram

After the discovery at the end of the 19th century of the electrical activity of the heart, it became technically possible to register it. The first, for real, was Willem Einthoven (Willem Einthoven) in 1902, using his megadevice — a string galvanometer (string galvanometer). By the way, he carried out the transfer of ECG over a telephone cable from the hospital to the laboratory and, in fact, implemented the idea of ​​remote access to medical data! nine0157
Three cans of “brine” and an electrocardiograph weighing 270 kg! This is how the method was born, which today helps millions of people around the world.

For his work in 1924 he won the Nobel Prize. It was Einthoven who first received a real electrocardiogram (he invented the name himself), developed the lead system — the Einthoven triangle and introduced the names of the EKS segments. The most famous is the QRS complex — the moment of electrical excitation of the ventricles and, as the most pronounced element of this complex in terms of its time and frequency properties, the R wave.

Painfully familiar signal and RR interval!

In modern clinical practice, various lead systems are used to record the pacemaker: limb leads, chest leads in various configurations, orthogonal leads (according to Frank), etc. From the point of view of measuring the pulse, you can use any leads, because. in a normal EX-R wave in one form or another is present in all leads.

Sports chest pulse sensors

When designing wearable gadgets and various sports simulators, the lead system was simplified to two electrode points. The most famous implementation of this approach is sports chest monitors in the form of a heart rate monitor strap — HRM strap or HRM band. We think that readers who lead a sports lifestyle already have such devices.

An example of the design of the strap and Mister Gadget 80 lvl. Sensor pad — these are two ECG electrodes on different sides of the chest. nine0157
HRM straps from Garmin and Polar are popular on the market, and there are also many Chinese clones. In such straps, the electrodes are made in the form of two strips of conductive material. The strap can be part of the entire device or fastened to it with clip-on fasteners. Heart rate values ​​are usually transmitted via Bluetooth using the ANT+ or Smart protocol to a sports watch or smartphone. It is quite convenient for sports activities, but constant wearing causes discomfort. nine0011

We experimented with such straps in terms of the possibility of assessing heart rate variability, considering them as a standard, but the data coming from them turned out to be very smoothed. Our team member Kvanto25 posted a post on how he figured out the Polar strap protocol and connected it to a computer via the Labview environment.

Two-handed

The next variant of the implementation of the two-electrode system is the spacing of the electrodes into two hands, but without the permanent connection of one of them. In such devices, one electrode is fixed on the wrist in the form of the back wall of a watch or bracelet, and the other is placed on the front of the device. To measure the pulse, you need to touch the facial electrode with your free hand and wait a few seconds. nine0011

An example of a front electrode heart rate monitor (Beurer Heart Rate Monitor)

An interesting device using this technology is the Phyode W/Me bracelet, which has had a successful Kickstarter campaign and is commercially available. There was a post about him on the forum.

PhyodeW/Me Electrode System

The top electrode is combined with the button, so many people, looking at the device from the pictures and reading the reviews, thought that the measurement was done simply by pressing the button. Now you know that on such bracelets, continuous registration with free hands is in principle not possible. nine0011

The advantage of this device is that heart rate measurement is not the main goal. The bracelet is positioned as a means of conducting and controlling breathing techniques, such as an individual trainer. We bought Phyode and lost with it. Everything works as promised, a real ECG is recorded, corresponding to the classic first ECG lead. However, the device is very sensitive to the movements of the finger on the front electrode, it moved slightly and the signal swam. Taking into account the fact that it takes about three minutes to collect statistics, the registration process looks stressful. nine0011

Here is another use of the two-handed principle in the FlyShark Smartwatch project, which is posted on Kickstarter.

Heart rate registration in the FlyShark Smartwatch project. Please hold your thumb.

What else is new in this area? Be sure to mention an interesting implementation of the ECG electrode — capacitive electric field sensor EPIC Ultra High Impedance ECG Sensor manufactured by Plessey Semiconductors.

EPIC capacitive sensor for non-contact ECG recording.

The primary amplifier is installed inside the sensor, so it can be considered active. The sensor is quite compact (10×10 mm), does not require direct electrical contact, therefore, it does not have polarization effects and they do not need to be wetted. We think this solution is very promising for gadgets with EKS registration. We have not yet seen ready-made devices on these sensors.

2. Pulse measurement based on plethysmography

Truly the most common way to measure the pulse in the clinic and at home! Hundreds of various devices from clothespins to rings. The plethysmography method itself is based on the registration of changes in the volume of blood supply to the organ. The result of such registration will be a pulse wave. The clinical possibilities of plethysmography go far beyond the simple determination of the pulse, but in this case it is he who is of interest to us.
Plethysmography-based pulse detection can be implemented in two main ways: impedance and optical. There is a third option — mechanical, but we will not consider it. nine0011

Impedance plethysmography

As the Medical Dictionary tells us, impedance plethysmography is a method for recording and studying pulse fluctuations in the blood filling of vessels of various organs and tissues, based on registering changes in the total (ohmic and capacitive) electrical resistance to high-frequency alternating current. In Russia, the term rheography is often used. This method of registration dates back to the research of the scientist Mann (Mann, 30s) and the domestic researcher Kedrov A.A. (40s). nine0157
Currently, the methodology of the method is based on a two or four-point scheme for measuring volume resistivity and is as follows: a signal with a frequency of 20 to 150 kHz is passed through the organ under study using two electrodes (depending on the tissues under study).

Impedance plethysmography electrode system. Picture from here

The main condition for the signal generator is the constancy of the current, its value is usually chosen no more than 10-15 μA. When the signal passes through the tissue, its amplitude is modulated by a change in blood supply. The second system of electrodes removes the modulated signal, in fact, we have an impedance-voltage converter circuit. With a point-to-point circuit, the electrodes of the generator and receiver are combined. Further, the signal is amplified, the carrier frequency is removed from it, the constant component is eliminated, and the delta we need remains. nine0157
If the device is calibrated (this is a prerequisite for the clinic), then values ​​in Ohms can be plotted along the Y-axis. The result is the following signal.

Examples of ECG time curves, impedance plethysmogram (rheogram) and its derivative during synchronous registration. (from here)

A very revealing picture. Pay attention to where the RR-interval is on the EX, and where is the distance between the peaks, corresponding to the duration of the cardiac cycle on the rheogram. Also note the sharp front of the R wave and the gentle front of the systolic phase of the rheogram. nine0011

Quite a lot of information can be obtained from the pulse curve on the state of the blood circulation of the studied organ, especially synchronously with the ECG, but we only need the pulse. It is not difficult to determine it — you need to find two local maxima corresponding to the maximum amplitude of the systolic wave, calculate the delta in seconds ∆T and then BMP = 60/∆T .

We have not yet found examples of gadgets that use this method. But there is an example of the concept of an implantable sensor to control the blood circulation of an artery. Here is an article about him. The active sensor sits directly on the artery and communicates with the host device via inductive coupling. We think this is a very interesting and promising approach. The principle of operation is clear from the picture. The match is shown for understanding the size 🙂 It uses a 4-point registration scheme and a flexible circuit board. I think, if you wish, you can finish the idea for a wearable micro-gadget. The advantage of this solution is that the consumption of such a sensor is vanishingly small. nine0011

Implantable blood flow and pulse sensor. Looks like a Johnny Mnemonic accessory.

At the end of this section, let’s make a remark. At one time, we believed that the pulse was measured in this way in the well-known startup HealBeGo, since in this device the basic functionality is implemented by impedance spectroscopy, which, in fact, is rheography, only with a variable frequency of the probing signal. In general, everything is already on board. However, according to the description of the characteristics of the device, the pulse in HealBe is measured mechanically using a piezo sensor (more on this method in the second part of the review). nine0011

Optical plethysmography or photoplethysmography

Optical is the most common way to measure heart rate in terms of mass application. The narrowing and expansion of the vessel under the influence of arterial blood flow pulsation cause a corresponding change in the amplitude of the signal received from the output of the photodetector. The very first devices were used in the clinic and measured the pulse from a finger in the lumen or reflection mode. The shape of the pulse curve repeats the rheogram. nine0011

Illustration of the working principle of photoplethysmography

The method was widely used in the clinic and soon the technology was applied in household devices. For example, in compact pulse oximeters that record the pulse and oxygen saturation of the blood in the capillaries of the finger. Hundreds of modifications are made in the world. For the home, for the family, it will do, but it is not suitable for constant wear.

Pulse oximeter and ear clip. Thousands of them!

Available with ear clips and headphones with built-in sensors. For example, this option from Jabra or the new Glow Headphones project. Functionality is similar to HRM straps, but more stylish design, familiar device, hands-free. You will not wear earplugs all the time, but just right for jogging in the fresh air to the music.

Jabra Sport Pulse™ Wireless and Glow Headphones. The pulse is recorded by the intra-ear (in-ear sensor) method.

Breakthrough

The most tempting was the measurement of the pulse from the wrist, because it is such a familiar and comfortable place. The first was the Mio Alpha watch with a successful Kickstarter company.

Product creator Liz Dickinson proudly proclaimed this device the Holy Grail of heart rate measurement. The sensor module was developed by the guys from Philips. To date, this is the highest quality device for continuous measurement of pulse from the wrist using photoplethysmography. nine0011

Next to the world of steel are such worthy things as Basis B1, Samsung Galaxy Gear and Gear Fit, Moto 360 and of course the expected by all fans of apple brands AppleWatch.

You give a lot of different smart watches!

Now we can say that the technology has been worked out and introduced into serial production. In all such devices, the pulse is measured by the reflected signal.

Selecting the wavelength of the emitter

Now a few words on how to choose the wavelength of the emitter. It all depends on the task at hand. The rationale for the choice is well illustrated by the graph of light absorption by oxy and deoxyhemoglobin with curves of the spectral characteristics of the emitters superimposed on it. nine0011

Curve of light absorption by hemoglobin and main emission spectra of pulse photoplethysmography sensors.

The choice of wavelength depends on the fact that we want to measure the pulse and/or oxygen saturation of the blood SO2.

Just a pulse. For this case, the area where the absorption is maximum is important — this is the range from 500 to 600 nm, not counting the maximum in the ultraviolet part. Typically, 525 nm (green) is selected, or with a slight offset of 535 nm (used in the OSRAM SFH 7050 — Photoplethysmography Sensor). nine0011

Green LED pulse sensor is the most common option in smart watches and bracelets. The sensor of the Samsung Galaxy S5 smartphone uses a red LED.

Oximetry. In this mode, it is necessary to measure the pulse and evaluate blood oxygen saturation. The method is based on the difference in absorption of bound (oxy) and non-bound (dezo) oxygen hemoglobin. The maximum absorption of deoxygenated hemoglobin (Hb) is in the “red” (660 nm) range, the maximum absorption of oxygenated (Hb02) hemoglobin is in the infrared (940 nm). To calculate the pulse, a channel with a wavelength of 660 nm is used.

Yellow for EMVIO. For our EMVIO instrument, we chose from two ranges: 525 nm and 590 nm (yellow). In doing so, we took into account the maximum spectral sensitivity of our optical sensor. Experiments have shown that there is practically no difference between them (within the framework of our design and the selected sensor). Any difference is interrupted by motion artifacts, individual skin properties, the thickness of the subcutaneous layer of the wrist and the degree of pressure of the sensor to the skin. We wanted to somehow stand out from the general “green” list and so far settled on yellow. nine0011

Of course, measurements can be taken not only from the wrist. There are non-standard options for choosing a pulse recording point on the market. For example, from the forehead. This approach was used in the project of a smart helmet for cyclists Life beam Smart helmet developed by the Israeli company Lifebeam. In the offers of this company there are also baseball caps and sun visors for girls. If you always wear a baseball cap, then this is your option.

The cyclist is happy not to wear an HRM strap. nine0169