ISOLOOP MAGNETIC COUPLERS

Varun kumar pathak 7th sem.(Elect. Engg.) Roll no.:0201EE081056

Submitted by:Submitted to:Mr. Ashish choubeyLecturerElect.Engg. Dept.

INTRODUCTION•A coupler is an an electronic circuit which is used to couple or (isolate) two pieces of an electronic equipment or two different euipments. •The couplers transmit signals and data between two circuits without any electrical connection.•conventional optocouplers take up a lot of space,are slow and have limitation on temperature range.Their age is also less.•Isoloop magnetic couplers are similar to optocoupler in many ways. They are galvanically isolated data couplers with integrated signal conversion in a single IC.My presentation will give a brief study about “ISOLOOP MAGNETIC COUPLERS”.

REQUIREMENT OF COUPLERSTo transmit data between two electronic

circuits without any electrical connection often this is because the source and destination are at different voltage levels, like a microprocessor which is operating from 5V DC but being used to control a triac which is switching 240V AC. In such situations the link between the two must be an isolated one, to protect the microprocessor from overvoltage damage.

When equipment using different power supplies is tied together (with a common ground connection) there is a potential for ground loop currents to exist. This is an induced current in the common ground line as a result of a difference in ground potentials at each piece of equipment. Normally all grounds are not in the same potential.

OTHER SIMILAR DEVICES1. Mechanical Relays can also provide

isolation, but even small relays tend to be fairly bulky compared with ICs. Because relays are electro-mechanical, they are not as reliable and are only capable of relatively low speed operation.

2. Transformer is similar, but only for AC but Magnetic coupler can be used for DC.

Where small size, higher speed and greater reliability are important, a much better alternative is to use a magnetic coupler. It consists of an on chip microscopic coil that generates a magnetic field and a GMR sensor that detects that field.A thin film of dielectric is used for galvanic isolation.

MAGNETIC COUPLER Magnetic couplers transmit signals via a

magnetic field, rather than a photon transmission, across a thin film dielectric that provides the galvanic isolation. As is true of opto couplers, magnetic couplers are unidirectional and operate down to DC. But in contrast to opto couplers, magnetic couplers offer the high-frequency performance of an isolation transformer, covering nearly the entire combined bandwidth of the two conventional isolation technologies.

PHYSICS OF GIANT MAGNETORESISTANCE Large magnetic field dependent changes in

resistance are possible in thin film ferromagnet / nonmagnetic metallic multilayers. The phenomenon was first observed in France in 1988, when changes in resistance with magnetic field of up to 70% were seen. Compared to the small percent change in resistance observed in anisotropic magneto resistance, this phenomenon was truly ‘giant’ magneto resistance.

The spin of electrons in a magnet is aligned to produce a magnetic moment. Magnetic layers with opposing spins (magnetic moments) impede the progress of the electrons (higher scattering) through a sandwiched conductive layer. This arrangement causes the conductor to have a higher resistance to current flow.

An external magnetic field can realign all of the layers into a single magnetic moment. When this happens, electron flow will be less effected (lower scattering) by the uniform spins of the adjacent ferromagnetic layers. This causes the conduction layer to have a lower resistance to current flow. Note that these phenomenon takes places only when the conduction layer is thin enough (less than 5 nm) for the ferromagnetic layer’s electron spins to affect the conductive layer’s electron’s path.

In fig.1 both a and b, the A layers are the nonmagnetic conductive layer and the B layers are adjacent magnetic layers of opposing orientation.

Figure -2For spin-dependent scattering to be a

significant part of the total resistance, the layers must be thinner than the mean free path of electrons in the bulk material.

For many ferromagnets the mean free path is tens of nanometers, so the layers themselves must each be typically <10 nm (100 Å). It is therefore not surprising that GMR was only recently observed with the development of thin film deposition systems.

The spins of electrons in a magnet are aligned to produce a magnetic moment. Magnetic layers with opposing spins impede the progress of the electrons (higher scattering) through a sandwiched conductive layer. This arrangement causes the conductor to have a higher resistance to current flow.

In a giant magneto resistive sensor, the resistance of two thin ferromagnetic layers separated by a thin nonmagnetic conducting layer can be altered by changing the moments of the ferromagnetic layers from parallel to antiparallel.

GMR MATERIALSThere are presently several GMR multilayer

materials used in sensors and sensor arrays. The following chart shows a typical characteristic for a GMR material:

Figure-3

Notice that the output characteristic is omnipolar, meaning that the material provides the same change in resistance for a directionally positive magnetic field as it does for a directionally negative field. This characteristic has advantages in certain applications.For example, when used on a magnetic encoder wheel, a GMR sensor using this material will provide a complete sine wave output for each pole on the encoder thus doubling the resolution of the output signal.

The material shown in the plot provides a 98% linear output from 10 to 70% of full scale, a large GMR effect(13 to 16%), a stable temperature coefficient (0.15%/°C) and temperature tolerance (+150°C) and a large magnetic field range (0 to ±300 Gauss).

CONSTRUCTION OF ISOLOOP MAGNETIC MATERIAL

In a GMR, isolator data travels via a magnetic field through a dielectric isolation to affect that resistance elements arranged in a bridge configuration.

FIGURE-4 Bridge configuration of resistances.

Figure-5 Basic circuit of Isoloop Magnetic Coupler.

A magnetic coupler consists of an on chip microscopic coil that generates a magnetic field and a GMR sensor that detects that field. The current in the planar coil produce a magnetic field. The magnetic field produced by the field coil of the input affects the spin of electrons in the anti-ferromagnetic layers, reducing the resistance of the bridge sensors.

The isolation transmitter is simply coil circuitry deposited on a layer between the GMR sensors layers and the thick film magnetic shielding layer (see Figure 5). Current through this coil layer produce the magnetic field, which overcomes the anti ferromagnetic layers there by reducing the sensor’s resistance.

The manufacturing process allows thick film magnetic material to be deposited over the sensor elements to provide areas of magnetic shielding or flux concentration. Various op-amp configurations can be used to supply signal conditioning from the bridge’s outputs. This forms the basis of an isolation receiver.

SENSOR ARRAY:GMR elements can be patterned to form

simple resistors, half bridges, Wheatstone bridges, and even X-Y sensors. Single resistor elements are the smallest devices and require the fewest components, but they have poor temperature compensation and usually require the formation of some type of bridge by using external components.

Alternatively they can be connected in series with one differential amplifier per sensor resistor. Half bridges take up more area on a chip but offer temperature compensation, as both resistors are at the same temperature. Half bridges can be used as field gradient sensors if one of the resistors is some distance from the other. They can function as field sensors if one of the resistors is shielded from the applied field.

Figure-6A portion of half bridge sensor array

SIGNAL PROCESSING:Adding signal processing electronics to the

basic sensor element increases the functionality of sensors. The large output signal of the GMR sensor element Introduction means less circuitry, smaller signal errors, less drift, and better temperature stability compared to sensors where more amplification is required to create a usable output.

The GMR Switch holds its precise magnetic operate point over extreme variations in temperature and power supply voltage. This is a low cost method.

FIGURE-7 A typical signal processing circuit.

WORKINGIn the Isoloop magnetic couplers, a signal

at the input induces a current in a planar coil (see figure no: 5).The current produces a magnetic field, which is proportional to the current in the planar coil. The resulting magnetic field produces a resistance change in the GMR material, which is separated from the planar coil by a high voltage insulating material. Since the GMR is sensitive parallel to the plane of the substrate, this allows a considerably more compact construction than would be possible with Hall sensors.

 

The resistance change in GMR material, which was caused by the magnetic field, is amplified by an electronic circuit and impressed upon the output as a reproduction of the input signal. Since changes in the ground potential at the input, output or both doesn’t produce a current in the planar coil, no magnetic field is created. The GMR material doesn’t change. In this way safe galvanic signal isolation is achieved and at the same time a corresponding common mode voltage tolerance.

ADVANTAGES Very fast operation. High bandwidth. Small footprint. Excellent noise immunity. Temperature stability.

DISADVANTAGESComplex circuitry.

APPLICATIONSMagnetic isolators are quickly finding their

way into process control and industrial applications.Some of it’s applications in digital isolation are:

ADCs DACsMultiplexed Data TransmissionData InterfacesDigital Noise ReductionGround Loop Elimination

CONCLUSIONMagnetic couplers will in time be even faster

and have more channels. More types of integrated bus transceivers will be available. Several manufacturers are planning to introduce magnetic couplers. The U.S. military is providing significant funding for advanced magnetic coupler development because of the value of their high speed and noise immunity in aircraft and other systems. It has reported prototype devices with speeds of 300 Mbaud and switching times of <1 ns. Also under development are higher-density parts (full byte-wide couplers) and more functionality (latching bus transceivers). Finally, the inherent linearity of a resistive coil and resistive sensing elements make magnetic couplers well suited for linear data protocols such as low-voltage differential signaling.

THANKYOU