GB2336473A

GB2336473A - An inductor

Info

Publication number: GB2336473A
Application number: GB9808040A
Authority: GB
Inventors: Stefan Lichterfeld
Original assignee: Motorola GmbH
Current assignee: Motorola Solutions Germany GmbH
Priority date: 1998-04-15
Filing date: 1998-04-15
Publication date: 1999-10-20
Also published as: GB9808040D0

Abstract

An inductor comprises two or more inductive elements 5, 6 arranged with their opposite poles adjacent one another. The inductive elements 5, 6 may be adjacent coils wound in the same direction which are electrically connected such that the north pole of one element is adjacent the south pole of the other. This arrangement reduces the level of external magnetic field created by the inductor and increases the coupling and quality factor of the inductor. As a result the inductor is less likely to require shielding means to prevent interaction with other nearby components. The inductor may be used in an oscillator circuit of a radio device.

Description

2336473 An Inductor Arrangement

Field Of The Invention

This invention relates to an inductor arrangement particularly, but not 10 exclusively, for use in a voltage controlled oscillator often abbreviated to Veo.

Backeround To The Invention VC0s are used in radio transmi and receiving apparatus to provide a local oscillator for modulation and demodulation purposes.

Current VC0s use capacitors and shielded coils to define their operating frequency range. The shielded coils are inductors and where the term coil is used in this specification its meaning is to be taken to be an inductor whether of a coil-like construction or other construction.

High specification coils are used in VC0s which are shielded in order to prevent a widespread magnetic field being generated. If the field were generated adjacent componentAs would start to interact with the field to affect the value of inductance of the coil. Such interaction could be made to vary as the components made minor movements because of vibration for example.

Such shielded coils are expensive because they require careful design and tend to be designed for specific applications and spedfic VC0s.

Summary Of The Invention

According to the invention there is provided an inductor arrangement comprising at least a first inductor and a second inductor wherein complementary poles of the inductors are adjacent.

2 By arranging for the complementary poles to be adjacent the magnetic field produced by the inductors tend to be more closely restricted to the location of the inductors alleviating or eliminating the requirement for shielding. By complementary poles it is meant the north pole of one inductor and the south of the other (or positive and negative poles). The magnetic field emitted from the north pole of a first inductor will enter the south pole of the other inductor.

A further advantage of such an arrangement is that the field will tend to be more concentrated than would otherwise be the case because of the mutual reinforcement of the field leading to an increase in the inductors' coupling factor typically of 15% and an increase in the Quality factor Q of 15%.

Advantageously, electrically complimentary ends of the inductors are electrically coupled. The advantage of this is that any externally generated field will be damped because the voltages induced in the inductors will added with inverted phase.

A specific embodiment of the invention will now be described by way of example only with reference to the drawings.

Brief Description Of The Drawinas

Figure 1 shows in schematic form an oscillator circuit in accordance with the invention; Figure 2 shows an inductor arrangement in accordance with a first embodiment of the invention; and Figure 3 shows an inductor arrangement in accordance with a second embodiment of the invention.

1 1 3 Detailed Description

With reference to Fig. 1, an oscillator 1 in accordance with the invention is represented by the oscillator equivalent diagram which includes an amplifier 2 having a feedback impedance 3, a tank resonator parallel capacitance 4, and tank coils 5 and 6. The tank coils are specific examples of inductors.

The operation of the oscillator 1 wW be well understood by the man skilled in the art and will thus not!be described. However, it is the orientation of the coils in the circuit that is the significant feature. From Fig 1 it will be seen that the coils 5 and 6 have a positive terminal marked by a "+" and a negative terminal marked by a "-". (It will be appreciated that positive and negative are relative terms). It will also be seen that complementary terminals or poles of the coils are adjacent that is to say the positive terminal of coil 5 is adjacent to the negative terminal of coil 6. In addition the negative terminal of coil 5 is adjacent the positive terminal of coil 6. Now since the coils are wound in the same direction this means that complementary magnetic poles of the coils are adjacent This results in the magnetic field being concentrated in the region immediately about the coils as shown in Fig.2.

As is shown in Fig.2, the magnetic flux emanating from the coil 5 at its positive end enters the coil 6.at its negative end. Similarly the flux emanating form the positive end of the coil 6 enters the negative end of the coil 5. This results in an almost circular field represented by the flux lines 7.

As is shown in the figures the ends of the coils are connected together such that like ends are connected. That is to say, the positive end of coil 5 is electrically connected to the positive end of coil 6. Similarly, the negative end of coil 5 is electrically- connected to the negative end of coil 6.

By arranging the coils such that their respective complementary magnetic poles are adjacent the magnetic field is constrained within a

4 more localised are than would otherwise be possible. This lessens the possibility of interference and allows the use of unshielded coils.

In the specific embodiment the coils are surface mount components placed parallel at a distance of 1m.m. apart.

Whilst the above described embodiment utilises two coils in other embodiments more coils may be used. Such an embodiment is shown in Fig.3.

In Fig.3 three coils 8, 9 and 10 are used. These produce a toroidal field represented by the flux lines 11. It will be seen that again the magnetic field is constrained the locality of the coils. Again complementary poles are adjacent with the coils being wound in the same sense and positive poles connected together and negative poles connected together.

In other embodiments more coils or other types of inductors may be used.

Claims

1. Aninductor arrangement comprising at least a first inductoranda second inductor wherein complementary poles of the inductors are 10 adjacent.

2. An arrangement as claimed in claim 1 wherein electrically complimentary ends of the inductors are electrically coupled.

is

3. An arrangement as claimed in claim 1 or claim 2 wherein the inductors include at least one coil.

4. An arrangement as claimed in claim 3 wherein the coil is a tank coil.

5. An arrangement substantially as hereinbefore described with reference to and as illustrated by figure 1 or figure 2 or figure 3 of the drawings.

6. An oscillator circuit including an inductor arrangement as claimed in any preceding claim.

7. A radio including an oscillator circuit as claimed in claim 6.