WO2000059180A1

WO2000059180A1 - Vertical buzzer/earphone to reduce humming sounds

Info

Publication number: WO2000059180A1
Application number: PCT/SE2000/000594
Authority: WO
Inventors: Göran PEHRSSON
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 1999-03-29
Filing date: 2000-03-27
Publication date: 2000-10-05
Also published as: DE10084392T1; CN1345508A; JP2002540485A; AU4159600A

Abstract

Electrodynamic components in a mobile phone are positioned such that their associated coils are perpendicular to the printed circuit board located within the exterior handset of the mobile phone. Positioning the electrodynamic components in this manner reduces the electromagnetic coupling between the coil associated with the components and the magnetic field of the pulsed current that is supplied to the mobile phone transmitter amplifier across the printed circuit board. Reduction of this electromagnetic coupling decreases noise commonly associated with mobile phone audio inputs and outputs.

Description

Vertical Buzzer/Earphone to Reduce Humming Sounds

BACKGROUND

The present invention relates generally to mobile telephones and, more particularly, to the mounting of electrodynamic elements within mobile telephones. As illustrated in Figure 1, a conventional mobile telephone 1 is typically constructed with electronics mounted on a printed circuit board 2 (PCB) which is itself mounted within the exterior handset 3. On the PCB 2, the antenna 4 is usually mounted at the top of the board with the transmitter power amplifier 5 mounted on the PCB in proximity to the antenna. Also in this top area of the mobile phone are typically mounted, in parallel to the PCB, an electrodynamic component such as an earphone 6. Earphones, loudspeakers, microphones, and buzzers are non-limiting examples of what are referred to herein as electrodynamic elements or components. These electrodynamic components consist of magnets 8 around which coils 7 are mounted on easily moving membranes (not shown). Applying electrical signals to the coils causes the membranes to move, which in turn, causes the air to vibrate and generate audible sounds.

In mobile phones using conventional TDMA (Time Division Multiple Access) principles, the transmitter is turned on and off in a periodic manner. As shown in Figure 2, this periodic switching of the mobile phone transmitter causes a pulsed current i to flow from the battery 9 to the transmitter power amplifier 10 over conductive traces 11 on the PCB. The frequency of the pulsing current and/ or the harmonics of the frequency typically occur in the audible region of the spectrum. As further illustrated in Figure 3, the pulsing current i flowing in the conductive traces 11 of the PCB additionally causes a varying magnetic field 12 that passes through the coils 7 of the neighboring electrodynamic components. In accordance with well known electromagnetic principles, this varying magnetic field induces a voltage in the coil which is proportional to the following:

N, the number of turns of the coil; A, the area of the coil; Cos θ, the cosine of the angle between the magnetic field and the normal to the plane of the coil; llr, where r is the distance between the coil and the current path; and dl/dt, where I is the current in the conductive trace.

This induced voltage in the coil causes a current I_coil to flow in the windings of the coil. The magnetic field originating from the magnet in the electrodynamic device creates a force F upon the coil according to the relation F=B_mag*I_coil*L, where B_mg is the magnet's magnetic field strength, I_coil is the current in the windings, and L is the length of the windings. Movement of the coil due to force F also moves the membrane fitted to the coil and thus creates a humming sound that is often called "bumble bee" noise. In conventional mobile phones the electrodynamic components are mounted parallel to the PCB (as shown in Fig. 3) thus minimizing the angle between the magnetic field induced by the current in the PCB trace and the normal to the plane of the coil (Cosθ → maximum). Minimization of this angle therefore serves to maximize the induced voltage in the coil and create noticeable "bumble bee" hummmg noise.

Creation of this humming noise in the mobile phone is further compounded by a number of recent trends in mobile technology. One trend is to use a lower battery voltage in the mobile phone. A lower battery voltage, however, creates higher current levels between the battery and the power amplifier, thus further creating stronger magnetic fields and higher induced voltages in the coils of the electrodynamic devices. Another trend is to construct mobile phones with smaller geometries. As the distances between components are reduced to fit into these smaller geometries, higher voltages are also induced in the coils of the electrodynamic devices.

Additionally, the need for improved performance in mobile phones also militates in favor of a reduction in "bumble bee" noise. Requirements for improved audio performance (e.g., decreased noise) and improved speech coding (e.g., increased dynamic range) necessitate a reduction in the electromagnetic coupling that induces audible "bumble bee" noise in mobile phones.

SUMMARY

These above described desirable characteristics and others are provided by the following exemplary embodiments of the invention.

According to a first exemplary embodiment of the invention an electronic device is provided. The electronic device of this exemplary embodiment comprises: a board with associated circuitry; and one or more electrodynamic elements with associated coils, wherein the electrodynamic elements are positioned within said electronic device such that angles created between the board and each of said coils reduces electromagnetic coupling between the coils and magnetic fields created by varying currents which traverse said board. According to a second exemplary embodiment of the invention a method for reducing noise in a mobile phone is provided. The method of this exemplary embodiment comprises the step of: mounting electrodynamic components with respect to a circuit board in said mobile phone such that electromagnetic coupling between magnetic fields associated with currents traversing said circuit board and coils associated with each of said electrodynamic components is substantially minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which: FIG. 1 shows the physical layout of components of a conventional mobile phone;

FIG. 2 is a block diagram of the interconnection of a transmitter power amplifier and battery in a mobile phone; FIG. 3 shows the electromagnetic coupling between current in a conductive trace on a PCB and a conventionally mounted coil in a mobile phone;

FIG. 4 shows the electromagnetic coupling between current in a conductive trace on a PCB and a coil mounted in accordance with exemplary embodiments of the invention; and

FIG. 5 shows a sound tube used in conjunction with a electrodynamic component mounted in accordance with exemplary embodiments of the invention.

DETAILED DESCRIPTION In accordance with exemplary embodiments of the invention, electromagnetic coupling between the current path to the power amplifier and the coils in the electrodynamic components is advantageously reduced by altering the position of the electrodynamic components within the mobile handset. The electrodynamic components are positioned within the handset such that their associated coils are aligned substantially perpendicular to the printed circuit board. Since, as discussed above, the induced voltage is directly proportional to the cosine of the angle θ between the magnetic field and the normal to the plane of the coil, placing the coils perpendicular to the PCB will increase the angle θ towards ninety degrees (Cos θ - 0) and thus minimize the induced voltage. An exemplary embodiment implementing this technique is illustrated in Figure 4. In this embodiment, the electrodynamic audio inputs and outputs 13 (only one is shown) are positioned at the sides of the mobile phone. As shown in the Figure, this configuration of the electrodynamic component 13 with respect to the conductive trace 11, increases the angle 15 between the magnetic field 12 associated with the pulsed current in the trace 11 and the normal 16 to the plane of the coil 7. With the electrodynamic component 13 positioned substantially perpendicular to the PCB 2 at the side 14 of the exterior handset 3 as shown, the angle θ approaches 90°, the cosine of the angle θ in turn approaches 0, and thus, the induced voltage 17 approaches zero. "Bumble bee" noise induced in the electrodynamic component 13 will therefore be substantially minimized.

An additional exemplary embodiment of the invention is shown in Figure 5. In this embodiment the electrodynamic components 13 are mounted in a manner substantially identical to the exemplary embodiment of Figure 4, except that a sound tube 18 is additionally provided. The sound tube 18 routes sound from the perpendicularly mounted electrodynamic component 13 to the front 19 of the mobile phone. Use of the sound tube 18 permits audio inputs/outputs to be made through the front of the mobile phone by the user as in a conventional mobile phone. Sound tubes are known in the art, and are described, for example in U.S. Patent Application No. 08/848, 189, filed April 29, 1997, and in U.S. Patent Application No. 08/919,365, filed August 28, 1997.

It is noted that mounting the electrodynamic components as shown in both of the exemplary embodiments of Figures 4 and 5 has the additional benefit of releasing area on the front of the mobile phone conventionally dedicated to the earphone and/or microphone and their associated electrodynamic components. By repositioning these components to the side of the exterior handset, additional area on the front of the phone is made available. This additional area can be used for purposes such as, for example, larger displays and/or additional or larger buttons on the front of the mobile phone.

The exemplary embodiments of the invention therefore advantageously provide for the reduction of "bumble bee" noise in a mobile phone through the repositioning of the electrodynamic components in relation to the printed circuit board within the exterior handset. This novel configuration will therefore mitigate the increased noise that results from using lower battery voltages in mobile phones and from reductions in the size of the mobile phone. Although a number of embodiments are described herein for purposes of illustration, these embodiments are not meant to be limiting. Those skilled in the art will recognize modifications that can be made in the illustrated embodiment. Such modifications are meant to be covered by the spirit and scope of the appended claims.

Claims

What is Claimed is:

1. An electronic device comprising: a board with associated circuitry; and one or more electrodynamic elements with associated coils, wherein the electrodynamic elements are positioned within said electronic device such that angles created between the board and each of said coils reduces electromagnetic coupling between the coils and magnetic fields created by varying currents which traverse said board.

2. The electronic device of claim 1, wherein said electronic device is a mobile phone.

3. The electronic device of claim 1 , wherein said currents are supplied to a transmitter power amplifier located on said board.

4. The electronic device of claim 1, wherein said one or more electrodynamic elements are selected from a group consisting of earphones, loudspeakers, microphones, and buzzers.

5. The electronic device of claim 1, wherein said one or more electrodynamic elements are positioned at a side of said electronic device.

6. The electronic device of claim 1, wherein sound tubes are used for conveying sound from said one or more electrodynamic elements to audio outputs on said electronic device.

7. The electronic device of claim 1, wherein sound tubes are used for conveying sound from audio inputs on said electronic device to said electrodynamic elements.

8. A method for reducing noise in a mobile phone comprising the step of: mounting electrodynamic components with respect to a circuit board in said mobile phone such that electromagnetic coupling between magnetic fields associated with currents traversing said circuit board and coils associated with each of said electrodynamic components is substantially minimized.

9. The method of claim 8, where said electrodynamic components are selected from a group consisting of earphones, loudspeakers, microphones, and buzzers.