Apparatus and method for reducing magnetic fields in radio telephones

• US 5,960,346 A
• Filed: 04/03/1997
• Issued: 09/28/1999
• Est. Priority Date: 04/03/1997
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Holshouser, Howard Eugene
• Primary Examiner(s): CUMMING, WILLIAM D
• Application Number:
  US08/832,491
• Time in Patent Office: 908 Days
• Field of Search: 455/73, 455/436, 330/285
• US Class Current: 455/436
• CPC Class Codes: H04B 1/56 with provision for simultaneous communication in two directions
• CPC Class Codes: H04B 15/00 Suppression or limitation of noise or interference by means associated with receiver H04B1/10
• CPC Class Codes: H04R 2225/33 Aspects relating to adaptation of the battery voltage, e.g. its regulation, increase or decrease
• CPC Class Codes: H04R 2225/55 Communication between hearing aids and external devices via a network for data exchange
• CPC Class Codes: H04R 2420/07 Applications of wireless loudspeakers or wireless microphones
• CPC Class Codes: H04R 2499/11 Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• CPC Class Codes: H04R 25/554 using a wireless connection, e.g. between microphone and amplifier or using Tcoils

Abstract

A novel method and apparatus are described for reducing the effect that magnetic field emissions from a radio telephone may have on devices sensitive to time-varying magnetic fields. The variance of the magnetic field is smoothed by the addition of a smoothing capacitor having a time constant significantly longer than the TDMA time frame which is connected in parallel with the transmitter. In addition, a counter-balancing magnetic field is generated by a field canceling loop connected in series with the transmitter which causes current to flow in a path approximately opposite from the path the current flows through the battery, in roughly parallel plane. The current flowing through the field canceling loop generates a magnetic field approximately coaxial with, and opposite in polarity from, the magnetic field generated by current flowing through the battery, partially negating the latter. Utilization of the method and apparatus result in a reduction in the effective magnitude of the time-varying magnetic field outside the telephone.

Claims

1. A method for modifying magnetic field emissions of a radio telephone, said radio telephone including a transmitter power circuit, said transmitter power circuit including a battery having a positive terminal and a negative terminal and a transmitter connected to said battery, comprising the step of directly electrically connecting a smoothing capacitor between said negative terminal and said positive terminal of said battery and in parallel with said transmitter so as to reduce the harmonics generated by the portion of said transmitter power circuit including said battery but not including said transmitter.

2. The method of claim 1 wherein said radio telephone transmits during a time slot in a TDMA time frame and said capacitor has a time constant significantly greater than said TDMA time frame.

3. A method for modifying magnetic field emissions of a radio telephone, said radio telephone including a battery having a positive terminal and a negative terminal, comprising the step of generating a magnetic field approximately coaxial with, and opposite in polarity from, the time-varying magnetic field generated by current flowing through said battery so as to at least partially cancel the magnetic field generated by said battery current.

4. The method of claim 3 wherein said generation step includes causing current to flow in a path approximately opposite from the path said current flows through said battery, but in a different plane.

5. The method of claim 3 wherein said battery includes a plurality of battery cells arranged in series and wherein current flowing through said battery flows through said battery cells.

6. The method of claim 3 wherein said radio telephone includes a transmitter connected to said battery and further comprising the step of electrically connecting a smoothing capacitor between said negative terminal and said positive terminal and in parallel with said transmitter.

7. The method of claim 6 wherein said radio telephone transmits during a time slot in a TDMA time frame and said capacitor has a time constant significantly greater than said TDMA time frame.

8. The method of claim 3 further including operating said radio telephone in a time-duplex fashion.

9. A method for modifying magnetic fields emitted from a radio telephone including a transmitter and a battery having a positive terminal and a negative terminal comprising the steps of:

a) forming a field cancellation loop in a plane generally parallel to and at least partially overlying said battery; and

b) electrically connecting said field cancellation loop in series with said positive terminal and said transmitter so that the electrical current flows through said field cancellation loop in a direction opposite to the current flow through said battery when the transmitter is activated.

10. The method according to claim 9 wherein said current path in said field cancellation loop mirrors the current path in said battery, in an opposite direction.

11. A method for modifying magnetic field emissions of a digital cellular telephone, said cellular telephone including a transmitter and a battery having a positive terminal and a negative terminal, comprising the steps of:

a) generating a magnetic field approximately coaxial with, and opposite in polarity from, the time-varying magnetic field generated by current flowing through said battery;

wherein said generating includes causing current to flow in a path approximately opposite from the path said current flows through said battery, but in a parallel plane;

b) electrically connecting said transmitter to said battery;

c) directly electrically connecting a smoothing capacitor between said negative terminal and said positive terminal and in parallel with said transmitter; and

d) wherein said telephone transmits during a time slot in a TDMA time frame and said capacitor has a time constant significantly greater than said TDMA time frame and wherein said battery includes a plurality of battery cells.

12. A radio telephone comprising:

a) a battery;

b) a transmitter electrically connected to said battery via a positive current path and a negative current path; and

c) a smoothing capacitor directly electrically connected to said positive current path and said negative current path and in parallel with and said transmitter.

13. The device of claim 12 wherein said radio telephone transmits in a time slot in a TDMA time frame and said capacitor has a time constant significantly larger than said TDMA time frame.

14. The device of claim 12 wherein said battery includes a plurality of battery cells.

15. A radio telephone comprising:

a) a battery;

b) a transmitter operating in a time-duplex fashion and electrically connected to said battery via a positive current path and a negative current path; and

c) a field cancellation loop electrically connected in series between said battery and said positive current path and disposed so as to generate a magnetic field approximately coaxial with, and opposite in polarity from, the time-varying magnetic field generated by current flowing through said battery.

16. The device of claim 15 further comprising a smoothing capacitor electrically connected to said positive current path and said negative current path and in parallel with said transmitter.

17. A radio telephone for operation in a TDMA time frame environment comprising:

a) a battery;

b) a transmitter operating in a time-duplex fashion and drawing power from said battery via a positive current path and a negative current path;

c) a field cancellation loop electrically connected in series between said battery and said positive current path; and

d) a smoothing capacitor directly electrically connected to said positive current path and said negative current path and in parallel with and said transmitter, wherein said capacitor has a time constant significantly longer than said TDMA time frame.