Wireless data transmission over quasi-static electric potential fields

• US 6,336,031 B1
• Filed: 12/22/1998
• Issued: 01/01/2002
• Est. Priority Date: 12/22/1998
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Schyndel, Andre Van
• Primary Examiner(s): Chang, Vivian
• Assistant Examiner(s): MOORE, JAMES K
• Application Number:
  US09/218,426
• Time in Patent Office: 1,106 Days
• Field of Search: 455/41, 455/209, 455/304, 455/334, 340/870.37
• US Class Current: 455/41.2
• CPC Class Codes: H04B 13/00 Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00

Abstract

A transmitter includes a pair of electrodes separated in space, and transmit circuitry for varying the voltage difference applied across the electrodes in order to vary the spatial gradient of the electric potential field generated by the transmitter in accordance with the data to be transmitted. The receiver includes a pair of electrodes separated in space and receive circuitry which detects these variations in the quasi-electrostatic potential field in order to receive the transmitted data. Thus the receive electronics unit includes a detector connected to said electrodes for producing a signal which varies as the spatial gradient of the electric potential field across the receive electrodes varies but which does not depend on changes in potential within any given electrode.

Claims

1. A method of data transmission comprising:

varying a voltage difference applied across a plurality of transmit electrodes at such a rate that the resulting electric potential field varies in a quasi-static manner, wherein the variation in said voltage difference depends on the data to be transmitted; and

producing a receive output signal which varies with a signal induced between a plurality of receive electrodes by said quasi-static variations in said electric potential field;

wherein said step of producing a receive output signal comprises;

varying a current applied to said receive electrodes in order to keep the potential difference between said receive electrodes constant; and

producing an output signal which varies with said varying current in order to recover the transmitted data.

2. The method as claimed in claim 1 wherein said step of varying a current applied to said receive electrodes in order to keep the potential difference between said receive electrodes constant comprises varying a current applied to each of said electrodes in order to keep each of said electrodes at a ground potential.

3. The method as claimed in claim 1 further comprising the steps of:

independently amplifying the induced signal from each receiver electrode and ground;

combining the outputs from each amplifier;

using the combined signal to adjust the gain of each amplifier in such a way as to increase the signal to noise ratio of the output signal.

4. The method as claimed in claim 1 wherein said step of varying a voltage difference applied across a plurality of transmit electrodes varies said voltage with a transmit oscillator frequency and wherein said step of producing an output signal comprises:

generating a plurality of oscillator signals from a local oscillator whose frequency is close to the transmit oscillator frequency, wherein each of said oscillator signals is phase shifted with respect to each other;

mixing said receive output signal with said plurality of oscillator signals;

low pass filtering each of said mixed signals;

processing each of said filtered signals with a non-linear characteristic which depends on the magnitude of the signal but does not depend on the sign; and

combining each of the processed signals to produce a demodulated output signal.

5. A wireless transmission system comprising:

a wireless transmitter; and

a wireless receiver;

wherein said transmitter comprises;

a plurality of transmit electrodes separated in space; and

means for varying a voltage difference across said electrodes at a rate that the resulting electric potential field varies in a quasi-static manner, wherein the variation in said voltage difference depends on the data to be transmitted;

wherein said receiver comprises;

a plurality of receive electrodes separated in space; and

means for producing a receive output signal which varies with a signal induced between said receive electrodes by the varying quasi-static electric potential field produced by said transmit electrodes;

wherein said means for producing a receive output signal comprises;

means for varying a current applied to said receive electrodes in order to keep the potential difference between said receive electrodes constant; and

means for producing an output signal which varies with said varying current.

6. The system as claimed in claim 5 wherein said signal induced between receive electrodes results from capacitive coupling between said transmit electrodes and said receive electrodes when said electrodes are placed in proximity to each other.

7. The system as claimed in claim 5 wherein said means for varying a current applied to said receive electrodes in order to keep the potential difference between said receive electrodes constant comprises means for varying a current applied to each of said electrodes in order to keep each of said electrodes at a ground potential.

8. The system as claimed in claim 7 wherein said means for varying a current applied to each of said electrodes in order to keep each of said electrodes at a ground potential comprises:

means for independently amplifying the induced signal from each receiver electrode and ground;

means for combining the outputs from each amplifier; and

means for using the combined output signal to adjust the gain of each amplifier in such a way as to increase the signal to noise ratio of the output signal.

9. A receiver comprising:

at least two electrodes separated in space; and

a detector connected to said electrodes for producing a signal which varies as the spatial gradient of the electric potential field across the receive electrodes varies but which does not depend on changes in potential within any given electrode.

10. A receiver comprising:

at least two electrodes separated in space; and

a detector connected to said electrodes for producing a signal which varies as the spatial gradient of the electric potential field across the receive conductors varies even when the potential is substantially constant at each point within any given electrode.

11. A receiver comprising:

at least two electrodes separated in space; and

a detector connected to said electrodes for producing a signal which varies as the spatial gradient of the electric potential field across the receive electrodes varies;

wherein said detector comprises;

means for varying a current applied to said receive electrodes in order to keep the potential difference between said receive electrodes constant; and

means for producing an output signal which varies with said varying current.

12. The receiver as claimed in claim 11 wherein said means for varying a current applied to said receive electrodes in order to keep the potential difference between said receive electrodes constant comprises means for varying a current applied to each of said electrodes in order to keep each of said electrodes at a ground potential.

13. The receiver as claimed in claim 12 wherein said means for varying a current applied to each of said electrodes in order to keep each of said electrodes at a ground potential comprises:

an amplifier coupled to each receive electrode for independently amplifying the induced signal from each receiver electrode and ground;

combining means for the outputs from each amplifier;

means for using the combined signal to adjust the gain of each amplifier in such a way as to increase the signal to noise ratio of the output signal.

14. The receiver as claimed in claim 11 wherein said detector further comprises a rolling phase detector for demodulating said receive output signal, and wherein the spatial gradient of the electric potential field is varied by a transmitter with a transmit oscillator frequency, wherein said rolling phase detector comprises:

a local oscillator whose frequency is close to the transmit oscillator frequency, for generating a plurality of oscillator signals;

a plurality of phase shifters for phase shifting said plurality of oscillator signals with respect to each other;

a plurality of mixers for mixing said receive output signal with said plurality of phase shifted oscillator signals;

a plurality of low pass filters for low pass filtering each of said mixed signals;

means for processing each of said filtered signals with a non-linear characteristic which depends on the magnitude of the signal but does not depend on the sign; and

means for combining each of the processed signals to produce to a demodulated output signal.

15. The receiver as claimed in claim 14 wherein said means for processing includes means for squaring or means for rectifying.