WO2002046859A2

WO2002046859A2 - Capacitively coupled e-field communications system

Info

Publication number: WO2002046859A2
Application number: PCT/US2001/042936
Authority: WO
Inventors: Robert A. Macy
Original assignee: Sybersay Communications Corporation
Priority date: 2000-11-10
Filing date: 2001-11-13
Publication date: 2002-06-13
Also published as: WO2002046859A3

Abstract

A low-power, short-range communications system (Figure 1) is disclosed. The communications system comprises a transmitter that is operative to generate a high impedance signal and a receiver that is operative to detect the high impedance signal. In this respect, the transmitter and the receiver (Figure 1, elements 12 and 14) are capacitively coupled by the high impedance electric field generated in response to the high impedance signal. Accordingly, information from the transmitter to the receiver is sent via the high impedance electric field. In accordance with the present invention, the transmitter is configured to generate the high impedance signal with a frequency in the range from about 20 KHz to 10 MHz. Similarly, the voltage of the high impedance signal is from about 1 Vrms to 300 Vrms.

Description

TITLE OF THE INVENTION CAPACITIVELY COUPLED E-FIELD COMMUNICATIONS SYSTEM

BACKGROUND OF THE INVENTION The present invention generally relates to wireless communication systems, and more particularly to a short-range, low-power wireless communication system.

Wireless communication systems typically generate a signal having a high frequency for transmission. The wireless communication system uses special antennas, high frequency electronics, and high power to launch the energy required to receive the signal. High frequency radio communications are typically regulated by governmental entities in order to ensure that interference with other devices do not occur. Therefore, governmental certification is needed for high frequency wireless communications systems.

Additionally, in order to obtain full duplex communication at high frequencies, the antenna for transmit and receive functions is the same. In this sense, the electronics for the transceiver will use the same antenna by utilizing a transmit/receive switch which requires synchronization between the transmit and receive functions. The transmit/receive switch will add complexity and cost to the system. Alternatively, wireless communication systems can use magnetic fields to send and receive signals. The magnetic field is created at a relatively low frequency and requires the transmitting field to be generated with a large amount of current. Furthermore, special low resistance switches and physically large parts are needed for magnetic field communication. Special magnetic material cores are used to concentrate the magnetic fields both at the source and the receiver and can only be operated over a fairly short range. The magnetic field drops off very quickly as a function of distance from the transmitter. Specifically, the strength of the magnetic field typically drops off inversely with the cube of the distance. Furthermore, in order to obtain full duplex communication with magnetic fields, two separate frequency channels must be used. In this sense, one channel is used for transmission and the other channel is used for reception of magnetic field signals. Additionally, magnetic fields can penetrate the body of a user thereby creating a concern about unwanted ELF radiation.

The present invention addresses the above-mentioned deficiencies in the prior art communication systems by providing a full-duplex wireless communication system that consumes very low power and is easy to implement. More specifically, the communications system of the present invention provides a low frequency communication system having a master and a slave transceiver which are operable to transmit and receive signals with low power consumption and in a small package.

BRIEF SUMMARY OF THE INVENTION A low power, short range communications system is disclosed. The communications system comprises a transmitter operative to generate a high impedance signal and a receiver operative to detect the high impedance signal. The transmitter and the receiver are capacitively coupled by the high impedance signal in order to transmit the signal from the transmitter to the receiver. In accordance with the present invention, the transmitter is configured to generate the high impedance signal with a frequency in the range from about 20 KHz to 10 MHZ. Similarly, the voltage of the high impedance signal is from about 1 Vrms to 300 Vrms.

In order to transmit the high impedance signal, the transmitter includes a conductor operative to generate a high impedance electric field in response to the high impedance signal. Similarly, the receiver includes a conductor operative to detect the high impedance electric field generated by the transmitter. The conductor of the transmitter and the conductor of the receiver are sized and configured to be capacitively coupled via the electric field. Furthermore, the transmitter may include a boost circuit connected to the conductor in order to generate the electric field. The boost circuit may be either an amplifier, op-amp, or transformer in order to increase the voltage of the high impedance signal. The receiver includes an impedance converter that lowers the impedance of die received signal. The impedance converter may be a FET having a high impedance input and a low impedance output. It will be recognized that the high impedance signal may be a communications signal operative to transmit information. In this respect, the communications signal may be frequency modulated or amplitude modulated. The transmitter and receiver will include the necessary circuit for modulation or demodulation of the communications signal. In accordance with the present invention, there is additionally provided a full-duplex, short-range, low-power communications system. The system has a master transceiver operative to generate a first high impedance signal and receive a second high impedance signal. Furthermore, the system includes a slave transceiver operative to detect the first high impedance signal and generate the second high impedance signal. In this respect, the master transceiver and the slave transceiver may be capacitively coupled together by either the first high impedance signal or the second high impedance signal.

For the full-duplex communications system, the frequency range of the first high impedance signal, as well as the second high impedance signal, will be from about 20 KHz to 10 MHZ. However, the frequency of the first high impedance signal will not be equal to the frequency of the second high impedance signal. Similarly, both the first and second high impedance signals will have a voltage in the range from about 1 Nrms to 300 Vrms, but the voltage of the second high impedance signal will not be equal to the voltage of the first high impedance signal.

In order to transmit the first high impedance signal, the master transceiver has a transmit conductor operative to generate a first high impedance electric field. The slave transceiver has a receive conductor operative to detect the first high impedance electric field. Similarly, the slave transceiver has a transmit conductor operative to generate the second high impedance electric field. The master transceiver will include a receive conductor operative to detect the second high impedance electric field. Both pairs of transmit and receive conductors are sized and configured to be capacitively coupled together.

For full-duplex communication, the first high impedance signal may be frequency modulated while the second high impedance signal may be amplitude modulated. Alternatively, the first high impedance signal may be amplitude modulated while the second high impedance signal may be frequency modulated. Also, it is possible for both the first and second high impedance signals to be both amplitude modulated or both frequency modulated.

In accordance with the present invention, there is provided a method of communicating between a transmitter and a receiver. The method comprises generating a high impedance electric field with the transmitter in response to a communications signal. Next, the high impedance electric field is detected with the receiver thereby establishing communications between the transmitter and the receiver. The communications signal may be frequency modulated or amplitude modulated and the signal will be demodulated upon detection by the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

These, as well as other features of the present invention will become more apparent upon reference to the drawings wherein: Figure 1 is a block level diagram of a first embodiment of the communication system constructed in accordance with the present invention;

Figure 2 is a block level diagram of a second embodiment of the communication system constructed in accordance with the present invention; and

Figure 3 is a block level diagram of a third embodiment of the communication system constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the present invention only, and not for purposes of limiting the same, Figure 1 is a block diagram illustrating a full- duplex, low-power communications system 10 constructed in accordance with a first embodiment of the present invention. The communications system 10 is operative to modulate and transmit audio signals having a frequency between 150 Hz to 5 KHz from a master transceiver 12 to a slave transceiver 14. Additionally, in accordance with the present invention, the communications system 10 is operative to modulate and transmit audio signals having a frequency of 150 Hz to 5 KHz from the slave transceiver 14 to the master transceiver 12. The communications system 10 is ideal for short range (i.e., 1 meter) communication between a wireless earpiece and a waist-mounted base station (i.e., cellular phone or PDA). In this respect, the master transceiver 12 is located within the earpiece and the slave transceiver 14 is located within the base station in order to provide communications between the earpiece and the base station. It will be recognized that the earpiece and base station are illustrative examples only and that the communications system 10 can be used in any wireless short-range application. The audio signals transmitted by the master transceiver 12 are generated by a microphone located on the earpiece. The microphone picks up the voice of the user and generates a corresponding audio signal. Similarly, the audio signals for the slave transceiver 14 are generated by the base station. If the base station is a cellular phone, then the audio signals will typically be the voice commumcation of the person the user is talking with over the cellular phone. In this respect, the communications system 10 can provide a wireless link between a cellular phone and an earpiece thereby permitting the user of the cellular phone to speak without holding the phone. Referring to Figure 1, the transceiver 12 of the communications system 10 has a voltage controlled oscillator (NCO) 16 that uses the audio signals from the earpiece microphone to frequency modulate a low frequency carrier signal in the range of from about 20 KHz to 10 MHZ. The peak deviation for the modulation by the NCO 16 is from about 10 KHz to 80 KHz. The NCO 16 can be either a simple RC oscillator or a crystal oscillator. It will be recognized that due to the size and power constraints of the earpiece, a simple RC oscillator is preferable due to the low power requirements and small size. As will become more evident below, the VCO 16 does not need to accurately derive an oscillation frequency because the signal is used in both the master transceiver 12 and the slave transceiver 14.

The frequency modulated signal from the VCO 16 is amplified with a boost circuit 18 to a higher voltage. The boost circuit 18 can amplify the voltage from about 1 Nrms to about 300 Vrms. Preferably, the boost circuit 18 of the transceiver 12 amplifies the voltage of the FM modulated signal to about 30 Nrms. As will be recognized by those of ordinary skill in the art, by increasing the voltage of the carrier signal to 30 Vrms, the boost circuit 18 consumes less power than an amplification to 100 Vrms such that the power supply for the master transceiver 12 and earpiece can be relatively small. The boost circuit 18 can be realized in the form of either a transformer or linear op-amp. The boost circuit 18 is operative to create a high impedance FM modulated signal by increasing the voltage of the signal from the VCO 16.

The amplified FM modulated signal from the boost circuit 18 is then fed to a transmit conductor 20 which is insulated from the circuitry of the transceiver 12. The transmit conductor 20 creates a high voltage electric field that is capacitively coupled to the slave transceiver 14, as will be further explained below. The transmit conductor 20 is typically a short piece of conductive wire electrically connected to the boost circuit 18. It will be recognized that due to the impedance of the FM modulated signal, the transmit conductor 20 can have an insulating covering without affecting the performance thereof. Furthermore, the transmit conductor 20 can be fabricated from other conducting material such as copper foil or carbon impregnated plastic with conductivity below free space or the human body. The transmit conductor 20 is operative to generate an electric field in response to the FM modulated signal.

In order to capacitively couple the earpiece to the base station, the slave transceiver 14 (located within the base station) has a receive conductor 22 operative to detect the high voltage electric field generated by the master transceiver 12. The receive conductor 22 may be electrically isolated from the electronics of the slave transceiver 14 and be capacitively coupled to the transmit conductor 20 of master transceiver 12 by the electric field generated in response to the FM modulated signal. In this respect, the FM modulated high impedance signal from the master transceiver 14 capacitively couple the transmit conductor 20 of the master transceiver 12 to the receive conductor 22 of the slave transceiver 14. In order to convert the high impedance FM signal to a usable low impedance FM signal, the slave transceiver 14 has an impedance converter 24 electrically connected to the receive conductor 22. The impedance converter 24 is a small FET with a high impedance input and a low impedance output. The high impedance input is connected to the receive conductor 22. Preferably, the impedance converter 24 is a FET configured as a source follower with unity gain such that all ambient signals (wanted and unwanted) coupled to the receive conductor 22 are converted to a lower impedance. It will be recognized, due to the broadband nature of the FET, that the impedance converter 24 will convert the impedance of all signals detected by the receive conductor 22. Accordingly, fewer cross modulation products from interfering signals are created during the impedance conversion because all signals are equally converted.

Next, the lower impedance FM modulated signal from the impedance converter 24 is fed to a bandpass filter (BPF) 26 to limit the range of frequency of the FM modulated signal to that which should be demodulated (i.e., 20 KHz to lOMHz/peak deviation 10 KHz to 80 KHz). The BPF 26 may be a bipole filter with five to seven sets of poles. The transceiver 14 includes a phase lock loop (PLL) 28 which is fed the signal from the output of the BPF 26. The PLL 28 follows the incoming FM signal such that the error signal from the PLL 28 produces a high quality audio signal that is presented as received audio to the electronics of the base station, as seen in Figure 1. As will be recognized by those of ordinary skill in the art, the electronics of the base station can further process and amplify the signal as necessary. By capacitively coupling the master transceiver 12 to the slave transceiver 14 with the high impedance FM signal, the power requirements for transmission of the signal from the earpiece to the base station are greatly reduced over conventional high frequency communication systems.

The communications system 10 is also operative to transmit an audio signal from the slave transceiver 14 to the master transceiver 12 (i.e., base station to earpiece). In this respect, the slave transceiver 14 has an input amplifier 30 operative to process and amplify an audio signal from the base station. As previously mentioned, the audio signal is typically a voice communication from a cellular phone connected to the base station. After processing and amplification with the input amplifier 30, the audio signal is used to amplitude modulate a carrier signal derived from the PLL 28 of the slave transceiver 14. The carrier signal from the PLL 28 will have the same frequency as the signal of the VCO 16 because it is derived from the received FM signal with the PLL 28. The slave transceiver 14 includes a phase adjust circuit 32 that is operative to pre-adjust the phase of the carrier signal derived from the PLL 28. The phase adjust circuit 32 will adjust the phase of the carrier signal from the PLL 28 by a predetermined amount in order to compensate for any predetermined phase drift. Ideally, the phase adjust circuit 32 will adjust the phase of the derived carrier signal from PLL 28 to be the same as the phase of the signal of the VCO 16.

After the phase of the carrier signal has been adjusted, the carrier signal is simultaneously fed to both a COS divider 34 and a SIN divider 36. Both of the dividers 34 and 36 divide the frequency of the carrier signal from the PLL 28 by four so that the frequency of the carrier signal is in the range from about 175 KHz to 2.5 MHZ. Additionally, the SIN and COS dividers 34 and 36 place the carrier signal in quadrature in order to solve for any indeterminancy of reception of the signal, as will be further explained below.

Each of the signals from the dividers 34 and 36 is fed into a respective modulator 38 and 40. Specifically, the carrier signal from the COS divider 34 is fed to modulator 38 which amplitude modulates the carrier signal by the audio signal from the input amplifier 30. Similarly, the carrier signal from SIN divider 36 is modulated by the audio signal with modulator 40. As will be recognized by those of ordinary skill in the art, the modulators 38 and 40 are standard amplitude modulating circuits such as mixers. The modulators 38 and 40 are operative to modulate the carrier 100% in order to each produce a suppressed carrier amplitude modulated signal (double side band - AM DSB) having a frequency that is the frequency of the VCO 16 divided by four. The output of the modulators 38 and 40 are then fed to an adder 42 which sums the signals together to form a combined AM DSB signal. The combined AM DSB signal will be in quadrature phase because the signals from the COS divider 34 and the SIN divider 36 are added together. The combined AM DSB signal is then passed through a bandpass filter 44 for the frequency of the DSB AM signal. Next, a boost circuit 46 amplifies the AM DSB signal to a higher voltage in the range of from about 1 Vrms to 300 Vrms. Preferably, the boost circuit 46 amplifies the voltage of the AM DSB signal to about 100 Vrms. The boost circuit 46 may be either an op-amp or transformer. It will be recognized that because the slave transceiver 12 is placed within a base station, the boost circuit 46 can be realized by a transformer because size limitations are not of a concern. Additionally, the boost circuit 46 can increase the voltage to 100 Vrms because the power supply of the base station will be larger than the power supply of the earpiece. By increasing the voltage of the AM DSB signal, the impedance thereof is increased accordingly. Accordingly, the boost circuit 46 is operative to generate a high impedance AM DSB signal.

The high impedance AM DSB signal is fed to a transmit conductor 48 of the slave transceiver 14. The transmit conductor 48 may be a conductive wire which is electrically isolated from the circuitry of the slave transceiver 14. In this respect, the transmit conductor 48 generates an electric field in response to the AM DSB signal.

The AM DSB signal is detected by a receive conductor 50 of the master transceiver 12. The receive conductor 50 is operative to detect the electric field of the high impedance AM DSB signal generated by the transmit conductor 48. The high impedance AM DSB signal capacitively couples the slave transceiver 14 to the master transceiver 12 via respective transmit and receive conductors 48 and 50. The received AM DSB signal from the receive conductor 50 is fed to an impedance converter 52 of the master transceiver 12. The impedance converter 52 may be a FET configured as a source follower with unity gain in order to convert all ambient signals and avoid cross modulation products, as previously discussed for the impedance converter 24 of the slave transceiver 14. The impedance converter 52 has a high input impedance to match the impedance of the detected AM DSB signal and a lower output impedance in order to convert the impedance of the AM DSB signal to a usable quantity.

The low impedance AM DSB signal is fed to a synchronous detector 54. The synchronous detector 54 may be an analog multiplier or mixer and is operative to demodulate the AM DSB signal in order to derive the original audio signal from the slave transceiver 14. In order to provide a synchronization signal to the synchronous detector 54, a local oscillator signal is fed to the synchronous detector 54. Specifically, the local oscillator signal is the output signal of the VCO 16 wherein the frequency is divided by four. As seen in Figure 1, the output of the VCO 16 is fed to a divider 56 of the master transceiver 12. The divider 56 divides the frequency of the signal generated by the VCO 16 by four so as to be the same frequency of the AM DSB signal. As previously mentioned above, the frequency of the AM DSB signal was generated by dividing the frequency of the detected FM signal by four with the dividers 34 and 36 of the slave transceiver 14. Therefore, the signal from the divider 56 that is fed to synchronous detector 54 will have the same frequency as the detected AM DSB signal. Additionally, because the AM DSB signal was added in quadrature from the SIN divider 36 and the COS divider 34, the phase of the AM DSB signal will match that of the VCO 16 thereby negating any indeterminancy in the demodulation of the signal by the synchronous detector 54.

The synchronous detector 54 demodulates the AM DSB signal to generate a demodulated signal which is passed through a low pass filter (LPF) 56 that produces a received audio signal. The audio signal may be further processed and amplified and presented at a speaker of the earpiece for listening by the user.

As is evident from the above discussion, both the master transceiver 12 and the slave transceiver 14 use the signal from the VCO 16 for modulation and demodulation thereby saving in manufacturing and parts content. Specifically, the frequency of the received signal at the slave transceiver 14 is used in the AM modulators 38 and 40. Furthermore, the signal generated by the VCO 16 is used to demodulate the AM DSB signal received by the transceiver 12. In this respect, the VCO 16 generates the reference signal for both modulating and demodulating by the master transceiver 12 and the slave transceiver 14.

Referring to Figure 2, a second embodiment of a low-power, short-range communication system 200 is shown. The second embodiment 200 is similar to die first embodiment 10 and has a master transceiver 212 located within an earpiece and a slave transceiver 214 located in a base station. The master transceiver 212 has a voltage controlled oscillator (VCO) 216 that is operative to frequency modulate a low frequency carrier signal with the audio signal. The frequency modulated (FM) carrier signal has a frequency of between about 20 KHz to 10 MHZ with a peak deviation in the range of 10 KHz to 80 KHz.

The FM carrier signal is amplified with a boost circuit 218 that increases the voltage of the FM carrier signal to a higher voltage in the range from 1 Vrms to 300 Vrms. By increasing the voltage of the FM carrier signal, the impedance thereof has been increased. The amplified FM carrier signal from the boost circuit 218 is fed to a transmit conductor 220 which creates a high impedance electric field. The high impedance FM carrier signal is detected by a receive conductor

222 of the slave transceiver 214. In this respect, the electric field created in response to the high impedance FM carrier signal capacitively couples the transmit conductor 220 and the receive conductor 222. The FM carrier signal is fed from the receive conductor 222 to an impedance converter 224 of the slave transceiver 214. The impedance converter 224 may be a FET configured as a source follower with unity gain, as previously discussed. The input of the impedance converter 224 matches the high impedance of the received FM carrier signal. The output of the impedance converter 224 has a lower impedance such that conventional electronic components may be used to demodulate the received FM carrier signal. After the received FM carrier signal has been converted to a lower impedance, the signal is passed through a bandpass filter (BPF) 226 in order to filter the signal to the desired frequency. The filtered FM carrier signal is then fed to a phase lock loop (PLL) 228 which demodulates the signal in order to produce a received audio signal. Specifically, the PLL 228 follows the incoming FM carrier signal and the error signal therefrom is used to produce a high quality audio signal which can be further processed and presented to the attached electronics of the base station as a received audio signal.

In order to transmit a return audio signal from the base station, the slave transceiver 214 uses the audio signal that is to be transmitted to amplitude modulate the detected FM carrier signal from the PLL 228. Specifically, the frequency of the carrier signal from the PLL 228 is divided by four by a divider 230.

Next any predetermined phase drift of the carrier signal from the PLL 228 (when compared to the phase of the carrier signal from the VCO 216) is compensated by phase adjust circuit 232. The phase adjusted carrier signal from the phase adjust circuit 232 is amplitude modulated by modulator 234. Specifically, the audio signal to be transmitted is amplified by input amplifier 236 and applied to an input of the modulator 234. The modulator 234 will 100% modulate the carrier signal to generate an amplitude modulated suppressed double side band (AM DSB) signal. As seen in Figure 2, the AM DSB signal will be fed to a band pass filter 238 which will filter the signal to the desired frequency. Next, a boost circuit 240 will amplify the voltage of the AM DSB signal in order to increase the impedance thereof. Preferably, the voltage of the AM DSB signal will be increased to about 100 Vrms and applied to a transmit conductor 242 of the slave transceiver 214. The transmit conductor 242 is operative to generate an electric field in response to the high impedance AM DSB signal.

The high impedance AM DSB signal is detected by a receive conductor 244 of the master transceiver 212. In this respect, the high impedance AM DSB signal capacitively couples the transmit conductor 242 of the slave transceiver and the receive conductor 244 of the master transceiver. The high impedance AM DSB signal is fed to an impedance converter 246 which converts the high impedance AM DSB signal to a lower impedance. In order to demodulate the AM DSB signal, the master transceiver 212 uses the frequency of the VCO 216 as a synchronization signal for two synchronous detectors 248 and 250. Specifically, the carrier signal of the VCO 216 is simultaneously fed into a SIN divider 252 and a COS divider 254 which lower the frequency of the carrier signal to the same frequency as the AM DSB signal. Additionally, the COS divider 254 and the SIN divider 252 place the carrier signal in quadrature in order to eliminate indeterminancy of the phase when demodulating the AM DSB signal.

The signal from the COS divider 254 is fed to synchronous detector 248 in order to demodulate the AM DSB signal and generate the audio signal. Similarly, the signal from the SIN divider 252 is fed to synchronous detector 250 which demodulates the AM DSB signal. As will be recognized by those of ordinary skill in the art, at least one of the synchronous detectors 248 and 250 will be in phase with the AM DSB signal because the synchronization signal from the dividers 252 and 254 are in quadrature with one another. The output of each of the synchronous detectors 248 and 250 are passed through respective low pass filters (LPF's) 256 and 258. Next, each of the demodulated signals from a respective LPF 256 and 258 is fed to an envelope detector 260 which presents the strongest demodulated signal to the electronics of the earpiece. Specifically, in order to reduce noise in the communications system 200, only the output from the synchronous detector 248 and 250 which has the largest pilot tone is selected by the envelope detector 260 as the received audio signal. Furthermore, the pilot tone of the received signal may be used to adjust the gain of the master transceiver 212 in order to present the best audio signal. Alternatively, the envelope detector 260 may add the two signals together such that the user will hear the signal with the greatest strength.

In accordance with the present invention, there is provided a third embodiment of a communication system 300. The third embodiment 300 is similar to the first embodiment 10 and the second embodiment 200 except that indeterminancy in the phase of the transmitted AM DSB signal is negated by multiplying the carrier signal. Specifically, referring now to Figure 3, the communication system 300 has a master transceiver 312 disposed within an earpiece and a slave transceiver 314 disposed within a base station. In order to send an audio signal from the master transceiver 312 to the slave transceiver 314, the master transceiver 312 has a voltage controlled oscillator (VCO) 316 which frequency modulates the audio signal of the earpiece, as previously mentioned above. The VCO 316 produces a frequency modulated (FM) signal in the frequency range of from about 20 KHz to 10 MHZ. The FM signal is amplified by a boost circuit 318 such that the impedance of the FM signal is increased. Preferably, the boost circuit 318 increases die voltage of the FM signal to about 30 Vrms. The amplified FM signal is applied to a transmit conductor 320 operative to produce an electric field in response thereto. In this respect, the high impedance FM signal will generate an electric field with the transmit conductor 320. In order to detect the electric field generated by the transmit conductor 320, the slave transceiver 314 has a receive conductor 322. More specifically, the receive conductor 322 capacitively couples with the transmit conductor 320 in order to detect the electric field generated by the transmit conductor 320. The signal from the receive conductor 322 is fed to an impedance converter 324, such as a FET configured as a source follower having unity gain. The impedance converter 324 is operative to convert the high impedance FM signal into a lower impedance FM signal. The lower impedance FM signal is passed through a bandpass filter (BPF) 326 and a phase lock loop (PLL) 328 of the slave transceiver 314. The PLL 328 demodulates the FM signal, as previously discussed to generate a received audio signal.

In order to transmit signals from the slave transceiver 314 of the base station to the master transceiver 312 of the earpiece, a carrier signal derived from the PLL 328 is amplitude modulated by the audio signal of the base station. More specifically, the PLL 328 is operative to demodulate the FM signal and derive the carrier signal therefrom. As previously mentioned, the carrier signal will have the same frequency as the signal generated by the VCO 316. The frequency of the carrier signal from the PLL 328 is increased by multiplier 330. Ideally, the multiplier 330 multiplies the frequency of the carrier signal by four. Next, the carrier signal from the multiplier 330 is fed to a phase adjust circuit 332 which compensates for any predetermined phase drift.

The carrier signal from die phase adjust circuit 332 is amplitude modulated by die audio signal of the base station with modulator 334. Specifically, the audio signal from the base station is amplified by input amplifier 336 and fed to modulator 334 which amplitude modulates the carrier signal. The modulator 334 produces an amplitude modulated double side band (AM DSB) signal which is passed through bandpass filter 338 to boost circuit 340. The boost circuit 340 amplifies the voltage of the AM DSB signal to produce a high impedance signal which is fed to a transmit conductor 342 of the slave transceiver 314. The transmit conductor 342 generates an electric field in response to the AM DSB signal.

In order to detect the AM DSB signal, the master transceiver 312 has a receive conductor 344 which capacitively couples with the transmit conductor 342 of the slave transceiver 314 via the AM DSB signal. The AM DSB signal is detected by the receive conductor 344 and fed to impedance converter 346 which reduces the impedance of the AM DSB signal, as previously discussed above. The AM DSB signal is fed to an input of a synchronous detector 348. In order to demodulate the AM DSB signal with the synchronous detector 348, the carrier signal from the VCO 316 is used as a local oscillator signal. However, as seen in Figure 3, the carrier signal from the VCO 316 is multiplied by four with multiplier 350. In this respect, die frequency of the signal from the multiplier 350 will be equal to the frequency of the AM DSB signal so that the modulator 348 can demodulate the AM DSB signal.

It will be recognized that by multiplying the frequency of the carrier signal instead of dividing the frequency, indeterminancy in the phase of the received AM DSB signal by the master transceiver is reduced. Accordingly, it is not necessary to use SIN and COS dividers, as described for the first embodiment 10 and the second embodiment 200.

After the AM DSB signal is demodulated by synchronous detector 348, d e demodulated signal is passed through low pass filter (LPF) 352 in order to generate the received audio. The received audio may be further processed and amplified in order to be presented to a speaker of the earpiece. It will be recognized that it is possible for the slave transceiver to send a signal to the master transceiver that is FM modulated. In this respect, a separate FM carrier signal may be used to synchronize the master transceiver to the slave transceiver. Separate FM channels may be used to transmit and receive the communications between the master transceiver and the slave transceiver. Additionally, the present invention may be embodied wherein only half duplex communication between the master transceiver and the slave transceiver is achieved. The master transceiver may be operative to generate the electric field which is detected by die slave transceiver such that the slave transceiver does not send a return signal. Similarly, the slave transceiver may only generate the electric field which is detected by the master transceiver.

The present invention has been disclosed as being a communications link for audio communication between a base station and an earpiece. However, other types of communication links may be possible. By capacitively coupling the base station and the earpiece, it is possible to create a low-power communications system that may not be subject to governmental regulations. Furthermore, conducting bodies, such as the user, actually increase die capacitive coupling thereby increasing the efficiency of the system. It will be recognized that the present invention may be embodied in other commumcation applications. For instance, die master transceiver and the slave transceiver may be operative to transmit signals between any two closely located devices, not just an earpiece and a base station. As such the transmitted signals can be audio, data, or video signals either analog modulated, as described above, or digitally modulated with a frequency from DC to 10 MHZ. Accordingly, the above examples are only illustrative and in no way limiting of alternative devices.

Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art such as varying the frequency of the signals. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices widiin the spirit and scope of the invention. Claims:

Claims

1. A communications system, comprising: a transmitter operative to generate a high impedance signal; and a receiver operative to detect the high impedance signal; wherein the transmitter and the receiver are capacitively coupled by the high impedance signal in order to transmit the signal from the transmitter to the receiver.

2. The communications system of Claim 1 wherein the transmitter is configured to generate the high impedance signal with a frequency in the range from about 20 KHz to 10 MHZ and a voltage in the range from about 1 Vrms to 300 Vrms.

3. The communications system of Claim 2 wherein the transmitter includes a conductor operative to generate an electric field in response to the high impedance signal and the receiver comprises a conductor operative to detect electric field.

4. The communications system of Claim 3 wherein the conductor of the transmitter is sized and configured to capacitively couple with the conductor of the receiver via the electric field created in response to the high impedance signal.

5. The communications system of Claim 4 wherein the transmitter further comprises a boost circuit operative to increase the voltage of the high impedance signal and the receiver further comprises an impedance converter operative to lower the impedance of the detected high impedance signal.

6. The communications system of Claim 5 wherein the impedance converter is a FET having a high impedance input and a low impedance output.

7. The communications system of Claim 5 wherein the boost circuit is an amplifier operative to increase the voltage of the high impedance signal.

8. The communications system of Claim 7 wherein the amplifier is selected from an op-amp and a transformer.

9. The communications system of Claim 7 wherein the high impedance signal is a communications signal.

10. The communications system of Claim 9 wherein the communications signal is frequency modulated.

11. The communications system of Claim 9 wherein the communications signal is amplitude modulated.

12. The communications system of Claim 9 wherein the high impedance signal is selected from an audio signal, a data signal, and a video signal.

13. The communications system of Claim 9 wherein the high impedance signal is analog modulated.

14. The communications system of Claim 9 wherein the high impedance signal is digital modulated.

15. The communications system of Claim 1 wherein the transmitter is configured as a master transceiver and the receiver is configured as a slave transceiver.

16. A communications system, comprising: high impedance signal generating means; and high impedance signal detecting means; wherein the generating means and the detecting means are capacitively coupled in order to transmit and receive a high impedance communications signal.

17. The communications system of Claim 16 wherein the signal generating means is operative to generate the high impedance communications signal having a frequency in the range of from about 20 KHz to 10 MHZ and a voltage in the range of from about 1 Vrms to 300 Vrms.

18. The communications system of Claim 17 wherein the signal generating means includes a conductor operative to generate a high impedance electric field in response to the high impedance communications signal.

19. The communications system of Claim 18 wherein the detecting means includes a conductor operative to detect the electric field generated by the conductor of the signal generating means.

20. The communications system of Claim 19 wherein the high impedance generating means comprises a boost circuit operative to generate the high impedance communications signal on the conductor.

21. The communications system of Claim 20 wherein the detecting means includes an impedance converter to convert the high impedance communications signal to a low impedance communications signal.

22. The communications system of Claim 20 wherein the generating means is operative to generate a frequency modulated high impedance communications signal.

23. The communications system of Claim 20 wherein the generating means is operative to generate an amplitude modulated high impedance communications signal.

24. The communications system of Claim 20 wherein the high impedance signal is selected from an audio signal, a data signal, and a video signal.

25. The communications system of Claim 20 wherein the high impedance signal is analog modulated.

26. The communications system of Claim 20 wherein the high impedance signal is digital modulated.

27. A full-duplex communications system, comprising: a master transceiver operative to generate a first high impedance signal and a receive a second high impedance signal; and a slave transceiver operative to detect the first high impedance signal and generate the second high impedance signal; wherein the master transceiver and the slave transceiver are capacitively coupled by one of the first high impedance signal and the second high impedance signal.

28. The communications system of Claim 27 wherein the first high impedance signal has a frequency in the range from about 20 KHz to 10 MHZ and the frequency of the second high impedance signal is in the range from about 20 KHz to 10 MHZ, the frequency of the second high impedance signal not being equal to the frequency of the first high impedance signal.

29. The communications system of Claim 28 wherein the voltage of the first high impedance signal is in the range from about 1 Vrms to 300 Vrms and the voltage of the second high impedance signal is in the range of from about 1 Vrms to 300 Vrms, the voltage of the second high impedance signal not being equal to the voltage of the first high impedance signal.

30. The communications system of Claim 29 wherein: the master transceiver has a transmit conductor operative to generate a first high impedance electric field in response to the first high impedance signal; and the slave transceiver has a transmit conductor operative to generate a second high impedance electric field in response to the second high impedance signal.

31. The communications system of Claim 30 wherein: the slave transceiver has a receive conductor operative to detect the first electric field; and the master transceiver has a receive conductor operative to detect the second electric field.

32. The communications system of Claim 31 wherein: the transmit conductor of the master transceiver is sized and configured to capacitively couple widi the receive conductor of the slave transceiver.

33. The communications system of Claim 31 wherein: the transmit conductor of die slave transceiver is sized and configured to capacitively couple with the receive conductor of the master transceiver.

34. The communications system of Claim 31 wherein the first high impedance signal is frequency modulated and the second high impedance signal is amplitude modulated.

35. The communications system of Claim 31 wherein the first high impedance signal is amplitude modulated and the second high impedance signal is frequency modulated.

36. The communications system of Claim 31 wherein both the first and second high impedance signals are frequency modulated.

37. The communications system of Claim 31 wherein both the first and second high impedance signals are amplitude modulated.

38. A method of communicating between a transmitter and a receiver, the method comprising the steps of: a) generating a high impedance electric field with the transmitter in response to a communications signal; and b) detecting the high impedance electric field with the receiver in order to communicate between the transmitter and the receiver.

39. The method of Claim 38 wherein step (a) further comprises modulating the communications signal with the transmitter and step (b) further comprises demodulating the communications signal with the receiver in order to communicate between the transmitter and the receiver.

40. The method of Claim 39 wherein step (a) comprises frequency modulating the communications signal.

41. The method of Claim 39 wherein step (a) comprises amplitude modulating the communications signal.

42. The method of Claim 39 wherein step (a) comprises generating a high impedance electric field in response to a communications signal having a frequency in the range from about 20 KHz to 10 MHZ and a voltage in the range from about 1 Vrms to 300 Vrms.

43. The method of Claim 42 wherein step (a) comprises generating the electric field with a transmit conductor of the transmitter and step (b) comprises detecting the electric field with a receive conductor of the receiver.

44. The method of Claim 43 wherein the transmitter is a master transceiver and the receiver is a slave transceiver, the method further comprising the steps: c) generating a second high impedance electric field with the slave transceiver in response to a second communication signal; and d) detecting the second high impedance electric field with the master transceiver in order to communicate between the slave transceiver and the master transceiver.

45. The method of Claim 44 wherein step (c) comprises generating the second high impedance electric field with a transmit conductor of the slave transceiver and step (d) comprises detecting the second high impedance electric field with a receive conductor of the master transceiver.

46. The method of Claim 45 wherein step (c) comprises amplitude modulating the second communication signal prior to generating the second high impedance electric field.

47. The method of Claim 45 wherein step (c) comprises frequency modulating the second communication signal prior to generating the second high impedance electric field.