System for short-range transmission of signals over the air using a high frequency carrier

• US 5,299,264 A
• Filed: 08/21/1991
• Issued: 03/29/1994
• Est. Priority Date: 08/21/1991
• Status: Expired due to Term

• Current Assignee: LS Research, LLC (Laird Limited)
• Original Assignee: L S Research, Inc.
• Inventors: Lofgren, John A., Buczkiewicz, Robert T., Schotz, Larry
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): Lefkowitz, Edward
• Application Number:
  US07/748,267
• Time in Patent Office: 951 Days
• Field of Search: 381/2, 381/14, 370/14, 370/120, 370/123, 370/50
• US Class Current: 381/14
• CPC Class Codes: H04B 1/04 Circuits
• CPC Class Codes: H04B 1/16 Circuits
• CPC Class Codes: H04B 7/00 Radio transmission systems, i.e. using radiation field H04B10/00, H04B15/00 take precedence
• CPC Class Codes: H04H 20/48 for FM stereophonic broadcast systems

Abstract

A system is provided which transmits either analog or digital data signals over the air. The system includes including a transmitter and a receiver. The transmitter and receiver are arranged to transmit signals using a carrier signal having a high frequency such as in the range of 902-928 MHz. The transmitter and receiver are configured to provide for the transmission of two channels of stereophonic signals while maintaining high signal-to-noise ratios, good frequency response, and low distortion. To provide for the proper transmission of signals between transmitter 10 and receiver 12, these devices include oscillating circuits having ceramic resonators which provide a base frequency which is readily modulated to facilitate proper transmission of either analog or digital signals between the transmitter and receiver. To further improve the transmission capability between the transmitter and receiver, the transmitter and receiver both include substantial buffering, isolation and shielding between selected circuit components to prevent unwanted areas of frequency modulation within the transmitter and receiver.

Claims

1. A system for the wireless transmitting over the air of at least two transmitted signals carried by radio waves the system comprising:

a transmitter including;

multiplexing means for multiplexing first and second input signals to produce a multiplexed signal,

first local oscillator means comprising;

a ground;

a varactor including a cathode and an anode wherein said anode is coupled to said ground;

a first ceramic resonator coupled to said ground, said resonator producing a carrier signal of a predetermined carrier frequency of at least 900 MHz determined by the first ceramic resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

modulation means for frequency modulating the carrier signal based upon the multiplexed signal to produce a first electric signal,

radiation means for radiating over the air without the use of wires said radio waves carrying said transmitted signals in response to said first electric signal, said radio waves having a frequency of at least 900 MHz, said radiation means comprising a first antenna,

first high impedance buffering means coupled between said first local oscillator means and said first antenna so that said first antenna is prevented from modulating the frequency of said first local oscillator means, said buffering means comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates,

said field effect transistor having a drain and a source, wherein said drain is coupled to said first antenna;

an impedance matching network comprising a capacitor and an inductor coupled between said first local oscillator means and one of said dual gates;

said voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network; and

a receiver including;

converting means for wireless receiving through the air of said radio waves carrying said transmitted signals and for converting said radio waves to a second electric signal, said converting means comprising a second antenna,

second local oscillator means comprising;

a ground;

a varactor including a cathode and an anode where the anode is coupled to the ground;

a second ceramic resonator coupled to said ground, said second ceramic resonator disposed to produce a local signal having a local frequency offset from the carrier frequency and determined by the second ceramic resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

mixing means for mixing a local signal, having a local frequency, with the second electric signal to lower the frequency of the carrier signal from the second electric signal to produce a third electric signal, where the local frequency is offset from the carrier frequency and is determined by the second ceramic resonator,

demodulation means for demodulating the third electric signal to produce a fourth electric signal, and

demultiplexing means for demultiplexing the fourth electric signal to produce fifth and sixth electric signals representative of the first and second input signals.

2. The system of claim 1, wherein the transmitted signals are digital signals.

3. The system of claim 1, wherein the transmitted signals are analog signals.

4. The system of claim 1, further comprising means for correcting the local frequency such that the local frequency is maintained offset from the carrier frequency by a predetermined offset frequency.

5. The system of claim 1 further comprising second high impedance buffering means, coupled between said second local oscillator means and said second antenna so that said second antenna is prevented from modulating the frequency of said second local oscillator, said buffering means comprising:

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates;

said field effect transistor having a drain and a source, wherein said drain is coupled to said second antenna;

a bandpass filtering network comprising a capacitor and an inductor coupled between said local oscillator and one of said dual gates;

a voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network.

6. The system of claim 1, wherein said transmitter additionally comprises output bandpass filtering means coupled to said radiation means.

7. In a system for the wireless transmitting of at least two transmitted signals carried by radio waves over the air, a transmitter comprising:

multiplexing means for multiplexing first and second input signals to produce a multiplexed signal;

local oscillator means comprising;

a ground;

a varactor including a cathode and an anode where said anode is coupled to said ground;

a ceramic resonator coupled to said ground, said resonator producing a carrier signal of a predetermined carrier frequency of at least 900 MHz determined by the ceramic resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

modulation means for frequency modulating the carrier signal based upon the multiplexed signal to produce a first electric signal;

radiation means for radiating over the air without the use of wires said radio waves carrying said transmitted signals in response to said first electric signal, said radio waves having a frequency of at least 900 MHz, said radiation means comprising an antenna; and

high impedance buffering means coupled between said local oscillator means and said antenna so that said antenna is prevented from modulating the frequency of said local oscillator means, said buffering means comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates

said field effect transistor having a drain and a source, wherein said drain is coupled to said antenna;

an impedance matching network comprising a capacitor and an inductor coupled between said local oscillator means and one of said dual gates;

said voltage source coupled to the other of said dual gates; and

said source between coupled to ground through a resistor and a capacitor network.

8. The transmitter of claim 7, wherein the transmitted signals are digital signals.

9. The transmitter of claim 7, wherein the transmitted signals are analog signals.

10. The system of claim 7, wherein said transmitter additionally comprises output bandpass filtering means coupled to said radiation means.

11. In a system for the wireless transmitting of at least two transmitted signals carried by radio waves over the air, a receiver comprising:

converting means for wireless receiving through the air of said radio waves, carrying said transmitted signals and for converting said radio waves, having a predetermined carrier frequency of at least 900 MHz, to a first electric signal including a carrier signal component, said converting means comprising an antenna;

local oscillator means comprising;

a ground;

a varactor including a cathode and an anode where the anode is coupled to the ground;

a ceramic resonator coupled to said ground, said resonator disposed to produce a local signal having a local frequency offset from the carrier frequency and determined by said resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground;

mixing means for mixing a local signal having a local frequency with the first electric signal to lower the frequency of the carrier signal component from the first electric signal to produce a second electric signal, where the local frequency is offset from the carrier frequency and is determined by the ceramic resonator;

demodulation means for demodulating the second electric signal to produce a third electric signal, the

multiplexed signal;

demultiplexing means for demultiplexing the third electric signal to produce fourth and fifth electric signals representative of the first and second input signals; and

high impedance buffering means coupled between said local oscillator means and said antenna so that said antenna is prevented from modulating the frequency of said local oscillator means said buffering means comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates

said field effect transistor having a drain and a source, wherein said drain is coupled to said antenna;

a bandpass filtering network comprising a capacitor and an inductor coupled between said local oscillator and one of said dual gates;

a voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network.

12. The receiver of claim 11, wherein the transmitted signals are digital signals.

13. The receiver of claim 11, wherein the transmitted signals are analog signals.

14. The receiver of claim 11, further comprising means for correcting the local frequency such that the local frequency is maintained offset from the carrier frequency by a predetermined offset frequency.

15. A system for the wireless transmitting over the air of first and second channel stereophonic signals carried by radio waves the system comprising:

a transmitter including;

a multiplexer disposed to multiplex first and second channel stereophonic signals to produce a composite signal,

a first local oscillator comprising;

a ground;

a varactor including a cathode and an anode where said anode is coupled to said ground;

a first ceramic resonator coupled to said ground, said resonator disposed to produce a carrier signal of a predetermined carrier frequency of at least 900 MHz determined by the first ceramic resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

modulation means for frequency modulating the carrier signal based upon the composite signal to produce a first electric signal,

a first antenna coupled to said modulating means to radiate over the air without the use of wires said radio waves carrying said first and second channel stereophonic signals in response to said first electric signal, said radio waves having a frequency of at least 900 MHz,

a first high impedance buffering circuit coupled between said first antenna and said first local oscillator, so that said first antenna is prevented from modulating the frequency of said first local oscillator, said buffering circuit comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates.

said field effect transistor having a drain and a source, wherein said drain is coupled to said first antenna;

an impedance matching network comprising a capacitor and an inductor coupled between said first local oscillator and one of said duel gates;

said voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network; and

a receiver including;

a second antenna arranged to wirelessly receive through the air said radio waves carrying said first and second channel stereophonic signals and to convert said radio waves to a second electric signal,

a second local oscillator comprising;

a ground;

a varactor including a cathode and an anode where the anode is coupled to the ground;

a second ceramic resonator coupled to said ground, said resonator disposed to produce a local signal having a local frequency offset from the carrier frequency and determined by the second ceramic resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

a mixer coupled to the second antenna and the second local oscillator to lower the frequency of the carrier signal from the second electric signal to produce a third electric signal,

a demodulator coupled to the mixer to demodulated the third electric signal to produce a fourth signal representative of the multiplexed signal,

a demultiplexer coupled to the demodulator to demultiplex the fourth electric signal to produce fifth and sixth electric signals representative of the first and second channel stereophonic signals, respectively.

16. The system of claim 15, further comprising an automatic frequency control circuit coupled to the local oscillator and the demodulator to correct the local frequency such that the local frequency is maintained offset from the carrier frequency by a predetermined offset frequency.

17. The system of claim 15, further comprising a second high impedance buffering circuit coupled between said second local oscillator and said second antenna, so that said second antenna is prevented from modulating the frequency of said second local oscillator, said buffering circuit comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates;

said field effect transistor having a drain and a source, wherein said drain is coupled to said second antenna;

a bandpass filtering network comprising a capacitor and an inductor coupled between said second local oscillator and one of said dual gates;

said voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network.

18. The system of claim 15, wherein said transmitter additionally comprises output bandpass filtering means coupled to said first antenna.

19. In a system for the wireless transmitting of first and second channel stereophonic signals carried by radio waves over the air, a transmitter comprising:

a multiplexer disposed to multiplex the first and second channel stereophonic signals to produce a composite signal;

a local oscillator comprising;

a ground;

a varactor including a cathode and an anode where said anode is coupled to said ground;

a ceramic resonator coupled to said ground, said resonator disposed to produce a carrier signal of a predetermined carrier frequency of at least 900 MHz determined by the ceramic resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

modulation means for frequency modulating the carrier signal based upon the composite signal to produce an electric signal,

an antenna coupled to said modulating means for radiating over the air without the use of wires said radio waves carrying said first and second channel stereophonic signals in response to said electric signal, said radio waves having a frequency of at least 900 MHz; and

a high impedance buffering circuit coupled between the antenna and said local oscillator, so that said antenna is prevented from modulating the frequency of said local oscillator, said buffering circuit comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates

said field effect transistor having a drain and a source, wherein said drain is coupled to said antenna;

an impedance matching network comprising a capacitor and an inductor coupled between said local oscillator and one of said dual gates;

p2 said voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network.

20. They system of claim 19, wherein said transmitter additionally comprises output bandpass filtering means coupled to said antenna.

21. In a system for the wireless transmitting of first and second channel stereophonic signals carried by radio waves over the air, a receiver comprising:

an antenna arranged to wirelessly receive through the air said radio waves carrying said first and second channel stereophonic signals and to convert said radio waves, having a predetermined carrier frequency of at least 900 MHz, to a first electric signal including a carrier signal component,

a local oscillator comprising;

a ground;

a varactor including a cathode and an anode where the anode is coupled to the ground;

a ceramic resonator coupled to said ground, said resonator disposed to produce a local frequency offset from the carrier frequency and determined by the ceramic resonator;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground;

a mixer coupled to the antenna and the local oscillator to lower the frequency of the carrier signal component from the second electric signal to produce a second signal;

a demodulator coupled to the mixer to demodulate the second electric signal to produce a third electric signal representative of the composite signal;

a demultiplexer coupled to the demodulator to demultiplex the third electric signal to produce fourth and fifth electric signals representative of the first and second channel stereophonic signals, respectively; and

a high impedance buffering circuit coupled between the local oscillator and the antenna, so that said antenna is prevented from modulating the frequency of said local oscillator, said buffering circuit comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor having dual gates;

said field effect transistor having a drain and a source, wherein said drain is coupled to said antenna;

a bandpass filtering network comprising a capacitor and an inductor coupled between said local oscillator and one of said dual gates;

a voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network.

22. The receiver of claim 21, further comprising an automatic frequency control circuit coupled to the local oscillator and the demodulator to correct the local frequency such that the local frequency is maintained offset from the carrier frequency by a predetermined offset frequency.

23. A system for the wireless transmitting of a digital signal carried by a radio waves, over the air, the system comprising:

a transmitter including;

a first local oscillator comprising;

a ground;

a first ceramic resonator coupled to said ground, said resonator disposed to produce a carrier signal of a predetermined carrier frequency of at least 900 MHz determined by a first ceramic resonator;

a varactor including a cathode and an anode where said anode is coupled to said ground, said varactor modulates the carrier signal based upon the digital signal to produce a first electric signal;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

a first antenna coupled to the first local oscillator to radiate over the air without the use of wires said radio waves carrying said digital signal in response to said first electric signal, said radio waves having a frequency of at least 900 MHz,

a high impedance buffering circuit coupled between the first local oscillator and the first antenna, so that said first antenna is prevented from modulating the frequency of said first local oscillator, said buffering circuit comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates

said field effect transistor having a drain and a source, wherein said drain is coupled to said first antenna;

an impedance matching network comprising a capacitor and an inductor coupled between said first local oscillator and one of said dual gates; and

said voltage source coupled to the other of said dual gates; and

a receiver including;

a second antenna arranged to wirelessly receive through the air said radio waves carrying said digital signal and to convert said radio waves, having a predetermined carrier frequency of at least 900 MHz, to a second electric signal,

a second local oscillator comprising;

a ground;

a second ceramic resonator coupled to said ground, said resonator disposed to produce a local frequency offset from the carrier frequency and determined by the second ceramic resonator;

a second varactor including a cathode and an anode where the anode is coupled to the ground, said varactor controls the local signal;

a first capacitor coupled between said resonator and said cathode of said varactor;

a second capacitor connected in series with a third capacitor, said second and third capacitors coupled between said ground and a junction between said first capacitor and said resonator, said third capacitor being an adjustable capacitor;

a common base Colpitts oscillator having a transistor including a base, a collector, and an emitter, wherein said base is coupled to said ground by a fourth capacitor;

a fifth capacitor coupled between said junction and said collector;

a sixth capacitor coupled between said collector and the emitter of said transistor;

a voltage source coupled to said collector and to said base;

a first filtering circuit coupled between said emitter and said ground; and

a second filtering circuit coupled between said base and said ground,

a mixer coupled to the second antenna and the local oscillator to lower the frequency of the carrier signal from the second electric signal to produce a third electric signal,

a demodulator coupled to the mixer to remove the carrier signal from the third electric signal to produce a fourth electric signal.

24. The system of claim 23, further comprising an automatic frequency control circuit coupled to the second local oscillator and the demodulator to correct the local frequency such that the local frequency is maintained offset from the carrier frequency by a predetermined offset frequency.

25. The system of claim 23, further comprising a high impedance buffering circuit coupled between said second local oscillator and said second antenna, so that said second antenna is prevented from modulating the frequency of said second local oscillator, said buffering circuit comprising;

a dual gate gallium arsenide metal oxide semiconductor field effect transistor, having dual gates;

said field effect transistor having a drain and a source, wherein said drain is coupled to said second antenna;

a bandpass filtering network comprising a capacitor and an inductor coupled between said second local oscillator and one of said dual gates;

said voltage source coupled to the other of said dual gates; and

said source being coupled to ground through a resistor and a capacitor network.

26. The system of claim 23, wherein said transmitter additionally comprises output bandpass filtering means coupled to said first antenna.