Full duplex FSK system

• US 5,241,566 A
• Filed: 12/13/1988
• Issued: 08/31/1993
• Est. Priority Date: 12/13/1988
• Status: Expired due to Fees

• Current Assignee: E-Systems Incorporated (Rtx Corporation)
• Original Assignee: E-Systems Incorporated (Rtx Corporation)
• Inventors: Jackson, Charles R.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Tse, Young
• Application Number:
  US07/283,854
• Time in Patent Office: 1,722 Days
• Field of Search: 375/62, 375/61, 375/65, 375/88, 375/91, 375/9, 375/45, 329/300, 329/302, 332/100, 370/24
• US Class Current: 375/277
• CPC Class Codes: H04L 27/12 Modulator circuits; Transmitter circuits
• CPC Class Codes: H04L 27/1525 using quadrature demodulation

Abstract

A frequency agile homodyne full duplex FSK system having a receiver section using an image-cancellation mixer wherein sum and difference signals generated by a pair of double-balanced mixers are added together with proper phase to cancel out the image response normally associated with heterodyne receivers and directly down-convert the carrier frequency to the baseband frequency. The transmitter section of the FSK system consists of an FSK modulator whose peak deviation is controlled by an active derivative of a crystal clock. The FSK modulator functions in the manner of a phasing single sideband (SSB) mixer with upper or lower sideband signals generated by the proper phasing of quadrature components of the carrier frequency and the peak deviation signal derived from a crystal clock.

Claims

1. A wideband single sideband FSK transmitter comprising:

a. a clock for providing a desired R.F. carrier frequency, f_c and a peak deviation frequency, Δ

f

b. means for generating baseband FSK data representing a mark or a space state, and

c. a single sideband modulator coupled to the clock and the FSK data generating means for producing quadrature components of the carrier frequency, f_c, and the deviation frequency, Δ

f, and generating a single sideband output R.F. carrier signal, f_c, having a peak deviation frequency of Δ

f and directly modulated with the baseband FSK data.

2. A single sideband FSK transmitter as in claim 1 wherein said modulator includes a single sideband mixer for receiving the peak deviation signal, Δ

f, and the R.F. carrier frequency, f_c, and generating upper or lower sideband FSK-modulated R.F. output signals by proper phasing of the quadrature components of the f_c and Δ

f signals.

3. A single sideband FSK transmitter as in claim 2 wherein the single sideband modulator further includes:

a. means for receiving the peak deviation signal, Δ

f, and generating a Δ

f reference signal and a Δ

f quadrature signal shifted 90°

with respect to the reference signal, and

b. means in the reference signal generating means for receiving the FSK signal and causing a +90°

phase-shifted Δ

f quadrature output signal when the FSK signal represents one of the mark and space states and a -90°

phase-shifted quadrature output signal when the FSK signal represents the other of the mark and space states.

4. A single sideband FSK transmitter as in claim 3 wherein the reference Δ

f signal generating means is a shift-left, shift-right TTL logic circuit.

5. An FSK transmitter as in claim 4 wherein said single sideband mixer further comprises:

a. a first mixer for receiving the ±

90°

phase-shifted Δ

f signal and a quadrature component of the R.F. carrier frequency f_c, and generating a first FSK-modulated output signal,

b. a second mixer for receiving the reference Δ

f signal and the R.F. carrier frequency, f_c, and generating a second FSK-modulated output signal, and

c. means coupled to the first and second mixers for summing the first and second FSK-modulated signals and producing a single sideband FSK-modulated R.F. carrier output signal, f_c, having a peak deviation frequency of Δ

f.

6. An FSK transmitter as in claim 5 wherein the ±

90°

phase-shifted Δ

f signals determine which of the upper or lower sidebands is transmitted.

7. An FSK transmitter as in claim 2 wherein the single sideband modulator further includes:

a. An R.F. switch for receiving the carrier frequency, f_c

b. said R.F. switch including means for receiving the FSK data and generating a first quadrature carrier frequency output signal, f_c, when the FSK data represents a mark and a second quadrature carrier frequency output signal, when the FSK data represents a space;

c. means for receiving the peak deviation signal Δ

f, and generating a Δ

f reference component signal and Δ

f quadrature component signal shifted 90°

with respect to the reference component signal;

d. said single sideband mixer having first and second quadrature ports for respectively receiving one of the first and second quadrature signals, f_c and a third and fourth ports for respectively receiving one of the quadrature components of the deviation frequency, Δ

f, said single sideband mixer generating upper or lower sideband FSK-modulated R.F. output signals in accordance with the first and second quadrature signals generated by the means for receiving the FSK data.

8. An FSK transmitter as in claim 7 further comprising:

a. said first quadrature port of said single sideband mixer comprising a first mixer having 0°

ports for receiving the first quadrature carrier frequency, f_c, and the reference component of the deviation frequency, Δ

f, and generating a first FSK-modulated output signal,

b. said second quadrature port of said single sideband mixer comprising a second mixer having 90°

ports for receiving the second quadrature carrier frequency, f_c, and the quadrature component of the deviation frequency, Δ

f, and generating a second FSK-modulated output signal, and

c. means coupled to the first and second mixers for summing the first and second FSK-modulated output signals and producing a single sideband FSK-modulated R.F. carrier signal, f_c, having a peak deviation frequency of Δ

f.

9. A wideband single sideband FSK receiver comprising:

a. an input R.F. amplifier for receiving and amplifying a single sideband carrier signal, f_c, FSK-modulated with baseband mark and space data and generating an output,

b. a local oscillator for generating a signal output at a frequency substantially equal to the frequency of the carrier signal, f_c,

c. a demodulator for receiving the output of the R.F. amplifier and the output of the local oscillator, and recovering the FSK data representing the baseband mark and space data directly at baseband frequency, said demodulator comprising;

a phase splitter for receiving said FSK-modulated carrier, f_c, and generating quadrature component signals,

a first balanced mixer receiving a respective one of the quadrature component signals and the local oscillator output generating a first demodulated output signal at baseband frequency,

a second balanced mixer receiving a respective one of the quadrature component signals and the local oscillator output generating a second demodulated output signal at baseband frequency, and

a second phase splitter having separate output channels and input channels coupled to the balanced mixers for receiving the first and second demodulated output signals and adding the first and second signals phase adjusted to minimize any adverse image response and generate baseband mark and space data signals at baseband frequency on separate output channels, and

d. means coupled to the demodulator for recovering signals representing the baseband mark and space data.

10. A receiver as in claim 9 wherein said means for recovering comprises;

a. first and second baseband filters individually coupled to a separate output channel from the second phase splitter for filtering the modulation data to reject adjacent channel signals,

b. first and second amplifiers individually coupled to the output of one of the baseband filters for amplifying the mark and space data signals,

c. first and second level detectors individually coupled to the output of one of the amplifiers, and

d. a differential amplifier for receiving the outputs of each level detector and generating data representing the FSK mark and space modulation data.

11. A receiver as in claim 10 further including:

a. a summing circuit coupled to the outputs of the first and second level detectors,

b. an AGC filter coupled to the output of the summing circuit and generating an output signal, and

c. an AGC amplifier coupled to the AGC filter for amplifying the output signal of the AGC filter for use by the input R.F. amplifier to control signal gain.

12. A full duplex FSK transmitting and receiving system comprising:

a. a clock circuit including a single frequency synthesizer for generating an R.F. carrier signal having a center frequency, f_c, for both the transmitter and the receiver,

b. a transmitter having a modulator for frequency-shift-keying the R.F. carrier with mark and space data directly at baseband frequency, said modulator comprising;

means for generating FSK data representing a mark or a space state, and

a single sideband modulator coupled to said clock circuit and the FSK data generating means for generating a single sideband output R.F. carrier signal, f_c, having a peak deviation frequency of Δ

F and modulated with the baseband frequency FSK data, and

c. a receiver for translating an input FSK-modulated carrier directly to baseband frequency for recovering the mark and space data.

13. A system as in claim 12 wherein said single sideband modulator comprises a single sideband mixer for receiving the peak deviation signal, Δ

f, and the R.F. carrier frequency, f_c, and generating upper or lower sideband FSK-modulated R.F. output signals by proper phasing of quadrature components of the f_c and Δ

f signals.

14. A system as in claim 13 wherein the single sideband mixer comprises:

a. means for receiving the peak deviation signal, Δ

f, and the FSK modulation signals and generating a reference Δ

f signal, and

b. means for receiving the FSK signal and to cause the quadrature Δ

f signal to be a +90°

phase-shifted Δ

f output signal when the FSK signal represents one of the mark and space states and a -90°

phase-shifted output signal when the FSK signal represents the other of the mark and space states.

15. A system as in claim 14 wherein the means for generating the quadrature and reference Δ

f signal comprises a shift-left, shift-right TTL logic circuit.

16. A system as in claim 15 wherein said single sideband mixer further comprises:

a. a first mixer for receiving the ±

90°

phase-shifted Δ

f signal and the R.F. carrier frequency, f_c, and generating a first FSK-modulated output signal,

b. a second mixer for receiving the reference Δ

f signal and the R.F. carrier frequency f_c, and generating a second FSK-modulated output signal, and

c. means coupled to the first and second mixers for summing the first and second FSK-modulated signals and producing a single sideband FSK-modulated R.F. carrier output signal, f_c, having a peak deviation frequency of Δ

f.

17. A system as in claim 16 wherein the ±

90°

phase-shifted Δ

f signals determine which of the upper or lower sidebands is transmitted.

18. A system as in claim 13 wherein the single sideband modulator further includes:

a. an R.F. switch for receiving the carrier frequency, f_c,

b. said R.F. switch receiving the FSK data and generating a first quadrature carrier frequency output signal, f_c, when the FSK data represents a mark and a second quadrature carrier frequency output signal, f_c, when the FSK data represents a space, and

c. means for receiving the peak deviation frequency, Δ

f, and generating a Δ

f reference component and a quadrature component shifted 90°

with respect to the reference component; and

wherein

said single sideband mixer includes first and second ports for receiving one of the first and second quadrature signals, f_c, and third and fourth ports receiving respective ones of the quadrature components of the deviation frequency, Δ

f, said single sideband mixer generating upper or lower sideband FSK-modulated R.F. output signals in accordance with the quadrature f_c signal received by the first or second ports.

19. A system as in claim 18 wherein said single sideband mixer further comprises:

a. a first mixer having 0°

ports for receiving the first quadrature carrier frequency, f_c, and the reference component of the deviation frequency, Δ

f, and generating a first FSK-modulated output signal,

b. a second mixer having 90°

ports for receiving the second quadrature carrier frequency, f_c, and the quadrature component of the deviation frequency, Δ

f, and generating a second FSK-modulated output signal, and

c. means coupled to the first and second mixers for summing the first and second FSK-modulated output signals and producing a single sideband FSK-modulated R.F. carrier output signal, f_c, having a peak deviation frequency of Δ

f.

20. A full duplex FSK transmitting and receiving system as in claim 12 wherein the receiver for translating the input carrier directly to baseband frequency further comprises:

a. an input R.F. amplifier for receiving and amplifying a single sideband carrier signal, f_c FSK-modulated with baseband mark and space data and generating an output,

b. a demodulator and image cancellation circuit receiving the output of the R.F. amplifier and the synthesizer frequency, and recovering the FSK data representing the baseband mark and space signal at the baseband frequency, said demodulator comprising;

means for receiving the output of the R.F. amplifier and generating quadrature component signals,

a double balanced mixer receiving the quadrature component signals and the carrier signal at center frequency, and generating a demodulated output signal at baseband frequency, and

means for receiving the demodulated output signals from said double balanced mixer for generating baseband mark and space data signals at baseband frequency on separate output channels.

21. The system as in claim 20 wherein said receiver further comprises:

a. first and second baseband filters individually coupled to a separate output channel from the means for receiving for filtering the modulation data to reject adjacent channel signals,

b. first and second amplifiers individually coupled to the output of one of the baseband filters for amplifying the mark and space data signals,

c. first and second level detectors individually coupled to the output of one of the amplifiers, and

d. a differential amplifier for receiving the outputs of each level detector and generating data representing the FSK mark and space modulation data.

22. A receiver as in claim 21 further including:

a. a summing circuit coupled to the output from each level detector,

b. an AGC filter coupled to the output of the summing circuit and generating an output signal, and

c. an AGC amplifier coupled to the AGC filter for amplifying the output signal of the AGC filter for use by the input R.F. amplifier to control signal gain.

23. A method of generating a single sideband FSK-modulated output R.F. carrier signal comprising the steps of:

a. generating a desired R.F. carrier frequency, f_c, and a baseband peak deviation frequency, Δ

f

b. generating baseband FSK data representing a mark or a space state, and

c. directly modulating quadrature components of the R.F. carrier frequency, f_c, with quadrature components of the baseband deviation frequency, Δ

f, and generating the single sideband output R.F. carrier, f_c, having a peak deviation frequency of Δ

f.

24. A method as in claim 23 wherein the step of directly modulating the R.F. carrier frequency further comprises the steps of:

a. mixing the generated quadrature components of the baseband peak deviation signal, Δ

f, and the R.F. carrier frequency, f_c, with a single sideband mixer, and

b. generating upper or lower sideband FSK-modulated signals with said mixer by proper phasing of the quadrature components of the f_c, and Δ

f, signals.

25. A method of recovering FSK data from a single sideband R.F. carrier signal, f_c, FSK modulated with baseband mark and space data comprising the steps of:

a. amplifying the single sideband R.F. carrier signal, f_c, FSK-modulated with the baseband mark and space data,

b. generating a local oscillator frequency of f_c,

c. generating quadrature component signals from the amplified FSK-modulated single sideband R.F. carrier signal, f_c,

d. double-balanced mixing each of the quadrature components and the local oscillator frequency, f_c,

e. generating a demodulated signal at baseband frequency in response to the double-balanced mixing of the quadrature components, the demodulated signal having a sum and a difference signal,

f. adding the sum and difference signals phase adjusted to minimize image response and generate the baseband mark and space data signals at baseband frequency on separate channels, and

g. recovering the FSK data represented by the generated baseband mark and space data signals in each channel.

26. A method of providing a full duplex FSK transmitting and receiving system comprising the steps of:

a. generating a R.F. carrier signal having a center frequency, f_c, for both a transmitter and a receiver by a common center frequency synthesizer,

b. frequency-shift-keying the R.F. carrier signal, said frequency-shift-keying comprising the steps of;

generating a baseband frequency FSK data signal representing a mark or space state, and

modulating the R.F. carrier signal with the baseband frequency FSK data to generate a single sideband output R.F. carrier signal, f_c, having a peak deviation frequency of Δ

f, and

c. translating an input FSK-modulated carrier directly to baseband frequency in a receiver for recovering the mark and space data.

27. A wideband single sideband FSK transmitter comprising:

a clock means for providing a desired R.F. carrier frequency signal, f_c, and a peak deviation frequency signal, Δ

f;

means for generating a baseband FSK data signal representing a baseband mark of a space state;

means for generating quadrature components of the R.F. carrier frequency signal f_c ;

means for generating quadrature components of the deviation frequency signal Δ

f from the FSK baseband signal wherein the quadrature components comprise a deviation frequency Δ

f reference signal and a 90°

shifted deviation frequency Δ

f signal such that there is a +90°

phase shift for a first baseband mark or space state and a -90°

phase shift for a second baseband mark or space state in the shifted deviation frequency Δ

f signal;

a single sideband modulator for receiving the quadrature R.F. carrier frequency signals, f_c and the shifted and reference deviation frequency Δ

f signals and generating direct FSK modulated R.F. single sideband output.

28. An FSK transmitter as in claim 27 wherein:

said single sideband modulator comprises;

a first mixer for receiving the ±

90°

phase-shifted deviation frequency Δ

f signal and a first quadrature component of the R.F. carrier frequency signal, f_c, and generating a first FSK-modulated signal,

a second mixer for receiving the deviation frequency Δ

f reference signal and a second quadrature component of the R.F. carrier frequency signal, f_c, and generating a second FSK-modulated signal, and

further comprising;

means coupled to the first and second mixers for summing the first and second FSK-modulated signals and generating a single sideband FSK-modulated R.F. carrier output signal at a carrier frequency f_c having a peak deviation frequency of Δ

f.

29. A method of generating a single sideband FSK-modulated output R.F. carrier signal comprising the steps of:

generating an R.F. carrier signal at a frequency f_c ;

generating a peak deviation signal deviating by a frequency Δ

f from the R.F. carrier signal;

generating baseband FSK data representing a mark or a space state;

shifting the deviation frequency Δ

f signal ±

90°

according to the mark or space state of the FSK baseband data to generate quadrature deviation frequency Δ

f signal components;

shifting the R.F. carrier frequency f_c signal to generate quadrature carrier frequency f_c components;

mixing a fist quadrature deviation frequency Δ

f signal component with a first quadrature carrier frequency f_c component to generate a first FSK-modulated signal;

mixing a second quadrature deviation frequency Δ

f signal component with a second quadrature carrier frequency f_c component to generate a second FSK-modulated signal; and

adding the first and second FSK-modulated output signals to output a direct FSK modulated R.F. carrier signal.