MODULATION SYSTEM

• US 3,778,718 A
• Filed: 04/28/1972
• Issued: 12/11/1973
• Est. Priority Date: 04/28/1972
• Status: Expired due to Term

• Current Assignee: JM Huber Corporation
• Original Assignee: Harland A. Bass, Yves C. Faroudja
• Inventors: Faroudja, Yves C., Bass, Harland A.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/248,556
• Time in Patent Office: 592 Days
• Field of Search: 178/DIG.3,6.6A 179/1.2MD,15BU,15BT 325/45,46,47,49,59,60,139,145 332/17,21
• US Class Current: 455/102
• CPC Class Codes: H03C 5/00 Amplitude modulation and angle modulation produced simultaneously or at will by the same modulating signal H03C7/00 takes precedence

Abstract

A system for modulating a wideband information signal, in which the information signal is separated into a multiplicity of frequency bands. The several frequency bands are used to modulate a carrier signal in two ways, i.e., frequency modulation and suppressed-carrier amplitude modulation, the modulated signals being added to provide a composite output signal. The composite signal has a maximum number of desirable characteristics and a minimum number of undesirable characteristics, in that the advantages of wide-deviation are partially utilized while the over-all band width is not excessive.

Claims

1. A modulation system comprising:

a source of modulating signal having a high-frequency portion and a low-frequency portion;

a frequency modulator for producing a frequency-modulated signal in response to said low-frequency portion of said modulating signal;

a suppressed-carrier amplitude modulator having an input coupled to the output of said frequency modulator for modulating said frequency-modulated signal by said high-frequency portion of said modulating signal to produce a suppressed-carrier amplitude-modulated signal; and

means coupled to the outputs of said frequency-modulator and said suppressed carrier amplitude modulator for combining said frequency-modulated signal and said suppressed-carrier amplitude modulated signal to provide a combined modulated signal.

2. The modulation system of claim 1, further comprising filter means for separating said modulating signal into a high-frequency component and a low-frequency component, said filter means comprising:

a low-pass filter for passing the portion of said modulating signal below a predetermined frequency the output of said low-pass filter being coupled to an input of said frequency modulator; and

a high-pass filter for passing the portion of said modulating signal above said predetermined frequency the output of said high-pass filter being coupled to an input of said suppressed carrier amplitude modulator.

3. The modulation system of claim 2, wherein the transfer impedance characteristics of said low-pass filter and said high-pass filter are tapered to provide a gradual transition between said low-frequency portion and said high-frequency portion of said modulating signal.

4. The modulation system of claim 2, wherein the transfer impedance characteristic of said high-pass filter is independent of the frequency of said modulating signal.

5. The modulation system of claim 2, wherein the transfer impedance characteristic of said high-pass filter varies with the frequency of said modulating signal.

6. The modulation system of claim 2, wherein said low-pass filter is characterized by a substantially constant time delay for all frequencies in said low-frequency portion of said modulating signal.

7. The modulation system of claim 6, wherein said low-pass filter comprises a Bessel filter.

8. The modulation system of claim 6, wherein said high-pass filter comprises:

time delay means for delaying said modulating signal by an amount substantially equal to said time delay of said low-pass filter to produce a delayed modulating signal; and

means for subtracting said low-frequency portion of said modulating signal from said delayed modulating signal to produce said high-frequency portion of said modulating signal.

9. The modulating system of claim 8, wherein said subtracting means comprises:

means for inverting said delayed modulating signal with respect to said low-frequency portion of said modulating signal; and

means for adding said inverted delayed modulating signal and said low-frequency portion of said modulating signal to provide said high-frequency portion of said modulating signal.

10. The modulation system of Claim 9, further comprising:

means for modifying the frequency response of said high-frequency portion of said modulating signal, and means for applying said modified frequency response high-frequency portion of said modulating signal to the input of said suppressed-carrier amplitude modulator.

11. The modulation system of Claim 2, wherein the ratio of a. the frequency deviation of said frequency-modUlated signal corresponding to the maximum amplitude of said modulating signal to (b) said predetermined frequency, is at least unity.

12. A modulation system comprising:

filter means for separating a modulating signal into a high-frequency portion and a low-frequency portion;

a frequency modulator for producing a frequency-modulated signal in response to said low-frequency portion of said modulating signal;

a 90* phase-shifter coupled to the output of said frequency-modulator for producing a 90* phase-shifted frequency-modulated signal;

a suppressed-carrier amplitude modulator coupled to the output of said 90* phase-shifter for modulating the 90* phase shifted frequency-modulated signal by said high-frequency portion of said modulating signal to produce a suppressed-carrier amplitude modulated signal; and

means coupled to the outputs of said frequency modulator and said suppressed-carrier amplitude modulator for combining said frequency-modulated signal and said suppressed-carrier amplitude modulated signal to produce a combined modulated signal.

13. The modulation system of claim 12, wherein said suppressed-carrier modulator comprises a balanced amplitude-modulator.

14. A modulation system comprising:

means for separating a modulating signal into a high-frequency portion and a low-frequency portion;

a frequency modulator for producing a frequency-modulated signal in response to said low-frequency portion of said modulating signal;

means coupled to the output of said frequency modulator for shifting the phase of said frequency-modulated signal by 90*;

a suppressed-carrier modulator having an input coupled to the output of said phase shifting means for modulating said phase-shifted signal by said high-frequency portion of said modulating signal to produce a suppressed-carrier modulated signal; and

means coupled to the outputs of said frequency modulator and said suppressed-carrier modulator for adding said frequency-modulated signal and said suppressed-carrier-modulated signal to produce a combined output signal.

15. The method of modulating a wide-band information signal, comprising the steps of:

separating said wide-band information signal into an upper frequency portion and a lower frequency portion;

frequency modulating a carrier signal by said lower frequency portion of said information signal to produce a frequency-modulated signal;

suppressed-carrier amplitude modulating said frequency-modulated signal by said upper frequency portion of said information signal to produce a suppressed-carrier amplitude modulated signal; and

adding said frequency-modulated signal and said suppressed-carrier amplitude modulated signal to produce a composite modulated signal.

16. The method of claim 15, wherein the step of separating said wide-band information signal into an upper frequency portion and a lower frequency portion comprises the steps of:

subtracting said low-frequency portion from said wide-band information signal to produce said high-frequency portion.

17. The method of claim 16, wherein the step of subtracting said low-frequency portion from said wide-band information signal comprises the steps of:

inverting said wide-band information signal; and

adding said low-frequency portion to the inverted wide-band information signal to produce said high-frequency portion.

18. The method of claim 15, further comprising the step of modifying the frequency response of said high-frequency portion of said information signal prior to the step of suppressed-carrier amplitude modulating said high-frequency portion.

19. A bandwidth reduction system adapted to have applied thereto a video signal extending over a wide frequency spectrum comprising:

means for separating the video spectrum into first and second subspectra, the first subspectrum containing predominantly lower-frequency video signal components and the secOnd frequency subspectrum containing predominantly upper frequency components;

means coupled to an output of said separating means for wide-deviation frequency-modulating the first subspectrum onto said carrier to produce a frequency-modulated signal;

means coupled to the output of said frequency modulating means for suppressed-carrier amplitude modulating the second subspectrum onto said frequency-modulated signal; and

means coupled to the outputs of said frequency modulating means and said suppressed-carrier amplitude modulating means for combining the resultant modulated signals to provide over-all modulated signals effectively occupying a band narrower than would be occupied by the entire video signal if said entire video signal were wide-deviation frequency modulated.

20. A system as in claim 19 further including means for causing a 90* phase shift between said frequency-modulated signal and the amplitude-modulated signal supplied to said combining means.

21. A system as in claim 19 further comprising a 90* phase shifter between the output of said frequency modulator and an input of said amplitude-modulator.

22. A system as in claim 1 further comprising a 90* phase shifter between the output of said frequency-modulator and the input of said suppressed carrier amplitude-modulator.

23. The method of producing a modulated carrier from a modulating signal having a high-frequency portion and a low-frequency portion comprising the steps of producing a carrier signal modulated by said high-frequency modulating signal portion so as to have sidebands of only first order, producing a second carrier signal of the same frequency as and coherent with said first carrier signal and wide deviation frequency-modulated by said low-frequency modulating signal portion and combining said two modulated signals to form a composite modulated signal.

24. The system of claim 22 wherein said 90* phase-shifter comprises a wide band 90* phase-shifter.

25. The system of claim 24 wherein said wide band 90* phase-shifter comprises:

a divide by two circuit coupled to the output of said frequency modulator, said divide by two circuit having first and second complementary outputs;

an inverter coupled to the output of said frequency modulator;

a first NAND circuit having a first input coupled to the output of said inverter and a second input coupled to said first complementary output of said divide by two circuit;

a second NAND having a first input coupled to the output of said inverter and a second input coupled to said second complementary output of said divide by two circuit; and

a flip-flop having a first input coupled to the output of said first NAND circuit and a second input coupled to the output of said second NAND circuit, the output of said flip-flop being connected to an input of said suppressed-carrier amplitude modulator.