Speech processor for processing analog signals

• US 4,410,764 A
• Filed: 06/29/1981
• Issued: 10/18/1983
• Est. Priority Date: 06/29/1981
• Status: Expired due to Term

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Craiglow, Robert L., Werth, Willard F.
• Primary Examiner(s): Kemeny, Emanuel S.
• Application Number:
  US06/278,017
• Time in Patent Office: 841 Days
• Field of Search: 179/1 VL, 179/1 A, 179/1 P, 179/1 SA, 179/15.55 R, 455/47, 455/109, 455/116, 455/126, 333/14, 364/513, 364/725
• US Class Current: 704/203
• CPC Class Codes: H03G 11/00 Limiting amplitude; Limiting rate of change of amplitude ; Clipping in general
• CPC Class Codes: H03G 3/3005 in amplifiers suitable for low-frequencies, e.g. audio amplifiers H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04

Abstract

Peak-limiting AGC for increased average power SSB transmission is improved by deriving a gain-control signal using Hilbert transform detection techniques to obtain a modulated envelope signal which is compared with a peak clipping reference to form the limiting gain-control signal.

Claims

1. A speech processor for processing an analog signal comprising:

gain control means for controlling the amplitude of the analog signal, the gain control means being controlled by a peak limited modulation envelope signal to provide a limited analog signal;

Hilbert transformer means for performing a Hilbert transform on the limited analog signal to provide thereby an inphase signal and a quadrature phase signal;

audio modulation detector means for detecting the peak limited modulation envelope signal, the audio modulation detector means includes a logic means for extracting the square root of the sum of the squares of the inphase signal and the quadrature phase signal to obtain thereby a peak limited signal, reference means for providing a peak reference signal, comparator means for comparing the peak reference signal with the peak limited signal to obtain an analog peak limited modulation signal thereby, and detector means for separating the peak limited modulation envelope signal from the analog peak limited modulation signal; and

feedback path means for coupling the peak limited modulation envelope signal to the gain control means.

2. The speech processor according to claim 1, wherein the logic means comprises:

a first squaring means for squaring the inphase analog signal to obtain a first squared signal;

a second squaring means for squaring the quadrature phase signal to obtain a second squared signal;

summing means for summing the first squared signal with the second squared signal to obtain a sum of the squares signal; and

square root means for taking the square root of the sum of the squares signal to obtain limited signal thereby.

3. The speech processor according to claim 1, wherein the logic means comprises:

first absolute value means for obtaining the absolute value of the inphase signal to obtain a first absolute signal;

square means for squaring the first absolute signal to obtain a first absolute squared signal;

second absolute value means for obtaining the absolute value of the quadrature phase signal to obtain, thereby a second absolute signal;

1st summing means for summing the second absolute signal with the peak limited signal to obtain a denominator signal;

divider means for dividing the first absolute squared signal by the denominator signal to obtain thereby, a quotient signal;

2nd summing means for summing the quotient signal with the second absolute signal to obtain thereby, the peak limited signal; and

feedback path means coupling the peak limited signal to the summing means.

4. The speech processor according to claim 1, further comprising:

transducer means for transducing sound waves into the analog signal, the analog signal being representative of the sound waves.

5. The speech processor according to claim 1, further comprising:

a radio transmitter means for transmitting the inphase signal.

6. A speech processor for processing an analog signal comprising:

A Hilbert transformer means for performing a Hilbert transform on the analog signal to obtain thereby an inphase signal and a quadrature phase signal;

1st variable gain amplifier means for amplifying the inphase signal to obtain a limited inphase signal;

2nd variable gain amplifier means for amplifying the quadrature phase signal to obtain a limited quadrature phase signal;

audio modulation detector means for detecting a peak limited modulation envelope signal, the audio modular detection means includes a logic means for extracting the square root of the sum of the squares of the inphase signal and the quadrature phase signal to obtain thereby a peak limited signal, reference means for providing a peak reference signal, comparator means for comparing the peak reference signal with the peak limited signal to obtain an analog peak limited modulation signal thereby, and detector means for separating the peak limited modulation envelope signal from the analog peak limited modulation signal; and

feedback path means for coupling the peak limited modulation signal to the first and second variable gain amplifiers, the gain of the first and second variable gain amplifier being controlled by the peak limited modulation envelope signal.

7. The speech processor according to claim 6, wherein the logic means comprises:

a first squaring means for squaring the inphase analog signal to obtain a first squared signal;

a second squaring means for squaring the quadrature phase signal to obtain a second squared signal;

summing means for summing the first squared signal with the first and second squared signal to obtain a sum of the squares signal; and

square root means for taking the square root of the sum of the squares signal to obtain the square root of the sum of the squares of the inphase signal and the quadrature phase signal to obtain the peak limited signal thereby.

8. The speech processor according to claim 6, wherein the logic means comrises:

first absolute value means for obtaining the absolute value of the inphase signal to obtain a first absolute signal;

square means for squaring the first absolute signal to obtain a first absolute squared signal;

second absolute value means for obtaining the absolute value of the quadrature phase signal to obtain thereby a second absolute signal;

1st summing means for summing the second absolute signal with the peak limited signal to obtain a denominator signal;

divider means for dividing the denominator signal into the first absolute squared signal to obtain thereby a quotient signal;

2nd summing means for summing the quotient signal with the second absolute signal to obtain thereby the peak limited signal; and

feedback means for coupling the peak limited signal to the summing means.

9. The speech processor according to claim 6, further comprising:

transducer means for transducing sound waves into the analog signal, the analog signal being representative of the sound waves.

10. The speech processor according to claim 6, further comprising:

a radio transmitter means for transmitting the inphase signal.

11. A method of speech processing of an analog signal comprising:

controlling the amplitude of the analog signal in response to a peak limited modulation envelope to obtain a limited analog signal;

performing a Hilbert transform on the limited analog signal to provide thereby an inphase signal and a quadrature phase signal; and

combining the inphase signal with the quadrature phase signal, said step of combining the inphase signal with the quadrature phase signal includes the steps of squaring the inphase signal, squaring the quadrature phase signal, summing the squared inphase signal with the squared quadrature phase signal, extracting the square root of the sum of the squares of the inphase signal and the quadrature phase signal to obtain thereby a peak limited signal, providing a peak limited reference signal, comparing the peak limited reference signal with the peak limited signal to obtain an analog peak limited modulation signal, and separating the peak limited modulation envelope signal from the analog peak limited modulation signal.

12. The method of speech processing according to claim 11, wherein the step of mathematically combining the inphase signal with the quadrature phase signal and detecting the peak limited modulation envelope signal comprises:

obtaining the absolute value of the inphase signal to obtain a first absolute signal;

squaring the first absolute signal to obtain a first absolute squared signal;

obtaining the absolute value of the quadrature phase signal to obtain thereby a second absolute signal;

summing the second absolute signal with the peak limited signal to obtain a denominator signal; and

dividing the denominator signal into the first absolute squared signal to obtain thereby a quotient signal; and

summing the second absolute signal with the quotient signal to obtain thereby the peak limited signal.

13. The method of speech processing according to claim 11, further comprising the step of:

transducing sound waves into an analog signal representative of the sound waves.

14. The method of speech processing according to claim 11, further comprising, the step of:

transmitting the inphase signal.

15. A method of speech processing for processing an analog signal comprising the steps of:

performing a Hilbert transform on the analog signal to obtain thereby an inphase signal and a quadrature phase signal;

amplifying with a 1st variable gain amplifier the inphase signal to obtain a limited inphase signal;

amplifying with a 2nd variable gain amplifier the quadrature phase signal to obtain a limited quadrature phase signal;

combining the limited inphase signal with the limited quadrature phase signal, the step of combining of the inphase signal with the quadrature phase signal includes the steps of squaring the inphase signal, squaring the quadrature phase signal, summing the squared inphase signal with the squared quadrature phase signal, extracting the square root of the sum of the squares of the inphase signal and the quadrature phase signal to obtain thereby a peak limited signal, providing a peak limited reference signal, comparing the peak limited reference signal with the peak limited signal to obtain an analog peak limited modulation signal, and separating the peak limited modulation envelope signal from the analog peak limited modulation signal,

the gain of the first and second variable gain amplifier being controlled by the peak limited modulation envelope signal.

16. The method of speech processing according to claim 15, wherein the steps of mathematically combining the inphase signal with the quadrature phase signal comprises:

obtaining the absolute value of the inphase signal to obtain a first absolute signal;

squaring the first absolute signal to obtain a first absolute squared signal;

obtaining the absolute value of the quadrature phase signal to obtain thereby a second absolute signal;

summing the second absolute signal with the peak limited modulation signal to obtain a denominator signal;

dividing the denominator signal into the first absolute squared signal to obtain thereby the peak limited modulation signal;

detecting the peak limited modulation envelope signal in the peak a quotient signal; and

summing the second absolute signal with the quotient signal to obtain thereby the peak limited signal.

17. The method of speech processing according to claim 15, further comprising, the step of:

transducing sound waves into an analog signal representative of the sound waves.

18. The method of speech processing according to claim 15, further comprising, the step of:

transmitting the inphase signal.