Correlation detector employing two level A/D conversion and arithmetic sign control

• US 5,623,520 A
• Filed: 11/28/1995
• Issued: 04/22/1997
• Est. Priority Date: 06/21/1994
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Kaiser, Stephen G.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): LUTHER, WILLIAM A
• Application Number:
  US08/563,555
• Time in Patent Office: 511 Days
• Field of Search: 375/343, 375/318, 375/328, 375/349, 375/351, 375/340, 375/346, 375/348, 375/322, 375/324, 375/261, 375/281, 375/285, 375/235, 329/304, 329/306, 329/345, 329/346, 329/358, 364/724.03, 364/728.03, 370/18, 370/107
• US Class Current: 375/343
• CPC Class Codes: G01S 7/2923 based on data belonging to a number of consecutive radar periods
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

A correlation detector, in which an input signal is applied to a first path and a second path. The correlation detector includes an arithmetic sign control device applied to the first path and the second path, replacing the more transitional digital multipliers. Additionally, a comparator is used in the present invention which replaces the more traditional A/D converters.

Claims

1. A correlation detector, in which an analog sinusoidal input signal having an SNR less than 1 is applied, after digitizing into a digitized input signal, to a first path and a second path, each of which paths has an output and is provided with a correlated sinusoidal signal for combination with said digitized input signal to produce combined signals and has a portion for integrating and a portion for squaring said combined signals, and wherein the outputs of said first and second paths are summed in a summer portion having an output and a threshold comparator compares the output of said summer portion to a predetermined limit, which correlation detector comprises:

limiter/comparator means for digitizing said analog sinusoidal input signal by performing a two level A/D conversion on said analog sinusoidal input signal to produce a digitized two level input signal having a value of either +1 or -1 for application to said first and second paths;

means for producing a sine output and a cosine output, said sine output being in electrical communication with said first path, and said cosine output being in electrical communication with said second path, said sine and cosine outputs comprising said correlated sinusoidal signals and each having one of the values of -1, or 0, or +1; and

a first arithmetic sign control device disposed in said first path before said portion for integrating, and a second arithmetic sign control device disposed in said second path before said portion for integrating, each of said first and second arithmetic sign control devices receiving respective inputs with one of the values of -1, or 0, or +1, from said means for producing a sine output and a cosine output, when acting to combine said digitized two level input signal respectively with said correlated sinusoidal signals, whereby said combined signals comprise an inverted value, or a null value, or the same value, respectively, as the value of said two level digitized input signal.

2. A correlation detector as in claim 1, wherein said means for producing a sine output and a cosine output comprises:

a local oscillator; and

clock means for inputting a frequency to said local oscillator four times that of said local oscillator to produce the output values -1, 0, and +1.

3. A method of performing digital multiplication in a correlation detector, in which a sinusoidal input signal having an SNR less than 1 is applied, after digitizing into a digitized input signal, to a first path and a second path, each of which paths has an output and is provided with a correlated sinusoidal signal for combination with said digitized input signal to produce combined signals and has a portion for integrating and a portion for squaring said combined signals, and wherein the outputs of said first and second paths are summed in a summer portion having an output and a threshold comparator compares the output of said summer portion to a predetermined limit, comprising the steps of:

digitizing said sinusoidal input signal by performing a two level A/D conversion thereon to produce a digitized two level input signal having a value of either +1 or -1 for application to said first and second paths;

providing an arithmetic sign control portion in each of said first and second paths between said digitized two level input signal and said portion for integrating; and

applying each of said correlated sinusoidal signals as outputs of a local oscillator respectively into said arithmetic sign control portions, each with one of the values of -1, or 0, or +1, when combining said digitized two level input signal with each of said correlated sinusoidal signals, whereby said combined signals comprise an inverted value, or a null value, or the same value, respectively, as the value of said digitized two level input signal.

4. A method as in claim 3, wherein a clocked input is provided to said local oscillator having a frequency four times that of said local oscillator to produce the output values -1, 0, and +1.

5. A correlation detector, having a first path and a second path, each of which paths is provided with a correlated sinusoidal signal for combination with a two level digitized input signal to produce a respective combined signal and has a portion for integrating and a portion for squaring said respective combined signal, comprising:

a hard limiter/comparator device which is configured to be operated with an S/N ratio of less than 1 for performing a two level A/D conversion on an analog sinusoidal signal input thereto, having an S/N ratio of less than 1, to provide said two level digitized input signal having values of either +1 or -1;

means for producing a sine output and a cosine output, said sine output being in electrical communication with said first path, and said cosine output being in electrical communication with said second path, said sine and cosine outputs comprising said correlated sinusoidal signals respectively provided to said first and second paths and each having one of the values of -1. or 0, or 1; and

a first arithmetic sign control device disposed in said first path and a second arithmetic sign control device disposed in said second path, said first and second sign control devices being disposed between said hard limiter/comparator device and said respective portion for integrating and each having one of the values of -1, or 0, or +1 input thereto from said means for producing a sine output and a cosine output when combining said two level digitized input signal respectively with said correlated sinusoidal signals, whereby said combined signals comprise an inverted value, or a null value, or the same value, respectively, as the value of said two level digitized input signal.

6. A correlation detector as in claim 5, wherein said means for producing a sine output and a cosine output comprises:

a local oscillator; and

clock means for inputting a frequency to said local oscillator four times that of said local oscillator to produce the output values -1, 0, and +1.