System and method for calibrating a signal detection threshold circuit

• US 6,304,828 B1
• Filed: 04/02/1999
• Issued: 10/16/2001
• Est. Priority Date: 04/02/1999
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Swanick, David J., Huntley, William P.
• Primary Examiner(s): Grimley, Arthur T.
• Assistant Examiner(s): Charioui, Mohamed
• Application Number:
  US09/287,171
• Time in Patent Office: 928 Days
• Field of Search: 702/107, 702/106, 702/69, 702/190, 702/191, 702/193, 702/195, 702/FOR.107, 702/FOR.164, 702/FOR.166, 702/FOR.170
• US Class Current: 702/107
• CPC Class Codes: G01S 7/021 Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals
• CPC Class Codes: G01S 7/292 Extracting wanted echo-signals
• CPC Class Codes: G01S 7/4021 of receivers

Abstract

The system and method for calibrating a signal detection threshold circuit is used in a radio frequency (RF) receiver, such as a in an early warning radar (EWR) system, in which a signal detection threshold circuit rejects signals below a predetermined threshold setting and prevents noise signals from causing false alarms. The system and method include setting an initial threshold setting and receiving noise signals in one or more channels. A threshold comparison circuit rejects noise signals below the threshold setting, and a pulse repetition frequency (PRF) detection circuit detects noise pulses above the threshold setting and determines the PRF. An automatic threshold determiner and setter determines whether the PRF has reached a predetermined frequency (e.g., 400 kHz) and lowers the threshold setting until the predetermined frequency is reached. When the predetermined frequency is reached the threshold setting is stored as a noise measurement. The process is repeated until a plurality of noise measurements are made in each signal channel, and the average value of the noise measurements are used to determine the calibrated threshold setting. A calibration indicator provides an indication of whether each of the signal channels has been properly calibrated.

Claims

1. A method of calibrating a signal detection threshold circuit comprising the steps of:

setting a threshold setting at an initial threshold value;

receiving noise signals in at least one signal channel in said signal detection threshold circuit;

rejecting each of said noise signals lower than said threshold setting;

determining a pulse repetition frequency of noise pulses greater than said threshold setting;

lowering said threshold setting by a predetermined increment and repeating steps a-c until said pulse repetition frequency of said noise pulses is greater than a predetermined frequency;

storing said threshold setting as a noise measurement when said pulse repetition frequency is greater than said predetermined frequency;

repeating the threshold setting step through the threshold lowering step until a predetermined number of noise measurements are made for said at least one signal channel;

determining an average value of said predetermined number of noise measurements and setting said threshold setting to said average value when a predetermined number of acceptable noise measurements are made in said at least one signal channel;

indicating successful calibration of said at least one signal channel in said signal detection threshold circuit when said predetermined number of acceptable noise measurements are made in said at least one signal channel; and

indicating unsuccessful calibration of said at least one signal channel in said signal detection threshold circuit when a predetermined number of unacceptable noise measurements are made in said at least one signal channel.

2. The method of claim 1 wherein receiving noise signals in at least one signal channel includes receiving noise signals in a plurality of signal channels, wherein said method steps are performed for each of said plurality of signal channels.

3. The method of claim 1 further including repeating said method steps for said at least one signal channel if said predetermined number of acceptable noise measurements are not made in said at least one signal channel.

4. The method of claim 3 further including the step of setting said threshold setting to a default value, if said predetermined number of acceptable noise measurements are not made in said at least one signal channel, after repeating the method steps a predetermined number of times.

5. The method of claim 1 wherein said predetermined frequency is about 400 KHz.

6. The method of claim 1 further including, after the step of storing said threshold setting as said noise measurement, the steps of:

determining whether said noise measurement is greater than a predetermined maximum acceptable value, wherein said noise measurement is deemed an unsuccessful noise measurement when said noise measurement is greater than said predetermined maximum acceptable value; and

determining whether said noise measurement is less than a predetermined minimum acceptable threshold value, wherein said noise measurement is deemed an unsuccessful noise measurement when said noise measurement is less than said predetermined minimum acceptable value.

7. The method of claim 6 further including the steps of:

providing an indication of excessive noise in said at least one channel when said noise measurement is determined to be greater than said predetermined maximum acceptable value; and

providing an indication of insufficient noise in said at least one channel when said noise measurement is determined to be less than said predetermined minimum acceptable value.

8. The method of claim 6 further including, after the step of storing said threshold setting as said noise measurement, the step of:

determining whether a predetermined number of unsuccessful noise measurements have been made in said at least one channel; and

setting a flag indicating improper calibration if said predetermined number of unsuccessful noise measurements have been made.

9. The method of claim 8 further including repeating the method steps for said at least one signal channel if said predetermined number of acceptable noise measurements are not made in said at least one signal channel.

10. An automatic signal detection threshold calibration system comprising:

a plurality of signal channels for receiving and carrying a plurality of signals including noise signals;

comparing means coupled to each of said signal channels for comparing each of said noise signals to a threshold setting and for rejecting each of said noise signals below said threshold setting;

detection means coupled to said comparing means for determining a pulse repetition frequency of each of said noise signals above said threshold setting; and

threshold determining and setting means coupled to said detection means for automatically determining said threshold setting by setting said threshold setting at an initial threshold value and lowering said threshold setting until said pulse repetition frequency of said each of said noise signals above said threshold setting is greater than a predetermined frequency.

11. The automatic signal detection threshold calibration system of claim 10 further including a calibration indicating means responsive to said automatic threshold determining and setting means for indicating proper or improper calibration of each of said plurality of signal channels.

12. The automatic signal detection threshold calibration system of claim 10 wherein said comparing means includes a plurality of comparators for receiving each of said noise signals and for comparing each of said noise signals to said threshold setting.

13. The automatic signal detection threshold calibration system of claim 12 wherein said detection means includes a plurality of pulse repetition frequency detection circuits for determining said pulse repetition frequency of each of said noise signals.

14. The automatic signal detection threshold calibration system of claim 13 wherein said threshold determining and setting means includes:

a microprocessor coupled to said pulse repetition frequency detection circuit, for determining whether said pulse repetition frequency of each of said noise signals is greater than said predetermined frequency and for determining said threshold setting; and

a digital to analog converter coupled to said microprocessor and coupled to each of said comparators for setting said threshold setting in each of said comparators.