Adaptive fixed-threshold pulse time-of-arrival detection apparatus for precision distance measuring equipment applications

• US 5,266,953 A
• Filed: 08/01/1991
• Issued: 11/30/1993
• Est. Priority Date: 08/01/1991
• Status: Expired due to Fees

• Current Assignee: Alliedsignal Inc.
• Original Assignee: Alliedsignal Inc.
• Inventors: Ireland, Howard H., Drutch, Gary A., Biggs, Michael G., Winter, Janice A., Kelly, Robert J.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US07/739,074
• Time in Patent Office: 852 Days
• Field of Search: 364/569, 364/514, 364/517, 364/450, 342/47, 342/33, 342/35, 342/36, 342/118, 342/125, 342/134, 307/361, 307/228, 307/246, 307/518, 328/132, 328/147
• US Class Current: 342/47
• CPC Class Codes: G01R 29/0276 the pulse characteristic being rise time measuring rate of change G01R19/12
• CPC Class Codes: G01S 13/785 Distance Measuring Equipment [DME] systems

Abstract

An apparatus to be employed within a precision distance measuring system for estimating pulse time-of-arrival. The apparatus facilitates the use of an Adaptive Fixed Threshold method for such estimation. The invention compensates for pulse time detection errors induced by variations in incident pulse amplitude and shape by adjusting the estimated time-of-arrival. This adjustment is performed as a function of the measured pulse slope between two low-amplitude threshold levels through the use of a predetermined reference table of error adjustment times.

Claims

1. A pulse time-of-arrival estimator comprising:

an amplifier coupled to receive and amplify a pulse waveform, said amplifier having an automatic gain control which normalizes the incoming pulse so that the peak amplitude of said amplified pulse are maintained within fixed limits;

a first responsive threshold detector having an input and an output, coupled to receive the pulse waveform output by the amplifier, said first threshold detector being responsive to the amplitude of the incoming pulse waveform so that upon the pulse waveform reaching a predetermined first amplitude level, A₁, said detector outputs a signal indicative of the time, t₁, at which the this first level was attained;

a second responsive threshold detector having an input and an output, coupled to receive the pulse waveform output by the amplifier, said second threshold detector being responsive to the amplitude of the incoming pulse waveform so that upon the pulse waveform reaching a predetermined second amplitude level, A₂, which is greater than said first amplitude level, said detector outputs a signal indicative of the time, t₂, at which the said second level was attained;

a slope calculating means coupled to receive the signals output by the first and second threshold detectors, and being responsive to the reception of said signals so as to calculate a slope ]value according to the formula ((A₂ -A₁)/(t₂ -t₁)), and output a signal indicative of said slope value;

a means for storing an addressable array of adjustment time values, each of said adjustment time values being addressable by a corresponding slope value;

a retrieval means coupled to said storage means and said slope calculating means, responsive to the reception of the signal indicative of the calculated slope value from the slope calculating means so as to retrieve and output the corresponding time adjustment value from said storage means;

a calculating means coupled to receive the rime adjustment value from the retrieval means, and the signal from the first detector means indicative of the time at which the pulse waveform attained the first amplitude level, said calculating means being capable of outputting a value equal to the sum of the time at which the pulse waveform attained the first amplitude level and the adjustment time value retrieved from said storage means.

2. The pulse time-of-arrival estimator of claim 1 wherein:

the predetermined first amplitude level, A₁, to which the first responsive threshold detector is calibrated, is equal to approximately 10 percent of the peak amplitude of a normalized pulse output by the amplifier; and

the predetermined second amplitude level, A₂, to which the second responsive threshold detector is calibrated, is equal to approximately 16 percent of the peak amplitude of a normalized pulse output by the amplifier.

3. The pulse time-of-arrival estimator of claim 1 wherein the amplifier normalizes the incoming pulse waveform to a peak amplitude of approximately 1 volt.