Pulse edge detector with wide dynamic range

• US 5,798,730 A
• Filed: 07/09/1997
• Issued: 08/25/1998
• Est. Priority Date: 07/09/1997
• Status: Expired due to Fees

• Current Assignee: Litton Systems Incorporated (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated (Northrop Grumman Corporation)
• Inventors: Sanchez, Louis Armando
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/891,859
• Time in Patent Office: 412 Days
• Field of Search: 342/89, 342/92, 342/99, 342/115, 342/137, 342/195, 342/204, 324/76.39, 324/76.77, 327/28, 327/21, 327/24
• US Class Current: 342/195
• CPC Class Codes: G01S 13/18 wherein range gates are used
• CPC Class Codes: G01S 13/524 based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi
• CPC Class Codes: G01S 7/2923 based on data belonging to a number of consecutive radar periods
• CPC Class Codes: G01S 7/32 Shaping echo pulse signals; Deriving non-pulse signals from echo pulse signals

Abstract

A pulse detector achieves high accuracy over a wide dynamic range in providing accurately spaced pulse edge markers that allow measurement of pulse to pulse time intervals. Received input pulses are transformed to a Gaussian like waveform and a single cycle AC signal having a first polarity initial half cycle is derived therefrom, accomplished by subtracting the Gaussian like waveform from a delayed, but substantially time overlapping, copy of that waveform. Upon completion of that initial half cycle, a pulse edge marker is generated. By measuring the time between the pulse edge marker obtained from one inputted pulse and that of the next, a measurement of the pulse to pulse interval is achieved that is of one nanosecond in accuracy.

Claims

1. An electronic pulse edge detector, comprising:

buffer means for inputting electronic pulses, said pulses having a leading edge and a trailing edge;

complementary high pass filter means for receiving electronic pulses from said buffer means and outputting a low frequency filtered pulse;

low pass filter means for receiving said low frequency filtered pulse and further filtering said pulse of high frequencies to output a first signal having a positive Gaussian like waveform, associated with said leading edge, followed an interval thereafter by a negative Gaussian like waveform, associated with said trailing edge;

branch circuit means containing an input, a first branch, and a second branch;

said first branch including a time delay means for delaying output from said first branch relative to output from said second branch for a predetermined short time interval less than the duration of either of said positive and negative Gaussian like waveforms;

said branch circuit means for receiving said first signal and producing a delayed copy of said first signal at an output of said first branch and reproducing said first signal at an output of said second branch;

first difference amplifier means having a positive input, a negative input and an output for producing at said output a signal equal to the difference between voltage applied to said negative input and that applied to said positive input;

said first difference amplifier means for subtracting said first signal from the delayed copy of said first signal to generate a difference signal comprising a single cycle AC signal having an initial half cycle of one polarity, associated with said leading edge, followed an interval thereafter by another single cycle AC signal, associated with said trailing edge, having an initial half cycle of a second polarity;

second difference amplifier means having a positive input, a negative input and an output for producing at said output a signal equal to the difference between voltage applied to said negative input and that applied to said positive input;

said second difference amplifier means for subtracting said delayed copy of the third signal from said signal to generate a second difference signal comprising a single cycle AC signal, associated with said leading edge, having an initial half cycle of said second polarity followed an interval thereafter by another single cycle AC signal, associated with said trailing edge, having an initial half cycle of said first polarity;

first comparator means, having first and second inputs, a gate input and an output, said comparator means providing a comparison of a voltage applied to said first input with any voltage applied to a second input and providing a high output voltage during any period when the latter voltage is greater than the former voltage, unless inhibited by an inhibit voltage applied to said gate input, and during other periods providing a low output voltage;

second comparator means, having first and second inputs, a gate input and an output, said second comparator means providing a comparison of a voltage applied to said first input with any voltage applied to a second input and providing a high output voltage during any period when the latter voltage is greater than the former voltage, unless inhibited by an inhibit voltage at said gate input, and otherwise providing a low voltage output;

bias means for biasing said second input of said first comparator means and said second input of said second comparator means at essentially zero volts;

said first comparator means for receiving said output of said first difference amplifier means at said first input and said bias voltage at said second input for commencing generation of a High output when the former is less in voltage than the latter and continuing said High output, during absence of an inhibit voltage at said respective gate, until said first difference amplifier output attains essentially zero volts, and thereupon reverting to a low voltage output, whereby said first comparator means detects completion of said initial half cycle of said AC signal and generates an output pulse having a trailing edge that marks termination of said initial half cycle of AC;

said second comparator means for receiving said output of said second difference amplifier means at said first input and said bias voltage at said second input for commencing generation of a High output when the former is less in voltage than the latter and continuing said High output, during absence of an inhibit voltage at said respective gate, until said second difference amplifier output attains essentially zero volts, and thereupon reverting to a low voltage output, whereby said second comparator means detects the termination of said initial half cycle of AC and generates an output pulse having a trailing edge that marks termination of said initial half cycle of AC;

summing amplifier means having first and second inputs for producing an output voltage representing the sum of the voltages applied at each of said first and second inputs;

said summing amplifier means for adding together said first signal from said first branch output with said delayed copy of said first signal from said second branch output and providing a sum signal at an output, said sum signal comprising a positive Gaussian waveform of said first polarity followed an interval thereafter by a negative Gaussian waveform of said second polarity to define first and second time windows;

third comparator means, having an sense input, a bias input and an output for producing an inhibit voltage output only when the voltage at said sense input is less than the voltage at said bias input;

said third comparator means having said sense input connected to the output of said summing circuit means to receive said positive and negative Gaussian sum waveforms, and having said output coupled to said gate of said first comparator means, whereby said third comparator means terminates said inhibit voltage only during said positive Gaussian sum waveform;

inverting amplifier means coupled to the output of said summing circuit means for inverting the polarity of said summing circuit output, whereby said positive Gaussian sum signal is converted to a negative Gaussian sum signal and said negative Gaussian sum signal is converted to a positive Gaussian sum signal;

fourth comparator means having an sense input, a bias input and an output for producing an inhibit voltage output only when the voltage at said sense input is less than the voltage at said bias input; and

said fourth comparator means having said sense input coupled to the output of said inverting amplifier means to receive said inverted positive and negative Gaussian sum signals and having said output coupled to said gate of said second comparator means, whereby said fourth comparator means terminates said inhibit voltage only during said inverted negative Gaussian sum waveform.

2. A method of measuring time between electronic pulses in an electronic pulse train, including a pulse and the next following pulse, said pulses containing a leading edge of a finite duration which includes the steps of:

(a) transforming the leading edge waveform of each pulse in said pulse train to a respective Gaussian like waveform, said Gaussian like waveform being of a duration substantially greater duration than the duration of the respective pulse'"'"'s leading edge;

(b) applying said Gaussian-like waveform to first and second propagation paths and delaying the propagation of said Gaussian-like waveform through said first propagation path by a predetermined short time interval, said predetermined short time interval being substantially less in duration than the duration of said Gaussian-like waveform, whereby said Gaussian-like waveform propagates along each propagation path to a respective path output with the output of one path being slightly delayed in time from the other path and with said outputs being substantially overlapping;

(c) subtracting said Gaussian-like waveform output from one branch from said delayed Gaussian-like waveform of the remaining branch to derive therefrom an AC waveform of one cycle duration having an initial half cycle of one polarity and a remaining half cycle of a second polarity, said AC waveform being of a greater duration than said duration of said Gaussian-like waveform;

(d) generating a first marker signal when said initial half cycle of said AC waveform cycles through zero upon the completion of a first half cycle to represent a leading edge for said pulse;

(e) repeating foregoing steps (a) through (c) upon said next following pulse in said pulse stream to derive therefrom another AC waveform of one cycle duration;

(f) generating a second marker signal when said another AC waveform cycles through zero upon the completion of a first half cycle to represent a leading edge for said next following pulse; and

(g) measuring the difference in time between the occurrence of said first and second marker signals.

3. A pulse edge detector for detecting and representing edges of electronic pulses, said pulses having a leading edge and a trailing edge, comprising:

input means for receiving a train of electronic pulses;

first means, coupled to said input means, for producing at an output a positive Gaussian like waveform, in response to a leading edge of each inputted pulse, said positive Gaussian like waveform having a duration greater than the duration of said leading edge of said pulse, and thereafter producing at said output a negative Gaussian like waveform in response to the trailing edge of said pulse, said negative Gaussian like waveform having a duration greater than the duration of said trailing edge of said pulse;

second means, coupled to said first means, responsive to said positive Gaussian like waveform, for producing in time overlapping time relationship with said respective positive Gaussian like waveform a sinusoidal like time varying waveform of one cycle in duration, said sinusoidal like time varying waveform cycling through zero volts in partially overlapping time relationship with said positive Gaussian like waveform, whereby at the end of a first half of said cycle said sinusoidal like waveform is at a level of zero volts, while said positive Gaussian like waveform is at that same instant at a voltage level other than zero volts; and

first detecting means for generating a time marker signal to represent said leading edge of said respective inputted pulse, responsive to the completion of said first half cycle of said first sinusoidal like waveform.

4. The invention as defined in claim 3, further comprising:

third means, coupled to said first means, responsive to said negative Gaussian like waveform, for producing in partially overlapping time relationship with said negative Gaussian like waveform a fourth signal having a sinusoidal like time varying waveform of one cycle in duration, said sinusoidal like time varying waveform cycling through zero volts in overlapping time relationship with said negative Gaussian like waveform, whereby at the end of a first half of said cycle said sinusoidal like wave form is at a voltage of zero volts, while said negative Gaussian like waveform is at that same instant at a voltage other than zero volts; and

second detecting means for generating a time marker signal to represent said trailing edge of said respective inputted pulse, responsive to the completion of said first half cycle of said second sinusoidal like waveform.

5. The invention as defined in claim 4, wherein said first circuit means comprises:

complementary high pass filter means; and

low pass filter means;

said complementary high pass filter means and said low pass filter means being connected in series.

6. The invention as defined in claim 5, wherein said complementary high pass filter means further comprises:

a delay line.

7. The invention as defined in claim 3, wherein said first means includes:

branching circuit means having first and second branches, said branching circuit means having an input connected to said output of said low pass filter to provide parallel propagation paths to outputs at said respective first and second branches for signals applied to said input, said second branch including delay circuit means for delaying propagation of signals propagating through said second branch for a predetermined interval, whereby two signals having like waveforms is obtained at outputs of said first and second branches, each signal containing a positive Gaussian portion and one of which signals is delayed slightly relative to the other; and

wherein said second means includes;

first difference means having first and second inputs for subtracting an output from one of said first and second branches from the other to produce a difference waveform;

said difference waveform defining a sinusoidally varying signal of one cycle that contains an initial half cycle of a first polarity and a remaining half cycle of a second polarity.

8. The invention as defined in claim 7, wherein said first detecting means comprises:

comparator means;

said comparator means having first and second inputs, an enabling gate and an output;

said first input being coupled to said output of said first difference means and said second input being biased at approximately zero volts;

said comparator means providing a first High output when a voltage at said first input is less than the voltage at said second input during the presence of an enabling voltage at said enabling gate, and providing a Low output during any period in which said said input voltage is equal to or greater than the voltage at said second input or in the absence of an enabling voltage at said enabling gate; and

, further comprising;

enabling means for providing an enabling voltage to said enabling gate only when the sum of voltages at the outputs of said first and second branches of said branching means exceeds a predetermined level;

said enabling means further comprising;

summing amplifier means having a pair of inputs coupled to outputs of said first and second branches of said branching means and an output for producing a voltage at said output that is the sum of voltages applied at said inputs; and

second comparator means;

said second comparator means having first and second inputs and an output;

said first input being coupled to said output of said summing amplifier means and said second input being set to a predetermined bias voltage;

said output of said second comparator means being coupled to said enabling gate of said first comparator means for applying an enabling voltage to said enabling gate during any period said sum voltage exceeds said bias voltage at said second input.

9. A pulse generator comprising:

generator means for generating an electronic pulse train, comprising a serial string of pulses, each having a leading edge and a trailing edge;

first means, coupled to said generator means, for producing at an output a positive Gaussian like waveform, in response to a leading edge of each inputted pulse, said positive Gaussian like waveform having a duration greater than the duration of said leading edge of said pulse, and thereafter producing at said output a negative Gaussian like waveform in response to the trailing edge of said pulse, said negative Gaussian like waveform having a duration greater than the duration of said trailing edge of said pulse;

second means, coupled to said first means, responsive to said positive Gaussian like waveform, for producing in time overlapping time relationship with said respective positive Gaussian like waveform a sinusoidal like time varying waveform of one cycle in duration, said sinusoidal like time varying waveform cycling through zero volts in partially overlapping time relationship with said positive Gaussian like waveform, whereby at the end of a first half of said cycle said sinusoidal like waveform is at a level of zero volts, while said positive Gaussian like waveform is at that same instant at a voltage level other than zero volts;

first detecting means for generating a time marker signal to represent said leading edge of said respective inputted pulse, responsive to the completion of said first half cycle of said first sinusoidal like waveform;

third means, coupled to said first means, responsive to said negative Gaussian like waveform, for producing in partially overlapping time relationship with said negative Gaussian like waveform a fourth signal having a sinusoidal like time varying waveform of one cycle in duration, said sinusoidal like time varying waveform cycling through zero volts in overlapping time relationship with said negative Gaussian like waveform, whereby at the end of a first half of said cycle said sinusoidal like wave form is at a voltage of zero volts, while said negative Gaussian like waveform is at that same instant at a voltage other than zero volts;

second detecting means for generating a time marker signal to represent said trailing edge of said respective inputted pulse, responsive to the completion of said first half cycle of said second sinusoidal like waveform; and

switching means for providing a pulse output, said switching means being coupled to said first detecting means for commencing a pulse responsive to said first marker signal and being coupled to said second detecting means for terminating each said pulse responsive to said second marker signal.

10. Electronic apparatus for detecting an edge of applied electronic pulses, each of said electronic pulses including an edge, comprising:

first means for transforming said pulse edge to a time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of a first polarity followed by a remaining half cycle of a second polarity; and

second means for detecting and signaling the completion of said initial half cycle to represent said pulse edge.

11. The invention as defined in claim 10 wherein said edge included in each said electronic pulses comprises a leading edge and, following said leading edge in time, a trailing edge;

and wherein said first means includes;

first transformation means for transforming said leading edge to a first time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of a first polarity followed by a remaining half cycle of a second polarity and for transforming said trailing edge to a second time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of said second polarity followed by a remaining half cycle of said first polarity; and

wherein said second means further comprises;

leading edge signaling means for signaling the completion of said initial half cycle of said first time varying AC signal.

12. The invention as defined in claim 11, wherein said second means further comprises:

trailing edge signaling means for signaling the completion of said initial half cycle of said second time varying AC signal.

13. The invention as defined in claim 12, further comprising:

pulse generating means responsive to said leading edge signaling means for commencing generation of a pulse and responsive to said trailing edge signaling means for terminating the pulse so commenced, whereby said pulse generating means generates a new pulse that contains a pulse width essentially equal to the pulse width of said electronic pulse.

14. The invention as defined in claim 11, wherein said first means includes:

first circuit means for producing at an output a first signal having a positive Gaussian like waveform, in response to a leading edge of said inputted electronic pulse, said positive Gaussian like waveform having a duration greater than the duration of said leading edge of said electronic pulse, and, thereafter, producing at said output a second signal having a negative Gaussian like waveform in response to the trailing edge of said electronic pulse, said negative Gaussian like waveform having a duration greater than the duration of said trailing edge of said electronic pulse.

15. The invention as defined in claim 14, wherein said first means further comprises:

second circuit means, coupled to said output of said first circuit means, for producing a delayed copy of said first signal that substantially overlaps in time said first signal;

said delayed copy being delayed by a predetermined interval with said predetermined interval being less than half said duration of said positive Gaussian like waveform.

16. The invention as defined in claim 15, wherein said second circuit means comprises:

branching circuit means having first and second branches;

said branching means having an input connected to said output of said first circuit means to provide parallel propagation paths for said first signal applied to said input at outputs to said respective first and second branches;

said second branch including time delay means for delaying propagation of signals propagating through said second branch for a predetermined interval, whereby a pair of like waveforms is obtained at said two outputs of said branching circuit means, each containing a positive Gaussian waveform portion, and in which one of said waveforms is delayed slightly relative to the other.

17. The invention as defined in claim 15, wherein said first means further comprises:

subtraction means for subtracting one of said first signal and said second signal from the other to produce at an output a time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of a one polarity followed by a remaining half cycle of an opposite polarity.

18. The invention as defined in claim 17, wherein said subtraction means comprises:

first subtraction means for subtracting said first signal from said second signal to produce at an output a difference signal, said difference signal including a first time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of a first polarity followed by a remaining half cycle of a second polarity and, following said first signal, a second time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of said second polarity followed by a remaining half cycle of said first polarity; and

second subtraction means for subtracting said second signal from said first signal to produce at an output a second difference signal, said second difference signal including a first time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of said second polarity followed by a remaining half cycle of said first polarity and, following said first signal, a second time varying AC signal of a single AC cycle in which said single AC cycle includes an initial half cycle of said first polarity followed by a remaining half cycle of said second polarity.

19. The invention as defined in claim 14 wherein said first circuit means further comprises:

complementary high pass filter means; and

low pass filter means;

said complementary high pass filter means and said low pass filter means being connected in series.

20. The invention as defined in claim 19, wherein said complementary high pass filter means includes a first predetermined bandwidth;

and wherein said low pass filter means comprises a second predetermined bandwidth; and

wherein said first predetermined bandwidth is substantially larger than said second predetermined bandwidth.

21. The invention as defined in claim 15, wherein said leading edge detection means further comprises:

first comparator means having first and second inputs, a control gate, and an output;

bias means for biasing said second input at a voltage equal to the level of voltage at which said first signal completes said initial half cycle;

summing means for producing a gating signal and applying said gating signal to said control gate during the presence of both said first time varying AC signal and said delayed copy of said first time varying AC signal to define a first enablement time window for said first comparator means;

said first comparator means for receiving said first signal at said first input and commencing generation of a pulse responsive to presence of said initial cycle of said first time varying AC signal at said first input and concluding said generated upon completion of said initial cycle, whereby said generated pulse contains a trailing edge that marks said leading edge of said applied electronic pulse.

22. The invention as defined in claim 21, wherein said trailing edge detection means further comprises:

second comparator means having first and second inputs, a control gate, and an output;

bias means for biasing said second input at a voltage equal to the level of voltage at which said second signal completes said initial half cycle;

and wherein said summing means includes means for producing a gating signal and applying said gating signal to said control gate of said second comparator means during the presence of both said second time varying AC signal and said delayed copy of said second time varying AC signal to define a second enablement time window for said second comparator means;

said second comparator means for receiving said second time varying AC signal at said first input and commencing generation of a pulse responsive to presence of the initial cycle of said second time varying AC signal at said first input and terminating said generated pulse upon completion of said initial cycle of said second time varying AC signal, whereby said generated pulse contains a trailing edge that marks said trailing edge of said applied electronic pulse.

23. The invention as defined in claim 14, further comprising:

second circuit means, coupled to said first circuit means, responsive to said positive Gaussian like waveform, for producing in overlapping time relationship with said respective positive Gaussian like waveform a third signal having a sinusoidal like time varying waveform of one cycle in duration, said sinusoidal like time varying waveform cycling through zero volts in overlapping time relationship with said positive Gaussian like waveform, whereby, at the end of a first half of said cycle, said sinusoidal like waveform is at a level of zero volts, while said positive Gaussian like waveform is at that same instant at a voltage level other than zero volts.

24. The invention as defined in claim 10, wherein said first means includes:

first circuit means for producing at an output a first signal having a positive Gaussian like waveform, in response to a leading edge of said inputted electronic pulse, said positive Gaussian like waveform having a duration greater than the duration of said leading edge of said electronic pulse, and, thereafter, producing at said output a second signal having a negative Gaussian like waveform in response to the trailing edge of said electronic pulse, said negative Gaussian like waveform having a duration greater than the duration of said trailing edge of said electronic pulse.