HIGH RESOLUTION TIME-OF-FLIGHT MEASUREMENTS

Abstract

This invention relates to apparatus and methods for measuring the time-of-flight of a signal. The signal may be acoustic energy or electromagnetic energy such as x-ray, radio frequency, microwave, millimeter-wave, radar, and laser. Unlike unambiguous ranging devices that measures the phases of two or more signals to determine the time-of-flight and requires long averaging to achieve some degree of accuracy, this invention phase lock one or more transmitter signals to the corresponding received signals in predetermined phase relationships and measures the frequencies of one or more variable frequency oscillators having frequencies several times higher than the frequency of the transmitter signal to determined the time-of-flight with much higher accuracy. An example of an embodiment of this invention is an apparatus that transmits a signal to a receiver and phase lock the transmitted signal to the received signal in a first selected phase relationship. A first frequency of the phase locked signal is determined and a second phase relationship that differs from the first phase relationship by a predetermined fraction of a cycle is selected. The transmitter signal relocks to the receiver signal in the second phase relationship and a second frequency of the relocked signal is determined. The time-of-flight is measured using the first and second frequencies and the predetermined fraction of a cycle difference in phase relationships.

Claims

1. A method for measuring the time-of-flight of a signal comprising: a. transmitting transmitter signals (6) to a receiver (12), wherein the transmitter signals are generated by one or more high frequency variable frequency oscillators; b. receiving and processing said transmitter signals; c. controlling the frequencies of said frequency oscillators to phase lock the corresponding generated transmitter signal to the corresponding received signal to form at least first and second phase locked signals with frequencies that differ by a predetermined number of cycles within the time of flight; d. making frequency measurements of said variable frequency oscillators for determining the frequency of said phase locked signals; e. using said frequency measurements and said predetermined difference in number of cycles to measure at least one of a set of measurable factors from a group consisting of time-of-flight of said transmitter signal, velocity of said transmitter signal, range of a target, and velocity of said target.

2. A method for measuring the time-of-flight of a signal as recited in claim lwherein forming said first phase locked signal further comprise transmitting a transmitter signal having a predetermined initial frequency to said receiver then adjusting the frequency to phase lock said transmitter signal to the corresponding receiver signal in a first predetermined phase relationship.

3. A method for measuring the time-of-flight of a signal as recited in claim lwherein forming said second phase locked signal further comprise transmitting a transmitter signal having the same frequency and phase as said first phase locked signal then adjusting the frequency to phase lock said transmitter signal to the corresponding receiver signal in a second phase relationship that differs from the phase of the first locked signal by a predetermined fraction of a cycle.

4. A method for measuring the time-of-flight of a signal as recited in claim 1 wherein measuring the time of flight further comprise determining the integral number of cycles within the time of flight of a phase locked signal and using said integral number of cycles and the frequency of the phase locked signal to measure subsequent time of flights with higher accuracy.

5. Apparatus for measuring the time-of-flight of a signal comprising: a. at least one transmitter (5) disposed to transmit a transmitter signal (6) to a receiver (12); b. at least one receiver (12) disposed for receiving and processing the received signal (11) from said transmitter; c. at least one variable frequency oscillator for generating at least one transmitter signal, wherein the frequency of said variable frequency oscillator further comprise frequencies that are several times higher than the frequency of said transmitter signal; d. means for selecting and applying a drive signal (4) to said transmitter to transmit said transmitter signal to said receiver, wherein said drive signal is provided by said at lease one variable frequency oscillator; e. means for receiving and processing said transmitter signal; f. means for controlling said at least one variable frequency oscillator to phase lock said transmitter signal to the corresponding received signal in predetermined phase relationships to form at least first and second phase locked signals having frequencies that differ by a predetermined number of cycles within the time of flight; g. measurement means to make frequency measurements of said at least one variable frequency oscillator; h. at least one processor circuit and electrical signals (1) configured for processing said transmitter signals, and for measuring said time of flight based on said frequency measurements and said predetermined difference in number of cycles.

6. Apparatus for measuring the time-of-flight of a signal as recited in claim 5 wherein transmitting a transmitter signal to a receiver further comprise means for transmitting energy onto a target and back to said receiver, wherein said energy is selected from a group consisting of acoustic energy and electromagnetic energy.

7. Apparatus for measuring the time-of-flight as recited in claim 5 wherein means for forming said first phase locked signal further comprise means for selecting a first phase relationship, a first mode having means for controlling one of said variable frequency oscillator to phase lock said variable frequency oscillator to a master oscillator for generating a first transmitter signal having a predetermined initial frequency; a second mode having means for controlling said variable frequency oscillator to phase lock said first transmitter signal to the corresponding received signal in said first phase relationship; and means for switching between said first and second modes.

8. Apparatus for measuring the time-of-flight as recited in claim 5 wherein means for forming said second phase locked signal further comprise means for changing the phase relationship of said first phase locked signal by a predetermined fraction of a cycle to relock said first phase locked signal to the corresponding received signal in a second predetermined phase relationship.

9. Apparatus for measuring the time-of-flight as recited in claim 5 wherein means for forming said second phase locked signal further comprise means for alternately selecting a first and a second of said variable frequency oscillators to transmit said first and second transmitter signals to said receiver; a first mode having means for controlling said first transmitter signal to form said first phase locked signal, a second mode having means for controlling said second variable frequency oscillator to phase lock said second transmitter signal to said first transmitter signal; a third mode having means for controlling said second variable frequency oscillator to phase lock said second transmitter signal to the corresponding received signal in a second phase relationship that differs from the phase of said first phase locked transmitter signal by a predetermined fraction of a cycle, and means for switching modes.

10. Apparatus for measuring the time-of-flight as recited in claim 5 wherein transmitting a transmitter signal to a receiver further comprise means for generating a carrier signal; means for modulating one or more transmitter signals on top of said carrier signal; means for applying said carrier signal to said transmitter; and means for demodulating said carrier signal by said receiver to produce receiver signals corresponding to said transmitter signals.

11. Apparatus for measuring the time-of-flight as recited in claim 5 wherein means for determining the frequency of said at least on variable frequency oscillator further comprise at least one counter for counting the cycles of said variable frequency oscillator to provide counter values at periodic intervals to determine said frequency.

12. Apparatus for measuring the time-of-flight as recited in claim 5 wherein means for phase locking the transmitter signal to the corresponding received signal in a predetermined phase relationship further comprise means for selecting one of said variable frequency oscillators (2) to generate said transmitter signal; means for detecting the arrival of a burst of said transmitter signal by said receiver for processing of said burst; means for generating a first square wave signal (7) indicative of zero-crossing of said transmitter signal; means for generating a second square wave signal (14) indicative of zero-crossing of said received signal; a phase detector (10) for comparing the phase of one of said square wave signal to the shifted phase (8) of the other square wave signal, wherein the phase is shifted by a predetermined fraction of a cycle for providing a control signal to control said selected variable frequency oscillator (2) to phase lock said transmitter signal to the corresponding received signal in said predetermined fraction of a cycle phase relationship; means wherein said control signal is held constant when said selected variable frequency oscillator is unselected or no receiver signal is being processed; and means for varying the response time (17) of said variable frequency oscillator to said control signal as a function of the time of flight and the frequency of said transmitter signal.

13. Apparatus for measuring the time-of-flight of a signal comprising: a. at least one transmitter (5) disposed to transmit a transmitter signal (6) to a receiver (12); b. at least one receiver (12) disposed for receiving and processing the received signal (11) from said transmitter; c. at least one variable frequency oscillator having a frequency several times higher than the frequency of said transmitter signal for generating said transmitter signal; d. means for receiving and processing said transmitter signal; e. means for transmitting said transmitter signal having a predetermined frequency and controlling the frequency of said transmitter signal to phase lock said transmitter signal to the corresponding received signal to form a phase locked signal; f. measurement means to make frequency measurements of said at least one variable frequency oscillator; g. measurement means to make approximate measurements of the time that it takes for a burst of said transmitter signal to travel from said transmitter to said receiver; h. at least one processor means disposed for determining the integral number of cycles within the time-of-flight of said phase locked signal based on said approximate time measurement and said frequency measurements, and means for using said integral number of cycles and said frequency measurements to make subsequent higher resolution measurement of at least one of a set of measurable factors from a group consisting of time of flight of said transmitter signal, velocity of said transmitter signal, range of a target, and velocity of said target.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 illustrates the basic concept of this invention; a phase detector (10) for phase locking the transmitter signal to the receiver signal, and a phase delay circuitry (8).

[0021] FIGS. 2 and 3 illustrate transmitter signals phase locked to the receiver signals in different phase locked relationships.

[0022] FIGS. 4 and 5 illustrate transmitting and receiving signals in bursts.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] In FIG. 1 processor and control electronics (1) provides electrical signals for controlling and processing the transmitter signals, Voltage Control Oscillator (VCO) (2) is selected to generate transmitter signal (6) and a square wave signal (7) indicative of zero-crossing of the transmitter signal. Phase delay circuitry (8) provides selectable predetermined fraction of a cycle phase delays of square wave signal (7) as a first input (9) to Phase Detector (10). A signal generated by reference oscillator (16) is selected as a second input (15) to the Phase Detector for controlling the frequency of the VCO to generate a transmit signal (6) having a predetermined initial frequency. When signal transmission and reception starts, signal arrival is detected by circuitry (13) to start processing the received signal. A receiver generated square wave signal (14) indicative of zero-crossing of the received signal is selected as the second input to the Phase Detector (10) to phase lock the transmitter signal to the receiver signal in the selected predetermined fraction of a cycle phase relationship. The processor monitors status information provided by the control electronics and adjusts the amplitude of the transmitter signal to maintain a preferred receiver signal level. Counter (19) counts the cycles of the VCO for providing periodic counter values to determine the frequency of the VCO. The frequency of the VCO is several times(M) higher than the frequency of the transmitter signal. A sine wave generator 3 is used to generate a drive signal (4) having a frequency to which the transmitter and receiver is most responsive.

[0024] FIG. 2 illustrate an Exclusive-OR (XOR) (23) used as a phase delay circuit. One input to the XOR is a transmitter generated square wave signal (26) and the other input is a logic 0 (24) to select a 0 phase delay (25). A phase detector compares the output of the XOR (21) to the zero crossing receiver signal (22) to phase lock the transmitter signal (20) to the received signal in the 0 phase delay relationship.

[0025] FIG. 3 illustrate the XOR (33) with a logic 1 input (34) to select a 180 phase delay (35), and the transmitter signal (30) phase locked to the received signal (32) in the 180 phase relationship.

[0026] FIG. 4 illustrates alternately transmitting bursts of first (40) and second (41) signals where the first signal is received before transmitting the second signal.

[0027] FIG. 5 illustrates alternately transmitting bursts of first (44) and second (45) signals where both signals are transmitted before receiving the first signal.