Method and apparatus for low signal to noise ratio instantaneous phase measurement

• US 5,808,895 A
• Filed: 05/31/1996
• Issued: 09/15/1998
• Est. Priority Date: 05/31/1996
• Status: Expired due to Fees

• Current Assignee: TSI Incorporated
• Original Assignee: Aerometrics, Inc. (TSI Incorporated)
• Inventors: Bachalo, William D., Ibrahim, Khalid M.
• Primary Examiner(s): Trammell, James P.
• Assistant Examiner(s): Nguyen, Cuong H.
• Application Number:
  US08/655,831
• Time in Patent Office: 837 Days
• Field of Search: 364/484, 364/485, 364/487, 364/574, 364/576, 324/76.12, 324/76.19, 324/76.21, 324/76.22, 324/76.24, 324/76.41, 324/76.42, 324/76.47, 324/76.82, 324/76.64, 324/76.55, 324/76.15 , 324/76.62, 324/76.48
• US Class Current: 702/79
• CPC Class Codes: G01R 25/00 Arrangements for measuring phase angle between a voltage and a current or between voltages or currents

Abstract

The system and method of the present invention generates high resolution phase measurements without the high processing and memory overhead requirements found in prior art circuits and methods. Each signal sample (of N samples) is divided further into J segments each segment having K samples. The frequency is computed with respect to one J segment and is used in the phase measurement computations performed for the remaining segments. The phase measurements performed with respect to each J segment are then averaged to compute a high resolution phase measurement for the corresponding N segment.

Claims

1. A method for measuring phase for N samples of a signal comprising the steps of:

determining a number of K samples within an N sample;

identifying a number of J segments within an N sample, each J segment composed of K samples;

computing a frequency measurement of the signal for one of the J segments;

computing a phase measurement of each J segment using the frequency computed for one of the J segments;

combining the phase measurement of each J segment to generate a combined phase measurement indicative of the phase measurement of the N sample of the signal.

2. The method as set forth in claim 1, wherein the step of determining the number of K samples comprises the step of determining K based upon the signal to noise ratio (SNR) of the signal.

3. The method as set forth in claim 1, wherein the step of determining the number of K samples comprises the step of determining K such that rms in phase measurement at the minimum expected signal to noise ratio (SNR) of the signal is less than π

.

4. The method as set forth in claim 1, wherein the step of identifying the number of J segments comprises determining J according to the following equation:

J=N/K.

5. The method as set forth in claim 1, wherein the step of computing the frequency comprises the steps of:

dividing the J segment of the signal into a plurality of sampled signals, each sampled signal sampled at a different sampling frequency;

performing a discrete Fourier transform (DFT) on each sampled signal; and

combining the results of the DFT sampled signals to determine the frequency.

6. The method as set forth in claim 1, wherein the step of computing the frequency comprises using zero crossing counting.

7. The method as set forth in claim 1, wherein the step of computing the frequency comprises using a fast Fourier transform (FFT).

8. The method as set forth in claim 1, wherein the step of computing a phase measurement for each J segment comprises determining the phase measurement according to the following:

If q_i =1 then φ

_i =θ

If q_i =2 then φ

_i =π

-θ

If q_i =3 then φ

_i =π

+θ

If q_i =4 then φ

_i =2π

-θ

where q_i represents the quadrant of the phase measurement, and θ

is determined according to the following;

##EQU15## where k_s is the estimated signal frequency normalized to the sampling frequency and 0≦

θ

<

π

/2.

9. The method as set forth in claim 1, wherein the step of combining the phase measurement of each J segment to generate a combined phase measurement comprises the steps of:

summing the phase measurement values of the J segments to generate a summed value Φ

_ACC ;

determining the number of phase measurements that fall into each quadrant; and

determining the combined phase measurement according to the following;

##EQU16## where J_VAL represents the number of valid phase measurements, q₁, q₂, . . . q_JVAL represent the quadrants of valid phase measurements, and q 4! represents the number of valid phase measurements that falls into the fourth quadrant.

10. A method for measuring phase for N samples of a signal comprising the steps of:

computing a frequency measurement of the signal for one of J segments within an N sample, each J segment composed of K samples;

computing a phase measurement of each J segment using the frequency computed for one of the J segments;

combining the phase measurement of each J segment to generate a combined phase measurement indicative of the phase measurement of the N sample of the signal.

11. The method as set forth in claim 10, wherein the number of K samples is determined based upon the signal to noise ratio (SNR) of the signal.

12. The method as set forth in claim 10, wherein the step of computing the frequency comprises the steps of:

dividing the J segment of the signal into a plurality of sampled signals, each sampled signal sampled at a different sampling frequency;

performing a discrete Fourier transform (DFT) on each sampled signal; and

combining the results of the DFT sampled signals to determine the frequency.

13. The method as set forth in claim 10, wherein the step of computing the frequency comprises using zero crossing counting.

14. The method as set forth in claim 10, wherein the step of computing the frequency comprises using a fast Fourier transform (FFT).

15. The method as set forth in claim 10, wherein the step of computing a phase measurement for each J segment comprises determining the phase measurement according to the following:

If q_i =1 then φ

_i =θ

If q_i =2 then φ

_i =π

-θ

If q_i =3 then φ

_i =π

+θ

If q_i =4 then φ

_i =2π

-θ

where q_i represents the quadrant of the phase measurement, and θ

is determined according to the following;

##EQU17## where k_s is the estimated signal frequency normalized to the sampling frequency and 0≦

θ

<

π

/2.

16. The method as set forth in claim 10, wherein the step of combining the phase measurement of each J segment to generate a combined phase measurement comprises the steps of:

summing the phase measurement values of the J segments to generate a summed value Φ

_ACC ;

determining the number of phase measurements that fall into each quadrant; and

determining the combined phase measurement according to the following;

##EQU18## where JVAL represents the number of valid phase measurements, q₁, q₂, . . . q_JVAL represent the quadrants of valid phase measurements, and q 4! represents the number of valid phase measurements that falls into the fourth quadrant.

17. A circuit for measuring phase for N samples of a signal comprising:

at least one sampling circuit for sampling the signal;

a frequency measurement unit coupled to the at least one sampling circuit that computes a frequency measurement for one of J segments within an N sample, wherein each J segment is composed of K samples; and

a phase measurement unit coupled to the at least one sampling circuit and the frequency measurement unit to compute a phase measurement of each J segment using the frequency computed for one of the J segments and to combine the phase measurement of each J segment to generate a combined phase measurement indicative of the phase measurement of the N sample of the signal.

18. The circuit as set forth in claim 17, further comprising a burst detector coupled to the output of the at least one sampling circuit and to the frequency measurement unit and phase measurement unit, said burst detector detecting the presence of the signal and enables the operation of the frequency measurement unit and phase measurement unit.

19. The circuit as set forth in claim 17, wherein the frequency measurement unit measures the frequency by dividing the J segment of the signal into a plurality of sampled signals, each sampled signal sampled at a different sampling frequency, performing a discrete Fourier transform (DFT) on each sampled signal, and combining the results of the DFT sampled signals to determine the frequency.

20. The circuit as set forth in claim 17, wherein the frequency measurement unit comprises a zero crossing counting circuit.

21. The circuit as set forth in claim 17, wherein the frequency measurement unit measures the frequency by using a fast Fourier transform (FFT).

22. The circuit as set forth in claim 17, wherein the phase measurement unit comprises:

circuitry to compute a phase measurement for each J segment according to the following;

If q_i =1 then φ

_i =θ

If q_i =2 then φ

_i =π

-θ

If q_i =3 then φ

_i =π

+θ

If q_i =4 then φ

_i =2π

-θ

where q_i represents the quadrant of the phase measurement, and θ

is determined according to the following;

##EQU19## where k_s is the estimated signal frequency normalized to the sampling frequency and 0≦

θ

<

π

/2.

23. The circuit as set forth in claim 17, wherein the phase measurement unit comprises:

circuitry to combine the phase measurement of each J segment to generate the combined phase measurement according to the following;

an adder circuit to add the phase measurement values of the J segments to generate a summed value Φ

_ACC ;

logic for determining the number of phase measurements that fall into each quadrant; and

logic for determining the combined phase measurement according to the following;

##EQU20## where JVAL represents the number of valid phase measurements, q₁, q₂, . . . q_JVAL represent the quadrants of valid phase measurements, and q 4! represents the number of valid phase measurements that falls into the fourth quadrant.

24. A circuit for measuring phase of N samples of a signal comprising the steps of:

at least one low resolution analog to digital converter (ADC) for sampling the signal;

a first logic computing a frequency measurement for one J segment of the sampled signal within an N sample, each J segment being composed of K samples;

a second logic for computing a phase measurement of each J segment using stored precomputed values; and

a third logic for combining the phase measurements of each J segment to generate the phase measurement for N samples.

25. The circuit as set forth in claim 24, wherein the signal is sampled using 1-bit ADC.

26. The circuit as set forth in claim 24, wherein the frequency is measured using the Discrete Fourier Transform (DFT).

27. The circuit as set forth in claim 24, further comprising memory and at least one latch, wherein the sampled signal is temporarily stored in memory and then latched by that at least one latch.

28. The circuit as set forth in claim 24, further comprising look-up tables (LUTs) used to store the precomputed values of several samples of the input signal with the correspondent values of the reference signal.

29. The circuit as set forth in claim 28, wherein the input to the LUTs are the sampled signal stored in the latches, the frequency and the phase of the reference signal.

30. The circuit as set forth in claim 28, wherein accumulators are used to sum the LUT'"'"'s outputs to produce values of x and y where, ##EQU21## where r(i) and q(i) represent sampled data, k_s represents an estimated signal frequency normalized to the sampling frequency, and K represents the number of samples within a segment.

31. The circuit as set forth in claim 30, wherein the second logic computes the phase φ

_j of a segment j by computing tan^-1 (x/y) and the quadrant of the phase measurement.

32. The circuit as set forth in claim 31, wherein the third logic computes the phase measurement of N samples by combining the phase measurements φ

_j '"'"'s of valid segments.

33. A circuit for measuring phase over a large amplitude dynamic range comprising:

a plurality of sampling circuits for sampling the signal, each sampling circuit sampling different segments, each segment sampled at a sampling frequency fs;

a frequency measurement unit coupled to one sampling circuit of the plurality of sampling circuits;

a phase measurement unit to measure the phase of each segment and to combine the phase measurements to generate a phase measurement.

34. The circuit as set forth in claim 33, wherein at least one sampling circuit of the plurality of sampling circuits comprises a one bit analog to digital converter (ADC).

35. The circuit as set forth in claim 33, wherein each sampling circuit samples the signal for a segment using the sampling frequency of a previous segment delayed by τ

, where τ

is a time delay.

36. The circuit as set forth in claim 33, wherein a pattern of the sampled data at fs/4, where s represents the sampling frequency, for each segment is different than that of other segments sampled.

37. The circuit as set forth in claim 33, wherein the sampling frequency for each segment is phase modulated.

38. The circuit as set forth in claim 33, wherein the frequency of one segment is computed using Fourier analysis.

39. The circuit as set forth in claim 33, wherein the phase of each segment is computed using Fourier analysis method.

40. The circuit as set forth in claim 33, wherein the phase measurement of N samples of the input signal are computed by combining the phase measurements of valid segments of N samples.