Precision digital phase meter
View Patent ↗A method of measuring phase includes receiving an analog signal; converting the analog signal into a digital signal; representing the digital signal as N sets of samples; aligning the N sets of samples to a common time frame; removing zero bias drift from the digital signal; and calculating a phase of the analog signal based on the digital signal with the zero bias drift removed. The phase can have a time resolution substantially equal to a time between adjacent samples.
1. A method of measuring phase comprising:
receiving an analog signal;
converting the analog signal into a digital signal;
representing the digital signal as N interleaved sets of samples wherein each set of samples is represented by a projection of a vector onto its corresponding axis;
aligning each of the N interleaved sets of samples to a common time frame;
removing zero bias drift from the digital signal; and
calculating a phase of the analog signal based on the digital signal with the zero bias drift removed based on the projections of the vectors.
2. The method of claim 1 , wherein the phase has a time resolution substantially equal to a time between adjacent samples.
3. The method of claim 1 , wherein:
axes oriented at the angles 360°/N relative to each other, with
A (1, j )= U Nj , A (2, j )= U Nj+1 , A (3, j )= U Nj+2 , . . . A ( N,j )= U Nj+N−1 , jε[ 0, 1, 2 . . . ∞], U being the analog signal;
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ε j =[B (1 ,j )+ B (2, j )+ . . . + B ( N,j )]/ N is the zero bias drift;
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represent the digital signal with the zero bias drift removed; and
the phase is calculated according to
φ( i,j )=arc tan [tan(π/ N )*[{ C ( i+ 1 ,j )+ C ( i,j )}/{( C ( i+ 1 ,j )− C ( i,j )}]].
4. The method of claim 1 , further comprising using linear interpolation to align the N sets of samples to each other.
5. The method of claim 1 , wherein each set of samples is represented by a projection of a vector onto axes oriented at 360°/N relative to each other, and wherein the zero bias drift is removed based on the vector projections.
6. An apparatus for measuring phase comprising:
an analog-to-digital converter that converts an analog signal into a digital signal;
a first circuit that represents the digital signal as N sets of interleaved samples and aligns the N sets of samples to a common time, wherein each set of samples is represented by a projection of a vector onto axes oriented at 360°/N relative to each other;
a second circuit that removes zero bias drift from the digital signal based on the vector projections; and
a third circuit that calculates phase of the analog signal based on the digital signal with the zero bias drift removed.
7. The apparatus of claim 6 , wherein:
A (1 ,j )= U Nj , A (2 ,j )= U Nj+1 , A (3, j )= U Nj+2 , . . . A ( N,j )= U Nj+N−1 , jε[ 0, 1, 2 . . . ∞], U being the analog signal;
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ε j =[B (1 ,j )+ B (2 ,j )+ . . . + B ( N,j )]/ N is the zero bias drift;
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represent the digital signal with the zero bias drift removed; and
the phase is calculated according to
φ( i,j )=arc tan [tan(π/ N )*[{ C ( i+ 1 ,j )+ C ( i,j )}/{( C ( i+ 1 ,j )− C ( i,j )}]].
8. The apparatus of claim 6 , wherein the first, second and third circuits are combined as a digital signal processing circuit.
9. The apparatus of claim 6 , wherein the first circuit uses linear interpolation to align the N sets of samples to each other.
10. The apparatus of claim 6 , wherein the phase has a time resolution substantially equal to a time between adjacent samples.
11. The apparatus of claim 6 , wherein the phase is stably measured ranging over multiples of π.
12. The apparatus of claim 6 , wherein the phase is stably measured in an input signal with 40 dB amplitude dynamic range and over 50% modulation.
13. The apparatus of claim 6 , wherein the phase is stably measured in an input signal with phase resolution of about 2π·10 −5 radian.
14. The apparatus of claim 6 , wherein the phase is stably measured without a phase range limitation.
15. The apparatus of claim 6 , wherein the digital signal is represented as N interleaved sets of samples.
16. An apparatus for measuring phase comprising:
a dual-channel analog-to-digital converter that converts a first analog signal and a second analog signal into a first digital signal and a second digital signal, respectively;
a sample divider that represents the first and second digital signals as a first N sets of samples and a second N sets of samples, wherein the first N sets of samples are interleaved relative to each other, and the second N sets of samples are interleaved relative to each other and wherein each set of samples is represented by a projection of a vector onto its corresponding axis;
a time aligner that aligns the first N sets of samples to a first common time and aligns the second N sets of samples to a second common time;
a zero bias drift remover that removes zero bias drift from the first and second digital signals based on the projections of the vectors; and
a phase calculator that calculates phase of the first and second analog signals relative to each other based on the first and second digital signals with the zero bias drift removed.
17. The apparatus of claim 16 , wherein the sample divider, the time aligner and the zero bias drift remover are combined as a digital signal processing circuit.
18. The apparatus of claim 16 , wherein the time aligner uses linear interpolation to align the first and second N sets of samples.
19. The apparatus of claim 16 , wherein the phase has a time resolution substantially equal to a time between adjacent samples.
20. The apparatus of claim 16 , wherein the phase is stably measured ranging over multiples of π.
21. The apparatus of claim 16 , wherein the phase is stably measured in an input signal with 40 dB amplitude dynamic range and over 50% modulation.
22. The apparatus of claim 16 , wherein the phase is stably measured in an input signal with phase resolution of about 2π·10 −5 radian.
23. The apparatus of claim 16 , wherein the phase is stably measured without a phase range limitation.
24. The apparatus of claim 16 , wherein each set of samples is represented by a projection of a vector onto axes oriented at 360°/N relative to each other, and wherein the zero bias drift is removed based on the vector projections.