Apparatus for frequency measurement

Patent metadata

Field	Value
Publication number	US-9778298-B2
Application number	US-201514735228-A
Country	US
Kind code	B2
Filing date	Jun 10, 2015
Priority date	Jun 10, 2015
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

An apparatus for frequency measurement (1ODMTM) which provides precise and accurate measurement of a single input tone frequency and/or multiple separable input tone frequencies. Tone separability can be achieved by proper selection of the parameter N, the sample length of the DFT/FFT.

First claim

What is claimed is:

1. An apparatus for frequency measurement, comprising:
a signal conditioner having an input and an output;
an analog-to-digital converter having an input and an output;
a parser having an input and an output;
a Fourier Transformer having an input and an output;
a selector having an input and an output; and
a processor having a signal input, an output, and a coefficient input, wherein,
an external analog signal to be measured is input into said input of said signal conditioner;
the output of said signal conditioner is connected to the input of said analog-to-digital converter;
the output of said analog-to-digital converter is connected to the input of said parser;
the output of said parser is connected to the input of said Fourier Transformer;
the output of said Fourier Transformer is connected to the signal input of said processor and to the input of said selector; and wherein
the output of said selector is connected to the coefficient input of said processor;

wherein said parser parses a digital output of said analog-to-digital converter x[n] into m data segments of length N, wherein the m th said segment is represented as x m [n];
wherein said Fourier Transformer performs an N-point Discrete Fourier Transform on x m [n], resulting in X m [k],
wherein k is the k th frequency bin along a discrete frequency independent variable, and
X m [k] is the Discrete Fourier Transform of any said data segment;

wherein said Fourier Transformer performs a Fast Fourier Transform on x m [n], resulting in X m [k], wherein
k is the k th frequency bin along a discrete frequency independent variable, and
X m [k] is the Fast Fourier Transform of any said data segment;

wherein said selector selects a set of frequency indices for which frequency measurements are to be performed;
wherein said selector performs a threshold and detect function;
wherein said processor performs a first step of processing a ratio represented by
V m [ k ]=( X m [ k ]+ X m [ k −1])/( X m [ k ]− X m [ k −1])

and
inputs the result into a second step of processing; and
wherein said processor performs a second step of processing represented by
C m [ k ]= jV m [ k ]−cot(π/ N )

and
inputs the result into a third step of processing.

2. The apparatus of claim 1 , wherein said processor performs a third step of processing represented by
D m [ k ]= e (−j2π(k−1)N) ·C m [ k ]

and;
inputs the result into a fourth step of processing.

3. The apparatus of claim 2 , wherein said processor performs a fourth step of processing represented by
f m [ k ]=−arg{e iπ ·e (iπ/N) ·D m [ k ]}

and;
inputs the result into a fifth step of processing.

4. The apparatus of claim 3 , wherein said processor performs a fifth step of processing represented by
ρ m [ k ]=0.5 f m [ k ]+0.5 f m [ k+ 1];

and
performs a scaler function.

5. The apparatus of claim 4 , wherein said scaler function further comprises the steps of processing represented by
β m [ k ]=−π·sign(ρ m [ k ])+ρ m [ k ]

when |f m [k]−f m [k+1]| is greater than π; and
processing
β m [ k ]=ρ m [ k ]

otherwise; and
processing an averaged and scaled frequency measurement represented by
w m [ k ]=(0.5 N /π)·β m [ k ].

Assignees

• The United States Of America As Represetned By The Secretary Of The Air Force
• Us Air Force

Inventors

• Noga Andrew J
• Stevens Daniel L

Classifications

• G01R23/16 Primary

  Spectrum analysis; Fourier analysis · CPC title