Method for determining the frequency of a signal

• US 6,351,505 B1
• Filed: 10/13/1998
• Issued: 02/26/2002
• Est. Priority Date: 10/10/1997
• Status: Expired due to Term

• Current Assignee: Daimler-Benz Aerospace AG (Mercedes-Benz Group AG)
• Original Assignee: Daimler-Benz Aerospace AG (Mercedes-Benz Group AG)
• Inventors: Herrmann, Franz, Schuster, Manfred
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): BAYARD, EMMANUEL
• Application Number:
  US09/170,200
• Time in Patent Office: 1,232 Days
• Field of Search: 375/324, 375/331, 375/340, 375/342, 375/346, 375/350, 375/224, 708/300, 708/309, 708/311, 708/322, 708/400, 708/403, 708/404, 708/405, 324/76.28, 324/76.29, 324/76.44, 324/76.68, 324/628, 324/615, 324/76.11, 324/76.19, 370/210
• US Class Current: 375/350
• CPC Class Codes: G01R 23/02 Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
• CPC Class Codes: G01R 23/167 with digital filters

Abstract

A method for determining a frequency of a signal includes transforming the analog signal to the complex frequency range through a digital filtering, preferably a FFT, so that result vectors with amplitude and phase components are generated in the frequency range. As a result, a continuous sequence of transformation intervals (FFT intervals) develops within a measuring interval that can be predetermined. Subsequently, pairs of result vectors, which belong to the same predetermined frequency, are selected from predetermined transformation intervals (FFT intervals). Associated phase differences are then formed from which a weighted phase difference is determined. The weighted phase difference is used to correct the signal frequency determined from the amplitude spectrum. This method permits very accurate frequency measuring, especially for pulsed HF signals.

Claims

1. A method for determining a frequency of a signal, comprising:

converting an electrical signal present in a time domain to a corresponding digitized signal with use of an analog/digital converter;

digital filtering the digitized signal for transforming the digitized signal to a frequency domain such that a line spectrum is generated which corresponds to the signal;

determining a signal frequency in the line spectrum from at least one predetermined spectral line belonging to the signal;

repeating the digital filtering periodically in time, at least within one predetermined measuring interval, so that a temporally continuous sequence of transformation intervals develops within the measuring interval;

carrying out the digital filtering such that in each transformation interval at least one complex result vector (p0 to pn) is created, which has an amplitude component and a phase component (φ

);

selecting within the measuring interval, pairs of result vectors (p0, p1), which correspond to the same predetermined spectral line and belong to different, predetermined transformation intervals according to a predetermined pattern;

forming an associated phase difference (Δ

φ

) for each pair of selected result vectors (p0, p1);

determining a frequency F belonging to the selected result vectors from the phase differences (Δ

φ

) in accordance with the following formula;

$F=f_{\mathrm{line}}+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>F_{\mathrm{line}}·<br><br>\frac{1}{2<br><br>\mathrm{\pi <br><br>}}·<br><br>\frac{\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\varphi <br><br>}}_i}{\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t_i}$

wherein

Δ

F_line=1/T_FFT=1/(scanning rate for the analog/digital conversion •

the number of scanning values within the transformation interval);

f_line=the frequency of the line selected from the amplitude spectrum of a single transformation interval;

T_FFT=length in time of the transformation interval;

Δ

t_i=distance in time between selected pairs of result vectors.

2. A method for determining the frequency of a signal according to claim 1, wherein the digital filtering includes using a complex wide-band Fast-Fourier-Transformation, uninterrupted in time.

3. A method for determining the frequency of a signal according to claim 1, wherein the time interval (Δ

t_i) between the selected pairs of result vectors is constant and comprises a predetermined number of transformation intervals.

4. A method for determining the frequency of a signal according to claim 1, wherein the length of time for the measuring interval to determine the frequency of a pulsed HF signal covers at least one pulse.

5. A method for determining the frequency of a signal in accordance with claim 1, wherein the length of time for the measuring interval to determine the frequency of a pulsed HF signal covers at least two pulses, and further including selecting the number of transformation intervals in each pulse to be n/2, wherein n indicates the total number of transformation intervals within the measuring interval.

6. A method for determining a frequency of a signal according to claim 1, wherein the signal is a disturbed analog signal, and the converting step includes initially frequency filtering the disturbed analog signal including:

performing an analog/digital conversion of the signal;

subsequently performing a Fast-Fourier-Transformation of the converted signal;

carrying out a predetermined digital frequency filtering of the Fast-Fourier-Transformation; and

carrying out an inverse Fast-Fourier-Transformation so that a sequence of filtered, complex result vectors (Time domain) develop which are used to determine the frequency.