Data processing: measuring – calibrating – or testing – Testing system – Signal generation or waveform shaping
Reexamination Certificate
2001-02-20
2003-10-07
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Signal generation or waveform shaping
C324S076270, C341S061000
Reexamination Certificate
active
06631341
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a signal analyzing apparatus for measuring frequency characteristics of a signal employed for a mobile communication system such as automobile telephone or portable telephone, and displaying a waveform of the signal, thereby analyzing the signal.
A signal employed for a mobile communication system such as automobile telephone or portable telephone, for example, is modulated by a variety of systems.
In addition, a TDMA (Time Division Multiple Access) system is employed as a communication system in order to efficiently use a communication line.
A frequency of a carrier wave for carrying a signal employed in such a mobile communication system ranges some hundreds MHz to some GHz, which is very high.
In general, a signal analyzing apparatus such as spectrum analyzer is employed for precisely measuring a variety of frequency components included in such a signal.
FIG. 3
is a block diagram depicting a general configuration of a conventional signal analyzing apparatus used for measuring frequency characteristics of a measured signal with its high frequency.
In a signal analyzing apparatus
21
shown in
FIG. 3
, a measured signal with its high frequency inputted via an input terminal
22
is adjusted to a predetermined, normalized level by an attenuator (ATT) (not shown).
Then, the level adjusted, measured signal with its high frequency is mixed with a local oscillation signal from a local oscillator
24
by means of a signal mixer
23
, and the mixed signal is converted into an intermediate frequency signal having its intermediate frequency.
Here, the oscillation frequency of the local oscillator can be swept (frequency swept) over the range of predetermined frequencies by means of a sweep control section (not shown).
In this manner, a frequency of the intermediate frequency signal outputted from the signal mixer
23
also changes in synchronization with a sweep operation.
Then, the intermediate frequency signal with its reduced frequency is inputted to a resolution bandwidth (hereinafter, referred to as RBW) filter
25
, an undesired frequency component is eliminated by means of the RBW filter
25
, and only a required intermediate frequency signal is selected.
A bandwidth (RBW) at a time when a peak level at the passage center frequency of the frequency characteristics of this RBW filter
25
drops by 3 dB indicates a frequency resolution in this signal analyzing apparatus.
A signal from the RBW filter
25
is gain adjusted by means of an amplifier (not shown), and a switching section
26
is switched to a LOG converter
27
side. In this state, a signal logarithm converted by means of a LOG converter
27
to be compressed is detected by means of a waveform detector (DET)
28
.
In contrast, when the switching section
26
is switched to the RBW filter
25
side, the signal from the RBW filter
25
is detected by means of a waveform detector (DET)
28
.
The signal detected by this waveform detector
28
within a sweeping period indicates the size of a time series waveform at the swept frequency.
The thus outputted signal by the waveform detector
28
is inputted to an anti-aliasing filter
29
.
The anti-aliasing filter
29
used here is composed of a filter for eliminating a high frequency component (noise component) of a frequency spectrum waveform finally displayed at a display section
34
provided at a panel of an apparatus main body.
The signal from this anti-aliasing filter
29
is converted into digital data by means of a next A/D converter
30
, and the converted digital data is stored in a data storage section
31
.
Predetermined processing is applied to the digital data stored in this data storage section
31
by means of a signal processing section
33
.
Then, the frequency spectrum waveform obtained by this processing is displayed in a frequency domain (frequency on horizontal axis and amplitude on vertical axis) on a display screen of the display section
34
.
In the meantime, in the signal analyzing apparatus
21
of such type, a signal employed in a mobile communication system such as automobile telephone or portable telephone, the signal being inputted as a measured signal is a burst shaped signal whose level changes with an elapse of time.
In the field of such mobile communication system, there is a demand to measure such burst shaped signal in detail by tracking a time.
The signal analyzing apparatus
21
shown in
FIG. 3
is provided with a function for performing time span sweeping such that a frequency of the local oscillator
24
is fixed so as to measure a time change of a signal bandwidth-restricted by the RBW filter
25
within a normalized bandwidth, thereby displaying the result of the time span sweeping while time and amplitude are defined on the horizontal and vertical axes, respectively, on the display screen of the display section
34
.
By this time span sweeping, in the case where a burst shaped measured signal is measured in detail by tacking a time, there have been conventionally employed a method of measuring the signal by changing a sampling rate of an A/D converter and a method of decimating unwanted data after sampling has been performed at a sufficiently high speed by employing an A/D converter that operates at a high speed.
However, in the method of changing the sampling rate of the A/D converter, it has been necessary to reacquire data every time the sampling rate is changed.
Moreover, in the case where the sampling rate is changed, thereby causing operation at a high speed, there has been a problem that a sufficient dynamic range cannot be obtained.
In the method of decimating unwanted data after sampling has been performed at a sufficiently high speed by using the A/D converter that operates at a high speed, it has been necessary to use a sampling rate of the lowest common multiple for the resolution of data per one time domain to be acquired.
For example, in the case where 1 &mgr;sec is required as a time span, assuming that 500 items of data are provided, a resolution of 2 nsec per one item of data is obtained. Thus, the sampling rate of the A/D converter is set to a frequency of 500 MHz.
Similarly, the sampling rate of the A/D converter at a resolution of 5 nsec is set to a frequency of 200 MHz.
In order to meet resolutions of both of the above 2 nsec and 5 nsec, it is required that the A/D converter operates when the sampling rate of the converter is set to a frequency of 1 GHz.
Therefore, with the above described method, the sampling rate of the A/D converter could not be changed freely.
Even if the sampling rate can be changed, in the case of a high speed operation, there has been a problem that a sufficient dynamic range cannot be obtained.
In addition, there has been a problem that a memory requires its capacity corresponding to the maximum operation.
Namely, in the case where the sampling rate is changed, thereby causing high speed operation, it is required to use an A/D converter that corresponds to the highest speed operation. In the A/D converter that corresponds to high speed operation, there has been a problem that a sufficient conversion bit cannot be allocated, processing must be done at the same conversion bit even during a low speed sampling, and there is a limitation to a dynamic range according to the conversion bit, thus making it impossible to obtain a sufficient dynamic range.
In the meantime, in the signal analyzing apparatus
21
shown in
FIG. 3
, a signal bandwidth-limited by the RBW filter
25
, the signal passing through the waveform detector
28
, is a base band signal having a bandwidth of the RBW filter
25
.
The inventors found that the bandwidth of the RBW filter
25
is sampling at a sampling rate that can be reproduced, and then, arbitrary time data is generated by means of re-sampling using a digital signal processing technique, whereby detailed time analysis can be performed without changing the sampling rate, and reached the present invention based on the findings.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in order
Hashimoto Yuichiro
Kameda Keiji
Matsuda Toshiyuki
Anritsu Corporation
Charioui Mohamed
Hoff Marc S.
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