JP2001249149A - Signal analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure average power at high speed through one sweep. SOLUTION: An analog signal to be measured which is inputted from an input terminal 2 is frequency converted by a frequency converting part 4 into an intermediate frequency signal, which is then band limited by an RBW filter 10 and a VBW filter 16. The band limited intermediate frequency signal is sampled by an A/D converter 19 at such a high sampling rate as to obtain data which are plural times greater than the number of points displayed per, e.g. one sweep of a sweep signal generator 12. The sampled data are sequentially stored in a data storage part 20. A signal processing part 21 performs averaging process by calculating the effective value of the data corresponding to the sweep time of one point of a display part 17, on the basis of the data stored in the data storage part 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention sweeps and measures a signal employed in a mobile communication system such as a cellular phone as a signal to be measured, measures its spectrum or measures other frequency characteristics, and displays the waveform as a result. The present invention relates to a signal analyzer.

[0002]

2. Description of the Related Art Signals used in mobile communication systems such as mobile phones are modulated by various methods. Also,
In order to use the communication line effectively, TD
The MA (Time Division Multiple Access) method is adopted. The carrier that carries the signals used in such mobile systems is very high, from several hundred MHz to several GHz.

Generally, a signal analyzer such as a spectrum analyzer is used to accurately measure various frequency components contained in such a signal. FIG. 3 is a block diagram showing a schematic configuration of a signal analyzer used for spectrum measurement of such a high-frequency signal.

In a signal analyzer 51 shown in FIG. 3, a high-frequency signal to be measured input through an input terminal 52 is mixed with a local oscillation signal from a local oscillator 54 by a signal mixer 53, and an intermediate signal having an intermediate frequency is output. It is converted to a frequency signal.

The oscillation frequency of the local oscillator 54 is
5 sweeps over a predetermined frequency range. As a result, the frequency of the intermediate frequency signal output from the signal mixer 53 also changes in synchronization with the sweep operation.

The intermediate frequency signal whose frequency has been reduced by the signal mixer 53 is output to the next RBW filter 56. The RBW filter 56 is constituted by an analog band-pass filter, and selects only a necessary intermediate frequency signal except for unnecessary frequency components. This RB
The bandwidth (RBW) at the point when the frequency characteristic of the W filter 56 is lowered by 3 dB from the peak level at the pass center frequency represents the frequency resolution in the signal analyzer.

Since the frequency of the intermediate frequency signal output from the signal mixer 53 changes in synchronization with the sweep operation, RB
The output signal output from the W filter 56 as time elapses within one sweep time (sweep period) becomes a time-series waveform of each frequency component of the signal under measurement that has been swept and converted to an intermediate frequency signal.

[0008] The intermediate frequency signal from the RBW filter 56 is output after the signal level is converted by the LOG conversion unit 57 into dB units, and is dropped to a DC (direct current) component.
The signal is input to the next analog VBW filter 58. VB
The W filter 58 removes high frequency components (noise components) of the frequency spectrum waveform finally displayed on the display unit 59 and outputs a signal. The signal output from the VBW filter 58 is detected by the next detector (DET) 60.

The detector 60 detects the peak value at each time axis position in the analog frequency spectrum waveform output from the VBW filter 58, and obtains a final frequency spectrum waveform in a state where the envelope detection is performed. And
The signal detected during the sweep period indicates the magnitude of the time-series waveform at the swept frequency. Therefore, if the horizontal axis is frequency and the vertical axis is amplitude, a frequency spectrum waveform is obtained.

[0010] The signal indicating the final frequency spectrum waveform is converted into digital data by the next A / D converter (A / D) 61 and stored in the data storage unit 62. Then, the digital data stored in the data storage unit 62 is subjected to signal processing in the next signal processing unit 63, and the frequency spectrum waveform obtained as a result of this signal processing is displayed on the display screen of the display unit 59 on the front panel as described above. Is displayed in the frequency domain (frequency on the horizontal axis and amplitude on the vertical axis).

The frequency of the local oscillator 54 is fixed,
The time variation of the frequency spectrum at that time can also be observed. In this case, the display screen is rather displayed in the time domain (the horizontal axis represents time, and the vertical axis represents amplitude). Whether to measure in the frequency domain or the time domain is determined by setting conditions from the display panel.

In signal analysis using this type of signal analyzer 51, for example, CDMA (Code Division)
When a modulated signal of the Multiple Access method is used as the signal under measurement, the peak value with respect to the average power greatly fluctuates, so that the average power within the frequency sweep (or time sweep: time span sweep) arbitrarily set by the user. Measurement was desired.

Therefore, in the conventional signal analyzer 51, for example, the oscillation frequency of the local oscillator 54 is varied by the sweeping unit 55 and the frequency sweeping is repeated a plurality of times, and the measurement is performed. To measure the average power of the signal under test. That is, for example, frequency sweeping is performed four times, four pieces of data of the same frequency are collected and averaged, and the average value is used as the average power of the frequency.

[0014]

However, in the above-described conventional measuring method, averaging is performed on a plurality of sweep results, so that a plurality of sweeps is indispensable.
Moreover, since the measurement time depends on the number of sweeps, there is a problem that the averaging process takes time.

Therefore, the present invention has been made in view of the above problems, and has as its object to provide a signal analyzer capable of performing average power measurement at high speed by one sweep.

[0016]

In order to achieve the above object, the invention according to claim 1 has a local oscillator 5, receives a signal to be measured, mixes the signal with the signal from the local oscillator, and mixes the signal with an intermediate frequency signal. , A sweep unit 12 that changes the oscillation frequency of the local oscillator by performing a frequency sweep according to a desired measurement frequency range, and an intermediate frequency signal output by the frequency conversion unit. Detector 1 to detect
8, an A / D converter 19 that samples the output of the detector at a predetermined rate and converts it into digital data, a data storage unit 20 that stores the output of the A / D converter, An output section 17 for outputting data of a predetermined number N of frequency points per frequency sweep of the sweep section as characteristics of the signal under measurement based on the output;
The / D converter has a point number k which is a multiple of k times a predetermined number of frequency points per one frequency sweep output from the output section.
While sampling the output of the detector at a rate of N and outputting digital data to be stored in the data storage unit, between the data storage unit and the output unit,
By receiving the digital data output from the data storage unit, averaging the digital data of the plurality of k frequency points adjacent to each other, newly obtaining the value as data of one frequency point, and sending the value to the output unit. A signal processing unit 21 for outputting the data of the predetermined frequency point number N per one frequency sweep is provided.

According to a second aspect of the present invention, there is provided a local oscillator 5,
A frequency converter 4 for receiving the signal to be measured, mixing with the signal from the local oscillator and outputting an intermediate frequency signal, and causing the oscillation frequency of the local oscillator to sweep in accordance with a desired measurement mode, or A sweep unit 12 for fixing the frequency over a predetermined time interval, a detector 18 for receiving and detecting the intermediate frequency signal output by the frequency conversion unit, and sampling the output of the detector at a predetermined rate to digital data An A / D converter 19 for conversion, a data storage unit 20 for storing the output of the A / D converter, and one or one frequency sweep of the sweep unit based on the output of the data storage unit.
An output unit 17 for outputting data of a predetermined number of points N per predetermined time interval as characteristics of the signal under measurement, wherein the A / D converter outputs the data per one frequency sweep or one predetermined time output from the output unit. The output of the detector is sampled at a rate that becomes a point number kN that is a multiple of k times the predetermined number of points per interval, digital data is output and stored in the data storage unit, and the data storage unit and the output unit are output. Receiving the digital data output from the data storage unit, averaging the digital data at the plurality of adjacent k points, newly obtaining the value as one-point data, and sending the obtained value to the output unit. A signal processing unit 2 for outputting the data of the predetermined number of points N per one frequency sweep or one predetermined time interval. Characterized by comprising a.

Generally, when data is digitally processed using an A / D converter and a memory and output or displayed, for example, in a display, if the horizontal axis is the frequency axis (or time axis), the horizontal axis is , 500 frequency points (this is referred to herein as the number of output points). The data between points is peak-held, and the peak value is set to the value of the next output point.

Therefore, according to the present invention, for example, the data is applied to the horizontal axis (that is, 1 in the frequency domain measurement mode).
In the time domain measurement mode, this corresponds to one predetermined time interval. ) Sweep measurement is performed at 2000 frequency points, one average value is calculated for every four adjacent points, and the average value is assigned to one output point.
It is decided to display at 00 frequency point. The above data can be an effective value, and the average value can be an average effective value.

In the signal analyzer according to the present invention, when a signal to be measured whose frequency is converted into an intermediate frequency signal and whose band is limited is input, the signal to be measured is output (displayed) point per sweep on the entire horizontal axis. Sampling at a high sampling rate so that multiple times the number of data can be obtained,
The sampled data is sequentially stored in the data storage unit, and based on the data stored in the data storage unit, an effective value of data corresponding to one point of sweep time of the display unit is calculated and an averaging process is performed. . Accordingly, it is not necessary to perform the averaging process by a plurality of sweeps, and the average power measurement can be performed at high speed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a schematic configuration of a signal analyzer according to the present invention, and FIG. 2 is an explanatory diagram of a processing outline of the signal analyzer.

Hereinafter, the configuration of the signal analyzer 1 of the present embodiment will be described with reference to FIGS. 1 and 2 along the signal processing procedure.

A high-frequency analog signal to be measured having a frequency of, for example, several hundred KHz to several GHz input through the input terminal 2 is:
The signal level is adjusted to a specified level by the attenuator (ATT) 3 and input to the frequency conversion unit 4.

The frequency conversion unit 4 includes a first local oscillator 5,
First signal mixer 6, BPF (bandpass filter)
7, a second local oscillator 8 and a second signal mixer 9. In the frequency converter 4, the high-frequency signal to be measured input from the attenuator 3 is combined with the local oscillation signal from the first local oscillator 5 by the first signal mixer 6 to form an intermediate frequency signal having an intermediate frequency. Converting. After this intermediate frequency signal is band-limited by the BPF 7, it is again synthesized with the local oscillation signal from the second local oscillator 8 by the second signal mixer 9 and input to the RBW filter 10 as the final intermediate frequency signal. You.

When the signal to be measured is frequency-converted by the frequency converter 4, one sweep time is set and input by the user via the sweep time setting means 11, and a control signal indicating that the sweep time has been set is received. When input to the sweep signal generator 12 as a sweep unit, the oscillation frequency of the first local oscillator 5 is variably controlled by the sweep signal generator 12 at the timing of the timing signal from the timing signal generator 13 and set. The sweep is performed over the sweep frequency range (measurement frequency range) at the sweep time. As a result, the frequency of the intermediate frequency signal output from the frequency converter 4 also changes in synchronization with the sweep operation.

The timing signal generating means 13 divides the frequency of the reference clock signal to generate a timing signal matching the drive frequency of each unit, and generates a timing signal of a fixed frequency (sampling rate: 200 Ksps, for example). Is output to a detector 18 and an A / D converter 19, which will be described later, and a timing signal having a frequency lower than the sampling rate is output to the sweep signal generator 12 in synchronization with the timing signal.

The RBW filter 10 is constituted by an analog band-pass filter, and the bandwidth (RBW) is variably set by a user. The RBW filter 10 passes only the intermediate frequency signal of the frequency component of the variably set bandwidth, excluding unnecessary frequency components of the intermediate frequency signal input from the frequency conversion unit 4, and the gain is adjusted by an amplifier (not shown). After the LOG conversion unit (LOG) 15
Is being entered.

The intermediate frequency signal input from the RBW filter 10 via an amplifier (not shown) is
, The signal level is converted to a dB unit and output.
C (direct current) component), and then the next analog VB
It is input to the W filter 16. The VBW filter 16 removes high frequency components (noise components) of the frequency spectrum waveform finally displayed on the display unit 17 as an output unit, and outputs a signal.

The signal output from the VBW filter 16 is detected by the next detector (DET) 18. The signal detected by the detector 18 is the following A / D
The data is sampled at a predetermined rate by a converter (A / D) 19 and converted into digital data. The digital data is sequentially stored and accumulated in the next data storage unit 20. The display unit 17 as an output unit outputs data of a predetermined number of points (N) per one frequency sweep (or per one predetermined time interval) of the sweep unit 12 based on the output of the data storage unit 20. The output is displayed as a characteristic.

The A / D converter 19 is connected to the display unit 1
7, the output of the detector 18 is sampled and digitalized at a rate that is a multiple (k) times the number of points (kN) of the predetermined number of points (N) per frequency sweep (or per predetermined time interval) output and displayed. Outputting data. Then, the digital data is sequentially stored in the data storage unit 20.

A signal processing unit 21 composed of a DSP, an MPU, a CPU, etc., has a horizontal axis (time axis or frequency axis) on the display screen of the display unit 17 based on the digital data stored in the data storage unit 20. The effective value of the data corresponding to the sweep time between one point of the display data on (axis) is calculated. That is, the signal processing unit 21 receives the digital data output from the data storage unit 20, averages the digital data at a plurality of adjacent points (k), and newly obtains the value as 1-point data. Data of a predetermined number of points (N) per frequency sweep or per predetermined time interval is output to the display unit 17.

For example, as shown in FIG.
When the sweep time between points is set to Ta and the sampling time of the A / D converter 19 is set to Tb, the sampling time T of the A / D converter 19 is detected by the detector 18.
The signal detected for each b is sampled for each sampling time Tb in the A / D converter 19, converted into a digital signal, and then stored in the data storage unit 20.

In the example shown in FIG. 2, since the number of data corresponding to the sweep time between one point on the display unit 17 is four, the signal processing unit 21 sequentially stores and stores the four data stored in the data storage unit 20. The average value of the effective value of each data is calculated. That is, the average effective value is obtained. The calculated effective value is stored in the display memory (display data storage unit) 22. Then, based on the effective value data stored in the display memory 22, the waveform of the signal under measurement is displayed on the display screen of the display unit 17 in the frequency domain (frequency on the horizontal axis and amplitude on the vertical axis) or in the time domain (horizontal axis). Time, vertical axis is amplitude).

As described above, in the signal analyzer 1 of the present embodiment,
An A / D converter 19 can acquire data of a multiple of the number of output (display) points per sweep on the entire horizontal axis of an analog signal under measurement (a signal whose frequency is converted to an intermediate frequency and band-limited). The data is sampled at a high sampling rate and stored in the data storage unit 20, and the average power is calculated from a plurality of data adjacent to the stored data and displayed as an average power waveform on the display screen of the display unit 17. . Accordingly, it is not necessary to perform the averaging process by a plurality of sweeps as in the related art, and the average power can be measured at high speed.

By the way, the configuration of the above-mentioned averaging process is as follows.
The oscillation frequency of the first local oscillator 5 is fixed, the time span is swept with a sweep time set to measure the time change of the signal band-limited to the specified band by the RBW filter 10, and the result is displayed on the display unit 17. Also, the present invention can be applied to a case where a waveform is displayed on the display screen with the horizontal axis representing time and the vertical axis representing amplitude.

In the above-described embodiment, the detector 1
8 is an analog intermediate frequency signal whose frequency is converted by the frequency converter 4 and band-limited by each of the filters (RBW filter 10 and VBW filter 16). Alternatively, the optical signal may be converted into an electric signal, detected by a detector, and then the above-described process of measuring the average power may be performed.

[0037]

As is apparent from the above description, according to the signal analyzer of the present invention, it is not necessary to perform the averaging process by a plurality of sweeps as in the conventional case, and the average power can be measured by one sweep. Can be performed at high speed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a signal analyzer according to the present invention.

FIG. 2 is an explanatory diagram of an outline of processing by the signal analyzer of FIG. 1;

FIG. 3 is a block diagram showing a schematic configuration of a generally known signal analyzer.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 signal analyzer 4 frequency converter 5 local oscillator 10 RBW filter 11 sweep time setting means
12: Sweep signal generator, 13: Timing signal generating means, 16: VBW filter, 17: Display unit (output unit)
18: detector, 19: A / D converter, 20: data storage unit, 21: signal processing unit.

Claims (2)

[Claims] A frequency converter having a local oscillator, receiving a signal to be measured, mixing the signal with the signal from the local oscillator to output an intermediate frequency signal, and oscillating the local oscillator. Sweep unit (12) for changing the frequency by sweeping the frequency according to a desired measurement frequency range
A detector (18) for receiving and detecting the intermediate frequency signal output from the frequency converter, and an A / D converter (19) for sampling the output of the detector at a predetermined rate and converting the output to digital data. A data storage unit (2) for storing the output of the A / D converter;
0), and an output section (17) for outputting data of a predetermined number of frequency points (N) per one frequency sweep of the sweep section as characteristics of the signal under measurement based on an output of the data storage section, The A / D converter samples the output of the detector at a rate that is a multiple (k) of the number of points (kN) of a predetermined number of frequency points per one frequency sweep output by the output unit, and outputs digital data. Is output and stored in the data storage unit. The digital data output from the data storage unit is received between the data storage unit and the output unit, and a plurality of (k) frequency points adjacent to each other are received. By averaging the digital data and newly obtaining the value as data of one frequency point and sending it to the output section, the predetermined frequency point per one frequency sweep is obtained. Signal analysis apparatus characterized by comprising signal processing unit allowed to output as data of the betting amount (N) to (21). 2. A frequency converter (4) having a local oscillator (5), receiving a signal to be measured, mixing the signal with the signal from the local oscillator and outputting an intermediate frequency signal, and oscillating the local oscillator. A sweep section (12) for sweeping the frequency in accordance with a desired measurement mode or fixing the frequency over a predetermined time interval; and a detector for receiving and detecting an intermediate frequency signal output from the frequency conversion section. (18), an A / D converter (19) that samples the output of the detector at a predetermined rate and converts it into digital data, and a data storage unit (2) that stores the output of the A / D converter.
0), and an output unit (17) for outputting data of a predetermined number of points (N) per one frequency sweep or one predetermined time interval of the sweep unit as characteristics of the signal under measurement based on the output of the data storage unit. The A / D converter has a point number (kN) that is a plurality of (k) times the number of predetermined points per one frequency sweep or one predetermined time interval output by the output unit. While sampling the output of the detector and outputting digital data to be stored in the data storage unit, between the data storage unit and the output unit, receiving the digital data output from the data storage unit, By averaging digital data at the plurality of (k) points adjacent to each other and newly obtaining the value as one-point data and sending it to the output unit, the one-frequency Signal analysis apparatus characterized by comprising signal processing unit allowed to output as data (21) of the predetermined number of points per or per predetermined time interval sweep (N).