JPH10142273A - Net work analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a net work analyzer which can complete measurement in a short time even in the case where the Q-value of a measured device (DUT) is large. SOLUTION: A multiple sine signal generating circuit 10 for generating a multiple sine signal being a signal composed of a plurality of sine-wave signals different in a frequency is provided, and the multiple sine signal is changed in frequency into a desired frequency band by an orthogonal modulation apparatus 16 and applied to the measured device 3. In addition, a measurement signal sent from the measured device 3 is converted into frequency and transformed into digital value by an A/D convertor 35, and then inputted into a digital signal processing section(DSP section). In the DSP section 30, the measured signal is converted into a complex frequency spectrum by an orthogonal detection section 36 and a complex high speed Fourier conversion section(FFT section) 43, and a variation in a phase and an amplitude is detected by a phase and amplitude comparator 44.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a network analyzer, and more particularly, to a network analyzer that performs signal processing by digital signal processing (DSP).

[0002]

2. Description of the Related Art A network analyzer inputs a sine wave signal to a device under test (DUT), and measures a reflection signal from an input terminal of the device to be measured and a transmission signal from an output terminal of the device to be measured. It is intended to analyze the reflection characteristics and transmission characteristics (pass characteristics) of a device under test, and is generally configured so that measurements at a plurality of equally spaced frequency points can be performed by continuous sweeping. I have. Devices to be measured by the network analyzer range from single components such as piezoelectric vibrators to linear circuit networks and systems.

FIG. 3 is a block diagram showing an example of the configuration of a conventional vector network analyzer. The network analyzer 50 includes an output terminal 51 for outputting a sine wave signal, an input terminal 52 for inputting a reference signal (R in the drawing), and two input terminals 53 and 54 for inputting a measurement signal.
(Illustrations A and B). When performing the measurement, a signal separator 55 for splitting the sine wave signal into two is connected to an output terminal 51, and one output from the signal separator 55 is input to an input terminal 52 for inputting a reference signal. And the other output is
Device under test (DUT) via directional bridge 56
57. At this time, the device under test 5
The reflected wave from 7 is separated from the input signal to the device under test 57 by the directional bridge 56, and this reflected wave is applied to the input terminal 53. An output signal (transmission wave) from the device under test 57 is input to the input terminal 54. The reflection characteristic is known from the voltage ratio (A / R) between the input terminal 53 and the reference signal input terminal 52, and the voltage ratio (B / R) between the input terminal 54 and the reference signal input terminal 52 is determined.
R) shows the transmission characteristics.

[0004] Inside the network analyzer 50,
A main synthesizer 61 and an offset synthesizer 62 for generating a sine wave signal, a local synthesizer 63 for generating a local signal to a receiving system, and frequency conversion based on a signal from the main synthesizer 61 and a signal from the offset synthesizer 62 Mixer 64 that performs
And a local mixer 65 that performs frequency conversion based on a signal from the main synthesizer 61 and a signal from the local synthesizer 63 to generate a local signal. An output signal from the mixer 64 is amplified by the The signal is output from the output terminal 51 as a wave signal. Also, for each of the input terminals 52 to 54, an amplifier 71 for amplifying an input signal, a mixer 72 for converting an output signal of the amplifier 71 into an intermediate frequency signal based on a local signal from a local mixer 66, and an intermediate frequency A mixer 73 for further frequency-converting the signal and a sample / hold (S / S) for sampling the output of the mixer 73
H) An A / D converter 75 for converting an output (analog value) of the circuit 74 and the sample / hold circuit 74 into a digital value, and performing digital signal processing on the digital signal output from the A / D converter 75 A DSP unit 76 is provided. Then, reflection characteristics and transmission characteristics are analyzed in accordance with the digital signal processing result in the DSP unit 76.

FIG. 4 is a functional block diagram for explaining the processing in the DSP unit 76 in the conventional network analyzer 50. The DSP unit 76 is constituted by a digital signal processor (DSP), and its function is realized by hardware or software. In any case, the content of the digital signal processing here is quadrature detection processing. This is represented by the combination of blocks as shown in FIG. FIG. 4 also shows a sample / hold circuit 74 and an A / D converter 75 connected to the input side of the DSP unit 76 for explanation. Note that the A / D converter 75 is a floating A / D converter whose range switches according to the level of the input signal.

[0006] The signal output from the A / D converter 75 is input to the DSP unit 76 and is branched into two. Each branch is provided with multipliers 81 and 82, respectively. The signal generators 83 and 8 generate digital values of a cosine signal and a sine signal of a predetermined frequency for each sampling, respectively.
4 are provided, and signals from the signal generators 83 and 84 are input to multipliers 81 and 82, respectively. As a result, the input signal to the DSP unit 76 is multiplied by the cosine signal and the sine signal from the signal generators 83 and 84 every sampling. On the output side of each of the multipliers 81 and 82, via averaging units 85 and 86 that perform averaging processing,
Low-pass filter 87 by digital filtering,
88 are connected. The output of the low-pass filter 87 represents a real number component (in-phase component) R and is connected to a terminal 89. Similarly, the output of the low-pass filter 88 represents an imaginary component (orthogonal component) X and is connected to a terminal 90. By performing calculations based on digital values from the terminals 89 and 90, amplitude, phase, group delay time characteristics, and the like can be measured.

[0007]

However, in the above-described conventional network analyzer, quadrature detection is performed by digital signal processing, and a sine wave signal of a discrete frequency is sequentially generated by a frequency synthesizer. In order to measure at a high accuracy frequency, it is necessary to increase the number of measurement points, that is, the number of frequency points. When the Q value of the device under test is large, this device under test can follow the frequency fluctuation,
It is necessary to reduce the frequency sweep speed. As a result, the conventional network analyzer has a problem that the time required for measurement is long, and particularly, in order to measure a device under test having a slow response with high accuracy, there is a problem that the measurement time is extremely long. .

An object of the present invention is to maintain high accuracy while
An object of the present invention is to provide a network synthesizer that can significantly reduce measurement time.

[0009]

SUMMARY OF THE INVENTION A network synthesizer according to the present invention is a network analyzer which applies a sine wave signal to a device under test to analyze the characteristics of the device under test. Multiple sine signal generating means for generating a multiple sine signal that is a signal obtained by combining a plurality of different sine wave signals, Fourier transform means for performing a Fourier transform on a measurement signal input from the device under test to obtain a characteristic value for each frequency, Having.

In the present invention, the multiple sine signal generating means can be constituted, for example, as a direct digital synthesizer. Also provided is a quadrature detection means for performing quadrature detection on the measurement signal by digital signal processing and supplying the in-phase component and the quadrature component to the Fourier transform means. The Fourier transform means performs complex fast Fourier transform (complex FF) by digital signal processing.
By performing T), it is possible to obtain a vector-type network analyzer whose main part is constituted by a digital signal processor. Of course, it is obvious to those skilled in the art that a frequency conversion circuit, a bandpass filter, and the like are added to perform measurement in a desired frequency band. In order to obtain a multiplexed sine signal frequency-converted into a signal of a desired frequency band, a cosine component and a sine component are simultaneously generated as a multiplexed sine signal, and a carrier (carrier) signal is generated using the cosine component and the sine component. Is preferably orthogonally modulated.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a network analyzer according to an embodiment of the present invention.

The network analyzer 1 measures a reflection characteristic and a transmission characteristic of a device under test (DUT) 3. An output terminal 2 for outputting a signal to be supplied to the device under test 3, Input terminal 4 for inputting the signal of In the illustrated example, only one input terminal 4 is provided. However, an input terminal for inputting a reference signal may be provided, or two input terminals may be provided corresponding to the reflected wave and the transmission wave, respectively. . In this case, as will be easily understood by those skilled in the art, it is necessary to add hardware after the input terminals according to the number of input terminals provided.

The network analyzer 1 of the present embodiment generates a plurality of sine wave signals of different frequencies at the same time and applies them to the device under test 3 so that a plurality of sine wave signals can be obtained during a measurement time for one conventional measurement point. , And the measurement time can be reduced by the frequency multiplicity. Therefore, the network analyzer 1 includes a multiple sine signal generator 10 for generating a multiple sine (multisine) signal, a complex FFT (fast Fourier transform) unit 43 for analyzing a signal from the device under test 3 for each frequency. It has. Hereinafter, the configuration of the network analyzer 1 will be described in detail. Here, the multiple sine signal is a signal obtained by superimposing (adding) a plurality of sine wave signals having different frequencies.

The multiplex sine signal generator 10 has a built-in waveform table storing time domain data of the multiplex sine signal. For each clock, the cosine component (in-phase component I) and the sine component (quadrature component) of the multiplex sine signal are provided. The digital value of the value of Q) is output. By changing the order of addresses given to the waveform table or changing the clock frequency, frequency sweeping can be performed while including sine wave signals of a plurality of frequencies. In order to generate the cosine component and the sine component at the same time, for example, both a cosine component waveform table and a sine component waveform table may be prepared. Further, the multiplexed sine signal generator 10 also generates information such as the frequency and amplitude of each sine wave signal included in the multiplexed sine signal, and supplies the information to the phase amplitude comparator 44 described later as reference information. The digital value signals of the in-phase component I and the quadrature component Q from the multiple sine signal generator 10 are respectively
The signals are input to D / A converters 12 and 13 and converted into analog signals. The sampling signals are supplied from the sampling signal generator 11 to the D / A converters 12 and 13. Here, the frequency of the sampling signal (sampling frequency f _SP ) is set to be at least twice the frequency range (frequency width) to be output. On the output side of the D / A converters 12 and 13, low-pass filters 14 and 15 are provided, respectively.

The multiple sine signal generator 10, the sampling signal generator 11, the D / A converters 12 and 13, and the low-pass filters 14 and 15 constitute a multiple sine signal generator. As is clear from the above description, here, a direct digital synthesizer (DDS) is used as the multiplexed sine signal generating means. A direct digital synthesizer that outputs a signal including a plurality of frequency components as described above is disclosed in Japanese Examined Patent Publication No. 3-50224, but the one disclosed in this publication can output only a single phase. However, it is not configured to simultaneously output both the in-phase component I and the quadrature component Q. In addition, in a direct digital synthesizer, the highest frequency that can be generated is relatively low, so that a frequency range required as a network analyzer cannot be covered in many cases. Therefore, in the network analyzer 1 of the present embodiment, the quadrature modulator 16 is provided so that a multiplexed sine signal in a desired frequency region is applied to the device under test 3.

The quadrature modulator 16 includes an oscillator 17 for generating a sine wave signal having a desired frequency f _RF and a phase shifter 1 for delaying the phase of the sine wave signal generated by the oscillator 17 by π / 4.
8, a mixer 19 for mixing the output of the low-pass filter 14 and the output of the phase shifter 18 to perform frequency conversion, a mixer 20 for mixing the output of the low-pass filter 15 and the output of the oscillator 17 to perform frequency conversion, and both mixers. And a multiplexer 21 for multiplexing the outputs of 19 and 20.
Is applied to the device under test 3 via the output terminal 2. The cosine component (in-phase component I) from the multiple sine signal generator 10 and the sine component from the oscillator 17 are input to one mixer 19, and the sine component from the multiple sine signal generator 10 is input to the other mixer 20. Since the (quadrature component Q) and the cosine component from the oscillator 17 are input, the sum frequency of the output frequency f _RF of the oscillator 17 and the multiplexed sine signal generated by the multiplexed sine signal generator 10 is eventually output from the multiplexer 21. Is output, and a signal obtained by superimposing a plurality of sine wave signals of different frequencies in a desired frequency region is applied to the device under test 3.

The signal from the device under test 3 is input to an input terminal 4
The input terminal 4 is connected to a mixer 32 for frequency-converting a signal from the device under test 3 into a signal having an intermediate frequency _fIF , and the mixer 32 is connected to the local oscillation circuit 3.
From 1 a local oscillation signal is input. And mixer 3
On the output side of _{No. 2,} a band-pass filter 33 of an intermediate frequency f _IF is provided. The 3 dB pass bandwidth of the band-pass filter 33 is １ ／ of the sampling frequency f _SP .
It is optimal to Further, an A / D converter 35 for sampling the intermediate frequency signal output from the band-pass filter 33 and converting it into a digital signal is provided. The A / D converter 35 is supplied with a sampling signal from the sampling signal generator 34, and the frequency (sampling frequency) of the sampling signal is
The digital signals from multiple sinusoidal signal generator 10 maintain a correspondence sampling frequency f _SP generated by sampling signal generator 11 to analog conversion. Instead of providing these two sampling signal generators 11, 34,
A single sampling signal generator may be used.

A DSP unit 30 is provided for processing a digital signal output from the A / D converter 35. The DSP unit 30 includes a digital signal processor (DS)
P), the functions of which are realized by hardware or software, or a combination thereof, wherein the content of digital signal processing is as follows.
It is represented by a combination of functional blocks as shown. D
In the SP unit 30, the digital signal from the A / D converter 34 is first input to the quadrature detection unit 36. Quadrature detector 36
Includes a signal generator 37 for generating a digital value of a sine wave signal of a predetermined frequency for each sampling, and a signal generator 3
7 multiplies the digital value from the A / D converter 35 by the digital value from the phase shifter 38, and the digital value from the A / D converter 35 And a multiplier 40 for multiplying the digital value from the A / D converter 35 by the digital value from the signal generator 37 and outputting the result. A / D
The digital value from converter 35 is applied to both multipliers 39, 40
And the signals from the signal generator 37 are supplied to the multipliers 39 and 49 while being shifted from each other by π / 4 to perform quadrature detection.
0 outputs a quadrature component Q and an in-phase component I, respectively. The outputs from the multipliers 39 and 40 are input to digital low-pass filters 41 and 42, whereby unnecessary high frequency components included in the quadrature component Q and the in-phase component I are removed. Then, the quadrature component Q and the in-phase component I output from the low-pass filters 41 and 42 are input to the complex FFT unit 43 and subjected to a complex fast Fourier transform (complex FFT). A complex frequency spectrum is obtained by the complex fast Fourier transform. As a result, the amplitude of the sine component and the cosine component is output from the complex FFT unit 43 for each frequency. A phase-amplitude comparator 44 is provided on the output side of the complex FFT unit 43.
Is provided, and based on the reference information from the multiple sine signal generator 10, the phase and amplitude comparator 44 provides a signal at a predetermined frequency point corresponding to the multiple sine wave signal generated by the multiple sine signal generator 10. Detect changes in phase and amplitude,
This is output for analysis of reflection characteristics and transmission characteristics.

According to the network analyzer of the present embodiment, the reflection characteristics and transmission characteristics of a device having a large Q value can be measured in a short time. FIG. 2 shows such a Q
FIG. 9 is a frequency characteristic diagram illustrating an example of a device having a large value. Here, it is assumed that a device having a 3 dB bandwidth of 10 Hz is a device under test (DUT) and the characteristics of the device are measured. According to the narrow bandwidth, the frequency interval Δf between the frequency points to be measured is set to, for example, 0.2 Hz, and the measurement is performed with a frequency sweep span of 100 Hz. With the conventional method, the number of frequency points is 5
Since the number of measurement points is 00, 500 times the measurement time per point is the measurement time as a whole. On the other hand, according to the present embodiment, since the multiplexed sine signal is used, the measurement time can be reduced by the frequency multiplicity. For example, if the multiplicity is 5, the measurement time per point is reduced. All measurements can be completed in 100 times the time.

In the network analyzer of the present embodiment described above, a direct digital synthesizer (D
Although a multiple sine signal generator of the DS) type is used, the mechanism for generating a multiple sine signal in the present invention is not limited to this. For example, a plurality of analog synthesizers may be prepared, and sine wave signals having different frequencies from these synthesizers may be synthesized. Further, the local oscillation frequency of the quadrature modulator (the above oscillator 17
, The frequency from the multiple sine signal generator 10 side is sequentially shifted and the signals are synthesized, so that measurement at more points and in a wider frequency range can be executed.

[0021]

As described above, according to the present invention, a multiple sine signal generating means is provided so that a plurality of sine wave signals having different frequencies are simultaneously applied to the device under test, and the measurement from the device under test is performed. Since the characteristic for each frequency is obtained by performing a Fourier transform on the signal, the measurement at a plurality of frequencies is substantially completed at one measurement point, and the frequency is compared with the case where the conventional network analyzer is used. There is an effect that the measurement time can be shortened by the multiplicity.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a network analyzer according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a frequency characteristic of a device having a large Q value.

FIG. 3 is a block diagram illustrating an example of a configuration of a conventional network analyzer.

4 is a DSP in the network analyzer of FIG.
FIG. 4 is a functional block diagram illustrating processing in a unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Network analyzer 2 Output terminal 3 Device under test 4 Input terminal 10 Multiple sine signal generator 11,34 Sampling signal generator 12,13 D / A converter 14,15 Low pass filter 16 Quadrature modulator 17 Oscillator 18 Phase shifter 19 , 20, 32 mixer 21 multiplexer 33 band-pass filter 30 DSP unit 31 local oscillation circuit 35 A / D converter 36 quadrature detection unit 37 signal generation unit 38 phase shift unit 39, 40 multiplier 41, 42 digital low-pass filter 43 Complex FFT unit 44 Phase amplitude comparator

Claims (3)

[Claims] 1. A network analyzer for applying a sine wave signal to a device under test and analyzing the characteristics of the device under test, wherein a signal obtained by combining a plurality of sine wave signals having different frequencies to apply to the device under test is used. A network analyzer comprising: a multi-sine signal generating means for generating a certain multi-sine signal; and a Fourier transform means for performing a Fourier transform on a measurement signal input from the device under test to obtain a characteristic value for each frequency. 2. The network analyzer according to claim 1, wherein the multiple sine signal generating means is constituted by a direct digital synthesizer. 3. A quadrature detector for performing quadrature detection of a measurement signal by digital signal processing and supplying an in-phase component and a quadrature component to the Fourier transform means, wherein the Fourier transform means performs complex fast Fourier transform by digital signal processing. The network analyzer according to claim 1, wherein the network analyzer performs the operation.