JPH0760976B2 - Signal suppressor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a signal suppressing device that can be used, for example, when measuring spurious characteristics of circuits under test, elements, etc., intermodulation distortion, and the like.

"Prior Art" To measure spurious characteristics or intermodulation distortion in various circuits such as high frequency amplifiers or frequency mixers, as shown in FIG. And the output signal 4 of the circuit under test 2 is applied to a measuring device 5 such as a spectrum analyzer.
Then, the state of the output signal 4 is displayed to determine the response state of the circuit under test 5.

Here, for example, it is assumed that the reference signal oscillator 1 gives the signal 3 having the frequency f shown in FIG. 8A, and the circuit under test 2 outputs the response signal 4 having the frequency component shown in FIG. 8B.

The response output signal 4 is the reference signal 3 given from the reference oscillator 1, its harmonics 3A, 3B, 3C ... And the nearby spurious signals SP ₁ ,
It contains SP ₂ and the noise component N appearing above and below the signal 3.

In the signal 4 given to the measuring device 5, the level ratio between the reference signal 3 and the nearby spurious signals SP ₁ and SP ₂ is generally large. Further, the level ratio between the reference signal 3 and the noise component N is also large.

That is, when the response output signal 4 of the circuit under test 2 is displayed on the spectrum analyzer, the high-level reference signal 3 of the frequency f and its second and third harmonic signals are displayed as shown in FIG.
3A and 3B are clearly displayed on the display screen, but the low-level neighboring spurious signals SP ₁ and SP ₂ and the noise component N appearing near the high-level reference signal 3 are actually clearly displayed on the display screen. Does not appear.

Therefore, the ratio of the levels of the signal 3 and the nearby spurious signals SP ₁ and SP ₂ or the ratio of the levels of the signal 3 and the noise component N, that is, SN
The ratio cannot be measured.

Therefore, conventionally, a notch filter 7 having a characteristic that sharply falls at the frequency f of the signal 3 as shown by reference numeral 6 in FIG. 9 is provided between the circuit under test 2 and the measuring instrument 5 as shown in FIG. And the component of the signal 3 is removed by this notch filter 7, whereby the nearby spurious signal SP ₁ , is not affected by the dynamic range of the spectrum analyzer.
The SP ₂ and the noise component N are made to be able to be greatly enlarged and displayed, and the level value thereof is measured.

"Problems to be solved by the invention" The notch filter 7 has a finite bandwidth even though its attenuation characteristic is steep, and therefore affects the levels of the spurious signals SP ₁ and SP ₂ generated in the vicinity of the desired frequency f. There is an inconvenience that an error occurs.

In addition, there is a so-called ripple 8 in the characteristic in a portion other than the desired frequency f, and the influence of the ripple 8 changes the levels of the harmonic components 3A, 3B, etc., which also causes a measurement error.

"Means for Solving Problems" In the present invention, a high-level reference signal output from the measured means by applying a reference signal of a desired frequency to the measured means and at least the vicinity of the reference signal Signal branching means for receiving and branching a signal under measurement consisting of signals of a plurality of frequency components including near-field spurious signals and harmonic signals generated in, and the high level from the signal under measurement supplied from this signal branching means Signal extracting means for extracting the reference signal, an oscillator for generating a signal composed of a single frequency component of a frequency synchronized with the reference signal extracted by the signal extracting means, and a signal of a single frequency component generated by the oscillator Phase adjusting means for adjusting the phase of the reference signal to obtain a signal having a phase opposite to that of the reference signal, and a single frequency component of the opposite phase from the phase adjusting means. An amplifier for amplifying a signal to a predetermined level and a signal under measurement from the signal branching means are supplied to an output terminal, and when the amplified signal of the opposite phase single frequency component is given, this opposite phase A signal of a single frequency component and a signal under measurement from the signal branching unit are combined to output a signal in which the reference signal in the signal under measurement is suppressed without changing the levels of signals of other frequency components. The signal suppressing device is configured by the signal coupling means supplied to the terminals.

According to the structure of the present invention, a desired frequency signal including the noise component N given to various circuits such as a high-frequency amplifier and a frequency mixer and a device to be measured such as a semiconductor device is extracted and an oscillator is synchronized with the desired frequency signal. By oscillating, it is possible to obtain a signal of a single frequency that matches the desired frequency and does not contain noise components.

The signal of this single frequency is amplified by an amplifier, and the phase is adjusted to have an opposite phase relation to the phase of the desired frequency signal,
Further, the level adjusting means adjusts the signal to the same level as the level of the desired frequency signal, and these signals are combined by a power combiner to obtain a signal from which the desired frequency signal is removed from the signal under measurement. You can

Therefore, according to the present invention, it is possible to suppress only the desired frequency signal without changing the vicinity spurious generated near the desired frequency signal and the high frequency level of the desired frequency signal.

Therefore, according to the present invention, the level of the signal of the desired frequency,
It is possible to accurately measure the level of the nearby spurious signal and the level of the noise component. Therefore, a measurement result with a very small measurement error can be obtained.

[Embodiment] FIG. 1 shows an embodiment of the present invention. 11 in FIG.
Shows a signal suppressor according to the invention. A signal suppressing device 11 according to the present invention has an input terminal 11A and an output terminal 11B, and a signal under test 4 output from a circuit under test 2 to the input terminal 11A.
give. A measuring device 5 such as a spectrum analyzer is connected to the output terminal 11B.

The signal under measurement applied to the input terminal 11A is split into two by the power splitter 12. The signal extracting means 13 is connected to one branch output terminal 12A of the power branching device 12, and the other branch output terminal 1
One input terminal 22A of the power combiner 22 is connected to 2B.

The signal extracting means 13 can be constituted by a circuit having a variable narrow band filter characteristic such as a tuning amplifier, and the measured signal 4 can be obtained by the variable narrow band filter characteristic.
Of the desired frequency, for example, the signal 3 of the frequency f shown in FIG. 2 is extracted.

The signal 3 extracted by the signal extracting means 13 is given to the phase comparator 14, for example. The oscillation signal 23 of the oscillator 15 is applied to the other input terminal of the phase comparator 14,
The phase of the signal 3 extracted by 23 and the signal extraction means 13 is compared, and the oscillation frequency of the oscillator 15 is controlled by the phase comparison output 24. Therefore, a voltage controlled oscillator may be used as the oscillator 15.

In this way, by controlling the oscillation frequency of the oscillator 15 by the phase comparison output, it is possible to obtain from the oscillator 15 a signal 23 of a single frequency that matches the frequency of the signal 3 of the desired frequency.

The single frequency signal 23 obtained from the oscillator 15 is phase-adjusted by the phase adjusting means 16. That is, in the power combiner 22, the suppression included in the signal under measurement 4 is adjusted so as to be out of phase with the desired phase of the signal 3.

The phase-adjusted signal 25 is amplified to a desired level by the amplifier 17, and is supplied to the level adjusting means 19 through the variable bandpass filter 18 as needed.

The level adjusting means 19 adjusts the level so that the level of the signal 3 desired to be suppressed matches the level of the signal 23 of the single frequency, and supplies the level-adjusted signal to the other input terminal 22B of the power combiner 22. . The switch 21 operates in the signal suppression mode when the contact A is selected, and the normal measurement mode when the contact B is selected.

When the reference signal 3 having the frequency f is given from the reference signal generator 1 to the circuit under test 2 in the above-mentioned configuration, the circuit under test 2 shows the reference signal 3, the noise component N and the spurious signal as shown in FIG. 2A. It is assumed that the output signal 4 including SP ₁ and SP ₂ and the _second and third harmonic waves 3A and 3B is output.

When this output signal 4 is input to the input terminal 11A, the output signal 4 is branched and output to the two output terminals 12A and 12B of the power branching device 12.

The signal extracting means 13 shows a case where the desired frequency signal in the response output signal 4 desired to be suppressed, in this example, the signal 3 is used as the desired frequency signal, and the signal 3 is extracted by tuning to the frequency f of this signal 3. . Here, the desired frequency signal 3 is extracted. However, since the desired frequency signal 3 has the noise component N and spurious signals SP ₁ and SP _{2 in the} vicinity thereof, the desired frequency signal 3 extracted from the signal extracting means 13 is a complete single signal. It cannot be extracted as a single frequency signal.

Therefore, in the present invention, the desired frequency signal 3 is applied to the phase comparator 14, the phase comparator 14 compares the phase with the oscillation signal of the oscillator 15, and the oscillation frequency of the oscillator 15 is controlled according to the result of the phase comparison. A signal 23 in which the oscillation frequency of the oscillator 15 matches the frequency f of the desired frequency signal 3 is obtained.

In this way, the signal 23 output from the oscillator 15 becomes a single frequency signal having the desired frequency f. That is, a single spectrum signal that does not include the noise component N and the spurious signals SP ₁ and SP ₂ can be obtained.

Therefore, the single frequency signal 23 is supplied by the phase adjusting means 16 to the signal 25 having the opposite phase to the phase of the desired frequency signal 3 (FIG. 2B).
The signal 25 having the opposite phase is amplified by the amplifier 17, and is supplied to one input terminal 22B of the power combiner 22 through the variable bandpass filter 18 and the level adjusting means 19.

The level adjuster 19 adjusts the level of the desired frequency signal 3 and the level of the signal 25 included in the signal under test 4 so that they match each other, so that the desired frequency signal 3 and the signal 25 cancel each other in the power combiner 22. The desired frequency signal is suppressed.

Therefore, by giving a signal in which the signal 3 in the signal under measurement 4 is suppressed to the measuring device 5 such as a spectrum analyzer, the dynamic range of the measuring device 5 is not disturbed by the signal 3 having a large level, As a result, a signal whose level is smaller than that of the signal 3, that is, noise N, spurious signals SP ₁ and SP ₂ , harmonics 3A and 3B, etc., can be displayed large as shown in FIG. Can be measured.

"Modified Embodiment of the Invention" FIG. 4 shows another embodiment of the present invention. In this example, the case where the frequency of the desired frequency signal is high is shown.

Therefore, as a configuration different from that of the embodiment of FIG. 1, the signal extracting means 13 includes the frequency mixers 13A and 13B and the band pass filter 1.
3C and 13D and the frequency mixer
13A, 13B and the point where two local oscillators 26, 27 for giving local oscillation signals f ₁ , f ₂ to the frequency mixers 28A, 28B constituting the frequency conversion means 28 described later are provided, and on the side that outputs the signal 25. The point is that the frequency conversion means 28 constituted by the frequency mixers 28A and 28B, the bandpass filter 28C and the lowpass filter 28D is provided.

In this way, as the signal extracting means 13, the frequency mixers 13A, 13B
And the bandpass filters 13C and 13D are used, even if the frequency F of the desired frequency signal is a high frequency such as several tens of MHz or more, the frequency f is compared with the local oscillation signals of the local oscillators 26 and 27. By mixing, frequency conversion can be performed and the signal can be taken out as a low frequency signal. Therefore, the oscillator 15 can use an ordinary voltage controlled oscillator.

The oscillation signal 23 of the oscillator 15 is phase-adjusted by the phase adjusting means 16 and converted into a signal 25 having a phase opposite to the phase of the desired frequency signal. A signal having the same frequency as the desired frequency signal contained in the measurement signal 4 but having the opposite phase can be obtained.

By applying this signal to the power combiner 22 through the amplifier 17, the variable band pass filter 18 and the level adjusting means 19, the desired frequency signal contained in the signal under test 4 can be suppressed. The same effect as that of the embodiment can be obtained.

In this embodiment, a third local oscillator 29 is provided, and instead of the local oscillation signal of the local oscillator 27, this third local oscillator 27 is used.
Is added to the frequency mixer 28A via the switch 31.

When the switch 31 is switched to the contact B by adding this configuration, the signal 32 is not in the signal suppression mode, and the signal 32 having a frequency determined by the oscillation frequency of the local oscillator 29 is output to the output terminal 11B in addition to the signal 3 as shown in FIG. Can be output.

When the frequency of the signal 3 is f, the oscillation frequency of the local oscillator 27 is f ₂ and the oscillation frequency of the local oscillator 29 is f ₂ + Δf, the frequency of the signal 32 is f + fΔf.

When switching the switch 31 to the contact B to operate it, the sixth
As shown in the figure, the reference signal 3 is applied from the reference oscillator 1 to the input terminal 11A of the signal suppressor 11, the circuit under test 2 is connected to the output terminal 11B, and the measuring instrument 5 is connected to the output side of the circuit under test 2. .

Therefore, when the reference signal 3 having the frequency f is supplied from the reference oscillator 1, the circuit under test 2 can be supplied with two signals whose frequencies f and f + Δf are close to each other and whose levels are equal to each other. When non-linear devices such as an amplifier or a frequency mixer are used as the circuit under test 2 by giving these two signals 3 and 32, the third-order intermodulation distortion of these non-linear devices can be measured. You can

[Advantageous Effects of the Invention] As described above, according to the present invention, a high-level reference signal having a desired frequency and at least the vicinity of the reference signal, which are output from the measured means such as various circuits, devices, and elements. A signal under measurement composed of signals of a plurality of frequency components including a near spurious signal and a harmonic signal generated in the, and the high-level reference signal in the signal under measurement are changed in level of signals of other frequency components. Since the suppressed signal can be selectively applied to the measuring device without being generated, it is generated not only in the level of the high-level reference signal but also in the vicinity of the high-level reference signal, which was difficult to measure in the past. It is possible to accurately measure the level of nearby spurious signals, the level of noise components, the level of harmonic signals, etc. There is a remarkable effect that the level ratio of the signal and the noise component, that is, the SN ratio can be accurately measured. In particular, by configuring the signal extracting means 13 so that the extraction frequency can be freely changed, it is possible to suppress a signal of an arbitrary frequency.

Also, as in the embodiment described in FIG. 4, the third local oscillator 29
It is convenient to measure the third-order intermodulation distortion of the nonlinear device by adding a configuration capable of generating a signal 32 having a frequency close to the signal of the reference signal oscillator 1 by providing the signal of the local oscillator 29. .

[Brief description of drawings]

FIG. 1 is a block diagram for explaining one embodiment of the present invention, FIG. 2 is a graph for explaining the operation of FIG. 1, and FIG. 3 is a desired frequency signal by the signal suppressing device of the present invention. FIG. 4 is a waveform diagram for explaining a state in which the noise is suppressed, FIG. 4 is a block diagram for explaining another embodiment of the present invention, and FIG. 5 is a graph for explaining the operation of the embodiment of FIG. Sixth
FIG. 7 is a block diagram for explaining a state in which the additional function of the embodiment shown in FIG. 4 is used, FIG. 7 is a block diagram for explaining a conventional measuring method, and FIG. 8 is FIG. 9 is a graph for explaining the operation of FIG. 9, and FIG. 9 is a graph for explaining an example of a method for improving the problems of the conventional measurement method.
FIG. 10 is a block diagram for explaining the configuration of the conventional improvement method described in FIG. 1: Reference signal oscillator, 2: Circuit under measurement, 3: Reference signal, 4: Signal under measurement, 5: Measuring instrument, 11: Signal suppressing device, 12: Power splitter,
13: signal extracting means, 14: phase comparator, 15: oscillator, 16: phase adjusting means, 17: amplifier, 18: variable band pass filter, 1
9: Level adjustment means.

Claims (1)

[Claims] 1. A high-level reference signal output from a device under test by applying a reference signal of a desired frequency to the device under test and a near-field spurious signal or a harmonic generated at least in the vicinity of the reference signal. An input terminal for receiving a signal under measurement composed of a plurality of frequency component signals including signals, a signal branching unit connected to the input terminal for branching the received signal under measurement, and a signal branching unit supplied from the signal branching unit. A signal extracting means for extracting the high-level reference signal from the measurement signal, an oscillator for generating a signal having a single frequency component of a frequency synchronized with the reference signal extracted by the signal extracting means, and an oscillator generated by the oscillator. Phase adjusting means for adjusting the phase of a signal of a single frequency component to obtain a signal of a phase opposite to that of the reference signal, and a single phase of the opposite phase from the phase adjusting means. An amplifier that amplifies the signal of the wave number component, and supplies the signal under measurement from the signal branching means to the output terminal, and when the amplified signal of the single frequency component of the opposite phase is given, the single signal of the opposite phase is supplied. An output terminal that combines a signal of one frequency component and a signal under measurement from the signal branching unit and suppresses the reference signal in the signal under measurement without changing the level of the signal of another frequency component And a signal coupling means for supplying the signal under measurement to the measurement position connected to the output terminal, the reference signal in the signal under measurement being selectively given, Signal level, the level of a nearby spurious signal generated near the reference signal, the level of a harmonic signal, the level of a noise component, etc. can be accurately measured. Pressure device.