JP2012208019A - Probe, measuring apparatus and circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probe, a measuring apparatus and a circuit board that can accurately measure a high frequency signal.SOLUTION: A probe 10 for acquiring a signal from a measuring object and supplying the signal to a measuring apparatus via a connection cable includes: a LC series resonance circuit (conductor plate 12) provided between the measuring object and the connection cable; and a grounding mechanism for connecting a ground wiring of the measuring object and an outside conductor of the connection cable. A resonance frequency of the LC series resonance circuit is different from a frequency of the signal to be the measuring object. A ratio of an impedance of the LC series resonance circuit in the frequency of the signal to an input impedance of the measuring apparatus is set to be equal to a desired attenuation ratio of the probe.

Description

  The present invention relates to a probe, a measuring device, and a circuit board.

  When measuring a signal that propagates through a signal line using a probe, the frequency characteristic of the measurement signal is affected by the disturbance of the frequency characteristic of the impedance of the probe itself (impedance between the signal line and the measuring device). As a result, accurate measurement may not be possible. In addition, by connecting the probe, the impedance of the probe itself and the input impedance of the measuring device are newly added between the input and output of the signal line, so the impedance of the measurement object changes, so accurate measurement cannot be performed. There is a case.

  As a method for preventing the influence of the former, for example, Patent Document 1 discloses a technique for reducing the influence of impedance by connecting the probe pin and the wiring of the measuring instrument with a strip-shaped wiring to prevent the impedance from becoming excessive. Has been.

  As a method for preventing the influence of the latter, a technique for reducing the influence on the measurement target by connecting a chip resistor having a relatively large resistance value in series with the probe pin and reducing the change in the impedance of the measurement target is known. .

JP 2000-258454 A

  By the way, the former technique has a problem that it does not correspond to an application in which a part of a signal propagating through a signal line is taken out and measured.

  In the latter technique, the impedance of the chip resistor itself changes in the high frequency band, so that there is a problem that accurate measurement cannot be performed. More specifically, the resistance value and the inductance value of the chip resistor itself vary depending on the frequency. FIG. 11 shows the variation of the resistance value of the chip resistor depending on the frequency. As shown in this figure, the resistance value of the chip resistor varies greatly depending on the frequency. For this reason, the attenuation factor of the probe using such a chip resistance is an ideal chip resistance, that is, a straight line as indicated by Y when the resistance value is constant regardless of the frequency, as shown in FIG. However, in practice, as indicated by X, it varies greatly depending on the frequency.

  Therefore, when the signal shown in the upper side of FIG. 13A is measured using a probe having a power attenuation factor of 20 dB and a flat characteristic (ideal), the lower side of FIG. A measurement result like this is obtained. On the other hand, when a probe having a power attenuation factor of 20 dB is configured using a chip resistor having the characteristics shown in FIG. 11 and the signal shown on the upper side of FIG. 13A is measured, the signal itself is obtained by connecting the chip resistor. Since the waveform changes under the influence, the signal waveform changes as shown in the upper diagram of FIG. 13B, and the measured waveform also becomes as shown in the lower diagram of FIG. 13B. That is, there is a problem that accurate measurement cannot be performed.

  Therefore, an object of the present invention is to provide a probe, a measuring apparatus, and a circuit board that can accurately measure a high-frequency signal.

In order to solve the above problems, the present invention provides an LC series resonance circuit provided between a measurement object and the connection cable in a probe that acquires a signal from the measurement object and supplies the signal to the measurement device via the connection cable. And a grounding mechanism for connecting the ground wiring to be measured and the outer conductor of the connection cable, and the resonance frequency of the LC series resonance circuit is the frequency of the signal to be measured. Are different frequencies, and the ratio of the impedance of the LC series resonance circuit at the frequency of the signal and the input impedance of the measuring device is set to be equal to a desired attenuation ratio of the probe. And
According to such a configuration, it is possible to accurately measure a high frequency signal.

In addition to the above invention, in another invention, the C component of the LC series resonance circuit includes a conductor plate disposed at a position facing a signal line through which the signal is propagated, and the signal line and the conductor plate. And a dielectric block disposed between the two.
According to such a configuration, a high-frequency signal can be accurately measured by selecting an appropriate dielectric.

According to another invention, in addition to the above invention, the L component of the LC series resonance circuit has a microstrip line having one end connected to the conductor plate and the other end connected to the center conductor of the connection cable. It is characterized by that.
According to such a configuration, the L component can be accurately configured with a simple structure.

According to another invention, in addition to the above invention, the LC series resonance circuit has a resistance component for adjusting a Q value.
According to such a configuration, it is possible to measure with high accuracy by adjusting the Q value and making the slope of the impedance characteristic around the signal frequency gentle.

Another invention is a measuring apparatus comprising the probe.
According to such a configuration, it is possible to accurately measure a high frequency signal.

According to another aspect of the present invention, there is provided a circuit board to be measured by the probe, wherein the circuit board has a ground structure with which the grounding mechanism is brought into contact when measurement is performed.
According to such a configuration, it is possible to accurately measure a high frequency signal.

In addition to the above invention, another invention is characterized in that the ground structure is a ground pad arranged in the vicinity of a signal line to be measured.
According to such a configuration, it is possible to accurately measure a high frequency signal.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the probe and measuring apparatus which can measure a high frequency signal correctly.

It is a figure which shows the structural example of the probe which concerns on embodiment of this invention. It is a figure which shows the equivalent circuit of the probe shown in FIG. It is a frequency characteristic of the impedance of the probe shown in FIG. It is a Smith chart of the impedance of the probe shown in FIG. It is a frequency characteristic of the line loss from port1 of the board | substrate shown in FIG. 1 to port2. It is the frequency characteristic of the line loss from port 1 to port 2 of the substrate when the probe is applied. It is a frequency characteristic of the line loss from port1 to port3 of the board | substrate shown in FIG. It is an example of the board | substrate used as the measuring object of a probe. It is a figure which shows the circuit structure of the board | substrate shown in FIG. It is a figure which shows the other structure of a ground pad. It is a frequency characteristic of resistance value and impedance value of chip resistance. It is a frequency characteristic of the attenuation factor of a probe using a chip resistor. It is a figure which shows the result of having measured a signal with the probe using an ideal probe and a chip resistance.

  Next, an embodiment of the present invention will be described.

(A) Description of Configuration of Embodiment FIG. 1 is a diagram illustrating a configuration example of a probe according to an embodiment of the present invention. In this figure, the probe 10 has a dielectric block 11, conductor plates 12, 13, and a ground pin 14, and is provided at the end of a connection cable 20 that connects the probe 10 and a measurement device (not shown).

  Here, the dielectric block 11 is made of, for example, Teflon (registered trademark) or ABS (Acrylonitrile Butadiene Styrene) resin having a block shape with a thickness D. A conductor plate 12 and a conductor plate 13 are provided on the upper surface 11 a of the dielectric block 11. Further, the lower surface 11b of the dielectric block 11 is in contact with a signal line to be measured at the time of measurement. The conductor plate 12 is formed of, for example, a copper foil having a convex shape. Here, the larger rectangle of the conductor plate 12 is called a main plate 12a, and the smaller rectangle is called a sub plate 12b. The main plate 12a has an area S and forms a capacitor with the signal line as will be described later. The sub-plate 12b has a length L and functions as an inductor connected in series with the above-described capacitor as will be described later.

  The conductor plate 13 is connected to the outer conductor 22 of the connection cable 20, and the conductor plate 13 is electrically connected to four ground pins 14. The ground pin 14 has one end connected to the conductor plate 13 and the other end protruding from the lower surface 11 b of the dielectric block 11 by a predetermined length. Each of the ground pins 14 is urged downward by a spring mechanism (not shown). When the dielectric block 11 is disposed on the substrate 30 to be measured, the ground pads 33 and 34 are arranged. To be electrically connected to the ground pads 33 and 34. As a result, the outer conductor 22 of the connection cable 20 and the ground of the substrate 30 are electrically connected.

  The connection cable 20 has an outer sheath 21, an outer conductor 22, an inner sheath 23, and a center conductor 24, and the other end (not shown) is connected to the input end of the measuring apparatus. Here, the outer coating 21 and the inner coating 23 are made of an insulating resin. The outer conductor 22 and the center conductor 24 are made of, for example, copper having high conductivity. In the example of FIG. 1, the outer sheath 21 is excluded from one end of the connection cable 20, and the outer conductor 22 is fixed in contact with the conductor plate 13. The center conductor 24 is fixed in electrical contact with the sub-plate 12b.

  The substrate 30 is a substrate to be measured. In this example, the substrate 30 includes a dielectric plate 31, a signal line 32, ground pads 33 and 34, and a ground layer 35. The dielectric plate 31 is made of, for example, epoxy resin, ceramics, or the like. A signal line 32 and ground pads 33 and 34 are formed on the upper surface 31a of the dielectric plate 31, and a ground layer 35 is formed on the lower surface 31b. The signal line 32 is made of, for example, copper, and a signal to be measured is propagated. The ground pads 33 and 34 are disposed on both sides of the signal line 32, and are disposed at positions where the four ground pins 14 come into contact when the probe 10 is disposed on the signal line 32. The ground pads 33 and 34 are electrically connected to the ground layer 35 disposed on the back surface of the substrate 30 through, for example, via holes.

  FIG. 2 is a diagram showing an equivalent circuit of the probe 10 shown in FIG. In the probe 10 shown in FIG. 1, the main plate 12a having an area S is disposed opposite to the signal line 32 with the dielectric block 11 interposed therebetween, and thus the capacitor 40 shown in FIG. Also, the inductor 41 shown in FIG. That is, the LC series resonance circuit including the capacitor 40 and the inductor 41 is constituted by the conductor plate 12 shown in FIG.

(B) Description of Operation of Embodiment Next, the operation of this embodiment will be described. In the following, the characteristic impedance of the signal line 32 of the circuit shown in FIG. 1 is 50Ω, the frequency of the signal is 30 GHz, the attenuation factor of the probe is 1:10 in voltage ratio, and the input resistance of the measuring device is The description will be made assuming that the resistance is 50Ω.

  When the input resistance of the measuring device is 50Ω, the impedance of the probe 10 needs to be 450Ω in order to obtain an attenuation factor of voltage ratio 1:10. That is, since the impedance of the probe 10 connected in series and the input resistance of the measuring device are connected to the signal line 32, the voltage applied to the input resistance is 1/10 of the voltage of the signal line 32. The impedance of the probe 10 needs to be 450Ω (50 / (450 + 50) = 1/10).

  When the impedance of the embodiment shown in FIG. 1 is set to 450Ω, the area S of the main plate 12a is adjusted, and the length L of the sub-plate 12b is adjusted to configure the equivalent circuit shown in FIG. The resonance frequency of the LC series resonance circuit to be adjusted is adjusted. Then, as shown in FIG. 3, the impedance of the LC series resonance circuit is set to 450Ω at 30 GHz which is the frequency of the signal to be measured. In FIG. 3, the horizontal axis indicates the frequency, and the vertical axis indicates the impedance of the LC series resonance circuit. In the example of FIG. 3, the resonance frequency of the LC series resonance circuit is set to around 4 GHz. That is, the resonance frequency (4 GHz) and the signal frequency (30 GHz) are different.

  Since the impedance Z of the LC series resonance circuit can be obtained by the following equation (1), the values of the capacitor and the inductor can be calculated from the signal frequency, the attenuation factor, and the input impedance of the measuring device. Specifically, when the signal frequency is 30 GHz and the target impedance is 450Ω, L = 2.4 nH and C = 1 pF are obtained.

・・・（１）

... (1)

  FIG. 4 is a Smith chart of the LC series resonance circuit. In this example, since the LC series resonance circuit is capacitive in the frequency range of 0 to 4 GHz, the lower half of the locus indicated by the solid line moves in the clockwise direction, and becomes inductive in the frequency range of 4 to 40 GHz. The upper half of the locus indicated by the solid line is moved clockwise.

  A case where the substrate 30 shown in FIG. 1 is measured using the probe 10 set as described above will be described. FIG. 5 shows line loss and return loss when the probe 10 is not connected. Specifically, when the left end of the substrate 30 shown in FIG. 1 is port 1 and the right end is port 2, the graph (S12) indicated by a square point in the figure shows the line loss from port 1 to port 2, and is indicated by a round point. The graph (S11) shows the return loss.

  FIG. 6 shows a measurement result in the same state as FIG. 5 when the probe 10 is brought into contact with the substrate 30 shown in FIG. From the comparison between FIG. 6 and FIG. 5, the characteristics of 10 GHz or less are different before and after contacting the probe 10, but the characteristics hardly change before and after the contact in the vicinity of the signal frequency of 30 GHz. That is, by applying the probe 10, the measurement object is hardly affected.

  FIG. 7 shows the frequency characteristics of the attenuation amount of power from port 1 to port 3 when the output end of the probe 10 is port 3. In this example, it can be seen that the power attenuation rate is −20 dB in the vicinity of the signal frequency of 30 GHz, and the attenuation rate at the target voltage is 1:10.

  As described above, according to the present embodiment, the LC resonance circuit is provided in the probe 10, the resonance frequency is set to a value different from the signal frequency, and the impedance of the LC resonance circuit is set to the attenuation rate at the signal frequency. Since the corresponding predetermined value is obtained, it is possible to prevent the frequency characteristics from being disturbed and the measurement not being performed accurately as in the case of using a chip resistor, for example. In other words, the inductor and the capacitor are more stable than the case where the element value in the high frequency band is a resistor. Therefore, by using such an element, stable and accurate measurement can be performed.

  Next, a case where measurement is performed using an actual substrate will be described. FIG. 8 is an example of a substrate to be measured. In the substrate 130 of FIG. 8, an input terminal 140 and an output terminal 141 are provided on both ends of the dielectric plate 131 on the left and right (left and right directions in the figure). The signal input from the input terminal 140 is input to the amplifier 142 via the signal line 132, where it is amplified with a predetermined gain, then output via the signal line 132, and input to the filter 143. The filter 143 performs a filtering process on the input signal and then outputs the signal through the signal line 132. The signal output from the filter 143 is supplied to the subsequent apparatus via the output terminal 141.

  FIG. 9 is a detailed circuit diagram of the substrate 130 shown in FIG. As shown in this figure, the signal input from the input terminal 140 has a predetermined bandwidth and amplitude as shown in the lower left of the figure. When such a signal is supplied to the amplifier 142, it is amplified there and output with an increased amplitude as shown in the lower center of the figure. The filter 143 has a band characteristic that narrows the bandwidth of the signal output from the amplifier 142, and the signal after passing through the filter 143 has a narrow bandwidth as shown in the lower right of the figure. Become. 8 and 9, the characteristic impedance of the signal line 132 is 50Ω, the frequency of the signal is 30 GHz, the attenuation factor of the probe is 1:10 in voltage ratio, and the input impedance of the measuring apparatus is 50Ω. This will be described below. The impedance element and the resistance element surrounded by a broken line in the figure indicate the impedance of the probe 10 and the input impedance of the measuring apparatus.

  When a signal output from the amplifier 142 is measured with respect to such a substrate 130 using a probe having a conventional chip resistance, the impedance characteristics of the chip resistance shown in FIG. In addition, the measurement result greatly deviates from the actual signal waveform. On the other hand, when measured using the probe 10 of the present embodiment shown in FIG. 1, the impedance of the LC series resonance circuit of the probe 10 has a slight slope near the signal frequency of 30 GHz as shown in FIG. However, there is no large variation as shown in FIG. For this reason, the waveform measured by the probe 10 of the present embodiment is a waveform that is as close as possible to the waveform shown in FIG. For this reason, compared with the conventional probe, according to the probe 10 of this embodiment, it becomes possible to measure with high accuracy without disturbing the measurement object.

  As described above, according to the probe 10 of the present embodiment, since the measurement is performed using the LC resonance circuit, a capacitor and an inductor having higher element value stability than the resistance element are used. Thus, the measurement can be performed without affecting the target or affecting the measured signal.

  In the present embodiment, the capacitor and the inductor constituting the LC series resonance circuit are configured using the dielectric block 11 and the conductor plate 12. For this reason, for example, by adjusting the material of the dielectric block 11 or adjusting the shape of the conductor plate 12, the stability of the element value in the frequency band of the measurement signal is improved, thereby increasing the measurement accuracy. It becomes possible.

(C) Description of Modified Embodiment It goes without saying that the above embodiment is merely an example, and the present invention is not limited to the case described above. For example, in the above embodiment, the inductor and the capacitor are configured using the dielectric block 11 and the conductor plate 13. However, for example, an LC series resonance circuit is configured using a capacitor element or a coil element. It may be. When chip capacitors and chip coils are used as capacitor elements and coil elements, unlike chip resistors, these elements are configured in advance with consideration of high-frequency characteristics. Therefore, stable characteristics can be obtained. Note that only one of the capacitor element and the coil element may be employed, and the other may be configured as shown in FIG.

  In the above embodiment, the Q value of the LC resonance circuit is not mentioned, but when the Q value is extremely high (for example, several hundreds or more), the slope of the curve shown in FIG. Therefore, it is assumed that the resonance frequency changes due to a slight deviation of the element value of the capacitor or inductor, and the impedance of the LC resonance circuit deviates from the target value. For this reason, it is desirable for the Q value to be a somewhat small value (for example, a value in the range of about 10 to about 100). Therefore, a dielectric having a large tan δ (a dielectric having a large loss) may be used as the dielectric block 11, or a resistor element may be connected to form an LCR series resonance circuit. Note that it is desirable to use an element having good high-frequency characteristics as the resistance element. Further, as the position where the resistance element is provided, for example, it can be provided between the central conductor 24 and the sub plate 12b, or the main plate 12a and the sub plate 12b can be divided and provided therebetween.

  Further, in the above embodiment, the case where the characteristic impedance of the circuit to be measured is 50Ω and the attenuation factor is 1:10 has been described as an example. It goes without saying that the invention is applicable. For example, when the characteristic impedance is 100Ω, the impedance of the LC resonance circuit may be set according to the attenuation factor. The same applies when the attenuation factor is, for example, 1: 100.

  In the above embodiment, the probe 10 is exposed as shown in FIG. 1. However, since it is assumed that the probe 10 is affected by the surrounding conductors, for example, a shield case (not shown) is shown. Or the like.

  In the above embodiment, the positioning mechanism between the probe 10 and the substrate 30 is not mentioned, but it is considered that the element value of the capacitor changes depending on the positional relationship between them. May be provided. Specifically, four recesses into which the four ground pins 14 are inserted are provided to the ground pads 33 and 34, and the positioning is performed by engaging these four recesses with the four ground pins 14. You may do it. According to such a configuration, it is possible to perform measurement more accurately by stabilizing the element value.

  Further, in the above embodiment, the case where the signal line of the measurement target substrate and the ground pads 133 and 134 have the shape shown in FIG. 10A has been described as an example. For example, FIG. As shown, a radial stub that can be regarded as a short circuit at a specific frequency may be used. At this time, the shape of the ground pad is appropriately determined so that the measurement target does not cause problems such as oscillation due to impedance change.

  In the above embodiment, the resonance frequency is set to a frequency different from the frequency of the signal to be measured. However, the probe 10, the signal line 132, or the measurement target is not caused to cause problems such as oscillation due to impedance change. It is desirable to determine the shapes of the ground pads 133 and 134 as appropriate.

  In the above embodiment, the numerical design using the LC resonance circuit has been described. However, the dimensions of each component may be determined using a coupler method using a λ / 4 line.

  In the above embodiment, the measurement apparatus is not mentioned, but examples of the measurement apparatus to which the connection cable 20 of the probe 10 is connected include a spectrum analyzer and an oscilloscope. Of course, other measuring devices may be used.

10 Probe 11 Dielectric block 12 Conductor plate (LC resonance circuit)
12a Main plate (C component)
12b Sub-plate (L component)
13 Conductor plate 14 Ground pin (grounding mechanism)
20 Connection cable 22 Outer conductor 24 Center conductor 30 Substrate 32 Signal line 33, 34 Ground pad

Claims (7)

In the probe that acquires the signal from the measurement object and supplies it to the measurement device via the connection cable,
An LC series resonance circuit provided between the measurement object and the connection cable, and a grounding mechanism for connecting the ground wiring of the measurement object and an outer conductor of the connection cable;
The resonance frequency of the LC series resonance circuit is a frequency different from the frequency of the signal to be measured, and the ratio between the impedance of the LC series resonance circuit and the input impedance of the measurement device at the frequency of the signal is A probe that is set to be equal to a desired attenuation ratio of the probe.   The LC component of the LC series resonance circuit includes a conductor plate disposed at a position facing a signal line through which the signal is propagated, and a dielectric block disposed between the signal line and the conductor plate. The probe according to claim 1, wherein the probe is provided.   The L component of the LC series resonant circuit has a microstrip line having one end connected to the conductor plate and the other end connected to a center conductor of the connection cable. Probe.   The probe according to any one of claims 1 to 3, wherein the LC series resonance circuit has a resistance component for adjusting a Q value.   A measuring apparatus comprising a probe having any one of claims 1 to 4.   5. The circuit board as a measurement target of the probe according to claim 1, wherein the circuit board has a ground structure with which the grounding mechanism is contacted when performing measurement.   The circuit board according to claim 6, wherein the ground structure is a ground pad disposed in the vicinity of a signal line to be measured.

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