JPH0379831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a high frequency signal measuring probe with reduced self-inductance of a grounding line.

<Prior art and problems to be solved by the invention> A common problem in measuring high-frequency signals is that a series resonant circuit is formed by the grounded self-inductance of the signal probe and the input capacitance of the signal probe, and as the frequency increases. This not only reduces the amplitude of the input signal but also causes ringing. This degrades the accuracy of the measuring device as the signal frequency increases. Typically, the ground connection to the signal probe is made by a stranded ground wire that is connected to the ground probe, both of which have a relatively high self-inductance.

High frequency measurements (on the order of 100 MHz and above)
The accuracy deteriorates as the signal frequency approaches the frequency of the series resonant circuit formed by the inductance of the signal path and the input capacitance of the signal probe. The resonant frequency f of such a circuit is determined by the following equation.

f=1/2π√ Here, L is the inductance of the signal path, and C
is the capacitance of the signal probe.

Typical signal probe capacitance for high frequency signal measurements is on the order of 10 to 15 picofarads. The self-inductance of the signal probe from the signal source to the contact to the ground wire, the self-inductance of the ground wire, and the ground probe from the contact to the ground wire to ground (this is the means to complete the circuit to ground). The self-inductance of is all part of the inductance of the signal path. However, the inductance of the ground wire occupies the largest value of all inductance values in the signal path.

Typical ground wire inductance is 200 to 300
It is on the order of nanohenry. Given the typical capacitance of the signal probe, as the signal frequency exceeds 100 MHz, the resonant frequency of the series resonant circuit degrades the accuracy of high frequency measurements. As the signal frequency increases, the loss of accuracy becomes more severe.

Measures that have been taken to alleviate the problem of reduced accuracy include shortening the length of the ground wire, using a conductor with a large circular cross-section as the ground wire, and using a direct ground instead of a ground probe. I connected it to the ground wire. However, these means have caused inconvenience in using the probe. If the length of the ground wire is limited, it becomes difficult to connect to a nearby ground point. Conductors with large circular cross-sections are also relatively inflexible and difficult to maintain a connection to ground. Furthermore, frequent bending of such conductors causes them to fail prematurely due to fatigue hardening of the metal. Additionally, removing the ground probe makes it difficult to manipulate the ground wire and maintain continuity of the ground connection.

Another way to alleviate the ground probe self-inductance problem mentioned above is to wrap one end of the wire around the tip of the signal probe,
By connecting the other end of the wire to ground, the signal probe can be connected to ground using a short wire. Although this solution could avoid the self-inductance of the signal probe, it did not allow the use of a reasonably long ground wire.

Therefore, there is a need for a high frequency signal probe that can easily and reliably make a ground connection while reducing self-inductance associated with the ground connection and signal degradation caused by the self-inductance.

An object of the present invention is to provide a high-frequency signal measurement probe that has a ground line with low self-inductance and can be extremely easily connected to a ground terminal without reducing the measurement accuracy of high-frequency signals.

<Means and effects for solving the problem> The present invention reduces the inductance of the material used for the grounding wire while maintaining the flexibility of the grounding wire, and reduces the inductance of the material used for the grounding wire without introducing a non-negligible additional inductance. This method solves the problem of low accuracy in high frequency measurements by using a grounding method to avoid the self-inductance of the grounding probe. The present invention extends the reach of the ground wire and expands the applications of signal probes and measurement equipment.

The present invention increases the resonant frequency of the series resonant circuit by reducing the self-inductance of the signal path, compared to the conventional use of a predetermined signal probe and a predetermined length of ground wire. This allows even higher frequency signals to be measured accurately.

The self-inductance of the signal path can be reduced without shortening the length of the ground wire by using a single strip of conductive material that has a relatively large surface area for a given cross-sectional area. Therefore, it is possible to prevent the generation of inductance in the grounding wire due to twisting of the wires together as in the currently used stranded wires.

The ground wire of the present invention is flexible even though it is made of a single wire. That is, it can be looped in its entirety, and the band can be looped repeatedly and returned to its original shape without the risk of becoming brittle or breaking. It is flexible because it has a shape that does not undergo significant fatigue stiffening even after repeated bending in at least one dimension. This is preferably achieved by using a relatively flat ground wire with a substantially rectangular cross section.

The present invention further reduces the inductance of the signal path by connecting the ground wire near the tip of the ground probe to avoid self-inductance of the ground probe. Non-inductively connecting one end of the signal probe to the ground wire to avoid self-inductance of the signal probe is also done in embodiments of the invention.

Other objects, features, and advantages of the present invention will become more apparent from the detailed description of embodiments with reference to the following drawings.

<Example> FIG. 1 is an overall view of a grounding wire based on the present invention, with one end connected to a grounding probe and the other end cut away. The ground wire in this figure is shown as comprising a single strip 10 of flexible copper material having a substantially rectangular cross-section and connected to a ground probe 20. This grounding probe may take any means of grounding the signal probe through a grounding wire. Typically, the ground probe is
It includes a handle 12 with an insulated handle, a metal tip 14 containing several gripping wires (not shown), and a push button 16 for operating the gripping wires and conveniently opening and closing the ground circuit. however,
The present invention aims to be able to connect to any other ground point while minimizing added inductance. Therefore, in the ground probe 20 shown in FIG. 1, the connection is made at the tip of the tip 14 closest to the ground point. Although forms of low inductance connections may be employed without departing from the spirit of the invention, preferred connectors with such capabilities are disclosed herein.

FIG. 2 shows the ground wire of the present invention connected to both the ground probe and the signal probe.
That is, one end of the band (ground wire) 10 is connected to a ground probe 20 at a connection point 18, as shown in FIG. 1, and the other end of the ground wire is connected to a signal probe 22 at a connection point 24. signal probe 2
2 comprises an insulated handle 26 enclosing a coaxial shaft having an outer cylindrical conductor 28 and an inner conductor 30 used for high frequency signal measurements. A ground wire is necessary to connect the outer conductor to the ground of the circuit being measured, and this outer conductor is the input ground to the instrumentation. Preferably, the ground wire has a self-inductance of up to about 20 nanoHenries per inch to take advantage of the present invention.
Connection point 24 is also made substantially non-inductive, such that the connection located at the signal inlet end of signal probe 22 substantially avoids any self-inductance of the signal probe. The advantages of the invention are most pronounced as the signal source frequency approaches or exceeds 100 megahertz. A typical resonant frequency with a conventional ground wire and signal probe is this 100 megahertz.

FIG. 3 is a cross-sectional view of a preferred embodiment of band 10. It is a single, monolithic strip of substantially rectangular cross-section, has a relatively large surface area in a given cross-section, is flexible on its thin side, and has one or more conventional Eliminates inductance that occurs when ground wires are twisted or wrapped around each other. However, the present invention also contemplates the use of two or more strips that do not twist or wrap around each other. The flexibility of the band 10 makes it more useful in actual measurements compared to inflexible wires that bend and harden due to fatigue. A strip made of thin metal foil, such as copper foil, 0.25 inch wide and 0.003 inch thick is suitable for flexible strips, with sufficient surface area in a given cross-section to reduce the strip's self-inductance. Make it sufficiently small. However, it is contemplated that other shapes of materials with similar properties may be employed without departing from the spirit of the invention.

FIG. 4 shows an example of a connector 32 for attaching strap 10 to ground probe 20. Connector 32 is made from a conductive material such as brass, copper, or gold and includes a flap 34 that wraps around strap 10.
, thereby substantially eliminating the additional inductance caused by the connector. This is different from the conventional method, which connects one end of the wire to the tip of the probe. Connector 3
The sleeve 36 of No. 2 is attached to the probe 20 shown in FIG.
shaped to fit over the tip of a grounding probe, the tip of the probe being inserted into the sleeve 36 to maximize contact area with the grounding probe;
Minimize inductance caused by connections.

FIG. 5 shows a connector 38 for connecting strap 10 to a signal probe, such as probe 22 shown in FIG. Connector 38 shown in FIG.
is similar in structure and method of use to the connector 32 shown in FIG. It has a flap 40 for attaching the connector 38 to the strap 10 and a sleeve 42 for inserting the signal probe. The sleeve 42 is also shaped to fit over the tip of the inserted signal probe to maximize contact area and reduce connection inductance.

This ground wire can be modified in various ways within the scope of the basic concept of the invention. In particular, connection point 14 can be configured to provide a direct ground connection without the use of a separate ground probe.

<Effects of the Invention> The high-frequency signal measurement probe of the present invention uses a monolithic strip-shaped conductor material as the grounding wire, thereby significantly reducing self-inductance and hardly deteriorating the measurement accuracy of high-frequency signals. Furthermore, since the signal probe and the ground probe can be inserted elastically into the connectors at both ends of the ground wire,
Not only can it be firmly grounded, but it can also be easily attached and detached. Moreover, since these connectors are connected to the conductor portions surrounding the tip of the signal probe and the ground probe, respectively, the additional impedance at the connection portion is also minimized.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a part of the high frequency signal measuring probe of the present invention, FIG. 2 is a diagram showing a preferred embodiment of the high frequency signal measuring probe of the present invention, and FIG. 3 is a diagram showing a part of the high frequency signal measuring probe of the present invention.
Cross-sectional view of the ground wire at line - in Figure 2, No. 4
The figure is a diagram of an embodiment of a connector that connects a ground wire and a ground probe, and FIG. 5 is a diagram of an embodiment of a connector that connects a ground wire and a signal probe. 10: Strip conductor material, 20: Ground probe, 2
2: Signal probe, 32 and 38: Connector.

Claims (1)

[Claims] 1. A signal probe having a signal input chip that receives a signal under test, a ground conductor formed around the signal input chip via an insulator, a ground conductor chip connected to a ground end, and a grounding probe having a grounding conductor part electrically connected to the grounding conductor chip and formed around the grounding conductor chip; and one end fixed to a conductive connector into which the grounding conductor part of the signal probe is elastically inserted. and a flexible monolithic strip-shaped conductive material whose other end is fixed to another conductive connector into which the ground conductor portion of the ground probe is elastically inserted, the self-inductance of the monolithic strip-shaped conductive material being: A high frequency signal measurement probe characterized by less than 20 nanohenries per inch (2.54cm).