JPH03274827A - Signal detector - Google Patents

Abstract

PURPOSE:To detect the voltage waveform of a signal flowing on a communication line with fidelity by providing a means provided with a function to generate a capacitance value approximated to coupling electrostatic capacitance generated between an unbalanced type communication line that is a line targeted to be monitored and an electrode between the electrode and the ground, and attaching external electrostatic capacitance for compensation which performs band compensation. CONSTITUTION:A compensation conductor 2 is the one to supply the coupling electrostatic capacitance CC equivalent to the coupling electrostatic capacitance CC generated when the line 1 targeted to be monitored is sandwiched with the electrode 3 between the electrode 3 and the ground 6. The external electrostatic capacitance 4CE for compensation to be attached is electrostatic capacitance to be attached fixedly to further expand a low frequency band area. When the coupling electrostatic capacitance CC by the compensation conductor 2 is attached, flat loss is generated extending over a high frequency area, however, a flat part is extended in a low frequency area, which enables the making of the area into a wideband area. The increment of the loss in the flat part can be sufficiently amplified at a high input impedance differential amplifier, which remarkably increases the effect of compensation. When the external electrostatic capacitance 4CE for compensation is attached at the outside, the flat part in the low frequency area can be further expanded. A balanced type communication line can be set similarly as the line targeted to be monitored other than the unbalanced type communication line.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacitively coupled signal detector that detects a signal without being directly connected to a communication line that is a line to be monitored.

[Conventional technology]

Conventionally, when observing the voltage or current waveform flowing in a communication line or power line, which is a line to be monitored, without touching the conductor, the line to be observed, such as a communication line, is electromagnetically coupled with a toroidal coil to measure the current waveform. A method is adopted in which the voltage waveform is extracted by capacitively coupling the wire to be extracted or observed between metal electrodes on the wire's coating. In particular, when observing signals flowing through a communication line, it is necessary to ensure that the transmission characteristics are not affected, so it is necessary to make the coupling as weak as possible, whether it is electromagnetic or electrostatic coupling, at the observation point. Consideration must be taken to prevent signal loss and impedance non-uniformity on the communication line.

Conventionally, when detecting signals flowing through communication lines without contact, 2
In this method, each pair of communication wires was sandwiched between electrodes above the external liquid of the core wire, and a signal was extracted through capacitive coupling, which was then amplified and detected using a high input impedance differential amplifier. FIG. 4 is a conceptual diagram of the electrostatic coupling method, and FIG. 5 is an equivalent circuit of FIG. 4.

FIG. 5(a) is a balanced equivalent circuit when the coupling capacitance between the communication line and the electrode is 2C, and the ground load resistance including the input impedance of the high input impedance differential amplifier is R/2. FIG. 5(b) is an unbalanced equivalent circuit completely equivalent to FIG. 5(a). Therefore, since the impedance of the detection system consisting of C and R is extremely large compared to the characteristic impedance ρ of the communication line, ρ can be almost ignored.

Therefore, if the voltage of the signal source is E8 and the detection voltage of the signal detector is vl, the voltage attenuation amount is 20Log (E s /
It is obvious that V + ) is expressed by the following formula.

Voltage attenuation = 20Log (E s / V r
) −10Log ((1+ρ/R) + (1/ωCR) t) 'ilOLog (1+ (1/ωCR) ” )
......(ρ(R)) E,: Voltage of signal source Vl: Detection voltage of signal detector ρ: Characteristic impedance of communication line R: Impedance of detection system C: Coupling capacitance between communication line and electrode ω: angular frequency (2πf, f: frequency) [Problem to be solved by the invention] In other words, FIG. 5 shows a simple high-pass filter in which the coupling capacitance C is uncertain due to mechanical contact; As shown in Figure 6, it is physically impossible to increase the coupling capacitance C with such a weakly coupled capacitive coupling method, where the transfer characteristics have frequency characteristics that vary significantly in the low frequency region. , it was difficult to secure a band with flat attenuation characteristics down to low frequencies.As a result, it was not possible to faithfully detect and observe broadband signal waveforms such as digital signals containing low-frequency acid components without contact. .

The present invention has been made in view of these circumstances,
It is an object of the present invention to provide a signal detector that solves problems caused by weak coupling and faithfully detects the voltage waveform of a signal flowing through a communication line.

[Means to solve the problem]

In order to solve the above problems, in the signal detector of the present invention, by actively utilizing the capacitance between the electrode and the ground,
Expands the low frequency range and faithfully detects wideband signals. In other words, ■Means that have the function of generating a capacitance value that approximates the coupling capacitance that occurs between the pair of balanced communication lines that are the lines to be monitored and the electrodes, specifically, a compensation center in the electrodes. Insert the line.

■Added an external compensating capacitor to perform band compensation.

In addition, in claim (2), (1) a means having a function of generating a capacitance value close to the coupling capacitance generated between the electrode and the monitored line of the unbalanced communication line between the electrode and the ground; To do this, insert a compensating core wire between the electrodes.

■Added an external compensating capacitor to perform band compensation.

[Effect]

According to such an authoritative signal detector, the transfer characteristic is flat up to a low frequency of about 100 Hz even if there is weak coupling due to capacitance.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. Figure 1 shows the connection of the electrode parts of the present invention; Figure 1 (a) is the side view of the electrode, Figure 1 (b) is the component country seen from the top of the electrode, and Figure 2 is the same view as Figure 1. This is the equivalent circuit of Hereinafter, the drawer numbers of the drawings in FIG. 1 will be indicated in parentheses and the correspondence will be explained.

The compensating core wire (2) has a coupling capacitance CC between the electrode (3) and the ground (6) that is equivalent to the coupling capacitance C8 that occurs when the wire to be monitored (1) is sandwiched between the electrodes (3). It is intended to be given to The additional compensating external capacitance (4) C is a fixed capacitance added in order to further widen the low frequency band.

The equivalent circuit of FIG. 1 is shown in FIG. 2 in an unbalanced form similar to FIG. 5.

The voltage attenuation amount in FIG. 2 is easily expressed by the following formula.

Voltage attenuation - 20Log (Es/Vr)
=10Log ([1+ (ρCs + R(C
c 1 C1))/RCs + [(ω” Cs (Cc + CE) ρR-1
)/Rωcs] ” ] ”;10Log ([1+ (Cc +Ct) /
Cs ] ”+[1/Rωc,] ” ) (ρξO): Voltage of signal source: Detection voltage of signal detector: Characteristic impedance of monitored line: Impedance of detection system: Coupling capacitance with monitored line: Coupling capacitance between the electrode and the compensating wire to ground CA: External capacitance for compensation: Angular frequency (2zf, f: frequency) 3 ■ Calculation ρ 8 Cc Figure 3 shows the frequency characteristics of the voltage attenuation amount. Addition of the coupling capacitance Cc by the compensating core wire 2 causes a flat loss over the high frequency region, but the flat portion spreads to the low frequency range, making it possible to widen the band. The increase in loss in the flat portion can be sufficiently amplified by a high input impedance differential amplifier (not shown), and the compensation effect is large. External capacitance for compensation (4)
By adding Ct, it is possible to further expand the flat part of the low frequency range.

Usually, the coupling capacitance C3 with the line to be monitored is several pF or less,
The characteristic impedance ρ of the line to be monitored is several hundred ohms or less. If CC+CE is made 10 times that of C8, the loss in the flat part will increase by about 20 dB, but the low frequency band will expand by an order of magnitude.
It becomes 1kHz from 1QkHz. On the other hand, in the high frequency region, by inserting CC + CE, the characteristic impedance ρ of the monitored line is affected and the loss increases;
If the gain of a high input impedance differential amplifier is about 4, it can obtain flat characteristics up to about 100MHz without any problem.
It is easy to set it to 0 dB, and Cc+C! is C8 1
It can be inserted up to about 00 times, and even with weak coupling due to capacitance, signals with a low frequency of about 100 Hz can be detected with flat characteristics.

In this embodiment, an example in which an unbalanced communication line is used as the line to be monitored has been described, but it goes without saying that the same applies to a balanced communication line.

〔effect〕

As explained above, the signal detector of the present invention has the function of generating a capacitance between two electrodes that approximates the coupling capacitance that occurs between the pair of balanced communication lines, which are the lines to be monitored, and the electrodes. In addition, we added a compensating external capacitor to perform band compensation.

Claim (2) also provides means for generating a capacitance between the electrode and ground, which approximates the coupling capacitance generated between the unbalanced communication line, which is the line to be monitored, and the electrode, and band compensation. An external capacitance was added for compensation. Therefore, the transfer characteristics are flat down to low frequencies.

[Brief explanation of drawings]

Fig. 1 is a connection diagram of the electrode portion showing one embodiment of the present invention, Fig. 2 is its equivalent circuit diagram, Fig. 3 is a frequency characteristic diagram of voltage attenuation according to the first embodiment, and Fig. 4 is A conceptual diagram of the conventional capacitive coupling method, FIG. 5 is its equivalent circuit diagram, and FIG. 6 is a frequency characteristic diagram of voltage attenuation amount by the conventional method. 1... Line to be monitored, 2... Compensating core wire, 3... Electrode, 4... External capacitance for compensation, 5... Load resistance, 6... Earth (earth).

Claims (2)

[Claims] (1) In a signal detector that is equipped with two electrodes that are capacitively coupled to a pair of balanced communication lines that are monitored lines, the coupling capacitance that occurs between the monitored line and the electrodes. A signal detector having a function of generating a capacitance value approximating to between the two electrodes, and further adding an external compensating capacitance for band compensation. (2) In a signal detector that is equipped with an electrode that is capacitively coupled to an unbalanced communication line to be monitored and is coupled by capacitance, a capacitance that approximates the coupling capacitance that occurs between the line to be monitored and the electrode. A signal detector comprising means for generating a value between the electrode and the ground, and an external compensating capacitance for performing band compensation.