JPH0712871A - Differential probe for detecting high frequency superposed microsignal - Google Patents

Abstract

PURPOSE:To allow easy detection of a microlevel signal using a differential probe comprising a high frequency wideband common mode choke coil, a differential voltage detecting element, and a narrow-band BPF. CONSTITUTION:When a differential probe 20 is connected with the terminal of a telephone receiver, the stray capacity Ciota is increased significantly by an attenuator 22 and a wideband common mode choke coil 21 inserted between each end of the probe 20 and the metal housing 16. Consequently, a common mode AM modulated wave VR flows from the terminal of telephone receiver to the ground on the probe 20 side. The microdifferential voltage VR detected by two FETs in an element 14 is amplified by a preamplifier 15 and only a micromodulation wave VL detected by a semiconductor circuit in a telephone set is selected by a filter 23, amplified by a main amplifier 18 and displayed on a differential output display means 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential probe for separating and detecting a minute modulated wave signal from a superposed signal in which an AM modulated high frequency signal contains a minute level modulated wave signal in the voice band. is there.

[0002]

2. Description of the Related Art Conventionally, a high impedance probe or a differential probe has been known as this type of detecting means for measuring a minute signal of high frequency or low frequency.

FIG. 4 shows the case where an AM modulated wave used in radio broadcasting, CB radio, etc. is applied to a communication line of a telephone.
A test system for evaluating the noise audible immunity characteristic, which is the limit at which a signal can be heard as noise from the handset. Insulating support for mounting the EUT 1 at a predetermined height h, 4 is an EUT communication line, V ₀ is a test signal such as an AM modulated wave applied in a common mode between the communication line and ground, and 5 is a handset code of the EUT , 6 are handsets, and R ₁ and R ₂ in the figure are receiver terminals of the EUT ₁ . Further, 7 is an earpiece in which a handset (not shown) is mounted in the handset 6, 8 is a condenser microphone, 9 is an acoustic coupler for acoustically coupling the earpiece 7 and the condenser microphone 8, and 10 is an electric signal of the condenser microphone 8. Is a level meter for indicating the sound pressure P of the handset, 11 is a pseudo hand simulating the case where a person holds the handset, and 12 is a sound insulation box for removing ambient noise from entering the acoustic coupler portion. 13 is the receiver terminal R
A conventional differential probe for measuring the voltage V _R generated between ₁ and R ₂ , 14 is a field effect transistor (hereinafter referred to as FE).
(Referred to as T), 15 is a preamplifier for amplifying the detection voltage of the FET, 16 is a metal housing of the differential probe surrounding the FET 14 and the preamplifier 15, 17 is a differential probe output cable such as a coaxial cable, 18 is a main amplifier to which the differential probe output cable 17 is connected,
Reference numeral 19 is a differential output display means such as an oscilloscope or a level meter.

Further, FIG. 5 (a) shows the waveform of the test signal V ₀ amplitude-modulated with the carrier wave frequency f _H at the modulating wave frequency f _L , and FIG. 5 (b) applies the test signal V ₀ to the communication line 4. At this time, it is the waveform of the voltage V _R generated between the receiver terminals R ₁ and R ₂ . The voltage V _R is the output of the common mode V ₀ converted to the normal mode due to the unbalance of the telephone circuit, and V ₀
AM modulated waves V _H and V _{0, which} have the same waveform as the above, become a superimposed waveform of the modulated wave V _L detected by the semiconductor circuit of the telephone set, and V _L
Has been reported to be at a micro level. (1992
IEICE, Spring National Convention Proceedings, SB-3-
2) In the method of evaluating the noise audible immunity characteristic of the telephone using such a test system, the level of the normal V _R waveform, particularly the V _L waveform included therein, is very small, so that the difference shown in FIG. It is difficult to detect using a dynamic probe. Therefore,
Instead of the detection of V _R is typically drives the handset by V _R is instructed to the sound output level meter 10 are performed by measuring the noise sound pressure P. That is, the level of the applied test signal V ₀ is gradually increased and the noise audible immunity characteristic of the EUT is evaluated by the magnitude of V ₀ when the sound pressure P becomes equal to the predetermined noise audible sound pressure P _0. is doing.

This method is an excellent method because it is evaluated by the final noise sound pressure regardless of the type of the handset.

[0006]

However, in the above-mentioned measuring method, the earpiece 7 is different depending on the telephone set, the fitting property with the acoustic coupler 9 is poor, and the detection level is easily changed, or the sound box 12 for measurement is inside. Insert handset into earpiece 7
Is required to be mounted on the acoustic coupler 9, so that the configuration and adjustment of the measurement system is troublesome. Therefore, handset a FET differential probe 13 as shown in FIG direct R ₁ · R
Voltage handset-terminal contacts the _second terminal corresponding to the noise sound pressure P ₀ V _R, electrical evaluation method are considered very useful if implemented in particular measuring the detected voltage V _L therein.

However, the conventional differential probe 13 is a FET
Although the stray capacitance Cl between them is small, the capacitances Cg and Cg ′ existing between each FET and the metal casing are large. Therefore, when the probes are brought into contact with the receiver terminals R ₁ and R ₂ , they are induced to the terminals. The induced common mode voltage similar to V _{H in} V _R shown in FIG. 5B passes from the metal housing 16 of the differential probe 13 to the output cable 17 through the capacitors Cg and Cg ′.
Since it flows to the ground from the main amplifier 18, the differential output display means 19, etc. via the outer conductor of, the detection voltage V _L also changes, the true value of V _R changes, and the correct noise audible sound pressure P
There is a problem that the value of V _L corresponding to ₀ cannot be measured.

In order to solve the above-mentioned problems, the present invention provides a means for providing a high impedance to a high frequency common mode current in the input part of a conventional differential probe, and selects a detection voltage V _L in the probe. It is an object of the present invention to provide a means for doing so that a signal of a minute level can be detected.

[0009]

In order to solve the above-mentioned problems, the present invention provides a differential probe for detecting a high-frequency superposed low-frequency minute signal generated between two terminals with a pair wire connected to two contact terminals. Is divided into a closed magnetic circuit core having a predetermined effective magnetic permeability, a common mode high frequency wideband choke coil, a differential voltage detecting element for connecting the output of the choke coil via a high frequency attenuator, and an output of the element. It is composed of an amplifier for amplification and a narrow band bandpass filter having a center frequency of the low frequency signal frequency connected to the output of the amplifier.

[0010]

According to the present invention, since it is configured as described above, the common mode high frequency wide band choke coil exhibits a high impedance with respect to the high frequency component output superimposed on the detection signal output to the differential signal output terminals. Therefore, even if a differential probe is brought into contact with the terminals, it does not disturb the test circuit, and it is amplified by a narrow band bandpass filter connected after the amplifier that amplifies the differential signal detected by the differential voltage detection element. Since the signal-to-noise ratio of the system is greatly improved, minute low frequency signals can be easily detected.

[0011]

1 is a block diagram of a first embodiment of the present invention.

In FIG. 1, 20 is a differential probe of the present invention, 21 is a high frequency wide band common mode choke coil having a small input / output winding capacitance C _S used in the probe tip circuit portion and a large inductance, and 22 is a high frequency region. Is a wideband attenuator with a constant attenuation characteristic up to 23, and the modulation wave frequency f _L
Is a narrow bandpass filter having a pass center frequency of. Reference numeral 14 is a differential voltage detecting element including an FET, 15 is a preamplifier, 16 is a differential probe metal housing, 17 is a differential probe output cable such as a coaxial cable, 18 is a main amplifier, 19 is an oscilloscope or It is a differential output display means such as a level meter. When the tip of the differential probe 20 having such a configuration is brought into contact with the handsets R ₁ and R ₂ terminals, each tip of the probe and its metal housing 16
Between the wide band common mode choke coil 21 and
Since the attenuator 22 is inserted, the stray capacitance C _t
Is extremely small, and a large stray capacitance Cg, Cg ′ is provided between the FET input portion of the differential voltage detection element 14 and the metal housing 16.
Even if there is, the common mode V _H generated at the handsets R ₁ and R ₂ does not flow from the probe side to the ground. Therefore, the two FETs of the differential voltage detection element 14 are
The minute differential voltage V _R detected in ₁ is amplified by the preamplifier 15, and after the V _L component is selected by the filter 23, it is amplified by the nine amplifier 18 and displayed by the differential output display means 19.

FIG. 3 shows the bandpass filter 2 of FIG.
3 shows the spectrum of V _R when 3 is removed. FIG. 3A shows the spectrum of the output part of the preamplifier 15 and FIG. 3B shows the spectrum of the output part of the main amplifier 18. As described above, V _H and V _L in V _R that give the noise audible sound pressure P ₀ , particularly V _L, are minute levels, and this is the preamplifier 15.
Even after being amplified by, it is usually below the detection limit level of the measuring instrument shown by V _S in FIG. Therefore, FIG.
It is necessary to further amplify the level of (a), and if this is passed through the main amplifier 18 of amplification degree A as it is, FIG.
As shown in, the levels of V _L and V _H are respectively A
It becomes V _L and AV _H , which is higher than the detection limit level V _S.

However, since these originally have a low input level to the main amplifier 18 and include other noise components, the output level V _{A in} which the amplified amount of white noise of the main amplifier 18 itself is added to these amplified components. Below, the state is buried in the level V _A.

In such a state, even if the output signal is directly input to the differential output display means 19 such as an oscilloscope, V _L
And V detection _H is difficult, in order to enable detection f
There are drawbacks such as the need for a large-scale and expensive measuring instrument having a frequency selection function such as a selective level meter or spectrum analyzer tuned only to _L or f _H. Further, even when these measuring instruments are used, there is a drawback that the detection resolution of the modulation frequency f _L and the carrier frequency f _H becomes insufficient depending on the bandwidth of the tuning frequency and the like.

On the other hand, in the present invention, as shown in FIG. 1, the output of the preamplifier 15 is input to the main amplifier 18 after passing through the bandpass filter 23. Figure 2 (a)
Is the output part of the bandpass filter 23 at this time, as shown in FIG.
3B shows the spectrum of the output section of the main amplifier 18, and the preamplifier 1 including the noise component as shown in FIG.
2 through the bandpass filter 23 from the output of FIG.
As shown in (a), only the V _L component is extracted and amplified by the main amplifier 15 to obtain an AV _L level as shown in FIG. 2B, which can be displayed by the differential output display means 19. If
_VL can be easily detected without a large-scale measuring instrument such as a selection level meter or a spectrum analyzer.

FIG. 6 is a first embodiment showing the structure of the high frequency wide band common mode choke coil 21 used at the tip of the differential probe 20 of the present invention. Reference numeral 24 is a square having a predetermined magnetic permeability up to the high frequency region. Closed magnetic circuit core, 25 is a winding wound loosely around the central magnetic path l ₁ part, 26 is a winding closely wound around the central magnetic path l ₀ part, and 27 is a central magnetic path l ₂ part The windings are sparsely wound, and each winding is formed by twisting two windings or by winding them in each magnetic path. Further, the length of the densely wound magnetic path l ₀ is shorter than that of the other loosely wound l ₁ and l ₂ . In such a choke coil, stray capacitances C ₁ , C ₀ , C ₂ are scattered between both ends of each winding 25, 26, 27,
C ₀ of the magnetic path l ₀ part provided with the dense winding 26 has a large value, but C ₁ and C ₂ have a large magnetic path and a large winding pitch in the l ₁ and l ₂ parts provided with the sparse winding. small. Therefore, the capacitance between the input and output windings of the entire choke coil 21 in which they are connected in series can be suppressed to be small even if a large C ₀ is present in a part thereof. Therefore, even if a high-frequency common-mode current enters from the input terminals of the differential probe 20, the influence of the capacitance between the input and output windings is small, and the deterioration of the blocking characteristic in the high-frequency region is small. In addition, since the concentrated winding 26 is provided on a part of the core, the inductance in the low frequency band becomes large, whereby the blocking characteristic is expanded to the low frequency band and the wide band characteristic can be realized as a whole. Further, for normal mode current between the probe input terminals such as when measuring the voltage V _R between the handset terminals, the two wires are aligned, or aligned and then twisted to form a stranded wire around the core. The leakage inductance between them is small, and the transmission loss is small.

FIG. 7 is a second embodiment showing the structure of the common mode choke coil 21 used at the tip of the differential probe 20 according to the present invention, and FIG. 8 is the third embodiment thereof, both of which are concentrated in FIG. The second core (auxiliary core) 2 in the winding 26 part
8 or 28 'is applied, and a common concentrated winding 26 is applied to the central magnetic paths of both closed magnetic paths. In such a structure, an inductance also occurs in the auxiliary core 28 or 28 'with respect to the common mode current, so that the blocking characteristic in the low frequency region can be improved. The core 29 of FIG. 8 is a rhombic core having a large distance between the opposing magnetic paths in the center instead of the rectangular core 24 of FIGS. 6 and 7. The same applies to an elliptical shape (not shown), but a concentrated winding. The number of turns can be increased because the distance between the center and the external magnetic path of the 26 part is increased, and there is an advantage that the blocking characteristic in the low frequency region can be further improved.

FIG. 9 shows an embodiment in which a partial coaxial cylindrical core is used in place of the rectangular core 24 of the common mode choke coil 21 of FIG. 6, and 30-1 and 30-2 are circular external magnetic paths. The core having a notch is cut in half at the central portion in the longitudinal direction, and the windings 25 to 27 as described above are provided on the cylindrical bobbin 31 into which the central magnetic path is inserted in advance.
Then, the cores 30-1 and 30-2 are inserted and fixed from both sides.

It has been described above that the choke coils as shown in FIGS. 6 to 9 are effective for the high-frequency common mode current. However, as shown in FIG. 1, the choke coils are combined with the wideband attenuator 22. It is obvious that the Cg can be further reduced and the blocking characteristics can be improved if the above is adopted. It should be noted that in the above description, the winding is shown in FIG.
Although it has been described that the windings are composed of dense and sparse windings such as Nos. 25 to 27, it is clear that the effect of the present invention will not be impaired even if the winding is performed uniformly without dividing into sparse and dense sections depending on the required characteristics. Is.

FIG. 10 shows the test system of FIG. 4 in which the receiver terminal R ₁
An example in which the fluctuation amount of the noise sound pressure P is obtained before and after contacting the conventional differential probe 13 of FIG. 4 and the differential probe 20 of FIG. 1, which is the first embodiment of the present invention, with R ₂ . Yes In FIG. 10, I is the characteristic when the conventional probe is used, and II is the characteristic when the differential probe according to the present invention is used. As shown in FIG. 10, in the case of the probe of the present invention, the sound pressure variation of 30 dB or more when the conventional probe was in contact was suppressed to about 3 dB, which clearly shows the improving effect of the present invention.

FIG. 11 shows a second embodiment of the differential probe of the present invention, and 32 is a normal mode choke coil having a large inductance with respect to the normal mode current and a small inductance with respect to the common mode current.

FIG. 12 is a structural comparison explanatory view of the common mode choke coil 21 and the normal mode choke 32 of FIG. 11, and as shown in the figure, the normal mode choke coil 32 has the same shape as the closed magnetic circuit core 24 shown in FIG. Windings 25 ', 26', 27 "are wound around the core 24 'of the core 24', and the winding position is wound on the same magnetic path as the windings 25, 26, 27 of the common mode choke coil 21. The winding directions are opposite to each other.

As shown in FIG. 11, the differential voltage detecting element 14
When the input side for inserting the normal mode choke coil 32 when the input line capacitance Cl of the two FET is large is shorted V _R signal of the high frequency produced between the probe input terminal with Cl, correct level can not be measured it is but, in such a case, the normal mode choke coil 32 is to act as a large inductance with respect to the normal mode current by V _R, it is possible to measure the correct V _R.

Next, SW ₁ and SW _{2 in} FIG. 11 are switches for turning on / off the bandpass filter 23. By switching the switches SW ₁ and SW ₂ to the bandpass filter side,
The same V _L waveform and level signal as the output of FIG. 1 is output. If these switches SW ₁ and SW ₂ are switched to the short-circuit side, a V _H and V _L superimposed waveform and level signal is output. Therefore, the level of V _{H having} a large level can be detected. That is, V _{H is changed} by switching the switches SW ₁ and SW _2.
Alternatively, the V _L waveform and the output level can be detected separately.

FIG. 13 shows a third differential probe according to the present invention.
2 is a block diagram of an embodiment of FIG. In the figure, reference numeral 33 denotes a high frequency band pass filter having a pass center frequency of f _H , which divides the output of the preamplifier 15 into two systems and outputs them through the low frequency band pass filter 23 and the high frequency band pass filter 33, respectively. to the main amplifier is also 18-1 and 18-2 which was used for each band, thereby be detected simultaneously by distinguishing the two waveforms and levels Ri V _L and V _H by using the display means 19 of the two channels.

FIG. 14 shows a fourth embodiment of the present invention, which is shown in FIG.
The low-frequency narrowband bandpass filter 23 'and the high-frequency narrowband bandpass filter 33' of the differential probe of the third embodiment shown in FIG. 6 are designed so that the pass center frequencies f _L and f _H can be changed by an external control voltage. Control terminal 34-
1 and 34-2 are provided. By applying an external signal such as a variable DC voltage to these terminals, the center pass frequency of each can be changed.
In the noise audible immunity test, when the frequency of at least one of f _H and f _L of the applied signal of the AM modulated wave is changed, an external signal synchronized with these is used for each control terminal 3.
By applying to 4-1 or 34-2, the pass frequency of each filter is selected in synchronization with the input signal frequency of the differential probe, so that the target measured voltage is correctly detected. Therefore, it is possible to automate the immunity test in which the applied signal is swept.

[0028]

As described in detail above, the present invention is
Between the two contact terminals of the differential probe and the differential voltage detecting element, which separate and detect the minute modulated wave signal from the superimposed signal in which the minute modulated wave of the voice band is included in the AM modulated high frequency signal, the coil of the coil is provided. Even if the number of windings is increased, the stray capacitance between the input and output windings is small and the leakage inductance between the wires is small. Since a band-pass filter is connected to amplify to the required level, even if the differential probe is brought into contact with the receiver terminal of the device under test, there is almost no effect on the load system such as noise and sound pressure, and the appropriate minute There is a remarkable effect that the modulated wave level can be detected.

Even if the input impedance between the elements such as the two FETs used for the differential voltage detection element of the differential probe is small, the detection voltage does not drop due to the probe contact with the measurement point, so that proper measurement can be performed. You can expect an effect.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an example of a spectrum of a detection signal when the differential probe of the present invention is used.

FIG. 3 is an explanatory diagram of an example of a spectrum of a detection signal and a carrier frequency by a conventional differential probe.

FIG. 4 is an explanatory diagram of a test system for evaluating a noise audible immunity characteristic.

FIG. 5A is a waveform diagram of an AM modulation wave having an amplitude V ₀ used as a test signal. (B) is a waveform diagram of the voltage V _R generated between the receiver terminals R ₁ and R _{2 of the} device under test when the test signal V ₀ is applied to the communication line.

FIG. 6 is a structural explanatory view of a high frequency broadband common mode choke coil using a rectangular core inserted in the differential probe input unit of the present invention.

FIG. 7 is a structural explanatory view of a high frequency broadband common mode choke coil using a rectangular core and a rectangular auxiliary core to be inserted in the differential probe input unit of the present invention.

FIG. 8 is a structural explanatory view of a high frequency broadband common mode choke coil using a rhombus core and a rectangular auxiliary core to be inserted in the differential probe input unit of the present invention.

FIG. 9 is an exploded structural explanatory view of a high frequency broadband common mode choke coil using a partial coaxial cylindrical core inserted into the differential probe input section of the present invention.

10 is a diagram showing fluctuations in noise sound pressure when a differential probe is contacted between the receiver terminals of the test system of FIG.

FIG. 11 is a block diagram of a second embodiment of the present invention.

FIG. 12 is a structural comparison explanatory diagram of a common mode and normal mode high frequency broadband choke coil to be inserted in the differential probe of the present invention.

FIG. 13 is a block diagram of a third embodiment of the present invention.

FIG. 14 is a block diagram of a fourth embodiment of the present invention.

[Explanation of symbols]

1 Equipment under test (EUT) 2 Pseudo ground plane 3 Insulated support base 4 Communication line of EUT 5 Handset cord 6 Handset 7 Earpiece 8 Condenser microphone 9 Acoustic coupler 10 Level meter 11 Pseudo hand 12 Sound insulation box 13 Conventional differential Probe 14 Differential voltage detection element 15 Preamplifier 16 Metal housing 17 Output cable 18, 18-1, 18-2 Main amplifier 19 Differential output display means R ₁ , R ₂ Receiver terminal f _H Carrier frequency f _L Modulated wave frequency 20 The differential probe 21 of the present invention 21 common mode choke coil 22 high frequency wide band attenuator 23 low frequency narrow band filter 23 'center frequency variable narrow band filter 24, 24' square core 24, 25 'winding 26, 26' winding 27 , 27 'Winding 28, 28' Square auxiliary core 29 Diamond-shaped core 30 Partial coaxial cylindrical core 31 Winding frame 32 normal mode choke coil 33 wideband bandpass filter 33 'center frequency variable bandpass filter 34-1, 34-2 control terminal

Claims (3)

[Claims] 1. A differential probe for detecting a minute signal generated between two terminals, wherein a high frequency wide band common mode choke coil connected to two contact terminals of the probe and an output terminal of the choke coil are respectively connected. A high frequency broadband attenuator, a high frequency broadband normal mode choke coil connected to the output end of the attenuator, a differential voltage detection element connected to the output end of the choke coil, and a preamplifier for amplifying the output from the element A differential probe for detecting high-frequency superimposed minute signals, which comprises a bandpass filter having a predetermined center frequency. 2. The high frequency wide band common mode choke coil comprises a pair of input and output windings from one end to the other end of a magnetic path in a long side direction of a closed magnetic circuit core having a predetermined shape having a predetermined effective magnetic permeability up to a high frequency region. 2. The high-frequency broadband normal-mode choke coil is formed by winding a pair of input and output windings in opposite directions in the magnetic path of the closed magnetic circuit core. A differential probe for detecting a high-frequency superposed minute signal described. 3. The winding of the choke coil according to claim 2, wherein the winding range on the magnetic path in the long side direction of the closed magnetic circuit core is divided into three with a predetermined width, the center is densely wound, and both sides are sparsely wound. A differential probe for detecting a high-frequency superimposed minute signal, which is formed by winding the common mode and normal mode choke coils.