JP3165561B2 - High frequency superimposed small signal detection differential probe - Google Patents

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 minutely modulated wave signal from a superimposed signal in which an AM modulated high frequency signal contains a minutely modulated wave signal in a voice band. is there.

[0002]

2. Description of the Related Art Conventionally, this type of detecting means for measuring a high-frequency or low-frequency minute signal includes a high-impedance probe and a differential probe.

FIG. 4 shows a case where an AM modulated wave used for radio broadcasting or CB radio is applied to a communication line of a telephone.
A test system for evaluating a noise audible immunity characteristic, which is a limit at which a signal can be heard as noise from a receiver, 1 is a device under test (hereinafter referred to as an EUT) such as a telephone, 2 is a pseudo ground, and 3 is a pseudo ground. An insulating support base on which the EUT 1 is installed at a predetermined height h, 4 is a communication line of the EUT, V ₀ is a test signal such as an AM modulated wave applied in a common mode between the communication line and the 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 . Reference numeral 7 denotes an earpiece in which a receiver (not shown) is mounted in the handset 6, reference numeral 8 denotes a condenser microphone, reference numeral 9 denotes an acoustic coupler for acoustically coupling the earpiece 7 and the condenser microphone 8, and reference numeral 10 denotes an electric signal of the condenser microphone 8. , A level meter for indicating the sound pressure P of the handset, reference numeral 11 denotes a simulated hand simulating a case where a person has a handset, and reference numeral 12 denotes a sound box for removing intrusion of ambient noise into the acoustic coupler portion. 13 is a receiver terminal R
A conventional differential probe 14 for measuring a voltage V _R generated between R ₁ and R ₂ is a field effect transistor (hereinafter referred to as FE).
T), a preamplifier for amplifying the detection voltage of the FET, a metal housing for a differential probe surrounding the FET and the preamplifier, 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,
19 is a differential output display means such as an oscilloscope or a level meter.

FIG. 5A shows a waveform of a test signal V _{0 obtained} by amplitude-modulating a carrier frequency f _H at a modulation frequency f _L , and FIG. 5B shows a waveform of the test signal V ₀ applied to a communication line 4. Occasionally, a waveform of the voltage V _R generated between the receiving machine terminal R _1, R _2. The voltage V _R output V ₀ which common mode is converted into the normal mode by imbalance of the telephone circuit, V ₀
AM modulated wave V _H and V ₀ which the same waveform becomes superimposed waveform of a modulated wave V _L which is detected by the semiconductor circuit such as a telephone and, V _L
Has been reported to be at a very low level. (1992
IEICE, Spring National Convention, SB-3-
Difference 2) Evaluation method of noise audible immunity characteristics of the telephone using such test system, since typically V _R wave, in particular the level of V _L waveform contained therein is very small, as shown in figure 13 It is difficult to detect using a moving 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 based on the magnitude of V ₀ when the sound pressure P becomes equal to a predetermined noise audible sound pressure P _0. are doing.

[0005] This method is an excellent method for evaluating the final noise sound pressure regardless of the type of receiver.

[0006]

However, in the above-described measuring method, the earpiece 7 varies depending on the telephone, and the fitting level with the acoustic coupler 9 is poor, so that the detection level tends to fluctuate. Insert the handset into the earpiece 7
However, there is a disadvantage in that the configuration and adjustment of the measurement system are troublesome, for example, it is necessary to provide the acoustic coupler 9 in the acoustic coupler 9. Therefore, handset a FET differential probe 13 as shown in FIG direct R ₁ · R
_It is considered to be extremely useful if an electrical evaluation method for measuring the receiver terminal voltage V _R corresponding to the noise sound pressure P ₀ , particularly the detection voltage _VL therein, by contacting the _two terminals can be realized.

However, the conventional differential probe 13 is an FET
Although the stray capacitance Cl between them is small, but the capacitances Cg and Cg 'existing between each FET and the metal casing are large, so that as soon as the probe is brought into contact with the receiver terminals R ₁ and R ₂ , the probe is induced to the terminals. An induced common mode voltage similar to V _{H in} V _R shown in FIG. 5B passes through the capacitors Cg and Cg ′ from the metal housing 16 of the differential probe 13 to the output cable 17.
Since flows from the external main amplifier 18 and the differential output display unit 19 conductor through like the ground, the detection voltage V _L also it alters, the correct noise audible pressure changes the value of the true V _R P
There was a problem that the value of V _L corresponding to ₀ could not be measured.

According to the present invention, in order to solve the above-mentioned problems, means for providing high impedance to a high-frequency common mode current is provided at an input portion of a conventional differential probe, and a detection voltage _VL is selected in the probe. It is an object of the present invention to provide a means for detecting a signal at a minute level.

[0009]

In order to solve the above-mentioned problems, the present invention provides a differential probe for detecting a high-frequency superimposed low-frequency small signal generated between two terminals by using a pair of wires connected to two contact terminals. A common mode high frequency broadband choke coil divided and wound around a closed magnetic circuit core having a predetermined effective magnetic permeability, a differential voltage detection element connecting the output of the choke coil via a high frequency attenuator, and an output of the element. It comprises an amplifier to be amplified and a narrow band-pass filter connected to the output of the amplifier and having the low frequency signal frequency as a center frequency.

[0010]

According to the present invention, the common mode high frequency broadband choke coil has a high impedance with respect to a high frequency component superimposed on the detection signal output to the differential signal output terminal. Therefore, even if the differential probe is brought into contact with the terminal, it does not disturb the test circuit, and is amplified by a narrow band-pass filter connected after the amplifier that amplifies the differential signal detected by the differential voltage detecting element. Because the signal-to-noise ratio of the system is greatly improved, very low frequency signals can be easily detected.

[0011]

FIG. 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 inductance C _S between input and output windings and a large inductance used in a probe tip circuit, and 22 is a high-frequency region. certain broadband attenuator attenuation characteristics up to 23 modulation wave frequency f _L
Is a narrow band-pass filter having a center frequency of the pass band. In addition, 14 is a differential voltage detecting element composed of an FET or the like, 15 is a preamplifier, 16 is a metal housing of a differential probe, 17 is a differential probe output cable such as a coaxial cable, 18 is a main amplifier, 19 is an oscilloscope or This 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 receivers R ₁ and R ₂ , each tip of the probe and its metal casing 16 are connected.
Between the broadband common mode choke coil 21,
Since the attenuator 22 is inserted, the stray capacitance C _t
Is extremely small, and large stray capacitances Cg and Cg ′ are provided between the FET input portion of the differential voltage detecting element 14 and the metal housing 16.
However, the common mode V _H generated in the receivers R ₁ and R ₂ does not flow from the probe side to the ground. Therefore, the two FETs of the differential voltage detecting element 14
Small differential voltage V _R which in detected is amplified by a preamplifier 15, is amplified by Nine amplifier 18 after only V _L component is selected by the filter 23 is displayed in the differential output display unit 19.

FIG. 3 shows the band-pass filter 2 shown in FIG.
Figure 3 3 shows the Supetokuramu of V _R in the case of removal of (a) the output of the preamplifier 15, Fig. 3 (b) is a spectrum of the output of the main amplifier 18. V _H and V _L in V _R giving noise audible pressure P _0, in particular V _L is very small levels as described above, this pre-amplifier 15
After the amplification, the voltage is usually equal to or lower than the detection limit level of the measuring instrument indicated 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 the amplification degree A as it is, the level of FIG.
Each level of the V _L and V _H as shown in A
It becomes V _L and AV _H a detection limit level V _S or higher.

However, since these are originally low in the input level to the main amplifier 18 and include other noise components, the output level V _{A obtained by} adding the amplification of the white noise of the main amplifier 18 to these amplifications. Below, the state is buried in the level _VA .

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
Expensive instruments in large with frequency sorting functions such _L and f _H only to the selected level meter or spectrum ram analyzer tuned there are drawbacks such as the need. Also, when these measuring instruments are used, there is a disadvantage 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, the output of the preamplifier 15 is input to the main amplifier 18 after passing through the band-pass filter 23 as shown in FIG. FIG. 2 (a)
Is the output of the band-pass filter 23 at this time, FIG.
FIG. 3B shows a spectrum of an output section of the main amplifier 18, and the preamplifier 1 including a noise component as shown in FIG.
5 through the band pass filter 23 from the output of FIG.
As shown in (a), only the _VL component is extracted and amplified by the main amplifier 15 to obtain an _AVL level as shown in FIG. 2 (b). If
_VL can be easily detected without a large-scale measuring instrument such as a selective level meter or a spectrum analyzer.

FIG. 6 is a first embodiment showing the configuration of a high-frequency broadband common mode choke coil 21 used at the tip of the differential probe 20 according to the present invention. Reference numeral 24 denotes a rectangular shape having a predetermined magnetic permeability up to a high-frequency region. A closed magnetic path core, 25 is a winding wound loosely on the l ₁ part of the central magnetic path, 26 is a winding wound densely on the l ₀ part of the central magnetic path, and 27 is a winding wound on the l ₂ part of the central magnetic path. The windings are sparsely wound, and each of the windings is arranged in two or aligned, and is stranded and wound around each magnetic path. The magnetic path l ₀ portion wound densely length compared to l _1, l ₂ portion wound on the other sparse is shorter. In such a choke coil, stray capacitances C ₁ , C ₀ , and C ₂ are scattered between both ends of each of the windings 25, 26, and 27, respectively.
C ₀ of the magnetic path l ₀ portion provided with the dense winding 26 has a large value, but C ₁ and C ₂ have large values in the l ₁ and l ₂ portions provided with the loose winding because the magnetic path is long and the winding pitch is large. small. Therefore, these capacitance between the input and output windings of the entire choke coil 21 connected in series is kept small even if there is a large C ₀ part. Therefore, even if a high-frequency common mode current intrudes from the input terminal of the differential probe 20, the influence of the above-mentioned input / output winding capacitance portion is small, and the decrease in blocking characteristics in the high-frequency range is small. In addition, since the concentrated winding 26 is provided on a part of the core, the inductance in the low frequency band is increased, whereby the blocking characteristic is expanded to the low frequency side, and a wide band characteristic can be realized as a whole. Also, for normal mode current between probe input terminals such as when measuring the voltage V _R between receiver terminals, two wires are aligned or twisted and then wound 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 a common mode choke coil 21 used at the tip of the differential probe 20 according to the present invention, and FIG. 8 is a third embodiment of the present invention. The second core (auxiliary core) 2
No. 8 or 28 'is applied, and a common concentrated winding 26 is applied to the center magnetic path of both closed magnetic paths. In such a structure, an inductance is also generated in the auxiliary core 28 or 28 'with respect to the common mode current, so that there is an effect that the blocking characteristic in a low band can be improved. The core 29 in FIG. 8 is a rhombic core having a large distance between the opposed magnetic paths at the center instead of the square core 24 in FIGS. 6 and 7, and the same applies to an elliptical shape (not shown). Since the distance between the center and the external magnetic path of the 26 portion is increased, the number of windings can be increased, and there is an advantage that the blocking characteristics in the low range can be further improved.

FIG. 9 shows an embodiment in which a partially coaxial cylindrical core is used in place of the square core 24 of the common mode choke coil 21 shown in FIG. 6. Reference numerals 30-1 and 30-2 denote circular external magnetic paths. This is a configuration in which a notched core is cut in half at the center in the length direction, and the above-described windings 25 to 27 are formed on a cylindrical bobbin 31 into which a center magnetic path is inserted in advance.
And the cores 30-1 and 30-2 are inserted and fixed from both sides.

As described above, the choke coils as shown in FIGS. 6 to 9 are effective for high-frequency common mode currents, but as shown in FIG. It is clear that Cg can further reduce the Cg and improve the blocking characteristics. In the description so far, the windings for all the cores are shown in FIG.
Although it has been described that the windings are composed of dense and sparse windings such as 25 to 27, it is apparent that the effect of the present invention is not impaired even if the winding is made homogeneously without separating the dense and dense depending on the required characteristics. It is.

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

FIG. 11 shows a second embodiment of the differential probe according to the present invention. Reference numeral 32 denotes a normal mode choke coil having a large inductance for a normal mode current and a small inductance for a common mode current.

FIG. 12 is a structural explanatory view of the structure of the common mode choke coil 21 and the normal mode choke 32 of FIG. 11. 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. The windings 25 ', 26', and 27 "are wound around the core 24 'of the common mode choke coil 21, and the windings are wound on the same magnetic path as the windings 25, 26, and 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 and off the band pass filter 23. If the switches SW ₁ and SW ₂ are switched to the bandpass filter side,
A _VL waveform and level signal similar to the output of FIG. 1 are output. If these switches SW ₁ and SW ₂ are switched to the short-circuit side, a waveform and level signal in which V _H and _VL are superimposed are output. Thus, the level of V _{H having} a large level can be detected. That is, by switching the switches SW ₁ and SW ₂ , V _H
Alternatively, the _VL waveform and the output level can be detected separately.

FIG. 13 shows a third embodiment of the differential probe according to the present invention.
FIG. 4 is a block diagram of an embodiment of FIG. 33 In the drawing is a bandpass filter for high-frequency pass center frequency f _H, so as to output through the respective output divided into two lines for low frequency band pass filter 23 and high-frequency band-pass filter 33, the preamplifier 15 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.
The low-frequency narrow band-pass filter 23 'and the high-frequency narrow band-pass filter 33' of the differential probe according to the third embodiment shown in FIG. 14 can change the respective pass center frequencies f _L and f _H by an external control voltage. The 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 Audible Noise immunity test, among the applied signal of the AM modulated wave, f of the _H and f _L, at least when performed by changing one of the frequency, the control terminal 3 the external signal synchronized thereto
By applying the voltage 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 measurement voltage is correctly detected. Therefore, the immunity test in which the applied signal is swept can be automated.

[0028]

As described in detail above, the present invention provides
A coil is disposed between two contact terminals of a differential probe and a differential voltage detecting element for separating and detecting a minutely modulated wave signal from a superimposed signal in which a minutely modulated wave of an audio band is included in an AM modulated high frequency signal. 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 low. 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 EUT, there is almost no effect on the load system such as noise and sound pressure. There is a remarkable effect that the modulation wave level can be detected.

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

[Brief description of the 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 noise audible immunity characteristics.

FIG. 5A is a waveform diagram of an AM modulated wave having an amplitude V ₀ used as a test signal. (B) is a waveform diagram of the voltage V _R generated between the handset terminal of the tester R ₁ · R ₂ when applying a test signal V ₀ to the communication line.

FIG. 6 is a structural explanatory view of a high-frequency broadband common mode choke coil using a square core inserted into a 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 inserted into a 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 diamond-shaped core and a rectangular auxiliary core inserted into the differential probe input unit of the present invention.

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

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

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

FIG. 12 is a diagram illustrating the structure of a common mode and normal mode high frequency broadband choke coil inserted into 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]

DESCRIPTION OF SYMBOLS 1 EUT (EUT) 2 Pseudo ground 3 Insulated support 4 EUT communication line 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 detecting element 15 preamplifier 16 the 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 frequencies 20 Differential probe 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' rectangular auxiliary core 29 rhombic core 30 partially coaxial cylindrical core 31 winding frame 32 Normal mode choke coil 33 Broadband bandpass filter 33 'Center frequency variable bandpass filter 34-1, 34-2 Control terminal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 29/26 G01R 19/00-19/32 H04B 1/60 H04B 3/46-3/48 H04B 17 / 00-17/02 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A differential probe for detecting a small signal generated between two terminals, comprising: a high-frequency broadband common-mode choke coil connected to two contact terminals of the probe; and an output terminal of the choke coil. A high-frequency wide-band attenuator, a high-frequency wide-band normal mode choke coil connected to an output terminal of the attenuator, a differential voltage detection element connected to an output terminal of the choke coil, and a preamplifier for amplifying an output from the element. A differential probe for detecting a high-frequency superimposed minute signal, comprising: a band-pass filter having a predetermined center frequency. 2. The high-frequency broadband common mode choke coil includes a pair of input / output windings extending 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 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 / output windings in opposite directions to the magnetic path of the closed magnetic path core. The differential probe for detecting a high-frequency superimposed small signal according to the above. 3. The winding of the choke coil according to claim 2, wherein a winding range on a magnetic path in a long side direction of the closed magnetic path core is divided into three by a predetermined width, a 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.