JPS6328539B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates generally to signal transmission systems. More specifically, the present invention relates to a system for transmitting signals having relatively high frequency components, in which unnecessary radiation from a signal source is effectively prevented.

FIG. 1 is a schematic block diagram showing the general hardware configuration of a product using a microcomputer, which is the background of the present invention. This device 1
The power supply circuit 20 includes a power supply circuit 20 that receives AC power, such as a commercial power supply, through a plug 10 and a power supply line 11. Although not shown, the power supply circuit 20 includes a well-known voltage conversion means (transformer), a DC power supply circuit, etc. , DC power is applied to the power line 21, and AC power is applied to the power line 22. The DC power that passes through the power line 21 from the power supply circuit 20 is connected to the digital circuit 3.
It is given as a power supply for 0 operation. The digital circuit 30 includes a substrate (not shown) on which, for example, a microcomputer and its related circuits are mounted. As is well known, microcomputers are
Contains a combination of ROM, RAM, ALU and I/O ports. The input port of the digital circuit (microcomputer) 30 is connected to an input device 40 via a signal line 31. The input device 40 includes a keyboard, a manual operation switch, etc., and receives operation signals (on/off signals) thereof. is given to the digital circuit (microcomputer) 30 as an input signal. The output port of digital circuit 30 provides an output signal (eg, a digital signal, an analog signal such as a video signal) to output device 50 via signal line 32 . Although not shown, the output device 50 includes a CRT display and an audio circuit.
Depending on the signal given from the digital circuit 30 through the signal line 32, an image or sound is output.

Digital devices, especially products using microcomputers, as shown in FIG. 1, have recently become widespread and are already widely used in ordinary households.
However, unnecessary electromagnetic wave radiation generated from such digital circuits is causing social problems. In other words, as the processing speed of microcomputers and other electronic circuits has increased in recent years, in reality, various frequency-divided signals and harmonic components centering on the fundamental frequency of a few MHz have been used to produce sounds below the audible level. Unnecessary electromagnetic waves with frequencies up to several hundred MHz are radiated into the air. Therefore, because such unnecessary radiation interferes with general radio or causes problems with commercial communications such as television broadcasting, many countries have very strict regulations against such unnecessary radiation, such as the FCC. and FTZ
It is about to be implemented.

Conventionally, several approaches have been known to prevent such unnecessary radiation in a device such as that shown in FIG. 1, for example. One of these is to house the signal source board (on which a microcomputer is mounted) in a shield case. However, even if only such a signal source is housed in a shield case, when a power supply or input/output equipment is connected, all the power supply lines and signal lines become antennas, and are almost ineffective. Therefore, another approach could be to remove the power supply circuit and other equipment and house it in a shield case. However, if all the power supply circuits and other equipment were to be housed in a shield case, the mechanism would become complicated and large, which not only significantly deteriorates work efficiency but also increases costs. . Therefore, as another approach, the following method has been proposed for power supply lines and signal lines that are unavoidably exposed to the outside from the shield case. For example, a signal line may be passed through a feedthrough capacitor to bypass high frequency components, or such a signal line may be relayed using a connector with a special bypass capacitor for removing high frequency components. However, with this approach that attempts to prevent unnecessary radiation by removing high-frequency components, even necessary information signals are affected by such feed-through capacitors and special connectors. The drawback was that the quality of signals, other synchronization signals, and clock signals was significantly degraded. Moreover, the frequency spectrum in which unnecessary radiation should be prevented is spread over a wide range as described above, and the number of required signal lines also varies. Therefore, there are fewer optimal parts, which further increases costs.
In addition, power lines and signal lines are sometimes shielded with metal pipes or special shielded cables, but approaches that use metal pipes and shielded cables also cause workability to deteriorate and costs to increase.

Therefore, the main object of the present invention is to reliably prevent unnecessary radiation without impairing workability or mass productivity, and without deteriorating the quality of necessary signals.
An object of the present invention is to provide an improved signal transmission system.

In summary, the present invention enhances the high-frequency components of a signal to be transmitted in advance, attenuates the high-frequency components of the signal whose high-frequency components have been enhanced, and thereby eliminates unnecessary radiation components, that is, unnecessary high-frequency components. This is a signal transmission system that significantly attenuates the

The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 2 is a schematic block diagram showing one embodiment of the present invention. In terms of configuration, this embodiment is the same as that shown in FIG. 1 above, except for the following points, and the explanation of these parts will be omitted here to avoid duplication of explanation. A digital circuit 30 such as a microcomputer is housed in a shield case 100 as shown in FIG. This shield case 100 is, for example, a rectangular parallelepiped, and is made of a mesh-like metal plate with one side open. The opening is located on the printed circuit board 101.
blocked by. This printed circuit board 101 includes unnecessary radiation prevention circuits 211 and 311 shown in FIG. 2 and explained in detail in FIGS. 4 and 6.
and 321 are formed. Unwanted radiation prevention circuit 2 connected to DC power line 21 of power supply circuit 20
For 11, a well-known feedthrough capacitor or a special connector may be used. This is because the power supply lines 21 have a high output impedance when viewed from the signal line (microcomputer), so that even a conventional feedthrough capacitor or the like can effectively prevent unnecessary electromagnetic waves from being fed to the power supply lines 21.

The unnecessary radiation prevention circuits 311 and 321 include active elements such as transistors and passive elements such as resistors and capacitors, and are constructed on the printed circuit board 101, as will be described later. Therefore,
Although not shown, the printed circuit board 101 has printed patterns necessary for each circuit. The printed circuit board 101 is preferably a so-called double-sided board, and copper foil is left as wide as possible in areas other than the patterns necessary for circuit wiring. Therefore, shield case 10
0 and the printed circuit board 101, an even greater shielding effect can be obtained.

The unnecessary radiation prevention circuit 311 is connected to the signal line 31 from the input device 40, and this circuit 31
A signal line 31 a is connected between the input port 1 and the input port of the digital circuit 30 . Unnecessary radiation prevention circuit 3
21 is connected to a signal line 32 from the output port of the digital circuit 30, and a signal line 32a is connected between this circuit 321 and the output device 50. That is, the unnecessary radiation circuits 311 and 321 are inserted between the signal lines 31 and 31a and between the signal lines 32 and 32a, respectively, so that unnecessary high frequency components are not fed to each signal line as described later. It works like this.

In this way, by configuring the unnecessary radiation prevention circuit on the printed circuit board 101 that cooperates with the shield case 100, a special There is no need for special design. That is, even if the number of signal lines 31, 32, etc. from the digital circuits housed in the shield case 100 increases or decreases, simply by increasing or decreasing the number of these circuits 311, 321, the shield case 100 and the printed circuit board 101 By working together, unnecessary radiation can be effectively prevented. Therefore, even when there are a large number of signal lines, there are no problems in design, workability, or mass production.

Next, details of the unnecessary radiation prevention circuits 311 and 321 will be explained.

FIG. 4 is a main circuit diagram showing a preferred embodiment of the unnecessary radiation prevention circuit 311. The input circuit 40 includes, for example, a manually operable switch 41. One end of this switch 41 is connected to a low level, so that a low level or high level signal (on/off signal) is derived to the signal line 31 depending on whether this switch 41 is turned on or off. This signal line 31 is connected to the signal line 3 via a complementary circuit CC included in an unnecessary radiation prevention circuit 312.
1a. The signal line 31a is connected to a digital circuit or an input port of the microcomputer 30. The signal line 31a is a capacitor C
Grounded via 2. The complementary circuit CC includes a complementary connection of an NPN transistor T1 and a PNP transistor T2, and the collector of the transistor T1 is connected to the power supply.
Vcc, and the collector of transistor T2 is grounded. The bases of transistors T1 and T2 are commonly connected to signal line 31, and their emitters are commonly connected to signal line 31a.
Note that the bases of transistors T1 and T2 are commonly grounded via a capacitor C1 for preventing chattering, and are connected to the power supply Vcc via a resistor R1 for regularly pulling up this line 31 to a high level. Ru. In addition, capacitor C2
is for preventing overshooting.

In operation, the signal line 31 is normally pulled up to the power supply Vcc via the resistor R1, so one transistor T1 of the complementary circuit CC is conductive. For this purpose, the signal line 31a is connected to the power supply Vcc, and a high level signal is obtained there.
When switch 41 is turned on, signal line 31 is forced to a low level, so that the other transistor T2 of complementary circuit CC becomes conductive. for that,
The signal line 31a is grounded via this transistor T2, and a low level signal is obtained there.
In this way, depending on whether the switch 41 is turned on or off, a low level or high level signal is output.
The signal is applied to the input port of the digital circuit 30 via the signal line 31, the unnecessary radiation prevention circuit 311, that is, the complementary circuit CC, and the signal line 31a. The digital circuit 30 receives the ON/OFF signal thus provided.
A predetermined processing operation is performed in response to the off signal.

Like this signal line 31, the digital circuit 30
For the signal line connected to the input port of the digital circuit 30, this digital circuit 30 acts as a signal source of unnecessary radiation components. That is, a digital circuit or a microcomputer has an operating clock of, for example, 64 KHz, and if the circuit 311 were not present, such an operating clock or its lower or higher harmonic components would be radiated to the outside through the signal line 31. It will be done. In the embodiment shown in FIG. 4, in the normal state, one transistor T1 constituting the complementary circuit CC is conductive as described above, so this signal line 31a is connected to the power supply (reference potential) Vcc. There is. Therefore, the unnecessary radiation component led out from this digital circuit 30 to the signal line 31a is dropped to the ground in an alternating current manner via this transistor T1. Even when the signal line 31 becomes low level, the transistor T2 is conductive, so the signal line 3
1a is grounded in an alternating current manner. In this way, unnecessary signal components leaking from the digital circuit 30 to the signal line 31a are primarily transmitted to the transistors T1 and T2 included in the complementary circuit CC, and secondarily to the capacitors C1 and C2. Even if it does, radiation to the outside can be effectively prevented.

FIG. 5 is a schematic block diagram showing an example of the unnecessary radiation prevention circuit 321. This unnecessary radiation prevention circuit 3
21 is for effectively preventing unnecessary radiation components from leaking into the signal line 32 from the digital circuit or microcomputer 30 to the output device 50.

In the configuration, the output port of the digital circuit or microcomputer 30 is connected to the signal line 32. The signal line 32 is the emphasis circuit EN
and the adder circuit AD. As shown in FIG. 5, the emphasis circuit EN is a circuit for amplifying the high-frequency components of, for example, a pulse signal (digital signal) led out to the signal line 32, and its output is given to the other input of the adder circuit AD. . The adder circuit AD adds the two applied signals, that is, the original signal and the enhanced signal, in a superimposed manner, and provides the output to the current booster circuit IB.
This current booster circuit IB includes an emitter follower circuit, etc., and its output is passed through a high-frequency attenuation filter.
Given to HRF. The high-frequency attenuation filter HRF appropriately removes or attenuates the high-frequency components thus enhanced. Since the high-frequency components of the signal have been enhanced first, this high-frequency attenuation filter
Even after passing through HRF, a signal having substantially the same waveform as the original signal is obtained on the signal line 32a. The signal line 32a is connected to the output device 50, and the output device 50 is thus able to receive a signal whose high frequency components are attenuated and whose waveform is substantially close to the original signal.

In this embodiment of FIG. 5, unnecessary high frequency components from the signal line 32 are blocked by the above-mentioned high frequency component attenuation filter HRF, so the signal line 32a
Such unnecessary high-frequency components will not be supplied with power. Therefore, the signal lines 32, 32a do not act as antennas and cause unnecessary radiation.

Note that in the conventional case where only the filter HRF was inserted without providing the emphasis circuit EN and the adder circuit AD, the waveform would be as shown by the dotted line in Fig. 5, and the signal to be transmitted would be The quality of the product deteriorates significantly. In contrast, in this embodiment, by emphasizing the high-frequency components in advance and feeding them with as low an impedance as possible, even after passing through the relay for high-frequency removal, that is, the high-frequency component attenuation filter HRF. , a digital signal with the same quality as the original signal can be obtained.

FIG. 6 is a circuit diagram of a main part showing a preferable example of the embodiment shown in FIG. A capacitor C11 and a resistor R11, which constitute an emphasis circuit, are connected to the signal line 32. The resistor R11 transmits the original signal sent to the signal line 32 as it is to the connection point P11 forming an adder circuit in the subsequent stage. Therefore, the additional point P1
1 adds the enhancement differentiated by the capacitor C11 and the original signal in a superimposed manner. This additional point P
The added signal obtained at 11 is given to the current booster IB. Current booster IB includes a pair of transistors T11 and T12 and is constituted by an emitter follower type complementary circuit. Transistor T1
1 and T12 bases are commonly added point P11
and their emitters are commonly connected to the signal line 32a. The collector of transistor T11 is connected to the power supply Vcc, and the collector of transistor T12
The collector of is grounded. Note that the transistor T
R12 and R13 connected to the bases of T11 and T12 determine the bias of these transistors and, in conjunction with the input impedance of these transistors, determine the charging and discharging time constants of the differential capacitor. Therefore, these resistances R
12 and R13 need to be selected as optimal values in consideration of the above, but may be omitted in some cases. A capacitor C1 is inserted between each emitter of transistors T11 and T12 and ground.
2 is for overshooting prevention as used in a normal emitter follower circuit. These resistors R15 and R16 can be omitted if necessary.

A capacitor C13 and a resistor R are connected to the signal line 32a.
14 is inserted, and these capacitor C13 and resistor R14 constitute an impedance matching circuit together with resistor R15. A resistor R1 is inserted between the signal line 32a and the ground.
6 is a bias resistor. By appropriately selecting the value of the impedance matching circuit, reflection of the signal from the terminal end of the signal line 32a can be effectively prevented and faithful transmission of the signal waveform can be achieved.

The signal line 32a is passed through the feedthrough capacitor C14 and connected to the output device 50. This feedthrough capacitor C14 constitutes a high frequency component removal filter, and its outer electrode is grounded. By this,
This feedthrough capacitor C14 removes high-frequency components, and as a result, it is possible to effectively prevent unnecessary radiation from occurring from this signal line 31a. As described above, even if the high-frequency components are attenuated in this manner, substantially the same waveform as the original signal is provided from the signal line 32a to the output device 50.

Note that in the embodiments of FIGS. 5 and 6 described above, the current booster IB may be omitted.
Further, it is also possible to provide more emphasis circuits as necessary, that is, depending on the amount of attenuation by the high-frequency component attenuation filter HRF.

7 to 10 are graphs for explaining the effects of the present invention, in which the horizontal axis represents frequency and the vertical axis represents the radiated electric field strength at a point 3 meters away. 7 and 8 show the horizontal component, and FIGS. 9 and 10 show the vertical component.
FIGS. 7 and 9 each show an example in which no measures against unnecessary radiation are taken in the apparatus shown in FIG. 1. FIG. 8 and FIG. 10 each show the case where each of the above-mentioned embodiments is applied. As can be seen from Figures 7 to 10, compared to the one without any unnecessary radiation measures,
When each of the above-described embodiments is applied, it is possible to sufficiently clear the limit values of FCC class B, which is a fairly strict standard.

In addition, in a certain design example, if a signal containing components from 60Hz to 300KHz is included in the digital circuit, in the embodiment of FIG. 4, R1 = 50Ω, C1 =
860pF, C2=390pF, T1=2SC1740, T2=
It was set as 2SA937. In the FIG. 6 embodiment, C1
1=30pF, R11=1KΩ, R12 and R13
= omitted, C12=390pF, C13=0.2μF, R1
4=22Ω, R15=68Ω, R16=omitted, C14
=2200pF, T11=2SC1740, T12=2SA937
And so.

The above embodiments have mainly been described in the case where the signal to be transmitted is a digital signal. However, the inventive concept can also be used when transmitting analog signals such as video signals.

FIG. 11 is a block diagram showing another example of the unnecessary radiation prevention circuit 321. This FIG. 11 embodiment is as follows:
Output device 50 using signal lines 32 and 32a
This is an example of a case where an analog signal such as a television signal is applied to the computer. Analog signal source 3
The analog signal sent from 0' to the signal line 32 is
Paths PA1 and PA with different frequency characteristics
2 to the mixer MIX. Therefore, the mixer MIX adds the analog signals that have passed through the paths PA1 and PA2 having different frequency characteristics and provides the output to the input of the amplifier AMP.
The amplifier AMP is a circuit for further amplifying the analog signal with enhanced high-frequency components from the mixer MIX, and includes a feedback loop having predetermined frequency characteristics. By appropriately adjusting the frequency characteristics of the amplifier AMP using this feedback loop, the high-frequency component attenuation filter in the subsequent stage is
High-frequency components can be enhanced by an arbitrary amount depending on the amount of attenuation caused by HRF. The output of this amplifier AMP is given to signal line 32a via an inverter and current booster IB. The inverter is necessary when the polarity is reversed by the amplifier AMP, and the current booster IB is shown in Figures 5 and 6 above.
It is similar to the current booster shown in the figure. The outputs of the inverter and current booster IB are connected to a signal line 32a, which is connected to an output device 50 via a high frequency component attenuation filter HRF. By the high frequency component attenuation filter HRF, the signal line 32
As in the previous embodiment, it is possible to effectively prevent unnecessary radiation from occurring from a. At this time, the analog signal uses paths PA1 and PA2, mixer MIX, and amplifier AMP to relatively enhance signal components in the frequency band that is attenuated by filter HRF compared to signal components in other frequencies. Therefore, the high-frequency component attenuation filter
Even if the high-frequency components are attenuated by the HRF, an analog signal substantially the same as the original analog signal is provided to the output device 50 through the output line 32a.

FIG. 12 is a circuit diagram illustrating the preferred embodiment of FIG. 11. In the configuration, capacitor C21 and resistor R21 each configure paths with different frequencies. Transistor T included in the amplifier
A parallel circuit of the capacitor C21 and the resistor R21 is connected between the base of the capacitor C21 and the signal line 32. Therefore, the input of this transistor T21 is given the sum of analog signals that have passed through paths with different frequency characteristics.
The collector of the transistor T21 is connected to the power supply Vcc via a resistor R22, and is also connected to a resistor R25.
Transistor T constituting the inverter via
22 base. Transistor T21
The emitter of is grounded via an impedance circuit consisting of resistors R23 and R24 and capacitor C22. The input impedance seen from the base of transistor Q21 is made different with respect to frequency by this impedance circuit. That is, for low frequency components, the input impedance is determined by resistor R23, and for high frequency components, the input impedance is determined by resistors R23 and R24.
Therefore, the transistor T2 constituting the amplifier
In the output of 1, high frequency components are derived as higher voltages than low frequency components. In other words, the high frequency components are enhanced here. The bias point of transistor T21 is determined by resistor R22 and an impedance circuit. The transistor T22 constituting the inverter has an associated resistance R
28, R29, R30 and R31 determine its operating bias. Since the polarity of the analog signal is inverted by the amplifier or transistor T21, the inverter T22 inverts its polarity again to make it the same polarity as the original signal. Transistor T2 constituting the current booster
The bases of T3 and T24 are commonly connected to the collector of inverter transistor T22.
Note that resistors R26 and R27 and a capacitor C23 are connected between the emitter of the inverter transistor T22 and the emitter of the amplifier transistor T21.
A feedback loop having predetermined frequency characteristics is connected. A signal line 32a commonly connected to the emitters of transistors T23 and T24 of the current booster passes through a feedthrough capacitor C24 that constitutes a high-frequency component attenuation filter.
It is connected to the output device 50. Since the operation of the embodiment in FIG. 12 will be easily understood from the explanation related to FIG. 11, detailed explanation thereof will be omitted here.

As described above, according to the present invention, the high frequency components are enhanced in advance, and then the enhanced high frequency components are attenuated together with the unnecessary components by the high frequency attenuation means, so that the original signal is It is possible to effectively prevent unnecessary radiation without impairing the quality of the image.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing an example of a microcomputer-based device that forms the background of the present invention. FIG. 2 is a schematic block diagram showing one embodiment of the present invention. FIG. 3 is an illustrative external view showing an example of the shield case according to the embodiment shown in FIG. FIG. 4 is a main circuit diagram showing a preferred example of the unnecessary radiation prevention circuit 311. FIG. 5 is a schematic block diagram showing an example of the unnecessary radiation prevention circuit 321. FIG. 6 is a circuit diagram of a main part showing a preferable example according to the embodiment of FIG. Figures 7 to 10
The figures each show the radiated electric field strength with respect to frequency, Figures 7 and 9 show the case where no unnecessary radiation measures are taken, and Figures 8 and 10 show the case where the unnecessary radiation measures according to the present invention are taken. shows. FIG. 11 is a schematic block diagram showing an example of the unnecessary radiation prevention circuit 321 when the signal to be transmitted is an analog signal. FIG. 12 is a main circuit diagram showing a preferred example according to the embodiment of FIG. 11. In the figure, 30 is a digital circuit or a microcomputer, that is, a signal source;
a, 32, 32a are signal lines, 40 is an input device, 5
0 is the output device, 100 is the shield case, 101
is a printed circuit board, and 211, 311 and 321 are unnecessary radiation prevention circuits.

Claims (1)

[Scope of Claims] 1. A signal processing means that processes a significant signal including a high frequency component and is a source of unnecessary electromagnetic waves; an external device that cooperates with the signal processing means; and an input device for the signal processing means. an unnecessary radiation prevention means disposed near the output signal connection section and connected to the signal processing means; and a signal line for connecting the external device and the unnecessary radiation prevention means, the unnecessary radiation prevention means , at least an attenuating means for amplifying only the high frequency signal component of the signal from the signal processing means, and an attenuating means for attenuating the high frequency component of the signal amplified by the amplifying means and providing it to the external device. A signal transmission system consisting of: 2. The significant signal is a signal including a rising edge and a falling edge having a certain slope, and the enhancing means includes a differentiating means for differentiating at least one of the rising edge and the falling edge of the significant signal. A signal transmission system according to claim 1. 3. The enhancement means includes: means for creating an enhancement component based on the signal from the signal processing means; and means for adding the enhancement component from the enhancement component creation means to the original signal in a superimposed manner. A signal transmission system according to claim 1. 4. The signal transmission system according to claim 1, wherein the unnecessary radiation prevention means further includes current amplification means that is connected between the reinforcement means and the attenuation means and amplifies only significant signals. 5. The signal transmission system according to claim 1, wherein the enhancement means includes signal paths having different frequency characteristics. 6. The signal transmission system of claim 5, wherein the boosting means includes amplifier means, and wherein the amplifier means includes an impedance circuit for providing different input impedances in response to different frequency components. 7. The signal transmission system according to claim 6, wherein the amplifier means includes a feedback loop having predetermined frequency characteristics. 8. The signal transmission system according to any one of claims 1 to 7, wherein the attenuation means includes a capacitor interposed between a signal line downstream of the amplification means and a reference potential.