JPH0430616A - Digital signal output circuit - Google Patents

Abstract

PURPOSE:To suppress noise radiation by inserting a simulated distributed constant type noise filter comprising an inductance L and a capacitance C, on the way of a signal line through which a digital signal outputted from a circuit in an electric device such as a computer to a connector. CONSTITUTION:Signal lines and power lines 5 are interconnected between a circuit 4 operated in various ways and a connector 3a in an electronic device main body 1, and a simulated distributed constant noise filter 10 is inserted between the signal lines and power lines 5. In the simulated distributed constant noise filter 10, a static capacitor C1 in existing between a lead wire 12 at the end of a conductor 11 and the vicinity of a lead wire 15 at the end of a ground conductor 14 is not connected in series with the inductance, then low impedance grounding is attained for a high frequency component even when the capacitance of the static capacitor C1 is small, but a high impedance is offered to a low frequency component. Thus, the excellent attenuation characteristic is realized over the entire frequency band from a low frequency to a high frequency band.

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention suppresses noise emitted from cables and connectors when outputting digital signals from the computer main body to peripheral devices such as display devices and printer devices. It relates to a digital signal output circuit.

(Prior Art) When a computer main body outputs a digital signal to a peripheral device, noise including a broadband frequency fi component is emitted from the cable or connector. Cables, etc. were shielded. However, no matter how strict the shielding is, it is extremely difficult to suppress noise radiation to the extent that it can pass various regulations.

(Problems to be Solved by the Invention) Therefore, the present invention aims to eliminate noise containing broadband frequency components emitted from cables and connectors when outputting digital signals from the main body of an electronic device such as a computer to a peripheral device. The goal is to effectively suppress it.

(Means for Solving the Problems) In order to solve these problems, the present invention provides a signal line in the middle of a signal line that leads digital signals output from a circuit in an electronic device such as a computer to a connector. A capacitance C formed between the inductance of a first coil that passes a signal and a second coil that is connected to the first coil via a dielectric and whose end or the vicinity of the end is grounded. A pseudo-distributed constant noise filter is inserted near the connector to suppress noise radiation.

(Embodiment) As shown in FIG. 1, the digital signal output circuit of the present invention is designed to output digital signals from an electronic device body 1 such as a computer to a peripheral device 2 through connectors 3a and 3.
In the electronic device main body 1, there are signal lines and power lines 5 from the circuit 4 that performs various operations to the connector 3a.
are connected to each other, so a pseudo distributed constant type noise filter 10 is inserted into these signal lines and power supply line 5.

As shown in the equivalent circuit of FIG. 2, this pseudo-distributed constant type noise filter IO consists of two conductors that are inductively coupled and inductively coupled, and these two conductors are connected to a current-carrying conductor 11 that passes a signal or power supply current. , and a ground conductor 14 whose end or the vicinity of the end is grounded, and both groove bodies 11.1
4 and the capacitance C distributed between both groove bodies 11. It's like being grounded at a certain point.

It is extremely difficult to use a calculation formula to explain the integral values of the distributed characteristics that exist between each distributed portion of the current-carrying conductor 11 from the input terminal to the output terminal and the grounding lead wire 15 of the grounding conductor 14. However, this can be qualitatively explained as follows.

The pseudo distributed constant type noise filter 10 of the present invention has a second
As shown in the equivalent circuit diagram in the figure, lead wires 12 and 13 are connected near both ends of the current-carrying conductor 11, and a lead 1115 is connected to one end of the ground conductor 14.

The capacitance C1 that exists near the lead wire 12 at the end of the current-carrying conductor 11 and the lead wire 15 at the end of the ground conductor 14 does not include inductance in series, so the value of the capacitance itself is small. However, high frequency components can be grounded with low isobedance, but low frequency components have high impedance.

The capacitance Cn existing in a portion far from each lead 1112.15 of each conductor 11 and wire 4 includes inductance Ln in series with the grounding lead wire 15, so it has a high impedance for high frequency components. However, each lead wire 1
2.15, the values of all capacitances 62 to Cn that exist in the region become larger, and the inductance L in series
Even if n is included, the impedance is low for low frequency components.

In this way, unlike a complete distributed constant circuit in which the ground conductor 15 is sufficiently grounded throughout, it forms a pseudo distributed constant circuit, so we decided to call it a pseudo distributed constant type noise filter. It is.

As is clear from the above qualitative explanation, the pseudo-distributed constant noise filter of the present invention can provide excellent attenuation characteristics over the entire frequency band from the low frequency range to the high frequency range.

For example, when a square wave on which a high frequency component is superimposed as shown in FIG. 3a is passed through the pseudo distributed constant type noise filter 10, as shown in FIG. The high frequency components radiated as noise can be effectively removed and output.

As an example of this pseudo distributed constant type noise filter 10, as shown in FIG. 4A, there are leads 1112.1 at both ends.
3 and the strip-shaped grounding conductor 14 with a lead wire 15 connected to one end thereof are stacked together with two dielectric sheets 16 interposed therebetween. As shown in Figure 4B, the sheet is
It is wound around the shaft core 17.

At this time, the core 17 and each lead 1112, 13, 15 are wound so that they are arranged on the straight line 19, and the end portion of the winding is fixed by heat welding or the like, and then pulled out from the core 17.

Then, by heating while pressing from a direction perpendicular to the straight line 19, it is crushed and molded into a flat shape as shown in Fig. 4C, and then coated with epoxy resin or the like, as shown in Fig. 4C. A pseudo distributed constant type noise filter 10 having a tubular shape as shown in the perspective view can be obtained.

As shown in the equivalent circuit of FIG. 2, the three-terminal noise filter 10 configured in this manner has inductance because the current-carrying conductor 11 is wound around it, and also has inductance over the entire length of the current-carrying conductor 11. Since a capacitance is formed between the conductor 14 and the ground conductor 14, a pseudo distributed constant circuit is formed in the current-carrying conductor 11, and it can have excellent attenuation characteristics over a wide frequency band.

In such a three-terminal noise filter 10,
By moving the connection position of the lead wire 15 connected to the ground conductor 14 closer to or away from the lead wire 12 or 13 connected to the current-carrying conductor 11, its attenuation characteristics can be adjusted. By connecting the 14 lead wires 15 close to the lead wires 12 inside the current-carrying conductor 11, excellent attenuation characteristics can be obtained over a high frequency band.

(Other Embodiments) (A) As a pseudo-distributed constant type noise filter used in the digital signal output circuit of the present invention, Japanese Patent Application No. 1-37077 and No. 1-59241 previously filed by the present applicant Patent application No. 1-71339 No. 1-101426 No. 1-101426 No. 1-119369 No. 1-279042 No. 1-335694 No. 7590 No. 2-7590 What was proposed in Hei 2-11540 etc. can be used.

CB) As shown in Figure 2, the pseudo-distributed constant type noise filter of the present invention is a three-terminal noise filter, and in addition to being used for the purpose of suppressing normal mode noise, it also suppresses four-terminal noise. - Can be used as a filter to suppress common mode noise. In this case, the grounding conductor 14 may also be a current-carrying conductor together with the current-carrying conductor 11, and lead wires 15, 16 may be provided at both ends thereof.

(Effects) According to a digital signal output circuit using such a pseudo-distributed constant noise filter, high-frequency components radiated as noise can be removed without substantially distorting the waveform of the fundamental wave component of the signal to be transmitted. It can be effectively removed and output. Furthermore, unlike noise filters using lumped constant noise filters, there is no need to consider reflection or resonance, so circuit design can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the digital signal output circuit of the present invention, FIG. 2 is an equivalent circuit diagram of a pseudo-distributed constant type noise filter used in the device shown in FIG. 1, and FIG. , a waveform diagram showing a state in which noise is removed by passing a signal through a pseudo-distributed constant noise filter;
FIG. 4 is a diagram showing the manufacturing process of an example of a pseudo-distributed constant type noise filter used in the circuit of the present invention, and the same parts are represented by the same symbols throughout the figures. 1... Electronic equipment (computer body) 2... Peripheral devices 3a, 3b... Connector 4... Digital signal generation circuit 5... Signal output line 10... Pseudo distributed constant type noise filter 11 ...
Current-carrying conductor 12.13.15...Lead wire 14...Grounding conductor 16...Dielectric sheet Fig. 3a Fig. 1 Fig. 2 Fig. 3 Fig. 4 B Fig. 4 C 7I44 Fig. D

Claims (1)

[Claims] (1) In an electronic device such as a computer that has a connector for outputting a digital signal to a peripheral device, a first signal line that passes the digital signal output from a circuit inside the electronic device to a signal line that leads to the connector. Pseudo distributed constant type noise consisting of an inductance L of the coil and a capacitance C formed between the first coil and a second coil connected via a dielectric and whose end or the vicinity of the end is grounded. A digital signal output circuit characterized by inserting a filter.