JPS62208734A - Common signal line for digital signal - Google Patents

Abstract

PURPOSE:To decrease the transmission distortion by connecting respectively a resistor to plural connecting points connected to a common signal line, and making the combined resistance equal to the surge impedance of the common signal line. CONSTITUTION:The common signal line A has the surge impedance, its length depends on the sent frequency band, the wavelength lambda is used, and connecting points X1, X2, X3,...Xn are arranged in lengthwise direction. C1-Cn are digital signal transmission/reception equipments connected respectively to the points X1-Xn of the digital line A. A matching resistor (resistance R) is provided respectively to the connecting points between the signal line A and the equipments C1-Cn. n-Set of the matching resistors R are supplied to the connecting points, each resistor R has the resistance being n-time of the surge impedance to match the combined resistance with the surge impedance of the signal line A. Thus, the reflection of the wave at the connecting points is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a shared signal line for digital signals, and more particularly to a transmission path for transmitting and receiving digital signals.

The shared signal line used for transmission requires many input/output ports in order to collect and distribute digital signals. In this case, since the shared signal line is a high-speed signal line, its length is limited depending on the frequency band to be transmitted. Furthermore, it is necessary to perform matching using the wave impedance of the shared signal line.

In FIG. 4, A is a shared signal line, 01 to CI are transmitting/receiving devices, and B is a signal input/output port. Here, λ is the length of the signal line determined by the frequency band to be transmitted, but when sending signals from the transmitting/receiving device C1 to Cn, it is usually necessary to match the input/output port B connection on the shared signal line path. Reflection of waves at such discontinuous portions occurs, causing distortion of the transmitted waveform, making it impossible to transmit correct digital signals.

In FIG. 5, the length of the shared signal line A is determined by the frequency band to be transmitted, has a wavelength λ, and the connection points are arranged as xl l X2 * X3, . . . xn in terms of length. A matching resistor RO2 corresponding to the wave impedance of the shared signal line is connected to the xn point. The digital signal transmitting/receiving devices C1 to Cn are connected to the shared signal line A.
They are connected in an array of 1 to xn. Transmitting/receiving device 01-C
Up to rL, transmit mode and receive mode are 1 each.
A transmitting/receiving circuit is established. Since the shared signal line A transmits at a high frequency, it is better to minimize propagation reflections at the connection points x1 to xn of the transmitting and receiving devices. Therefore, it is better for the shared signal line A to match the wave impedance.

However, there are many disadvantages in the following situations. For example, when transmitter/receiver C3 is selected for transmission and CrL is selected for reception, the main paths for the wave to depart from 03 and reach CrL are a, b, and c, as shown in Figure 6. . In this path c, the connection point x1 terminates with ■Ω impedance, so the wave at this connection point is 10
0% reflection. The reflections at these connection points are combined and become transmission distortion of the digital signal.

FIG. 7 is a chart showing the attenuation rate when waves pass through connection points on paths a, b, and c. Based on this, route a: The digital signal output from the transmitting device C3 is (
In this case, the output impedance of C3 is OΩ) connection point X3
It branches off at , turns in the direction of the connection point xn, has an amplitude of 70%, reaches the connection point xn, passes through the matched resistor RO2, and reaches the receiving device CrL.

Path b: The digital signal output from the transmitter C3 reaches the connection point x3, branches and bends in the direction of the connection point x1, the amplitude becomes 70%, and is reflected in the direction of the connection point x3 with a reflectance of +100% at the X3 point. Then, it passes through point X3 again, and the amplitude further increases to 70% in the direction of connection point xn, reaches xn, and receiver
Reach rL. On the time diagram, X, and X3
The propagation time increases by the round trip time between points.

Path C: The digital signal output from the transmitter C3 branches through the connection point x3, has an amplitude of 70%, and then passes through the connection point x1.
direction, reflects +100% at point X3, passes point X3 again in direction C3 with an amplitude of 70%, and -1 at transmitter C3
00% reflection, passes point X3 again with an amplitude of 70% in the direction of the receiving device CrL, reaches the connection point xn, and connects the matching resistor RO2.
The signal passes through +100% and reaches the receiving device CrL. On the time diagram, X1+
The round trip time between x3 and the time between X 1 + C3 increase.

That is, the transmission distortion of the digital signal on the shared signal line between the transmitting device C3 and the receiving device CrL increases by the above amount.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and aims to provide a shared signal line for digital signals with less distortion.

[Structure of the Invention] (Means and Effects for Solving the Problems) The present invention provides a shared signal line for transmitting and receiving signals, a plurality of transmitting and receiving devices connected to this shared signal line, and a shared signal line for transmitting and receiving signals. A device is selected to transmit and receive signals, and a resistor is connected to each connection point between the plurality of transmitting/receiving devices and the shared signal line, and the combined resistance value of the resistors is the wave impedance of the shared signal line. It is characterized by having equivalence with . That is, by increasing the matching resistor of the shared signal line by n times and using n matching resistors as described above, the connection points x1 to x
By equally distributing matching resistors to the reflection points located at n (dispersion matching, so to speak), the overall transmission distortion of digital signals transmitted through coexisting signal lines is reduced.

(Example) An example of the present invention will be described below with reference to the drawings. 1st
In the figure, A is a shared signal line, which is a signal line having wave impedance. The length of the shared signal line A is determined by the frequency band to be transmitted, has a wavelength λ, and has a connection point Xl in terms of length.

X2. X3. ...xn. 01~Cr
L is a digital signal transmitting/receiving device connected to the shared signal line A in an arrangement of X1 to xrL. Transmitting/receiving devices C1 to cn
In any of the above, one transmission mode and one reception mode are selected, and a transmission/reception circuit is established. Connection points between the shared signal line A and the transmitting/receiving devices 01 to CrL each have a matching resistor R. That is, the matching resistor RO2 shown in FIGS. 5 and 6 is not included. For the n transmitting/receiving devices C1 to cn, the shared signal line A has a total of n matching resistors R at the connection points of the transmitting/receiving devices, and has a matching function. Each R is selected to have a resistance value n times the wave impedance (nXR2o), so that the combined resistance value is matched to the wave impedance of the shared signal line A.

To describe the characteristics of FIG. 1 with reference to FIG. 2, the matching resistor RO2 at point xrL on the shared signal line,
Instead, a matching resistor with a resistance value equal to or close to the number n of connected transmitting/receiving devices is installed at each connection point x.
Connect to or around 1 to xn. This equalizes the unevenness of waves due to the conventionally used concentrated matching resistor and suppresses wave reflections at the connection point. In this case, the reflectance of the connection point is rK-1-1/rL
J, the transmission distortion of the digital signal can be reduced compared to the conventional method.

FIG. 3 shows a chart in which the attenuation rate when a wave passes through the connection points on paths a, b, and c (only the main parts are shown) of this embodiment is shown. The explanation below will be based on this chart.

Path a: The digital signal output from the transmitter C3 branches at the connection point x3, bends in the direction of the connection point xn, and has an amplitude of 7.
0%, and connection point X4. rl-1 every time it passes through X5
/rLJ, that is, rK-1-(1/rL) J, the amplitude decreases until it reaches point xn, and reaches the receiving device CrL.

Path b = The digital signal output from the transmitter C3 branches at the connection point x3, heads toward the connection point x1, and returns to the connection point x
When it passes through 2, the amplitude decreases to %, it reflects to % at point X1, passes through point X2 again at %, and the amplitude decreases to 70% at point X3.
It decreases to x4° x5. rl-1 every time it passes...
/rLJ, that is, reaches the connection point xrL while attenuating by %, and reaches the receiving device Cn.

Path C: The digital signal output from the transmitting device C3 passes through a branch at the connection point x3, the amplitude becomes 70%, heads toward the connection point x1, passes through the connection point X2, and becomes the amplitude K%, % reflected at point X1, passed through point X2, decreased K% amplitude, branched at point
It heads in the direction of the point, and the amplitude attenuates by 70% again at point X3, and heads in the direction of the connection point xn, x4, x5*...
It passes through point xn while the % amplitude attenuates each time it passes through, and reaches the receiving device CrL.

As mentioned above, Xl causes transmission distortion of digital signals.
, the round trip time between X3 points and X3. % attenuation occurs during the time between C3, thereby reducing transmission distortion.

[Effects of the Invention] As explained above, according to the present invention, by increasing the number of matching resistors on the shared signal line by n times and using n matching resistors as described above (distributed matching in other words), By distributing matching resistors equally to the reflection points at connection points X1 to Attenuation is improved and transmission distortion can be reduced.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. FIG. 3 is an explanatory diagram of the operation of the same configuration, FIGS. 4 and 5 are configuration diagrams of a conventional shared signal line for digital signals, and FIGS. 6 and 7 are explanatory diagrams of the operation of the same configuration. A...shared signal line, 01-CrL...transmitter/receiver,
x1~xrL...Connection point, R...Resistance. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] A shared signal line for transmitting and receiving signals is provided, a plurality of transmitting and receiving devices are provided connected to the shared signal line, and the transmitting and receiving device is selected to transmit and receive signals, and the plurality of transmitting and receiving devices are connected to each other. A shared signal line for digital signals, characterized in that a resistor is connected to each connection point of the shared signal line, and the combined resistance value of the resistors is equivalent to the wave impedance of the shared signal line.