JPH1198197A - Characteristic impedance matching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To match automatically a characteristic impedance with a single circuit corresponding to a connected transmission medium. SOLUTION: An interface circuit section 11 taking impedance matching connects to a connector section 2 that is a connection place of an interface cable 1 generated by mismatching of impedance, a reflection waveform extract circuit section 15 extracts a prescribed pulse signal received from the connector section 2 via the interface circuit section 11 and an algorithm calculation circuit section 16 calculates a degree of mismatching from extracted waveform information based on a prescribed algorithm. The interface circuit section 11 is provided with a parameter variable element and applies automatic matching to its own characteristic parameter with respect to the connected computer cable 1 based on the calculation result. As a result, the characteristic impedance is automatically matched by at least one waveform extraction and processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a characteristic impedance matching circuit for matching a characteristic impedance with a transmission medium when connecting the transmission medium, and more particularly, to a characteristic impedance matching circuit corresponding to the connected transmission medium. The present invention relates to a characteristic impedance matching circuit capable of automatically matching.

[0002]

2. Description of the Related Art Generally, cables as transmission media include:
Even with a standard-compliant network, a plurality of types having different characteristic impedances are defined as connection targets, respecting the use of infrastructure in each country and region.
However, when the characteristic impedance of the network device is different from that of the cable, signal reflection occurs on the transmission path, and normal communication is hindered.

For this reason, in a network device constructed for existing equipment, the characteristic impedance of a cable to be connected is recognized in advance, and a characteristic impedance matching circuit is individually provided so as to obtain an interface characteristic matching the characteristic impedance. Setting is the mainstream, and there is a problem that the same device cannot always be used at any place.

In order to solve this problem, there is provided a device in which a plurality of resistors having different impedances are prepared in advance, and a desired resistance value is selected by external control including remote control to achieve impedance matching. There is.

[0005] In this method, too, the setting of the impedance is artificial and may be erroneous. In addition, in the transmission of a high-frequency signal, matching cannot be performed by setting only the resistance value, and it is difficult to manage in the frequency domain. There's a problem.

Techniques for solving these problems include, for example,
It is described in JP-A-60-1929.

This device has means for determining the impedance matching on the transmission line interface by itself. That is, this technique is a method of preparing a plurality of interface circuits having different characteristic impedances in a network device in advance, injecting, for example, a rectangular wave pulse from a transmitting side, and detecting an average value of a voltage waveform appearing on a receiving side. is there.

In this case, all the prepared interface circuits are sequentially switched, rectangular wave pulse injection and detection of the average value of the voltage waveform are performed in each of the interface circuits, and the minimum value among the detected values is detected. The interface circuit is automatically selected as the matched circuit.

[0009]

Among the above-mentioned conventional characteristic impedance matching circuits, the automatic matching circuit disclosed in the above-mentioned publication which solves the above-mentioned problem has the problem that the physical quantity and cost increase and the judgment time increases. There is. Furthermore,
There is a practical problem that a high resolution of impedance matching cannot be expected due to trade-offs between physical quantity, cost, determination time, and information storage capacity.

The reason is that it is necessary to prepare and match a plurality of similar interface circuits in the apparatus, so that a large amount of equipment is required due to the redundancy, and furthermore, it is necessary to measure and detect square wave pulses in each interface circuit. This is because pulse generation, pulse injection, voltage waveform potential detection, etc. are required and it takes a long time to make a final determination, and means for storing detection results for all interface circuits is required. This is because the resolution of impedance matching depends on the number of interface circuits.

An object of the present invention is to solve the above-mentioned problems and to provide a characteristic impedance matching circuit capable of automatically matching a characteristic impedance corresponding to each connected transmission medium with a single circuit.

[0012]

A characteristic impedance matching circuit according to the present invention is a characteristic impedance matching circuit for matching a characteristic impedance with a transmission medium when a transmission medium is connected. A reflected waveform generated by transmitting a predetermined pulse is extracted, and the degree of mismatch is calculated by a predetermined algorithm from the information of the extracted reflected waveform, while the characteristic parameter of the interface connected to the transmission medium is calculated by the algorithm. A matching unit is provided for automatically matching based on the result of the calculation.

Another characteristic impedance matching circuit extracts a waveform amplitude of a data signal input from a transmission medium and calculates a degree of mismatch from the extracted information of the waveform by a predetermined algorithm. There is provided matching means for automatically matching the characteristic parameters of the interface connected to the medium based on the result of the calculation.

According to these means, the degree of mismatch is calculated by a predetermined algorithm from the information of the waveform extracted by the circuit connected to the transmission medium, and the characteristic parameter of the interface connected to the transmission medium is added to the result of the calculation. Automatic matching based on a single circuit realizes matching.

In a specific characteristic impedance matching circuit, the former includes a pulse transmitting means for transmitting a predetermined pulse to a connection point of the transmission medium generated by impedance mismatch, and a reflected waveform for extracting a reflected waveform generated as a result. Extraction means, algorithm calculation means for calculating the degree of mismatch from the extracted information on the reflected waveform by a predetermined algorithm, and connection to the transmission medium and own characteristics for the transmission medium based on the calculation result Interface means for automatically matching parameters is provided.

The latter includes a signal level detecting means for extracting a waveform amplitude of a data signal inputted from the transmission medium, and an algorithm calculating means for calculating a degree of mismatch from the extracted waveform information by a predetermined algorithm. And interface means for connecting to the transmission medium and automatically matching its own characteristic parameter to the transmission medium based on the calculation result.

In both the former and the latter, the characteristic impedance with the transmission medium is matched by at least one waveform detection operation.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings.

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

In the characteristic impedance matching circuit shown in FIG. 1, a LAN device 10 having a connector section 2 for connecting an interface cable 1 as a transmission medium includes an interface circuit section 11, a register circuit section 12, an analog switch section 13, and a switch. It is assumed that a control circuit unit 14, a reflected waveform extraction circuit unit 15, an algorithm calculation circuit unit 16, and a pulse transmission circuit unit 17 are provided.

The interface circuit section 11 connects the interface cable 1 via the connector section 2 on the one hand,
On the other hand, the LSI is connected to the reflected waveform extraction circuit section 15 and the pulse transmission circuit section 17 via the analog switch section 13,
(Large scale integrated circuit) It is assumed that a parameter variable element such as a variable capacitor and a variable resistor is provided inside. The interface circuit unit 11 sets the characteristic impedance of the cable to be connected, such as the characteristic impedance, the drive circuit, and the sense circuit, based on the calculation result data received from the algorithm calculation circuit unit 16 to match the characteristic impedance. .

The interface circuit unit 11 stores the calculation result data received from the algorithm calculation circuit unit 16 in the register circuit unit 12, and stores the calculation result data at a predetermined time.
For example, it is assumed that the data held by polling the register circuit unit 12 is periodically taken out and the built-in parameter variable element is matched to the characteristic impedance of the interface cable 1 based on the data.

The analog switch section 13 connects the one interface circuit section 11 to the other reflected waveform extraction circuit section 15 and the pulse transmission circuit section 17, and makes the above connection by a switching control signal from the switching control circuit section 14. Shall be canceled.

Upon receiving the waveform information from the reflected waveform extraction circuit 15, the switching control circuit 14 instructs the analog switch 13 to release the connection, and transfers the received waveform information to the algorithm calculation circuit 16. Shall be.

The reflection waveform extraction circuit 15 receives the reflection signal generated at the connection point with the interface cable 1 in the connector 2 through the analog switch 13 and the interface circuit 11 by the pulse signal transmitted from the pulse transmission circuit 17. It is assumed that a waveform is extracted, and waveform information such as a potential level, a rise time, and a fall time of the waveform is recognized and output to the switching control circuit unit 14.

The algorithm calculation circuit unit 16 uses the waveform information received from the reflected waveform extraction circuit unit 15 via the switching control circuit unit 14 to calculate the interface cable 1 of the interface cable 1 by a correlation algorithm between the preset waveform information and the mismatch impedance. It is assumed that the characteristic impedance is specified and this calculation result data is sent to the interface circuit unit 11.

The pulse transmission circuit section 17 transmits a pulse signal to a transmission line connected to the interface cable 1 in the connector section 2 via the interface circuit section 11. In this case, the transmission line impedance for this transmission line is set in advance to a specific characteristic impedance,
If there is a difference between the characteristic impedance and the characteristic impedance of the interface cable 1, signal reflection occurs at the connection point, and the reflected wave is extracted by the reflected waveform extraction circuit unit 15.

Next, a processing procedure according to the first embodiment of the present invention will be described with reference to FIG. 1 and FIG.

First, when the processing is started, the pulse transmission circuit unit 1 is started.
7 is driven to generate and transmit a pulse (procedure S1), and the analog switch unit 13 is driven to connect a transmission path (procedure S2). As a result, the pulse is reflected by the connector unit 2 and a reflected signal is extracted by the reflected waveform extraction circuit unit 15 (procedure S3) and recognized as waveform information (procedure S4).

The recognized waveform information is released from the connection of the analog switch unit 13 by the switching control circuit unit 14 (step S5), and is further calculated by the algorithm calculation circuit unit 16 (step S6), and the characteristic impedance is specified. (Step S7). Next, the parameter of the variable element is set for the specified characteristic impedance for impedance matching in the interface circuit unit 11 (procedure S
8).

This processing flow is started each time the power of the LAN device 10 is turned on, or is repeatedly started at regular intervals by a watchdog timer to periodically detect the characteristic impedance of the connected cable. it can.

As described above, the interface circuit section 11 can periodically poll the contents stored in the register circuit section 12 to check the characteristic impedance.

Next, a second embodiment of the present invention will be described with reference to FIG.

In general, if the characteristic impedance of the cable is different, a difference occurs in the amplitude of the normal transmission data signal on the transmission line. For example, in the case of ATM-LAN (asynchronous transfer mode / local area network), 15
In the 5 Mbps UTP (unshielded twisted pair) cable interface and the 25 Mbps UTP cable interface, according to this standard, the amplitude of a signal on a transmission path is specified by a value depending on the characteristic impedance of a connection cable.

The second embodiment is a method of matching impedances by utilizing this difference.

In the characteristic impedance matching circuit shown in FIG. 2, the LAN device 20 having the connector section 2 for connecting the interface cable 1 as a transmission medium includes an interface circuit section 11, a register circuit section 12, an analog switch section 13, and a switch. The control circuit section 14, the received signal detection circuit section 25, and the algorithm calculation circuit section 26 are provided.

FIG. 2 is different from the first embodiment of FIG. 1 in that the pulse transmission circuit 17 of FIG. 1 is eliminated and a received signal detection circuit 25 is provided instead of the reflected waveform extraction circuit 15. That is, the algorithm of the algorithm calculation circuit unit 26 is different.

Components having the same functions as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The reception signal detection circuit 25 detects the amplitude of the data signal waveform received from the connection destination of the interface cable 1 via the connector 2, interface circuit 11, and analog switch 13, and performs switching control as waveform information. It is to be sent to the circuit section 14.

The algorithm calculation circuit 26 specifies the characteristic impedance of the interface cable 1 based on the received waveform information by a predetermined correlation algorithm between the level of the received data signal and the characteristic impedance of the cable. Shall be sent to

This processing flow is based on the analog switch unit 1
3 starts when a data signal is connected from the transmission line to the reception signal detection circuit unit 25 by the drive of the third embodiment. The subsequent procedure is almost the same as the procedure in the above-described first embodiment. The processing restarted in the first embodiment is also possible in the same manner as in the first embodiment.

As described above, since the algorithm calculation circuit unit specifies the characteristic impedance of the interface cable by the correlation algorithm based on the waveform information received via the connector unit to achieve the impedance matching of the interface circuit unit, the impedance mismatch is reduced. Automatic compensation becomes possible, and high-quality communication can be expected without the user being aware of the type of cable connected to the LAN device.

In the above description, the functional blocks and the processing procedure have been illustrated and described. For example, the waveform information may be directly transferred to the algorithm calculation circuit unit without passing through the switching control circuit unit. The calculation of the waveform information may be performed in parallel, for example, the separation and merging of the functions for the blocks or the change of the procedure are free as long as the above functions are satisfied, and the above description does not limit the present invention.

[0044]

As explained above, according to the present invention, the characteristic impedance of the interface cable is specified by the correlation algorithm based on the waveform information received by the algorithm calculation circuit unit through the connector unit, and the impedance matching of the interface circuit unit is performed. Therefore, the following effects can be obtained.

First, the first effect is that a user of the network device can match each other's impedance without special consideration of the characteristic impedance of the interface cable to be connected, and causes a communication failure such as reflection of a transmission line. High-quality communication in an optimal environment.

The second effect is that the user is not required to select a network device suitable for the characteristic impedance of the cable or to perform the complicated setting of the network device, which is unnecessary for the manufacturer. Since it is not necessary to commercialize a plurality of types of products whose impedance is specified, it is possible to reduce costs of design, manufacturing, and management, and to avoid trouble risks.

The third effect is that a change in the use environment of the cable due to the movement of the installation place or the replacement of the cable does not limit the use environment of the network device. Therefore, a highly flexible network configuration is possible.

The fourth effect is that the user does not need to detect and set the characteristic impedance of the cable,
Since the characteristic impedance can be obtained by one processing flow, a high-speed response can be expected, and
That is, a memory capacity for storing information can be reduced.

Further, in the present invention, since the parameters are changed by the variable elements in the interface circuit section which interfaces with the cable, the following effects can be obtained.

The fifth effect is that the redundancy of the circuit can be avoided.
That is, it is possible to contribute to downsizing of the device, cost reduction, and reduction of the failure rate.

The sixth effect is that, with a simple configuration having no redundancy, it is possible to easily cope with a demand for high resolution of characteristic impedance without requiring much overhead.

Further, according to the present invention, the following effects can be obtained because it is easy to periodically recognize the characteristic impedance of the connection cable in the processing flow.

That is, the seventh effect is that an unexpected cable change can be automatically dealt with without any problem.

In the second embodiment, the following effects can be obtained because there is no pulse transmission circuit.

That is, the eighth effect is that since unnecessary pulses are not generated in the network, the circuit has a simple circuit configuration and can perform impedance matching without affecting the network at all. is there.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing one embodiment of a main processing procedure in FIG.

FIG. 3 is a functional block diagram showing an embodiment of the present invention which is different from FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Interface cable 2 Connector part 10, 20 LAN device 11 Interface circuit part 12 Register circuit part 13 Analog switch part 14 Switching control circuit part 15 Reflection waveform extraction circuit part 16, 26 Algorithm calculation circuit part 17 Pulse transmission circuit part 25 Received signal level Detection circuit

Claims (9)

[Claims] 1. A characteristic impedance matching circuit for matching characteristic impedance between a transmission medium and a transmission medium when the transmission medium is connected to the transmission medium. Matching means for extracting and calculating a degree of mismatch from the information of the extracted reflected waveform by a predetermined algorithm, and automatically matching characteristic parameters of an interface connected to the transmission medium based on the result of the calculation. A characteristic impedance matching circuit characterized in that: 2. A characteristic impedance matching circuit for matching characteristic impedance with a transmission medium when a transmission medium is connected, extracting a waveform amplitude of a data signal input from the transmission medium, and extracting the extracted waveform. Characteristic impedance matching circuit, comprising a matching means for calculating a degree of mismatch from the information of the transmission medium by a predetermined algorithm, and automatically matching characteristic parameters of an interface connected to the transmission medium based on a result of the calculation. . 3. The characteristic impedance matching circuit according to claim 1, further comprising register means for holding said calculation result, wherein said matching means uses the calculation result held by said register means at a predetermined time. A characteristic impedance matching circuit for automatically matching characteristic parameters of the interface. 4. A characteristic impedance matching circuit for matching characteristic impedance with a transmission medium when connecting the transmission medium, wherein a pulse for transmitting a predetermined pulse to a connection place of the transmission medium generated due to impedance mismatch. Transmission means, reflection waveform extraction means for extracting a reflection waveform generated as a result, algorithm calculation means for calculating the degree of mismatch from the information on the extracted reflection waveform by a predetermined algorithm, and connection with the transmission medium Interface means for automatically matching its own characteristic parameter to the transmission medium based on the calculation result, and matching the characteristic impedance with the transmission medium by at least one reflected waveform detection operation. Characteristic impedance matching circuit. 5. A connector for connecting a cable of a transmission medium, a pulse transmitting circuit for generating and transmitting a predetermined pulse, and a pulse for connecting and transmitting the pulse transmitting circuit is connected to the cable by the connector. A reflection waveform extraction circuit for receiving and extracting a reflected waveform generated by the impedance mismatch, and outputting waveform information; and a pulse output from the pulse transmission circuit for passing and transmitting the pulse to the connector. An interface circuit unit that sets the parameters of the variable element based on instruction information received separately while automatically matching the characteristic impedance with the cable while passing the pulse reflected in the unit in the reverse direction; Unit, the other side of which is connected to the pulse sending circuit and the reflected waveform extracting circuit unit, and is controlled by a switching control signal. An analog switch unit for disconnecting the connection, a switching control circuit unit for receiving the waveform information and transmitting the switching control signal to the analog switch unit, and receiving the waveform information to determine a degree of mismatch with the cable. A characteristic impedance matching circuit, comprising: an algorithm calculation circuit unit that calculates by an algorithm and sends a calculation result to the interface circuit unit as the instruction information for the variable element. 6. A characteristic impedance matching circuit for matching characteristic impedance with a transmission medium when connecting the transmission medium, a signal level detecting means for extracting a waveform amplitude of a data signal input from the transmission medium, An algorithm calculating means for calculating the degree of mismatch from the extracted waveform information by a predetermined algorithm, and an interface for connecting to the transmission medium and automatically matching its own characteristic parameter to the transmission medium based on the calculation result Means for matching a characteristic impedance with the transmission medium by at least one waveform detection operation. 7. A connector for connecting a cable of a transmission medium, a reception signal level detection circuit for receiving and extracting waveform amplitude of a signal input from the cable via the connector, and outputting waveform information, An interface circuit unit for automatically setting the characteristic impedance between the cable and the parameter by setting the parameters of the variable element based on the instruction information received separately, and connecting and switching the interface circuit unit on one side and the reception signal level detection circuit unit on the other side An analog switch unit that disconnects the connection by a control signal, a switching control circuit unit that receives the waveform information and sends the switching control signal to the analog switch unit, and a degree of mismatch with the cable that receives the waveform information. Is calculated by a predetermined algorithm, and the calculation result is used as instruction information for the variable element. A characteristic impedance matching circuit, comprising: an algorithm calculation circuit for sending to the base circuit. 8. The characteristic impedance matching circuit according to claim 4, further comprising a register circuit for receiving and holding the instruction information for the variable element, wherein the interface circuit includes: A characteristic impedance matching circuit, wherein the instruction information held by the register section is taken out at a predetermined time, and the parameters of the variable element are reset. 9. A characteristic impedance matching circuit according to claim 1, wherein a waveform amplitude of an input signal is extracted, and a degree of mismatch is determined from information of the extracted waveform. The characteristic impedance matching circuit, wherein the procedure for automatically matching characteristic parameters of an interface based on a result calculated by a predetermined algorithm is automatically started at a predetermined time and repeated.