JP2001127740A - Bidirectional signal transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bidirectional signal transmission system with low power consumption (low power). SOLUTION: The bidirectional signal transmission system is equipped with a transmitter receiver 10, a transmitter receiver 20, and a transmission line 30 which connects the transmitter receivers 10 and 20 to each other. The transmitter receiver 10 is equipped with a constant-current circuit 12 which outputs a current having a quantity varying with the logical level of a signal IN1 and a current difference compensating circuit 14 which compensates the difference between the current flowing out of the constant current circuit 12 and a current flowing through a transmission line 30. The transmitter receiver 20 has a constant current circuit 22 in which a current having a quantity varying with the logical level of a signal IN2 flows and a current difference compensating circuit 24 which compensates the difference between the current flowing in the constant current circuit 22 and the current flowing through the transmission line 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission system for transmitting signals simultaneously and bidirectionally between two transmission / reception devices.

[0002]

2. Description of the Related Art Conventionally, as a system for transmitting a signal simultaneously and bidirectionally between two ports, a system described in the following literature is known.

[0003] 1 Gb / s Current Mode
Bidirectional I / O buffer
r ", 1997 Symposium on VSLI
Circuits Digest of Techn
FIG. 6 shows a configuration of a conventional system described in the above-mentioned document.

[0004] The transmitting side of each port transmits signals IN1, IN2.
Switches on and off according to the logic level of Thereby, the current flowing from the constant current circuit to the transmission line Zo is controlled.

[0005] From the port of the chip CHIP1 to the transmission line Z
at the same time as the signal is transmitted to the port of the chip CHIP2 through the transmission line Z
A signal is transmitted to the chip CHIP1 via o.

Table 1 shows the operation of the conventional system shown in FIG.

[0007]

[Table 1] As shown in Table 1, the receiving side of each port is connected to the node O
1 and the voltage of the node O2,
The logical level of the signal transmitted from the transmitting side of each port is determined.

[0008]

The above-described conventional system has the following problems (1) and (2).

(1) Large power consumption. For example, when each of the ports transmits the signals IN1 and IN2 at the logical level "1"("high"), the current of 4 * I flowing out of the four constant current sources is consumed. Here, I indicates a current flowing from one constant current source. In particular, it is a serious problem that the power consumption increases as the number of ports operated simultaneously increases.

[0010] (2) the direction of the current I ₃ flowing through the transmission line Zo varies in accordance with the logic level of the signal to be transmitted. When the direction of the current I ₃ is changed, it is difficult to suppress the electromagnetic radiation generated around the transmission line Zo. Further, when the direction of the current I ₃ varies, if must flow a current from the low side of the power supply potential to the high side of the power supply potential is generated. This is because when a power supply potential is supplied to each port via a power supply line, a voltage drop occurs due to the resistance of the power supply line. It is very difficult to flow a current from a lower power supply potential to a higher power supply potential because it is contrary to natural principles.

The present invention has been made in view of the above problems, and (1) to provide a bidirectional signal transmission system with low power consumption (low power); and (2) the direction of current flowing through a transmission line. It is an object of the present invention to provide a bidirectional signal transmission system that does not change according to the logic level of a signal transmitted.

[0012]

A bidirectional signal transmission system according to the present invention comprises a first transmission / reception device, a second transmission / reception device, and a transmission line connecting the first transmission / reception device and the second transmission / reception device. A bidirectional signal transmission system, wherein the first transmission / reception device transmits a first signal to the second transmission / reception device while the second transmission / reception device transmits a second signal to the first transmission / reception device, A first transmitting / receiving device configured to output a current having an amount that varies according to a logical level of the first signal; a current flowing out of the first constant current circuit and a current flowing through the transmission line; And a first current difference compensating circuit for compensating for the difference between the second constant current circuit and the second constant current circuit. , The second constant current circuit And a second current difference compensation circuit for compensating the difference between the current which the current flows through the transmission line, thereby the objective described above being achieved.

The difference between the current flowing out of the first constant current circuit and the current flowing in the first current difference compensating circuit is:
It is preferable that the difference between the current flowing out of the second current difference compensating circuit and the current flowing into the second constant current circuit is larger than the difference.

A power supply potential is supplied to the first transceiver and the second transceiver via a power line.
The direction in which the voltage of the power supply line drops is preferably the same as the direction in which the current flows through the transmission line.

[0015] The bidirectional signal transmission system may be configured to reduce a current consumption in the bidirectional signal transmission system to the first signal.
The power supply apparatus may further include a current consumption stabilizing circuit for keeping the current consumption constant without depending on the logic levels of the signal and the second signal.

[0016] Another bidirectional signal transmission system of the present invention comprises:
A first transmission / reception device, a bidirectional signal transmission system that performs signal transmission between a second transmission / reception device, wherein the bidirectional signal transmission system includes a plurality of transmission units, and each of the plurality of transmission units includes: A transmission line connecting the first transceiver and the second transceiver;
At the same time as transmitting the first signal from the transmitting / receiving device to the second transmitting / receiving device, transmitting the second signal from the second transmitting / receiving device to the first transmitting / receiving device, regardless of the values of the first signal and the second signal. From the first transmitting / receiving device to the second
Of the first direction toward the transmitting / receiving device and the second direction from the second transmitting / receiving device to the first transmitting / receiving device, any one of predetermined directions for each of the plurality of transmission units. Generating a current on the transmission line, and, among a plurality of transmission units included in the bidirectional signal transmission system, the number of transmission units for generating the current in the first direction on the transmission line; The number of transmission units that generate a direction current on the transmission line is substantially equal, thereby achieving the above object.

Each of the plurality of transmission units includes a first constant current circuit that outputs a current having an amount that varies according to a logic level of the first signal, and a current that flows out of the first constant current circuit. A first current difference compensating circuit for compensating for a difference from a current flowing through the transmission line; a second constant current circuit into which a current having an amount varying according to a logical level of the second signal flows; A second circuit for compensating for a difference between the current flowing into the current circuit and the current flowing in the transmission line.
A current difference compensation circuit, wherein the first constant current circuit and the first current difference compensation circuit are respectively connected to the first transmission / reception device side of the transmission line, and the second constant current circuit And the second current difference compensating circuit may be connected to the transmission line on the side of the second transceiver.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a configuration of a bidirectional signal transmission system 1 according to Embodiment 1 of the present invention.

The bidirectional signal transmission system 1 includes a transmitting / receiving device 10 as a first transmitting / receiving device, a transmitting / receiving device 20 as a second transmitting / receiving device, the transmitting / receiving device 10 and the transmitting / receiving device 20
And a transmission line 30 that connects

In the bidirectional signal transmission system 1, the transmission / reception device 10 transmits the signal IN1 having a logical level of "0" or "1" to the transmission / reception device 20 via the transmission line 30, and at the same time, the transmission / reception device 20 transmits "1". 0 ”or“
A signal IN2 having a logical level of 1 ″ is transmitted to the transmission / reception device 10 via the transmission line 30.

In the following description, the logic level is "0".
Corresponds to “low”, and the logic level “1” corresponds to “high”.
h), but this correspondence may be reversed, ie the logic level "0" changes to "hi".
gh ”, and the logic level“ 1 ”may correspond to“ low ”.

The transmission / reception device 10 includes a constant current circuit 12 as a first constant current circuit and a current difference compensation circuit 14 as a first current difference compensation circuit.

The constant current circuit 12 outputs a current having an amount that varies according to the logic level (ie, “0” or “1”) of the signal IN1 transmitted from the transmitting / receiving device 10 to the transmitting / receiving device 20. For example, the signal I of the logic level “0”
When transmitting N1, the constant current circuit 12 outputs a current of I (mA), and when transmitting the signal IN1 of the logical level "1", the constant current circuit 12 outputs a current of 2 * I (mA). leak. Here, I is an arbitrary number.

The function of the constant current circuit 12 is, for example, as shown in FIG.
This is achieved by configuring the constant current circuit 12 to include the constant current source 12b of a and I (mA) and the switch 12c. One end of the constant current source 12a is connected to the power supply potential V _CC , and the other end is connected to the transmission line 30 via the switch 12c.
It is connected to the. One end of the constant current source 12b is connected to the power supply potential V
_The other end is connected to the transmission line 30. The power supply potential V _CC is, for example, 1.5V.

When transmitting the signal IN1 of the logic level "0", the switch 12c is turned off. As a result, the current of I (mA) output from the constant current source 12b flows out of the constant current circuit 12. When transmitting the signal IN1 of the logic level "1", the switch 12c is turned on. As a result, the current I (mA) output from the constant current source 12a and the current I (mA) output from the constant current source 12b are output.
A total current of 2 * I (mA) including the current of (mA) flows out of the constant current circuit 12.

The current difference compensating circuit 14 compensates for the difference between the current flowing out of the constant current circuit 12 and the current flowing through the transmission line 30 by controlling the current I ₁ .

The transmission / reception device 20 includes a constant current circuit 22 as a second constant current circuit and a current difference compensation circuit 24 as a second current difference compensation circuit.

The constant current circuit 22 receives a current having an amount that changes according to the logic level (ie, “0” or “1”) of the signal IN 2 transmitted from the transmitting / receiving device 20 to the transmitting / receiving device 10. For example, when transmitting the signal IN2 of the logic level “0”, the constant current circuit 22 receives 1.5 *
A current of I (mA) flows, and the signal I of the logic level "1"
When transmitting N2, the constant current circuit 22 has 2 * I (m
The current of A) flows. Here, I is an arbitrary number.

Such a function of the constant current circuit 22 is, for example, as shown in FIG. 1 by a constant current source 22a of 1.5 * I (mA) and a constant current source of 0.5 * I (mA). This is achieved by configuring the constant current circuit 22 to include the switch 22c and the switch 22c. One end of the constant current source 22 a is connected to the ground potential V _SS , and the other end is connected to the transmission line 30. One end of the constant current source 22b is connected to the ground potential V _SS , and the other end is connected to the transmission line 30 via the switch 22c. The ground potential V _SS is, for example, 0 V
It is.

When transmitting the signal IN2 of the logic level "0", the switch 22c is turned off. Thus, a current of 1.5 * I (mA) flowing into the constant current source 22a flows into the constant current circuit 22. When transmitting the signal IN2 of the logical level "1", the switch 22c is turned on. As a result, a total of 2 * I (m) is obtained by adding the current of 1.5 * I (mA) flowing into the constant current source 22a and the current of 0.5 * I (mA) flowing into the constant current source 22b.
The current A) flows into the constant current circuit 22.

The current difference compensating circuit 24 compensates for the difference between the current flowing into the constant current circuit 22 and the current flowing through the transmission line 30 by controlling the current I ₂ .

Table 2 shows the operation of the bidirectional signal transmission system 1.

[0034]

[Table 2] In Table 2, IN1 represents the logic level of a signal transmitted from the transceiver 10 to the transceiver 20, IN2 denotes the logic level of a signal transmitted from the transceiver 20 to the transceiver 10, I ₁ is a current difference compensation A current flowing into the circuit 14 is shown, I ₂ is a current flowing out of the current difference compensating circuit 24, and I ₃ is a current flowing through the transmission line 30.

The logic level of the signal IN1 is "1"("hi").
gh ") and the logic level of the signal IN2 is"
1 "(" high "), the switch 12c
Is turned on, and the switch 22c is turned on. In this case, 2 * I flowing out of the constant current circuit 12
(MA) current flows through the transmission line 30 and the constant current circuit 22
Flows into. Therefore, I ₁ = 0, I ₂ = 0, I ₃ = 2 * I
(MA).

The logic level of the signal IN1 is "1"("hi").
gh ") and the logic level of the signal IN2 is"
When it is 0 "(" low "), the switch 12c is turned on and the switch 22c is turned off, in this case, 2 * I (m) flowing out of the constant current circuit 12.
Of the current A), a current of 0.5 * I (mA) flows into the current difference compensating circuit 14, and a current of 1.5 * I (mA) flows into the constant current circuit 22 through the transmission line 30. . Therefore,
I ₁ = 0.5 * I (mA), I ₂ = 0, I ₃ = 1.5 * I
(MA).

The logic level of the signal IN1 is "0"("lo").
w ”), and the logic level of the signal IN2 is“ 1 ”.
In the case of ("high"), the switch 12c is turned off and the switch 22c is turned on. In this case, I (mA) flowing out of the constant current circuit 12
-0.5 * I flowing into the current difference compensating circuit 14
A total current of 1.5 * I (mA) including the current of (mA) (ie, the current of 0.5 * I (mA) flowing out of the current difference compensation circuit 14) flows through the transmission line 30. A total current of 2 * I (mA), which is the sum of 1.5 * I (mA) flowing through the transmission line 30 and 0.5 * I (mA) flowing out of the current difference compensating circuit 24, is constant. Current circuit 2
Flow into 2. Therefore, I ₁ = −0.5 * I (mA),
I ₂ = 0.5 * I (mA) and I ₃ = 1.5 * I (mA).

The logic level of the signal IN1 is "0"("lo").
w ”), and the logic level of the signal IN2 is“ 0 ”.
In the case of ("low"), the switch 12c is turned off and the switch 22c is turned off.
In this case, the current of I (mA) flowing out of the constant current circuit 12 flows through the transmission line 30. I flowing through the transmission line 30
(MA) and the current of 0.5 * I (mA) flowing out of the current difference compensation circuit 24, for a total of 1.5 * I
The current of (mA) flows into the constant current circuit 22. Therefore,
I ₁ = 0, I ₂ = 0.5 * I (mA), I ₃ = I (mA)
It is.

The current consumption in the bidirectional signal transmission system 1 is determined by the current flowing out of the constant current circuit 12 and the constant current circuit 2
2, which is the larger of the currents flowing into the second. Therefore, the maximum current consumption is 2 * I (mA) (see Table 2). on the other hand,
The current consumption in the conventional system shown in FIG. 6 is the sum of the current flowing out of the constant current circuit of each port. Therefore, the maximum current consumption is 4 * I (mA). Thus, according to the bidirectional signal transmission system 1 of the present invention,
As compared with the conventional system shown in FIG. 6, an effect that power consumption can be significantly reduced can be obtained.

The logic level of the signal IN1 and the signal IN2
Irrespective of the combination of the logic levels of
₃ flows through the transmission line 30 in a single direction (that is, a direction from the transmission / reception device 10 to the transmission / reception device 20). This is because the difference (I ₃ ) between the current flowing out of the constant current circuit 12 and the current flowing into the current difference compensating circuit 14 is the difference between the current flowing out of the current difference compensating circuit 24 and the current flowing into the constant current circuit 22. This is because the difference is larger than the difference (−I ₃ ).

The power supply circuit 80 supplies the power supply potential V _CC to the transmission / reception device 10 and the transmission / reception device 20 via the power supply line 40. Although not shown in FIG. 1, the power supply line 40 is connected to the power supply potential V _CC in the constant current circuit 12, the current difference compensation circuit 14, and the current difference compensation circuit 24. In FIG. 1, an arrow ΔV indicates a direction in which the voltage of the power supply line 40 drops.

The power supply line 40 is preferably arranged such that the direction in which the voltage of the power supply line 40 decreases matches the direction of the current I ₃ flowing through the transmission line 30. In the case where the direction of the current I ₃ the voltage of the power supply line 40 flows through direction and the transmission line 30 to drop the power supply line 40 is arranged so as to coincide,
The effect is obtained that the signal transmission between the transmission / reception device 10 and the transmission / reception device 20 is hardly affected by the voltage drop in the power supply line 40.

Table 3 is used in the transmitting / receiving device 10 to determine the logical level of the signal IN2 transmitted from the transmitting / receiving device 20.

[0044]

[Table 3] Logic level of the signal IN2 is represented by the direction and magnitude of the current I ₁ flowing to the current difference compensation circuit 14.
Therefore, by detecting the direction and magnitude of the current I ₁ in the transmission and reception device 10, it is possible to determine the logic level of the signal IN2. Direction and magnitude of the current I ₁ may be converted to a voltage level of the voltage V _out1 output from the current difference compensation circuit 14. Therefore, the logic level of the signal IN2 can be determined by detecting the voltage level of the voltage V _out1 in the transmitting / receiving device 10.

Table 4 is used in the transmitting / receiving device 20 to determine the logical level of the signal IN1 transmitted from the transmitting / receiving device 10.

[0046]

[Table 4] Logic level of the signal IN1 is represented by the magnitude of the current I ₂ flowing out of the current difference compensation circuit 24. Therefore,
By detecting the magnitude of the current I ₂ in the transmitting and receiving device 20, it is possible to determine the logic level of the signal IN1. The magnitude of the current I ₂ can be converted to the voltage level of the voltage V _out2 output from the current difference compensation circuit 24. Therefore, the logic level of the signal IN1 can be determined by detecting the voltage level of the voltage V _out2 in the transmitting / receiving device 20.

As described above, when the logic level of the signal IN1 transmitted from the transmission / reception device 10 to the transmission / reception device 20 is the same, the signal IN1 changes according to the logic level of the signal IN2 transmitted from the transmission / reception device 20 to the transmission / reception device 10. By detecting the amount of current in the transmitting and receiving device 10, it becomes possible for the transmitting and receiving device 10 to determine the logical level of the signal IN <b> 2.

Similarly, when the signal IN2 transmitted from the transmission / reception device 20 to the transmission / reception device 10 has the same logical level, the signal IN2 changes according to the logic level of the signal IN1 transmitted from the transmission / reception device 10 to the transmission / reception device 20. By detecting the amount of current in the transmitting and receiving device 20, it becomes possible for the transmitting and receiving device 20 to determine the logical level of the signal IN <b> 1.

This enables the signal IN1 and the signal IN2 to be transmitted simultaneously and bidirectionally between the transmitting / receiving device 10 and the transmitting / receiving device 20.

FIG. 2A shows a configuration example of the current difference compensating circuit 14. In the current difference compensating circuit 14, the logic level of IN1 is "
high ", 0 (mA) to + 0.5 * I
And is configured to provide a compensation current I ₁ in the range of (mA), if the logic level of the IN1 is "low" is in the range from -0.5 * I (mA) 0 of (mA) To provide a compensation current I ₁ .

The current difference compensating circuit 14 comprises a constant current source 14a of I (mA), a transistor 14b,
4c and a comparator 14d. Transistor 1
4b sets the current flowing through the transistor 14b to 0.5 * I
(MA). The comparator 14d is used to detect a voltage across the transistor 14b.

FIG. 2B shows a configuration example of the current difference compensating circuit 24. The current difference compensating circuit 24 outputs 0 (mA) to +0.5
It is configured to provide a compensation current I ₂ within the range of * I (mA).

The current difference compensating circuit 24 includes a constant current source 24a of I (mA), a transistor 24b,
4c and a comparator 24d. Transistor 2
4b sets the current flowing through the transistor 24b to 0.5 * I
(MA). The comparator 24d is used to detect a voltage across the transistor 24b.

(Embodiment 2) FIG. 3 shows a configuration of a bidirectional signal transmission system 2 according to Embodiment 2 of the present invention.

The bidirectional signal transmission system 2 includes, in addition to the components included in the bidirectional signal transmission system 1 (FIG. 1),
It further includes a current consumption stabilizing circuit 50.

In FIG. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 3, the current consumption stabilizing circuit 50 includes a constant current source 50a of 0.5 * I (mA), a switch 50b, a switch 50c, and a 0.5 * I (m
A) the constant current source 50d. One end of the constant current source 50a is connected to the power supply potential V _CC , and the other end is connected to the switch 50.
It is connected to the transmission line 30 via b. Constant current source 5
One end of Od is connected to the ground potential V _SS , and the other end is connected to the transmission line 30 via the switch 50c.

The logic level of the signal IN2 is "0"("lo").
w "), and the voltage level of the voltage _Vout2 is" lo ".
w ", switch 50b and switch 5
0c is turned on. In other cases, the switches 50b and 50c are turned off.

When the switches 50b and 50c are on, the constant current source 50a
A current of 0.5 * I (mA) flows toward 0d. As a result, the current consumption increases by 0.5 * I (mA).

As described above, the current consumption stabilizing circuit 50
The logic level of the signal IN1 is “0” (“low”), and the logic level of the signal IN2 is “0” (“low”).
w "), the current consumption is 2 * I (mA).

Table 5 shows the operation of the bidirectional signal transmission system 2.

[0062]

[Table 5] Referring to Table 5, the logic level of the signal IN1 is "
0 "(" low ") and the logic level of the signal IN2 is" 0 "(" low "), the current consumption is 2
* I (mA) is found.

As described above, by using the current consumption stabilizing circuit 50, the current consumption stabilizing circuit 50 is not dependent on the combination of the logic level of the signal IN1 and the logic level of the signal IN2.
The current consumption can be made constant (that is, 2 * I (mA)). The fact that the current consumption is constant means that the power supply line 40
Means that the current flowing through is constant. Thus, it is possible to suppress the voltage fluctuation of the power supply line 40 caused by the current fluctuation. As a result, an effect that the power supply is stabilized can be obtained. Further, an effect that electromagnetic radiation is not generated through the power supply line 40 can be obtained.

Although power consumption stabilizing circuit 50 is provided inside transmitting / receiving device 20 in the example shown in FIG. 3, the arrangement of power consumption stabilizing circuit 50 is not limited to this.

(Embodiment 3) FIG. 4 shows a configuration of a bidirectional signal transmission system 3 according to Embodiment 3 of the present invention.

In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The bidirectional signal transmission system 3 includes a transmission / reception device 10, a transmission / reception device 20, and transmission lines 30 and 31 connecting the transmission / reception device 10 and the transmission / reception device 20. The transmission lines 30 and 31 are arranged so as to be adjacent to each other.

In the bidirectional signal transmission system 3, the transmission / reception device 10 transmits the signal IN1 having the logical level of “0” or “1” to the transmission / reception device 20 via the transmission line 30, and at the same time, the transmission / reception device 20 transmits “1”. 0 ”or“
The signal IN2 having the logical level of "1" is transmitted to the transmitting / receiving apparatus 10 via the transmission line 30. Further, the transmitting / receiving apparatus 20 transmits the signal I having the logical level of "0" or "1".
At the same time as transmitting N3 to the transmission / reception device 10 via the transmission line 31, the transmission / reception device 10 transmits a signal IN4 having a logical level of "0" or "1" to the transmission / reception device 20 via the transmission line 31.

Transmitting / receiving apparatus 10 further includes a constant current circuit 62 and a current difference compensation circuit 64 in addition to constant current circuit 12 and current difference compensation circuit 14. The configuration and operation of the constant current circuit 62 and the current difference compensation circuit 64 are the same as those of the first embodiment.
This is the same as the configuration and operation of the constant current circuit 22 and the current difference compensation circuit 24 described in.

The transmission / reception device 20 further includes a constant current circuit 72 and a current difference compensation circuit 74 in addition to the constant current circuit 22 and the current difference compensation circuit 24. The configurations and operations of the constant current circuit 72 and the current difference compensating circuit 74 are described in the first embodiment.
This is the same as the configuration and operation of the constant current circuit 12 and the current difference compensation circuit 14 described above.

The logic level of the signal IN1 and the signal IN2
Irrespective of the combination of the logic levels of
₃ flows in a single direction (that is, a direction from the transmitting / receiving device 10 to the transmitting / receiving device 20). Independent of the combination of the logic level of signal IN3 and the logic level of signal IN4, current I ₆ is in a single direction (ie,
(The direction from the transmitting / receiving device 20 toward the transmitting / receiving device 10).

As described above, by flowing the currents I ₃ and I ₆ in the opposite directions, the electromagnetic fields around the transmission lines 30 and 31 can be canceled each other. This makes it possible to suppress voltage fluctuations in the transmission lines 30 and 31.

FIG. 4 shows the transmitting / receiving apparatus 10 and the transmitting / receiving apparatus 20.
In this example, there are two transmission lines (transmission lines 30 and 31). However, in the bidirectional signal transmission system of the present invention, the number of transmission lines between the transmission / reception device 10 and the transmission / reception device 20 is not limited to this.

FIG. 5 shows the transmitting / receiving apparatus 10 and the transmitting / receiving apparatus 20.
2 shows a configuration of a bidirectional signal transmission system 4 in which four transmission lines (transmission lines 30 to 33) are provided. The bidirectional transmission system 4 includes a plurality of transmission units 401 to 404. The transmission units 401 and 402 respectively correspond to FIG.
Has the same configuration as the portions indicated by reference numerals 401 and 402. The transmission unit 403 includes the transmission unit 4
01, and the transmission unit 404 has the same configuration as the transmission unit 402. Transmission unit 40
1 to 404 have transmission lines 30 to 33, respectively.
Each of the transmission units 401 to 404 performs bidirectional signal transmission between the transmission / reception device 10 and the transmission / reception device 20.

As already described with reference to FIG. 4, the currents (currents I ₃ and I ₉ ) flowing through the transmission lines included in each of the transmission units 401 and 403 are transmitted and received by the transmission / reception device 10 by the respective transmission units. And transceiver 2
The signal flows in a single direction (a direction from the transmission / reception device 10 to the transmission / reception device 20: a first direction) without depending on a combination of logic levels of signals transmitted between the transmission and reception devices. Similarly, currents (current I ₆ and current I ₁₂ ) flowing through the transmission lines included in the transmission units 402 and 404, respectively.
Is a single direction (a direction from the transmission / reception device 20 to the transmission / reception device 10: the first direction) without depending on a combination of logical levels of signals transmitted between the transmission / reception devices 10 and 20 by the respective transmission units. 2 direction)
Flows to

As described above, when the number of transmission units included in the bidirectional transmission system is plural, the number of transmission units having transmission lines in which current flows in the first direction and the number of transmission units in which current flows in the second direction are determined. By making the number of transmission units having lines substantially equal, the electromagnetic fields around the plurality of transmission lines can cancel each other. This makes it possible to suppress voltage fluctuations in the transmission line. "Make substantially equal" means that the number of transmission units having transmission lines through which current flows in the first direction is completely equal to the number of transmission units having transmission lines through which current flows in the second direction. Not only that, if the number of transmission units included in the bidirectional transmission system is odd,
It also means that the number of transmission units having transmission lines through which current flows in the first direction and the number of transmission units having transmission lines through which current flows in the second direction are made as equal as possible.

When a plurality of transmission lines 30 to 33 are bundled on the same wiring, each transmission line may have a twisted configuration. Further, the space between the transmission lines may be shielded.

[0078]

According to the bidirectional signal transmission system of the present invention, the difference between the current flowing out of the first constant current circuit and the current flowing through the transmission line is compensated by the first current difference compensating circuit, and the second current difference is compensated. The difference between the current flowing into the second constant current circuit and the current flowing through the transmission line is compensated by the compensation circuit. This makes it possible to provide a low power consumption (low power) bidirectional signal transmission system. further,
According to the bidirectional signal transmission system of the present invention, the difference between the current flowing out of the first constant current circuit and the current flowing in the first current difference compensating circuit is the difference between the current flowing out of the second current difference compensating circuit and the second current. It is larger than the difference from the current flowing into the constant current circuit.
Thereby, the direction of the current flowing through the transmission line can be made a single direction without depending on the combination of the logic level of the first signal and the logic level of the second signal. Further, according to the bidirectional signal transmission system of the present invention, the direction in which the voltage of the power supply line drops is the same as the direction in which current flows in the transmission line. Thus, an effect is obtained that the signal transmission between the first transmission / reception device and the second transmission / reception device is hardly affected by the voltage drop in the power supply line.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a bidirectional signal transmission system 1 according to a first embodiment of the present invention.

FIG. 2A is a diagram showing a configuration example of a current difference compensation circuit 14;

FIG. 2B is a diagram showing a configuration example of a current difference compensation circuit 24;

FIG. 3 is a diagram showing a configuration of a bidirectional signal transmission system 2 according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a bidirectional signal transmission system 3 according to a third embodiment of the present invention.

FIG. 5 shows a configuration of a bidirectional signal transmission system 4 in which four transmission lines are provided between the transmission / reception device 10 and the transmission / reception device 20.

FIG. 6 is a diagram showing a configuration of a conventional system.

[Explanation of symbols]

 1, 2, 3 bidirectional signal transmission system 10, 20 transmission / reception device 12, 22, 62, 72 constant current circuit 14, 24, 64, 74 current difference compensation circuit 30 to 33 transmission line 40 power supply line 50 current consumption stabilization circuit 401-404 transmission unit

Claims (6)

[Claims] A first transmitting / receiving device, a second transmitting / receiving device,
A transmission line connecting the first transceiver and the second transceiver, wherein the first transceiver transmits a first signal to the second transceiver, and the second transceiver transmits a second signal. A first constant current circuit that outputs a current having an amount that varies according to a logic level of the first signal. A first current difference compensating circuit for compensating for a difference between the current flowing out of the first constant current circuit and a current flowing in the transmission line, wherein the second transmitting / receiving device has a logic of the second signal. A second constant current circuit into which a current having an amount varying with the level flows, and a second current difference compensating circuit for compensating for a difference between the current flowing into the second constant current circuit and a current flowing through the transmission line. Has Bidirectional signal transmission system. 2. The difference between the current flowing out of the first constant current circuit and the current flowing into the first current difference compensating circuit is the difference between the current flowing out of the second current difference compensating circuit and the second constant current. Greater than the difference from the current flowing into the circuit,
The bidirectional signal transmission system according to claim 1. 3. A power supply potential is supplied to the first transmission / reception device and the second transmission / reception device via a power supply line, and the voltage of the power supply line decreases in a direction in which the current flows through the transmission line. 3. The bidirectional signal transmission system according to claim 2, wherein the flow direction is the same. 4. The circuit according to claim 1, further comprising a current consumption stabilizing circuit for keeping the current consumption in said bidirectional signal transmission system constant without depending on the logic levels of said first signal and said second signal. A two-way signal transmission system as described. 5. A bidirectional signal transmission system for performing signal transmission between a first transmission / reception device and a second transmission / reception device, wherein the bidirectional signal transmission system includes a plurality of transmission units; Each of the units has a transmission line connecting the first transceiver and the second transceiver, and the first transceiver is connected to the second transceiver by the first transceiver.
Transmitting a second signal from the second transmitting / receiving device to the first transmitting / receiving device at the same time as transmitting the signal; and transmitting the second transmitting / receiving signal from the first transmitting / receiving device regardless of the values of the first signal and the second signal. A first direction toward the device, and a second direction from the second transceiver to the first transceiver.
Of the plurality of transmission units, a current in one of predetermined directions for each of the plurality of transmission units is generated on the transmission line, and among the plurality of transmission units included in the bidirectional signal transmission system, A bidirectional signal transmission system, wherein the number of transmission units that generate a current in a first direction on a transmission line is substantially equal to the number of transmission units that generate a current in the second direction on a transmission line. 6. Each of the plurality of transmission units includes: a first constant current circuit that outputs a current having an amount that varies according to a logic level of the first signal; and the first constant current circuit that flows out of the first constant current circuit. A first current difference compensation circuit for compensating for a difference between a current and a current flowing through the transmission line; a second constant current circuit into which a current having an amount that varies according to a logic level of the second signal flows; (2) a second current difference compensation circuit for compensating for a difference between the current flowing into the constant current circuit and the current flowing through the transmission line, wherein the first constant current circuit and the first current difference compensation circuit are The second constant current circuit and the second current difference compensating circuit are connected to the transmission line on the side of the second transceiver, respectively. Claim 5 On-board bidirectional signal transmission system.