JPS6361815B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC-coupled balanced bus matched termination method, particularly a DC-coupled balanced bus matched termination method in a DC-coupled balanced bus circuit in which one or more transmitting circuits and receiving circuits are connected to the same balanced transmission path. Regarding.

The DC-coupled balanced bus circuit is widely used in information processing devices and the like when transferring information between one or more transmitting circuits and receiving circuits.

Figure 1 is a diagram showing an example of a conventional DC-coupled balanced bus circuit.
DV and receiving circuit RC are connected to balanced transmission line B,
Information is transferred via the balanced transmission path B. Further, the balanced transmission line B is terminated at both ends by a terminating resistor R1, and the terminating resistor R1 is matched equally to the characteristic impedance Zb between the two balanced transmission lines,
This prevents reflected waves from being generated at both ends of the balanced transmission line B with respect to the signal sent out from the transmitting circuit DV. However, no consideration is given to matching with respect to the characteristic impedance Zu between the two lines of the balanced transmission line B. Here, when a signal is transmitted over a short distance using the balanced transmission line B, the reflected waves generated between the two wires of the balanced transmission line B and the ground generally do not pose a problem. However, in the case of long-distance transmission, large noise (called common mode noise) is generated, especially due to external noise and fluctuations in ground voltage between devices.
This common mode noise is reflected by the resistances R ₂ and R ₃ of the balanced transmission line B, which is not matched terminated between the two lines and the ground, and remains as a standing wave throughout the balanced transmission line B.
Passes through the transmission circuit DV.

FIG. 2 shows the output characteristics of the transmitting circuit DV. In the figure, two output voltages “H” of the transmitting circuit DV,
When both "L" (see FIG. 1) are in the +Vo region, that is, in the positive region, the output impedance is high, so even if a standing wave passes through this circuit, no reflected wave is generated from this circuit. However, when in the -Vo region, this circuit has a low output impedance, so when a standing wave passes through this circuit, a reflected wave is generated from this circuit.

Here, the output voltages "H" and "L" of the transmitting circuit DV fluctuate up and down as shown by the arrows due to the above standing wave.
If it enters the −Vo region, the output voltage “L”
Reflected waves are generated only for

In other words, each time a standing wave passes through the transmitting circuit DV, an unbalanced reflected wave is generated, but this unbalanced reflected wave is output as is when the voltage difference between the two wires is extracted as a signal, so it cannot be extracted. The signal-to-noise ratio of the transmitted signal deteriorates, preventing accurate transfer of information.

Furthermore, when the output impedance of all the transmitting circuits DV becomes high, the received differential input voltage to the receiving circuit RC becomes 0, so the output of the receiving circuit RC becomes undefined. In order to prevent such an indefinite state,
In a conventional DC-coupled balanced bus circuit, a measure as shown in FIG. 3 has been taken. In Figure 3, the resistor R1 at both ends of the balanced transmission line B
is selected to be equal to the two-wire characteristic impedance Zb of the balanced transmission line B, as in FIG.
Furthermore, when the output impedance of all transmitting circuits DV is high, the potential for determining the output of the receiving circuit RC +
E connects to balanced transmission line B via resistors N2 and R3.
is applied to. Note that the values of the resistors R2 and R3 are selected to be sufficiently large so as not to significantly change the matching condition for the balanced transmission line B of the resistor R1. Therefore, no consideration is given to matching the characteristic impedance Zu between the two wires of the balanced transmission line B and the ground, and as in FIG. 1, reflected waves may still occur between the two wires of the balanced transmission line B and the ground.

It is an object of the present invention to eliminate the above-mentioned drawbacks of conventional DC-coupled balanced bus circuits, to prevent the generation of reflected waves between the two wires of the balanced transmission line and to the ground, and to ensure that all transmitting circuit outputs are high impedance. The object of the present invention is to realize a DC coupled balanced bus matching termination method that can determine the receiving circuit output and accurately transfer information even when the following occurs.

The purpose of this is to calculate the characteristic impedance between two wires and between two wires and ground of the balanced transmission path as Zb and Zu in a DC-coupled balanced bus circuit in which one or more transmitting circuits and receiving circuits are connected to the same balanced transmission path. When the resistance R ₄ = 4Zb・Zu/4Zu−Zb, the resistance R ₅ = R _{6 = 2Zu} is connected in series to form a termination resistance circuit, and _the resistance R ₄ terminating at least one end of the two wires of the balanced transmission line, and applying a potential between both ends of the terminating resistor circuit to set the potential determined by the voltage division by the resistors R ₅ , R ₄ , and R ₆ as described above. This is achieved by applying it as the potential for determining the output of the receiving circuit connected between two lines of the balanced transmission line.

A DC-coupled balanced bus circuit according to an embodiment of the present invention will be explained below with reference to FIG. In FIG. 4, both ends of a balanced transmission line B that transfers information between the transmitting circuit DV and the receiving circuit RC are terminated by matching termination resistor circuits composed of resistors R4, R5, and R6. The values of the resistors R4, R5, and R6 are selected to satisfy equations (1) and (2), respectively.

R4=4Zb・Zu/4Zu−Zb...(1) R5=R6=2Zu...(2) However, Zb: Characteristic impedance between two lines of balanced transmission line B.

Zu: Characteristic impedance between two wires and ground of balanced transmission line B.

Further, a potential +E is applied to one ends of the resistors R5 and R6. The impedance seen between the two wires of the balanced transmission line B and the impedance seen from the two wires to the ground of the matched termination resistor circuit are equal to Zb and Zu, respectively, and the impedance seen between the two wires of the balanced transmission line B and between the two wires and the ground Characteristic impedance Zb and
Both are in a consistent state with Zu. Therefore, not only reflected waves from signals transmitted between the two lines of balanced transmission line B, but also reflected waves from signals generated between the two lines and the ground or external noise are prevented from occurring. Furthermore, due to the potential +E supplied from the resistors R5 and R6, a potential R4・E/R4+R5+R6 is generated between the two lines of the balanced transmission line B, and is input to each receiving circuit RC, so the output of the receiving circuit RC is determined. be done.

As is clear from the above explanation, according to this embodiment, both ends of the balanced transmission line B have not only the characteristic impedance Zb between the two lines but also the two
Since it is also matched to the line-to-ground characteristic impedance Zu, there is no risk of negative reflected waves occurring for signals or external noise occurring between the two lines of balanced transmission line B, and the output of the transmitting circuit DV Impedance is also prevented from becoming low. Also, since the potential R4・E/R4+R5+R6 for determining the receiving circuit is supplied between the two wires of the balanced transmission line B from the matching termination resistor circuit, all the transmitting circuits DV connected to the balanced transmission line B Even when the output impedance of the receiving circuit RC is high, the output of the receiving circuit RC is prevented from becoming unstable.

Note that FIG. 4 is merely one embodiment of the present invention, and the effects of the present invention do not change even if, for example, the number of transmitting circuits DV or receiving circuits RC connected to the same balanced transmission path B is not limited to a plurality. As another embodiment of the present invention, FIG. 5 shows a DC-coupled balanced bus circuit to which one transmitting circuit DV and a plurality of receiving circuits RC are connected. In FIG. 5, a matching termination resistor circuit composed of resistors R4, R5 and R6 is connected to one end of the balanced transmission line B. Each resistance R
4, R5 and R6 are selected so as to satisfy equations (1) and (2), respectively, as in FIG. This is prevented from occurring between the two lines of the balanced transmission line B and between the two lines and the ground. Further, even when the output impedance of the transmitting circuit DV is high, the output of the receiving circuit RC is determined by the potential R4·E/R4+R5+R6 supplied from the matching termination resistor circuit.

As described above, according to the present invention, in a DC-coupled balanced bus circuit in which one or more transmitting circuits and receiving circuits are connected to the same balanced transmission line, reflected waves of signals or external noise are generated between two wires of the balanced transmission line and the ground. This can be prevented, and even if all the transmitting circuit outputs become high impedance, the receiving circuit output can be determined, making it possible to accurately transfer information.

[Brief explanation of drawings]

Figure 1 shows an example of a conventional DC-coupled balanced bus circuit, Figure 2 shows an example of the output impedance characteristics of a transmitting circuit, and Figure 3 shows another example of a conventional DC-coupled balanced bus circuit. 4 is a diagram showing a DC-coupled balanced bus circuit according to one embodiment of the present invention, and FIG. 5 is a diagram showing a DC-coupled balanced bus circuit according to another embodiment of the present invention. In the figure, B...balanced transmission line, DV...transmission circuit, RC...reception circuit, R1, R2, R3, R
4, R5, R6...Resistance.

Claims (1)

[Claims] 1. In a DC-coupled balanced bus circuit in which one or more transmitting circuits and receiving circuits are connected to the same balanced transmission line, the characteristic impedance between two lines of the balanced transmission line and between two lines and the ground is defined as Zb. and Zu, resistor R ₄ = 4Zb・Zu/4Zu−Zb resistor R ₅ = R ₆ = 2Zu The above resistors R ₅ , R ₄ and R ₆ are connected in series to form a terminating resistor circuit, and At least one end of the two lines of the balanced transmission line is terminated with a resistor _R4 , and a potential is applied between both ends of the terminating resistor circuit, and the voltage is determined by the voltage division by the resistors _R5 , _R4 , and _R6 . A DC-coupled balanced bus matching termination method, characterized in that a potential is provided as a potential for determining the output of the receiving circuit connected between two lines of the balanced transmission line.