JPH025629A - Transmission line terminating equipment - Google Patents

Abstract

PURPOSE:To reduce noises entering from power supply wiring together with induced noised by providing a filter circuit in addition to a potential generation circuit and impedance matching circuit and giving characteristics for interrupting the frequency band of transmission signals to the filter circuit. CONSTITUTION:When the interrupted frequency of a filter circuit 12B is made sufficiently lower than the frequency band of transmission signals, the output impedance of the circuit 12B in the transmission signal band becomes the sum of resistors 12b12 and 12b22 irrespective of values of resistors 12a1 and 12a2 of a potential generation circuit 12A. Since the DC potential given to a transmission line 13 is given by dividing a supply voltage by means of resistors 12a1, 12b11, 12b12, 12c, 12b22, 12b21 and 12a2, a circuit constant can be fixed easily. Moreover, since unbalanced noised from the power supply wiring are absorbed by the filter circuit 12B, no noises are transmitted to the line 13 and, since the line is connected to a sufficiently low impedance against the ground, induced noises can also be suppressed to a small amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a transmission line terminator that is connected to a transmission line for information exchange of information equipment such as a computer and used to transmit information with fewer errors. It is.

Prior Art FIG. 3 is a block diagram showing the configuration of a bus-type information transmission system using a conventional transmission line terminator. One unit is connected to each end.

Reference numeral 5 indicates a transmitter, and reference numeral 6 indicates a receiver. At least one of the transmitter 5 and the receiver 6 are connected to the transmission line 4.

FIG. 4 is a block diagram showing the configuration of a conventional transmission line terminator. 1 is a power supply, 2 is a transmission line terminator connected to the power supply 1, and the transmission line 4 is connected to an appropriate ground potential. and an impedance matching circuit that prevents the generation of reflected waves due to impedance mismatching for signals traveling from the transmission line 4 to the transmission line terminator 2. 2B are connected in series.

Note that the transmission line terminator 3 shown in FIG. 3 is also configured similarly to the transmission line terminator 2.

FIGS. 5 and 6 are circuit diagrams showing specific examples of conventional transmission line terminators.

Figure 5 shows a general transmission line terminator 2 in the transmission line 4.
In one example, the transmission line terminator 2 is composed of a resistor 2m for the purpose of matching the characteristic impedance of the transmission line 4, and prevents the generation of reflected waves.

FIG. 6 shows an example of the transmission line terminator 2 equipped with the potential generation circuit 2A shown in FIG. 4, including resistors 2a11+2a□,
One end is connected to the power supply device 1, and the other end is connected to one end of the resistors 2m12 and 2a22, respectively.

The other end of the resistor "12s" 22 is grounded, and the resistor 2a11t2"21 and the resistor 2a
A transmission line 4 is connected to the connection point with 12 and 2m22.

In addition, the resistor 2a11, the resistor 2a21, and the resistor 2a1
In many cases, the resistance values of resistor 2 and resistor 2a22 are the same, and in order to match the characteristic impedance of transmission line 4, the power supply voltage is applied to resistor 2a11, resistor 2a12, and resistor 2a11, resistor 2a12, and resistor 2a21 and resistor 2-2
It outputs a ground potential divided by 2 to prevent reflected waves from occurring.

In the information transmission system configured as described above, when information is transmitted from one of the transmitters 5, the information can be transmitted to the receiver 6 via the transmission line 4.

Problems to be Solved by the Invention However, in the conventional transmission line terminator described above, when the transmission line terminator 2 is configured with only an impedance matching circuit 2B, as shown in FIG. When stopped, transmission line 4 is high with respect to ground.
Since it becomes an impedance, there is a problem in that it is not possible to prevent superimposition of induced noise.

If clearly different potentials are not applied to the two transmission lines 4, when the transmitter 5 stops transmitting signals, the potentials of the transmission lines 4 will be approximately equal, and will be near the threshold of the receiver 6. Become.

Therefore, if the noise superimposed on the transmission line 4 increases the hysteresis of the receiver 6, the receiver 6 will malfunction. For example, as shown in FIG. When the prevention circuit 7 is provided on the input side of the receiver 6, there are problems in that the circuit configuration of the receiver 6 becomes complicated, the sensitivity of the receiver 6 decreases, and the load increases.

As shown in FIG. 8, there is also a transmitter/receiver integrated circuit 8 that includes a transmitter 8T and a receiver 8R to which the malfunction prevention circuit 7 shown in FIG. 7 cannot be connected.

Furthermore, when the transmission line terminator 2 is equipped with a potential generating circuit 2A as shown in FIG. 6, for example, if the potential of the transmission line 4 is designed to be separated from the threshold value of the receiver 6 by more than the amplitude of the noise. Although malfunction of the receiver 6 can be prevented, it is not possible to clearly separate the potential generation circuit 2A and the impedance matching circuit 2B, and the transmission line 4 is connected to the power supply device 1 through the transmission line terminator 2. There was a problem in that it was impossible to prevent noise generated in the electronic circuits from entering through the power supply wiring.

The present invention is intended to solve these conventional problems, and it is an object of the present invention to provide a transmission line terminator that can reduce not only inductive noise but also noise mixed in from power supply wiring.

Means for Solving the Problems In order to achieve the above object, the present invention provides a filter circuit in addition to a potential generation circuit and an impedance matching circuit.

Therefore, according to the present invention, by providing the filter circuit with the characteristic of blocking the frequency band of the transmission signal, no matter what value the output impedance of the potential generation circuit takes, the impedance matching circuit side Since the output impedance of the filter circuit in the transmission signal band becomes approximately constant, it is no longer affected by reflected waves.

In addition, by giving the filter circuit a characteristic that allows the direct current output from the potential generation circuit to pass through and blocks the noise frequency band, noise that has entered the wiring from the power supply device can be prevented from entering the transmission line. It can be prevented.

Embodiment FIG. 1 is a block diagram showing the configuration of a transmission line terminator according to an embodiment of the present invention.

In FIG. 1, 11 is a power supply device, and 12 is a power supply device 11.
A potential generating circuit 1 which is connected to a power supply device 11, provides an appropriate ground potential to a balanced transmission line 13, and serves as an appropriate load for the transmitter.
2A, and a filter circuit 12B that is connected in series to the potential generation circuit 12A and allows only a predetermined frequency band to pass through.
The impedance matching circuit 12G is connected between the filter circuit 12B and the transmission line 13 to adjust the impedance seen from the transmission line 13.

FIG. 2 is a circuit diagram showing a specific example of the transmission line terminator 12 shown in FIG. , different DC potentials are applied to the two balanced transmission lines 13.

The filter circuit 12B includes resistors 12b11, 12b12 and resistor 12 connected in series between the input end and the output end.
b21.12b22 and resistor 12b, .

The capacitor 12b is connected between the connection point of 12b12 and the connection point of resistors 12b21 and 12b22.

The impedance matching circuit 12G consists only of a resistor 12o connected between the input end and the output end, which are short-circuited.

Next, the operation of the above embodiment will be explained.

In the above embodiment, if the cutoff frequency of the filter circuit 12B is made sufficiently lower than the frequency band of the transmission signal, no matter what value the resistors 12a1 and 12a2 of the potential generation circuit 12A take, the transmission signal band of the filter circuit 12B will be The output impedance of resistor 12b12 and resistor 12b
It becomes the sum of 22.

The DC potential applied to the transmission line 13 is connected to the power supply voltage by resistor 12m1.12b11.12b12゜12G.
, 12b2212b21 and 12a2, the circuit constants can be easily determined.

In addition, unbalanced noise from the power supply wiring is removed by the filter circuit 12.
Since the unbalanced noise is absorbed by B, unbalanced noise is not transmitted to the transmission line 1a, and since the transmission line 13 is connected to the ground at a sufficiently low impedance, the induced noise can also be suppressed to a small amplitude.

Furthermore, the potential of the transmission line 13 is determined from the threshold value of the receiver.
Since the potential generation circuit 12A separates the potential, there is no malfunction of the receiver when the transmitter stops transmitting.

Effects of the Invention As is clear from the above-mentioned embodiments, the present invention is capable of suppressing induced noise because the transmission line is connected to the ground at low impedance by the filter circuit and the potential generation circuit. effective.

Further, since the transmission line is connected to the power supply device through the filter circuit, there is an effect that noise intrusion from the power supply wiring can be suppressed.

Furthermore, by connecting a filter circuit, it is easy to apply different potentials to the balanced transmission line using a potential generation circuit, so even if the receiver is not equipped with a malfunction prevention circuit, when the transmitter stops transmitting, This has the effect of making it possible to construct a stable system that does not malfunction due to the influence of noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a transmission line terminator according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of the transmission line terminator shown in FIG. 1, and FIG. 3 is a bus-type A block diagram showing the configuration of an information transmission system, FIG. 4 is a block diagram showing the configuration of a conventional transmission line terminator, and FIGS. 5 and 6 are circuit diagrams showing specific examples of conventional transmission line terminators, respectively. FIG. 7 is a circuit diagram showing a malfunction prevention circuit, and FIG. 8 is a block diagram of a transmitter/receiver integrated circuit including a transmitter and a receiver. 11... Power supply device, 12... Transmission line terminator, 12A... Potential generation circuit, 12B...
...Filter circuit, 12C... Impedance matching circuit, 13... Transmission line. Name of agent: Patent attorney Toshio Nakao (1 person)

Claims (1)

[Claims] a potential generation circuit that generates a ground potential connected to the power supply device; a filter circuit that is connected in series with the potential generation circuit and passes only a predetermined frequency band; and a filter circuit that is connected between the filter circuit and the transmission line; A transmission line terminator comprising: an impedance matching circuit for adjusting impedance seen from the transmission line.