JPH0424650Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a line terminator installed in the middle of a transmission line to absorb reflections and ringing due to impedance mismatch between the signal source and the receiving end. It is.

[Prior art]

In general, in a signal transmission path, if the signal source impedance, line impedance, and receiving end impedance are not always matched, not only will efficient power transmission be impossible, but multiple reflections will occur between the signal source and receiving end, causing harmful effects. It is well known that there is a high possibility that this will become radiated noise and cause damage to other electronic devices. In systems where the impedance between the signal source and receiving end has a one-to-one correspondence and can always maintain a constant value, as in the example of the transmitter, transmitting antenna, and receiver's receiving antenna, an appropriate transmission path must be provided. The above-mentioned problems can be easily overcome.

[Problem that the invention attempts to solve]

However, when transmitting signals from modern digital devices, the impedance of the signal source and receiving end changes dynamically, and in systems where only the transmission line maintains a certain value, impedance mismatch may occur. This causes multiple reflections of pulses and ringing phenomena at the rise of pulses, contributing to electromagnetic interference.

[Means for solving problems]

In view of these points, the present invention provides a line termination circuit for efficiently absorbing unnecessary reflections and ringing.

The present invention provides a line terminator that is installed on a transmission line in order to absorb reflections and ringing due to impedance mismatch between the transmission line and the signal source or receiving end. The line terminator includes a ferrite bead placed on the transmission line, a winding wound around the ferrite bead, and a resistor connected between both ends of the winding.

The contents of the present invention will be explained in detail below with reference to the drawings. The present invention is characterized in that it utilizes a ferrite magnetic core for resistor termination.

〔Example〕

FIG. 1 shows the simplest embodiment of the invention. In this embodiment, the ferrite magnetic core 3 is passed through the line 1 as a primary winding conductor, and the other winding conductor 2
The following circuit is formed. The secondary circuit is terminated by a terminating resistor R. This is shown in a circuit diagram as shown in FIG. 5 is the high frequency loss r of the ferrite magnetic core, and the inductance L coupled to the secondary circuit
is 6.

Here, when the current flowing through the primary winding 1 is direct current, r and L do not occur, so it is not affected by the ferrite magnetic core or the resistance R, that is, the resistance seen from the primary side.
_RX is 0. When the current flowing through the primary winding 1 is alternating current, its frequency increases and the effects of r and L appear, and the resistance R on the secondary side comes into play. Therefore, the impedance R _X seen from the primary side
As shown in FIG. 4, as the frequency increases, R becomes higher and approaches the pure resistance R _X0 . This pure resistance _R
is expressed as R _X0 =(n ₁ /n ₂ ) ² ×R, where n ₁ is the number of turns of the primary winding and n ₂ is the number of turns of the secondary winding.

As is clear from the above, the ferrite bead core 3 is placed around the track 1, and the core 3 has two
When the secondary winding 2 is wound and both ends of the secondary winding 2 are connected with a pure resistor 4, the resistance has no or almost no effect on the line when the current flowing through the line is direct current or in a low frequency band. However, in a high frequency region where reflection and ringing are a problem, it acts as a pure resistance R _X0 and can minimize transmission energy loss.

Referring to FIG. 5, according to the present invention, parallel transmission lines 1 _-1 , 1 which are often used in digital transmission
_-2 ,...1-n pass through one ferrite annular magnetic core 3, and one secondary winding 2 is terminated with a resistor 4, thereby terminating the entire line with one terminator. be able to.

The equivalent circuit seen from the primary side in the case of FIG. 5 is shown in FIG. 6.

[Effect of idea]

According to the present invention, a line terminator that can absorb high-frequency reflected waves and ringing without directly connecting a resistor to the line can be realized with a simple configuration.
Furthermore, even in a multi-channel system, lines can be terminated at the same time using a single terminator, which is extremely effective as a countermeasure against electromagnetic interference in digital electronic equipment.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing one embodiment of the present invention;
The figure shows the circuit diagram, Figure 3 is an equivalent circuit diagram at high frequency, Figure 4 is a diagram showing the variation of the equivalent resistance _R 6 are equivalent circuit diagrams thereof. 1 _-1 , 1 _-2 , 1-n...Line as primary winding, 2...Secondary winding, 3...Ferrite annular magnetic core, 4...Pure resistance, _Rx ...Equivalent resistance.

Claims (1)

[Scope of utility model registration request] A line terminator installed on a transmission line to absorb reflections and ringing due to impedance mismatching between the transmission line and the signal source or receiving end, which terminates on the transmission line by passing through or wrapping around the transmission line. Ferrite beads placed in
A line terminator comprising a winding wound around the ferrite bead and a pure resistor connected between both ends of the winding.