JP2008131141A - Termination circuit for transmission line - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a termination circuit for a transmission line that has a waveform compensating function free of waveform deterioration due to overcompensation in high-speed signal transmission even for a line length with which loss is small. <P>SOLUTION: The termination circuit for the transmission line includes a diode 4a connected to a terminal portion of a transmission line 2 and a resistance 5a which is connected between the diode 4a and ground 100 and has a resistance value nearly equal to the characteristic impedance of the transmission line 2, and the direction from the transmission line 2 to the resistance 5a is the forward or backward direction of the diode 4a. Alternatively, the termination circuit for transmission line has the diode connected to the terminal portion of the transmission line and a resistance connected between the diode and a power source, and the direction from the transmission line to the resistance is the backward direction or forward direction of the diode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transmission line termination circuit, and in particular, prevents waveform degradation due to overcompensation even when transmission line attenuation is small.

  Conventional termination circuits in digital data transmission have realized a function to reduce waveform distortion, such as suppression of reflection or suppression of overshoot, by connecting a signal line to a ground or a power supply via a resistor or a diode ( For example, see Patent Document 1).

  In addition, in order to cope with waveform distortion due to attenuation of the frequency dependence of the transmission path that has become apparent with the recent increase in signal transmission rate, it is composed of elements such as resistors, capacitors, inductors, etc., and the frequency dependence of the transmission path is reduced. There has also been proposed an equalizer circuit that flattens the frequency dependence and compensates the waveform by having a canceling characteristic (see, for example, Non-Patent Document 1).

JP-A-61-128646 IEICE Transactions C Vol. J87-C No. 11 pp. 873-880, November 2004

  However, the above-described conventional termination circuit is intended to suppress reflection, overshoot, etc., and causes waveform distortion due to attenuation of the frequency dependence of the transmission line that has become apparent with the recent increase in signal transmission rate. There was a problem that it was not effective.

  The above-described conventional equalizer circuit is intended to compensate for waveform distortion due to attenuation of the frequency dependence of the transmission line. However, when the attenuation is small, such as when the length of the transmission line is short, the equalizer circuit There is a problem that the flatness of the frequency characteristics is impaired, and the waveform deteriorates. For this reason, it has been difficult to apply to a system in which the wiring length changes due to operation such as transmission using a cable or transmission using a backplane.

  The present invention has been made to solve the above-described problems. In high-speed signal transmission, the termination of a transmission line having a waveform compensation function that does not cause waveform degradation due to overcompensation even for a line length with little loss. The purpose is to realize a circuit.

  The transmission line termination circuit according to the present invention includes a diode connected to a termination portion of the transmission line, and a resistor connected between the diode and the ground, and the direction from the transmission line toward the resistance is The forward or reverse direction of the diode is set, and the value of the resistance is substantially equal to the characteristic impedance of the transmission line.

  In addition, a diode connected to the terminal end of the transmission line, and a resistor connected between the diode and the power source, the direction from the transmission line toward the resistor is the reverse direction or forward direction of the diode, The resistance value is substantially equal to the characteristic impedance of the transmission line.

  Furthermore, a first diode connected to the terminal end of the transmission line, a first resistor connected between the first diode and the ground, and a second diode connected to the terminal end of the transmission line A diode and a second resistor connected between the second diode and a power source, and a direction from the transmission line toward the first resistor is a forward direction or a reverse direction of the first diode. The direction from the transmission line toward the second resistor is the reverse or forward direction of the second diode, and the values of the first and second resistors are substantially equal to the characteristic impedance of the transmission line. It is characterized by.

  According to the present invention, by providing a circuit composed of a diode and a resistor at the end of the transmission line, a waveform compensation circuit that does not cause waveform deterioration due to overcompensation even when the transmission line is attenuated can be realized.

Embodiment 1 FIG.
1 is a block diagram showing a transmission line termination circuit according to Embodiment 1 of the present invention. The anode of the diode 4a is connected to the input part of the receiver 3, which is the terminal part of the transmission line 2 provided between the driver 1 for sending the signal and the receiver 3 for receiving the signal, and the cathode of the diode 4a is The resistor 5a is connected to the ground 100. It is assumed that the resistance value of the resistor 5a is substantially equal to the characteristic impedance of the transmission line 2.

  That is, a diode 4a connected to the terminal end of the transmission line 2 and a resistor 5a connected between the diode 4a and the ground 100 are provided, and the direction from the transmission line 2 toward the resistor 5a is defined as the forward direction of the diode 4a. Yes.

  Next, the operation will be described. The data pattern transmitted from the driver 1 reaches the receiver 3 via the transmission line 2. Since the transmission line 2 has frequency dependent losses such as conductor loss and dielectric loss, the amplitude of each bit of the waveform reaching the receiver 3 is in a non-uniform state.

  FIG. 2 is a diagram showing a general IV characteristic of the diode. As shown in FIG. 2, when paying attention to the positive voltage range, current hardly flows at a voltage equal to or lower than the cut-in voltage, and current rapidly flows when the voltage is equal to or higher than the cut-in voltage. That is, the diode has a high impedance when the applied voltage is equal to or lower than the cut-in voltage, and has a low impedance when the applied voltage is equal to or higher than the cut-in voltage.

  In FIG. 1, the diode 4a behaves as a high-impedance circuit for a signal that is equal to or lower than the cut-in voltage of the diode 4a, so that large regular reflection occurs and the amplitude at the input end of the receiver 3 increases. On the other hand, with respect to a signal equal to or higher than the cut-in voltage of the diode 4a, the diode 4a has a low impedance, so that a current flows to the ground 100 through the resistor 5a and is terminated.

  Therefore, according to the first embodiment, rather than relying on the frequency as in the conventional waveform compensation circuit, when the signal level that actually reaches the receiver 3 is small, large reflection occurs and the amplitude is increased. Therefore, even if the transmission path attenuation is small, waveform compensation that does not cause overcompensation can be realized.

Embodiment 2. FIG.
FIG. 3 is a block diagram showing a transmission line termination circuit according to Embodiment 2 of the present invention. The termination circuit of the transmission line according to the second embodiment shown in FIG. 3 is obtained by changing the connection destination of the termination circuit from the ground 100 to the power source 101 in the configuration diagram shown in FIG. . In FIG. 2, the diode is denoted by reference numeral 4b and the resistor is denoted by reference numeral 5b. It is assumed that the resistance value of the resistor 5b is substantially equal to the characteristic impedance of the transmission line 2.

  In the second embodiment shown in FIG. 3, the reference of the signal amplitude is the power source 101. Other than that, as in the first embodiment, for a signal whose voltage is small when viewed from the power supply voltage, the diode 4b becomes high impedance, and the amplitude increases due to the reflected wave. For a signal having a large voltage as viewed from the power supply voltage, the diode 4b has a low impedance and a current flows through the resistor 5b to be terminated.

  Therefore, according to the second embodiment, the waveform compensation function of the first embodiment based on the power supply voltage can be realized.

Embodiment 3 FIG.
FIG. 4 is a configuration diagram showing a transmission line termination circuit according to Embodiment 3 of the present invention. The transmission line termination circuit according to Embodiment 3 shown in FIG. 4 is obtained by connecting both of the transmission line termination circuits according to Embodiment 1 shown in FIG. 1 and Embodiment 2 shown in FIG. The cut-in voltage of the diodes 4a and 4b is assumed to be smaller than half of the power supply voltage 101. It is assumed that the resistance values of the resistors 5a and 5b are substantially equal to the characteristic impedance of the transmission line 2.

  The operation in the third embodiment shown in FIG. 4 is similar to that in the first and second embodiments. A signal having a small amplitude with respect to the ground 100 and a signal having a small amplitude with respect to the power supply voltage 101 are respectively connected to the diode 4a or 4b. Either one is terminated because it has a low impedance. With respect to a signal in the vicinity of about half of the power supply voltage 101, the diodes 4a and 4b have high impedance, so that a reflected wave is generated and the amplitude is amplified.

  Therefore, according to the third embodiment, a waveform compensation function suitable for general digital signal transmission can be realized.

Embodiment 4 FIG.
FIG. 5 is a block diagram showing a transmission line termination circuit according to Embodiment 4 of the present invention. The transmission line termination circuit according to the fourth embodiment shown in FIG. 5 is obtained by reversing the direction of the diode 4a in the configuration diagram of the first embodiment shown in FIG.

  Focusing on the negative voltage range of FIG. 2 showing the general IV characteristics of the diode, the current hardly flows at the reverse voltage below the reverse breakdown region, and the current flows rapidly when the reverse voltage exceeds the reverse breakdown region. There is. That is, in the fourth embodiment, by using the reverse breakdown region by reversing the direction of the diode 4a, it is possible to perform waveform compensation similar to the first embodiment in which the reference value of the signal is different.

  Therefore, according to the fourth embodiment, it is possible to realize the waveform compensation function of the first embodiment in which the reference value of the signal is different.

Embodiment 5. FIG.
FIG. 6 is a configuration diagram showing a transmission line termination circuit according to Embodiment 5 of the present invention. The transmission line termination circuit according to the fifth embodiment shown in FIG. 6 is obtained by reversing the direction of the diode 4b in the configuration diagram of the second embodiment shown in FIG.

  Therefore, according to the fifth embodiment, by using the reverse breakdown region with the direction of the diode 4b reversed, it is possible to perform waveform compensation similar to that of the second embodiment in which the reference value of the signal is different.

Embodiment 6 FIG.
FIG. 7 is a configuration diagram showing a transmission line termination circuit according to Embodiment 6 of the present invention. The transmission line termination circuit according to the sixth embodiment shown in FIG. 7 is obtained by reversing the directions of the diodes 4a and 4b in the configuration diagram of the third embodiment shown in FIG.

  Therefore, according to the sixth embodiment, by using the reverse breakdown region by reversing the directions of the diodes 4a and 4b, it is possible to perform waveform compensation similar to that of the third embodiment where the reference values of the signals are different. Become.

It is a block diagram which shows the termination circuit of the transmission line which concerns on Embodiment 1 of this invention. It is the figure which showed the general IV characteristic of a diode. It is a block diagram which shows the termination circuit of the transmission line which concerns on Embodiment 2 of this invention. It is a block diagram which shows the termination circuit of the transmission line which concerns on Embodiment 3 of this invention. It is a block diagram which shows the termination circuit of the transmission line which concerns on Embodiment 4 of this invention. It is a block diagram which shows the termination circuit of the transmission line which concerns on Embodiment 5 of this invention. It is a block diagram which shows the termination circuit of the transmission line which concerns on Embodiment 6 of this invention.

Explanation of symbols

  1 driver, 2 transmission line, 3 receiver, 4a, 4b diode, 5a, 5b resistance, 100 ground, 101 power supply.

Claims (6)

A diode connected to the end of the transmission line;
A resistor connected between the diode and the ground, and a direction from the transmission line toward the resistor as a forward direction of the diode,
The transmission line termination circuit, wherein the resistance value is substantially equal to the characteristic impedance of the transmission line. A diode connected to the end of the transmission line;
A resistor connected between the diode and a power source, and a direction from the transmission line toward the resistor as a reverse direction of the diode,
The transmission line termination circuit, wherein the resistance value is substantially equal to the characteristic impedance of the transmission line. A first diode connected to the end of the transmission line;
A first resistor connected between the first diode and ground;
A second diode connected to the end of the transmission line;
A second resistor connected between the second diode and a power source, a direction from the transmission line toward the first resistor is a forward direction of the first diode, and from the transmission line The direction toward the second resistor is the reverse direction of the second diode,
A transmission line termination circuit, wherein the values of the first and second resistors are substantially equal to the characteristic impedance of the transmission line. A diode connected to the end of the transmission line;
A resistor connected between the diode and the ground, and a direction from the transmission line toward the resistor as a reverse direction of the diode,
The transmission line termination circuit, wherein the resistance value is substantially equal to the characteristic impedance of the transmission line. A diode connected to the end of the transmission line;
A resistor connected between the diode and a power source, and a direction from the transmission line toward the resistor as a forward direction of the diode,
The transmission line termination circuit, wherein the resistance value is substantially equal to the characteristic impedance of the transmission line. A first diode connected to the end of the transmission line;
A first resistor connected between the first diode and ground;
A second diode connected to the end of the transmission line;
A second resistor connected between the second diode and a power source, and a direction from the transmission line toward the first resistor is a reverse direction of the first diode, and from the transmission line The direction toward the second resistor is the forward direction of the second diode,
A transmission line termination circuit, wherein the values of the first and second resistors are substantially equal to the characteristic impedance of the transmission line.

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