JP6876735B2 - Variable reduction equalizer, loss compensation method using it, error rate measuring device, and error rate measuring method - Google Patents

Description

The present invention relates to a variable reduction equalizer for compensating for a loss on a transmission line, a loss compensation method using the same, an error rate measuring device for measuring an error rate of an object to be measured including a transmission line, and an error rate measuring method.

Various digital communication devices are required to have a larger capacity transmission capacity as the number of users increases and multimedia communication becomes widespread. Further, as one of the indexes for quality evaluation of digital signals in these digital communication devices, a bit error rate defined as a comparison between the number of received data in which a code error has occurred and the total number of received data (hereinafter, errors). The rate) is known.

Further, in the above-mentioned digital communication device, a test signal including fixed data is transmitted to a device under test such as a photoelectric conversion component to be tested, and serves as a reference with a signal under test input via the device under test. As a wired error rate measuring device that measures the error rate of the signal to be measured by comparing the reference signal in bit units, for example, the bit error measuring device disclosed in Patent Document 1 below is known.

By the way, in measuring the error rate of the signal to be measured described above, when a high-speed digital signal is passed through a transmission line such as a cable or a substrate, the higher the speed of the transmitted signal, the more the conductor loss and dielectric loss of the transmission line. The body loss becomes large and signal transmission becomes difficult.

In particular, in a low frequency band of several GHz (for example, 1 GHz) or less, a phenomenon called a skin effect occurs in which a large amount of high-frequency current flows near the surface of the conductor due to the inductance in the conductor and does not flow much near the center. The loss curve due to the conductor loss of is drawn. Moreover, the loss curve in the low frequency band of several GHz or less tends to draw a curve larger than the loss curve in the high frequency band of several tens of GHz or more, and there is a problem that the baseline is thickened. Therefore, especially when measuring the error rate of the PAM4 signal with an error rate measuring device, the fineness of the baseline directly affects the opening of the eye. Moreover, the error rate measuring instrument is supposed to receive the PAM4 signal through the loss of various transmission lines, and a variable equalizer for compensating for the loss of the transmission line is required.

Therefore, conventionally, as variable equalizers for compensating for loss of transmission lines, for example, FFE and DFE are generally known. These equalizers are suitable for compensating for signal components near the Nyquist frequency of the signal rate for high-speed digital signal transitions.

The following Patent Document 2 discloses an emphasis circuit that suppresses waveform deterioration in a high frequency band of an output signal, and the following Patent Document 3 discloses a multi-band equalizer that has low loss and supports a wide range of bit rates. There is.

Japanese Unexamined Patent Publication No. 2007-274474 Japanese Patent No. 5859168 Japanese Patent No. 6226945

However, in the variable equalizer by FFE or DFE, it is necessary to increase the number of taps in order to compensate for the loss in the low frequency band due to the skin effect, and there is a problem that the circuit scale becomes large.

Further, when the emphasis circuit on the transmitting side disclosed in Patent Document 2 is adopted as the variable equalizer on the receiving side, there is a problem that the circuit scale becomes large in order to compensate for the loss in the low frequency band due to the skin effect. there were. Similarly, even when the multi-band equalizer disclosed in Patent Document 3 is used, it is necessary to arrange and configure a plurality of circuits for compensating for loss in a low frequency band due to the skin effect, which causes a problem that the circuit scale becomes large. There is.

Therefore, the present invention has been made in view of the above problems, and is a variable reduction equalizer capable of compensating for loss in a low frequency band by a simple circuit configuration, a loss compensation method using the variable reduction equalizer, and an error rate measurement. It is an object of the present invention to provide a device and a method for measuring an error rate.

In order to achieve the above object, the variable low frequency equalizer according to claim 1 of the present invention includes an inductor L1 connected to a transmission line Wa for transmitting a high-speed digital signal and an inductor L1.
A variable attenuator 2 connected to the inductor and capable of varying the amount of attenuation,
A control unit 3 that variably controls the amount of attenuation of the variable attenuator according to the loss of the transmission line is provided .
A plurality of the variable attenuators are connected in parallel to the inductor .

The loss compensation method using the variable low-frequency equalizer according to claim 3 of the present invention includes a step of connecting the inductor L1 to a transmission line Wa for transmitting a high-speed digital signal and a step of connecting the inductor L1.
A step of connecting a variable attenuator 2 having a variable amount of attenuation to the inductor, and
A step of variably controlled in accordance with the attenuation amount of the variable attenuator to the loss of the transmission line,
It is characterized by including a step of connecting a plurality of the variable attenuators in parallel to the inductor.

The error rate measuring instrument according to claim 3 of the present invention compensates for the loss of the transmission line Wa of the measured object W by the variable low frequency equalizer 1 of claim 1 and obtains a signal transmitted from the measured object. It is characterized in that the error rate of the measured object is measured based on the result of comparison between the received signal and the known signal input to the measured object.

The error rate measuring method according to claim 4 of the present invention compensates for the loss of the transmission line Wa of the measured object W by the error rate measuring method using the variable low frequency equalizer according to claim 2, and is said to be the measured object. It is characterized in that the signal transmitted from is received and the error rate of the measured object is measured based on the comparison result between the received signal and the known signal input to the measured object.

According to the present invention, by variably controlling the attenuation amount of the variable attenuator according to the loss of the transmission line, waveform compensation is performed with a simple configuration by focusing on a wide frequency band in particular for the loss of a wide transmission line. be able to.

(A) It is a figure which shows the schematic structure of the variable low-pass equalizer which concerns on this invention, and (b) is the circuit structure figure of the variable attenuator. It is a figure which shows the other structure of the variable low-pass equalizer which concerns on this invention. It is a flowchart of the loss compensation method using the variable low-pass equalizer which concerns on this invention. It is a figure which shows the specific example in the case of loss compensation using the variable low-pass equalizer which concerns on this invention. FIG. 4A shows the frequency characteristics of a transmission line having a loss of 1.5 dB at a Nyquist frequency of 25 GHz and a transmission line having a loss of 4.5 dB at a Nyquist frequency of 25 GHz, and FIG. 4B shows an attenuation of 1 dB in FIG. It is a figure which shows the frequency characteristic of the variable low region equalizer at the time of 10dB. It is a figure which shows the eye waveform of each part of FIG. 4 in the transmission line which the loss at a Nyquist frequency 25GHz is 1.5dB. It is a figure which shows the eye waveform of each part of FIG. 5 in the transmission line which the loss at a Nyquist frequency 25GHz is 4.5dB. It is a block block diagram of the error rate measuring instrument using the variable low-pass equalizer which concerns on this invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the attached drawings.

[Overview of the present invention]
The LR equalizer provided with the inductor (coil) L and the resistor R is known as a low-frequency equalizer that works from several GHz with a small inductor L, and the circuit scale can be small.

However, it is difficult to change the inductor L. Therefore, considering that the resistor R is variable, for example, an electronically controlled variable resistor such as a digital potentiometer has a parasitic capacitance that cannot be ignored, and performance deterioration due to this parasitic capacitance and unnecessary resonance of the inductor cannot be avoided.

Therefore, in the present invention, a variable low frequency equalizer is realized by using a variable attenuator having a frequency band up to several GHz instead of the resistor R. This makes it possible to compensate for the loss of a wide range of transmission lines. Further, the error rate measuring device using this makes it possible to measure the error rate while dealing with the loss of a wide range of transmission lines.

[About the configuration of the variable low-frequency equalizer]
As shown in FIG. 1A, the variable low-frequency equalizer 1 (1A) of the present embodiment changes the attenuation amount in the low frequency band by changing the attenuation amount, so that the inductor (coil) L1 is variable. It is roughly configured with an attenuator 2 and a control unit 3.

The inductor L1 includes, for example, a minute inductance due to a conical coil or wire bonding, and is set to an arbitrary inductance according to the loss of the target transmission line Wa. As shown in FIG. 1A, one end of the inductor L1 is connected to the transmission line Wa, and the other end is connected to the variable attenuator 2.

The variable attenuator 2 is composed of an attenuator capable of varying the amount of attenuation by electronic control, and attenuates a high-speed digital signal (for example, 50 Gbaud, 1 Vpp) input from the transmission line Wa via the inductor L1 with a predetermined amount of attenuation. ..

The variable attenuator 2 has terminals 2a and 2b and a control terminal (not shown), the terminal 2a is connected to the inductor L1, and the one-sided DC termination resistor RL for preventing the influence of reflection is connected to the terminal 2b. To.

The terminal 2b of the variable attenuator 2 may be opened because a high resistance is required to increase the variable amount of the attenuation.

As shown in FIG. 1 (b), the variable attenuator 2 can be configured by, for example, a variable attenuator 2A.

The variable attenuator 2A is a T-type connection of a first variable resistor R1, a second variable resistor R2, and a third variable resistor R3. That is, one end of the first variable resistor R1 is connected to the terminal 2a, and the other end is connected to one end of the second variable resistor R2. One end of the second variable resistor R2 is connected to the other end of the first variable resistor R1, and the other end is connected to the terminal 2b. One end of the third variable resistor R3 is connected between the first variable resistor R1 and the second variable resistor R2, and the other end is grounded.

In the variable attenuator 2A, the resistance values of the first to third variable resistors R1, R2, and R3 are variably controlled by the control unit 3, and the attenuation amount is continuously changed in a predetermined step (for example, 0.5 dB step). ..

The control unit 3 variably controls the amount of attenuation of the variable attenuator 2 according to the loss of the transmission line Wa. When the variable attenuator 2A shown in FIG. 1B is used as the variable attenuator 2, the control unit 3 sets the resistance values of the first to third variable resistors R1, R2, and R3 according to the loss of the transmission line Wa. Variable control.

The variable attenuator 2 is not limited to the variable attenuator 2A shown in FIG. 1 (b). For example, a switching type step attenuator that combines a plurality of attenuators and obtains a desired amount of attenuation by a switching operation can be used as the variable attenuator 2.

Further, the variable low frequency equalizer 1A of FIG. 1A has a configuration in which one variable attenuator 2 is connected to the transmission line Wa via the inductor L1, but a plurality of variable attenuators 2 are connected via the inductor L1. It may be configured to be connected to the transmission line Wa. For example, as shown in FIG. 2, if two variable attenuators 2 are connected in parallel to the inductor L1 to form a variable low frequency equalizer 1 (1B), a variable range of attenuation is obtained as compared with the case where one variable attenuator 2 is used. Can be expanded. In FIG. 2, the same components as those in FIG. 1 (a) are assigned the same numbers.

[About loss compensation method]
Next, an example of the loss compensation method using the variable low-frequency equalizer 1 (1A, 1B) configured as described above will be described with reference to FIG.

When the control unit 3 receives a high-speed digital signal (for example, a PAM4 signal) via the transmission line Wa, the control unit 3 variably controls the amount of attenuation of the variable attenuator 2 depending on whether or not the loss of the transmission line Wa is lower than the reference loss. To do.

Specifically, if the received high-speed digital signal is 50 Gbaud, 1 Vpp, and a predetermined loss (for example, -3 dB) at a Nyquist frequency of 25 GHz is used as the reference loss, the variable attenuation is lower than this reference loss (ST1-Yes). The attenuation amount is variably controlled for each predetermined step in the direction of lowering the attenuation amount of the device 2 (ST2). On the other hand, when it is higher than the reference loss (ST1-No), the attenuation amount is variably controlled for each predetermined step in the direction of increasing the attenuation amount of the variable attenuator 2 (ST3).

Then, when the optimum signal waveform having a narrow baseline and the most open eye is output (ST4-Yes, ST5-Yes), the control unit 3 stops the variable control of the attenuation amount of the variable attenuator 2 (ST4-Yes, ST5-Yes). ST6).

The amount of attenuation of the variable attenuator 2 may be variably controlled at each predetermined step from 0 dB or the amount of attenuation stopped last time. Further, the attenuation amount of the variable attenuator 2 suitable for the loss of the transmission line Wa is stored in the storage unit in advance by simulation, and when the loss of the transmission line Wa to be used is known, the transmission line Wa to be used is used. It is also possible for the control unit 3 to read the attenuation amount of the variable attenuator 2 corresponding to the loss from the storage unit and control the attenuation amount of the variable attenuator 2.

[Simulation results]
Next, as shown in FIG. 4, the result when the variable low-frequency equalizer 1 (1A) is connected to the object W having the transmission line Wa and the signal source Wb and the simulation is performed will be described.

Here, as an example of a high-speed digital signal, an object W having a signal source Wb that generates a PAM4 signal of 50 Gbaud and 1 Vpp is used, and as shown in FIG. 5 (a), a loss of a transmission line Wa at a Nyquist frequency of 25 GHz is used. According to the variable low frequency equalizer 1 (1A) under the condition a (loss of transmission line Wa: 1.5 dB and loss of transmission line Wa at Nyquist frequency 25 GHz) is high (loss of transmission line Wa: 4.5 dB). A simulation was performed.

In this simulation, the inductance of the inductor L1 was set to 8 nH, and the attenuation amounts of the variable attenuator 2 of the variable low frequency equalizer 1 (1A) were measured at 1 dB and 10 dB, respectively.

As a result, under the condition a where the loss of the transmission line Wa is low, the eye of the PAM4 waveform was opened when the attenuation amount of the variable attenuator 2 was 1 dB (Set1) as compared with when the loss amount was 10 dB (Set2).

On the other hand, under the condition b in which the loss of the transmission line Wa is high, when the attenuation amount of the variable attenuator 2 is 10 dB (Set2), the eye of the PAM4 waveform is opened more than when the loss amount is 1 dB (Set1).

From the above, when receiving a high-speed digital signal, the loss of the transmission line Wa can be compensated by variably controlling the amount of attenuation of the variable attenuator 2 according to the loss of the transmission line Wa.

The variable low frequency equalizer 1 described above inputs a known pattern signal (high-speed digital signal, for example, PAM4 signal) to the object W to be measured, and receives a pattern signal folded back from the object W to be measured along with the known pattern signal. Then, it can be incorporated into the error rate measuring device 11 of FIG. 8 for measuring the error rate of the measured object W based on the comparison result between the received pattern signal and the known pattern signal input to the measured object W. ..

In the error rate measuring device 11, when measuring the error rate of the object W to be measured, the operation display unit 12 sets various parameters related to the error rate measurement. Then, the pattern generation unit 13 transmits a known pattern signal (high-speed digital signal) based on the setting to the object W to be measured as a test signal under the control of the control unit 14.

Subsequently, the variable low-frequency equalizer 1 compensates for the loss of the transmission line of the object to be measured W by the control of the control unit 14, and is measured as the pattern generation unit 13 transmits the test signal to the object W to be measured. The pattern signal returned from the object W is received and output to the error detection unit 14.

After that, the error detection unit 15 bit-compares the signal received by compensating for the loss of the transmission line Wa from the object W via the variable low-frequency equalizer 1 and the known signal under the control of the control unit 14. An error is detected and the result is displayed on the operation display unit 12.

As described above, according to the present embodiment, the variable attenuator 2 having a frequency band up to several GHz is used instead of the resistor, and the attenuation amount of the variable attenuator 2 is variably controlled according to the loss of the transmission line. For the loss of a wide range of transmission lines, waveform compensation can be performed with a simple configuration by focusing on the low frequency band in particular.

The best form of the variable reduction equalizer according to the present invention, the loss compensation method using the same, the error rate measuring device, and the error rate measuring method has been described above, but the present invention is limited by the description and drawings in this form. There is no. That is, it goes without saying that all other forms, examples, operational techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

1 (1A, 1B) Variable low-frequency equalizer 2 Variable attenuator 2a, 2b terminal 2A Variable attenuator 3 Control unit 11 Error rate measuring instrument 12 Operation display unit 13 Pattern generator 14 Control unit 15 Error detection unit L1 Inductor R1. R2, R3 Variable resistor RL One-sided DC termination resistor W Measured object Wa Transmission line Wb Signal source

Claims (4)

An inductor (L1) connected to a transmission line (Wa) that transmits high-speed digital signals,
A variable attenuator (2) connected to the inductor and capable of varying the amount of attenuation,
A control unit (3) that variably controls the amount of attenuation of the variable attenuator according to the loss of the transmission line is provided .
The variable attenuator is a variable low frequency equalizer characterized in that a plurality of the variable attenuators are connected in parallel to the inductor. The step of connecting the inductor (L1) to the transmission line (Wa) that transmits high-speed digital signals, and
A step of connecting a variable attenuator (2) having a variable amount of attenuation to the inductor, and
A step of variably controlled in accordance with the attenuation amount of the variable attenuator to the loss of the transmission line,
A loss compensation method using a variable low-frequency equalizer, which comprises a step of connecting a plurality of the variable attenuators in parallel to the inductor. The variable low frequency equalizer (1) of claim 1 compensates for the loss of the transmission line (Wa) of the object to be measured (W), receives the signal transmitted from the object to be measured, and receives the received signal and the object to be measured. An error rate measuring device for measuring an error rate of the object to be measured based on a comparison result with a known signal input to the object. The error rate measuring method using the variable low frequency equalizer according to claim 2 compensates for the loss of the transmission line (Wa) of the measured object (W), receives the signal transmitted from the measured object, and receives the received signal. An error rate measuring method, characterized in that the error rate of the measured object is measured based on the result of comparison with a known signal input to the measured object.

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