Transceiver and bidirectional communication system

Abstract

To provide a transmitting / receiving device and a bidirectional communication system capable of easily setting a data rate or the like for each of first and second signals in bidirectional communication employing the frequency division method.SOLUTION: A bidirectional communication system 1 includes a transmitting / receiving device 10 and a transmitting / receiving device 20 that perform bidirectional communication via a transmission path 30. The transmitting / receiving device 20 includes a driver 21, a filter 22, a receiver 23, and a control unit 24. The receiver 23 recovers a clock by performing frequency locking on a training pattern output from passing through the filter 22, and outputs the recovered clock to the control unit 24. The control unit 24 inputs the recovered clock output from the receiver 23 and controls the cutoff frequency of the filter 22 and controls the operation of the driver 21, based on frequency information of the recovered clock.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a transmission / reception device and a bidirectional communication system.

Background Art

[0002] As a method of bidirectional communication between a first transmission / reception device and a second transmission / reception device, a space division method, a time division method, a common modulation method, an echo cancellation method, and a frequency division method are known. Hereinafter, a signal transmitted from the first transmission / reception device to the second transmission / reception device is referred to as a "first signal", and a signal transmitted from the second transmission / reception device to the first transmission / reception device is referred to as a "second signal".

[0003] In the space division method, a transmission path for transmitting the first signal and a transmission path for transmitting the second signal are provided separately. In this method, although full-duplex communication is possible, there are problems of an increase in the number of transmission paths and connectors, weight, and cost.

[0004] In the time division method, a transmission path for transmitting the first signal and a transmission path for transmitting the second signal are provided in common. During the period of transmitting the first signal, the transmission of the second signal is stopped. Conversely, during the period of transmitting the second signal, the transmission of the first signal is stopped. In this method, since it is impossible to transmit the other signal during the transmission period of one signal, there is a problem that the latency becomes long.

[0005] In the common-mode modulation scheme (Patent Document 1), a transmission line for transmitting the first signal and a transmission line for transmitting the second signal are provided in common. The transmission line described in Patent Document 1 consists of two pairs of lines, with the first signal transmitted as a differential signal and the second signal transmitted using common-mode modulation. A differential signal is a signal inverted relative to the other signal across two pairs of lines; for example, if one is 0.5V, the other is -0.5V. A common-mode signal is a signal in which the two pairs of signals are identical; for example, if one is 0.5V, the other is also 0.5V. In this scheme, because the signals of a differential signal are inverted relative to each other, the currents flowing through the transmission line are inverted across the two pairs, and the magnetic fields generated by the current are canceled out. On the other hand, in common-mode modulation, the currents flow in phase, so the magnetic fields generated by the current cannot be canceled out, leading to EMI (Electromagnetic Interference) radiation problems.

[0006] In the echo cancellation method (Patent Document 2), full-duplex communication is enabled by echo-canceling the second signal at the receiver that is supposed to receive the first signal in the second transceiver. The same applies to the first transceiver. In this method, when the data rate of the second signal is high, the required cancellation characteristics change due to the usage environment such as the load on the transmission line, making complete cancellation difficult. To achieve complete cancellation, an AD converter and advanced digital processing based on DSP are required, which increases the circuit area and power consumption. Even if the data rate of the second signal is kept low enough to not be affected by the usage environment, it becomes necessary to add a high-speed buffer for electrical isolation before the receiver that is supposed to receive the first signal, as well as a high-speed buffer that adds the superimposed signal and the cancellation signal, which increases power consumption.

[0007] In the frequency division scheme (Patent Document 3), a common transmission path is provided for transmitting the first signal and a common transmission path for transmitting the second signal. The frequency bands of the first and second signals are different from each other, and filters for signal selection are provided before each of the first and second receivers. The cutoff frequencies of the filters in the first and second receivers are different from each other. These filters prevent the second signal from being input to the receiver that is supposed to receive the first signal in the second transceiver. The same applies to the first transceiver.

[0008] Comparing the five methods above in terms of weight, cost, latency, EMI, and power consumption, the frequency division scheme is the most suitable. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 10-145436 [Patent Document 2] Patent No. 5638095 [Patent Document 3] U.S. Patent No. 7177288 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The inventors have found that when a frequency division scheme is adopted as the method for bidirectional communication between the first transceiver and the second transceiver, the following problems arise.

[0011] Let's consider, as an example, a system that performs bidirectional communication between a host device and a peripheral device. Assume that the host device has a first transceiver and the peripheral device has a second transceiver. The host device includes a computer and has superior processing capabilities in various respects. In contrast, the peripheral device primarily consists of a touch-panel display. The peripheral device displays an image on the display based on the first signal received from the host device and sends information input via human finger operation on the touch panel as a second signal to the host device. Specific examples of such systems include in-car display systems and amusement equipment systems such as game consoles.

[0012] In such cases, generally, the data rate of the first signal used to transmit video information, which contains a large amount of information, is high, while the data rate of the second signal used to transmit touch panel operation information, which contains less information, is low.

[0013] In systems like the one described above, the display standards for peripheral devices vary, and the specifications required also vary depending on the application.

[0014] For example, peripheral device displays are transitioning from HD (High Definition) to FHD (Full High Definition) resolution, and further increases in resolution are expected. Furthermore, as peripheral device displays become higher resolution, the data rate of the first signal sent from the host device to the peripheral device needs to be increased. On the other hand, some applications require minimizing the data rate of the first signal to enable long-distance transmission using inexpensive cables, or to reduce power consumption as much as possible. Here, a transmission line refers to a line that transmits two pairs of differential signals, or a line that transmits one pair of single signals.

[0015] Furthermore, operation of touch panels on peripheral devices is no longer limited to simple single-finger touches; simultaneous operation with multiple fingers is now possible, and the amount of information in the second signal sent from the peripheral device to the host device is also increasing. For operators of the touch panel on the peripheral device, it is required that the information entered through their operation is quickly sent to the host device, and that the corresponding image is quickly displayed on the screen. Therefore, the data rate of the second signal sent from the peripheral device to the host device must also be as fast as possible.

[0016] However, in conventional bidirectional communication systems employing frequency division schemes, it is difficult to flexibly set the data rates of the first and second signals according to the application. In particular, peripheral devices often have limited functionality, making it difficult to configure the transceiver on the peripheral device side to operate according to the desired data rates of the first and second signals.

[0017] The present invention was made to solve the above-mentioned problems, and aims to provide a transceiver and a bidirectional communication system that allows easy setting of the data rates of the first signal and the second signal in bidirectional communication employing a frequency division scheme. [Means for solving the problem]

[0018] The present invention is a transceiver that, through bidirectional communication with a counterpart transceiver via a transmission path, receives a first signal sent from the counterpart transceiver that has reached the input / output terminal, and sends a second signal having a lower data rate than the data rate of the first signal from the input / output terminal to the counterpart transceiver.

[0019] The first aspect of the transceiver of the present invention includes: (1) a filter connected to an input / output terminal, selectively passing and outputting the first signal among the first signal and the second signal, and selectively attenuating the second signal; (2) a receiver that inputs the first signal output after passing through the filter, and recovers and outputs data and a clock based on this first signal; (3) a driver that sends the second signal from the input / output terminal to the other transceiver; and (4) a control unit that controls the cut-off frequency of the filter and the data rate of the second signal output by the driver based on the frequency of the clock recovered and output by the receiver.

[0020] The transceiver of the present invention may also be in the following aspects. In the second aspect, in addition to the first aspect, before receiving the start of the first signal from the other transceiver, the receiver receives a training pattern from the other transceiver, performs frequency locking on this training pattern, and outputs a recovery clock having a frequency that matches the data rate of the first signal.

[0021] In the third aspect, in addition to the second aspect, the control unit controls the cut-off frequency of the filter to be lower as the frequency of the recovery clock is lower, and controls the cut-off frequency of the filter to be higher as the frequency of the recovery clock is higher.

[0022] In the fourth aspect, in addition to the second or third aspect, the control unit controls the data rate of the second signal to be lower as the frequency of the recovery clock is lower, and controls the data rate of the second signal to be higher as the frequency of the recovery clock is higher.

[0023] In the fifth aspect, in addition to any one of the second to fourth aspects, the control unit controls the slew rate of the waveform of the second signal to be lower as the frequency of the recovery clock is lower, and controls the slew rate of the waveform of the second signal to be higher as the frequency of the recovery clock is higher.

[0024] In the sixth aspect, in addition to any one of the second to fifth aspects, the driver notifies the other transceiver device using the second signal that the receiver has finished frequency locking to the training pattern.

[0025] In the seventh aspect, in addition to the sixth aspect, after the driver notifies the other transceiver device that the frequency locking has finished, the receiver starts receiving the first signal from the other transceiver device.

[0026] In the eighth aspect, in addition to any one of the first to seventh aspects, the filter includes a high-pass filter or a band-pass filter.

[0027] The bidirectional communication system of the present invention includes the transceiver device of the present invention described above and another transceiver device that performs bidirectional communication with this transceiver device via a transmission line.

Advantages of the Invention

[0028] According to the present invention, in a bidirectional communication system adopting a frequency division method, it is possible to easily set data rates and the like of each of the first signal and the second signal.

Brief Description of the Drawings

[0029] [Figure 1] FIG. 1 is a diagram showing the configuration of the bidirectional communication system 1A. [Figure 2] FIGS. 2(a) and (b) are diagrams schematically showing the frequency bands of the first signal and the second signal and the frequency characteristics of the filter 22. [Figure 3] FIGS. 3(a) and (b) are diagrams schematically showing the waveform and frequency band of the second signal. [Figure 4] FIG. 4 is a diagram showing the configuration of the bidirectional communication system 1. [Figure 5] FIG. 5 is a flowchart showing an operation example of the bidirectional communication system 1.

Embodiments for Carrying Out the Invention

[0030] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference numerals, and redundant descriptions will be omitted. The present invention is not limited to these examples, but is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0031] Figure 1 shows the configuration of a bidirectional communication system 1A. The bidirectional communication system 1A includes a transceiver 10A and a transceiver 20A. Transceivers 10A and 20A communicate bidirectionally via a common transmission line 30. Transceiver 10A is located on the host device side, and transceiver 20A is located on the peripheral device side. The data rate of the first signal transmitted from transceiver 10A to transceiver 20A via the transmission line 30 is higher than the data rate of the second signal transmitted from transceiver 20A to transceiver 10A via the transmission line 30. The input / output terminal 19 of transceiver 10A and the input / output terminal 29 of transceiver 20A are connected to each other by the transmission line 30.

[0032] The transceiver 10A comprises a driver 11, a filter 12, and a receiver 13. The filter 12 may be part of the receiver 13. The output terminal of the driver 11 and the input terminal of the filter 12 are connected to the input / output terminal 19. The driver 11 receives a first signal output from the host device as serial data and sends the first signal to the transceiver 20A via the input / output terminal 19 and the transmission line 30.

[0033] Filter 12 receives the second signal, which has arrived at the input / output terminal 19 via the transmission line 30 from the transceiver 20A, as serial data. Filter 12 also receives the first signal output from the driver 11. Filter 12 selectively passes the second signal through to the receiver 13 and selectively attenuates the first signal. Filter 12 may include a low-pass filter or a band-pass filter. The receiver 13 receives the second signal output after passing through filter 12, recovers data and clock based on this second signal, and outputs the recovered data and recovery clock to the host device.

[0034] The transceiver 20A comprises a driver 21, a filter 22, and a receiver 23. The filter 22 may be part of the receiver 23. The output terminal of the driver 21 and the input terminal of the filter 22 are connected to the input / output terminal 29. The driver 21 receives a second signal output from a peripheral device as serial data and sends the second signal to the transceiver 10A via the input / output terminal 29 and the transmission line 30.

[0035] Filter 22 receives the first signal, which has arrived at the input / output terminal 29 via the transmission line 30 from the transceiver 10A, as serial data. Filter 22 also receives the second signal output from the driver 21. Of the first and second signals, filter 22 selectively passes the first signal through to the receiver 23 and selectively attenuates the second signal. Filter 22 may include a high-pass filter or a band-pass filter. The receiver 23 receives the first signal output after passing through filter 22, recovers data and clock based on this first signal, and outputs the recovered data and recovery clock to the peripheral device.

[0036] Figure 2 schematically shows the frequency bandwidths of the first and second signals, as well as the frequency characteristics of filter 22. In this figure, filter 22 is assumed to be a high-pass filter (HPF), and its frequency characteristics are shown. In order to perform bidirectional communication using frequency division, the frequency bandwidth of the first signal must be within the passband of filter 22, and the frequency bandwidth of the second signal must be within the cutoffband of filter 22. Therefore, the frequency bandwidths of the first and second signals, as well as the cutoff frequency of filter 22, must be set in relation to each other.

[0037] Figure 2(a) shows the case where the frequency bandwidth of the first signal is relatively low. Figure 2(b) shows the case where the frequency bandwidth of the first signal is relatively high. As shown in Figure 2(a), when the frequency bandwidth of the first signal is low, the cutoff frequency of filter 22 and the frequency bandwidth of the second signal are set low accordingly. On the other hand, as shown in Figure 2(b), when the frequency bandwidth of the first signal is high, the cutoff frequency of filter 22 and the frequency bandwidth of the second signal can be set high accordingly. In other words, the cutoff frequency of filter 22 and the data rate of the second signal are set according to the data rate of the first signal required by the application. If there is a requirement to make the data rate of the second signal as fast as possible, the data rate of the second signal is set as high as possible within the cutoff bandwidth of filter 22.

[0038] The same requirements apply to the frequency characteristics of filter 12. Specifically, in order to perform bidirectional communication using the frequency division scheme, the frequency band of the second signal must be within the passband of filter 12, and the frequency band of the first signal must be within the cutoffband of filter 12.

[0039] The higher the data rate of the second signal, the shorter the period of the second signal becomes. Due to attenuation during transmission, the amplitude of the second signal decreases, and it becomes possible for the amplitude of the second signal to not reach a predetermined voltage within 1 UI (Unit Interval). As a result, intersymbol interference (ISI) occurs, and the receiver 13 is unable to receive the second signal normally. Therefore, when increasing the data rate of the second signal, it may be important to increase the slew rate of the waveform of the second signal in order to ensure that the amplitude of the second signal is large enough to prevent ISI from occurring. However, increasing the slew rate increases the harmonics of the second signal, which interfere with the first signal, so increasing the slew rate is not desirable. Therefore, the slew rate needs to be appropriately adjusted to suppress interference with the first signal while preventing ISI from occurring. Note that the slew rate is an indicator that represents the speed of change of the signal waveform.

[0040] Figure 3 schematically shows the waveform and frequency band of the second signal. Figure 3(a) shows the case where the slew rate of the second signal waveform is relatively low. Figure 3(b) shows the case where the slew rate of the second signal waveform is relatively high. The higher the slew rate, that is, in the case of Figure 3(b) compared to the case of Figure 3(a), harmonic components appear larger around frequencies that are integer multiples of the data rate of the second signal. If these harmonic components are large and within the passband of filter 22, these harmonic components will also be received by receiver 23, and receiver 23 will not be able to receive the first signal normally. Therefore, it is important to set not only the data rate of the second signal but also the slew rate of the waveform of the second signal so that receiver 23 can receive the first signal normally.

[0041] Based on the above, it is preferable to set the maximum cutoff frequency of the filter 22 that can pass the first signal according to the data rate of the first signal required by the application, set the maximum slew rate of the waveform of the second signal that can be sufficiently attenuated by the filter 22, and set the maximum data rate of the second signal that the driver 21 can output at that slew rate.

[0042] However, peripheral devices often have limited functionality, making it difficult to input setting information for configuring the various operating conditions of the transceiver 20A on the peripheral device side. To resolve this problem, the technology described in Patent Document 2 transmits setting information input in the host device from the transceiver 10A to the transceiver 20A via a transmission path separate from the transmission path for transmitting the first and second signals, and sets the various operating conditions of the transceiver 20A based on that setting information. However, this technology has problems with increased weight and cost due to the large number of transmission paths and connectors.

[0043] Figure 4 shows the configuration of the bidirectional communication system 1. This bidirectional communication system 1 (Figure 4) can resolve the problems of the bidirectional communication system 1A (Figure 1). The bidirectional communication system 1 can appropriately set the cutoff frequency of the filter 22, the slew rate of the waveform of the second signal, and the data rate of the second signal according to the data rate of the first signal required by the application, without increasing the number of transmission lines or connectors.

[0044] The bidirectional communication system 1 comprises a transceiver 10 and a transceiver 20. The transceiver 10 and the transceiver 20 communicate bidirectionally via a common transmission line 30. The transceiver 10 is located on the host device side, and the transceiver 20 is located on the peripheral device side. The data rate of the first signal transmitted from the transceiver 10 to the transceiver 20 via the transmission line 30 is higher than the data rate of the second signal transmitted from the transceiver 20 to the transceiver 10 via the transmission line 30. The input / output terminal 19 of the transceiver 10 and the input / output terminal 29 of the transceiver 20 are connected to each other by the transmission line 30.

[0045] The transceiver 10 includes, in addition to the configuration of the transceiver 10A in Figure 1, a control unit 14, a training pattern generation unit 15, and a selection unit 16. The training pattern generation unit 15 generates and outputs a training pattern used by the receiver 23 when frequency locking is performed. The training pattern may be, for example, a clock in which high and low levels alternate at a constant period. The selection unit 16 inputs the first signal output from the host device as serial data, and also inputs the training pattern output from the training pattern generation unit 15, and selects either the first signal or the training pattern to output to the driver 11. The driver 11 sends the first signal or training pattern output from the selection unit 16 to the transceiver 20A via the input / output terminal 19 and the transmission line 30.

[0046] The receiver 13 receives the second signal output after passing through the filter 12, recovers the data and clock based on this second signal, and outputs the recovered data and recovery clock to the host device and the control unit 14. The control unit 14, having received the recovered data and recovery clock, controls the operation of the training pattern generation unit 15 to generate training patterns, and also controls the operation of the selection unit 16 to select one of the first signal and training patterns.

[0047] The transceiver 20 includes a control unit 24 in addition to the configuration of the transceiver 20A shown in Figure 1. The receiver 23 recovers the data and clock by frequency locking the first signal or training pattern output after passing through the filter 22, and outputs the recovered data and recovery clock to the peripheral device, as well as the recovery clock to the control unit 24. The frequency of this recovery clock matches the data rate of the first signal. The control unit 24 receives the recovery clock output from the receiver 23 and obtains the frequency information of this recovery clock. Based on this frequency information, the control unit 24 controls the cutoff frequency of the filter 22 and controls the operation of the driver 21. Details of the control by the control unit 24 are as follows.

[0048] The control unit 24 determines the cutoff frequency of the filter 22 that allows the first signal to pass through, based on the frequency information of the recovery clock. The control unit 24 controls the cutoff frequency of the filter 22 to be lower as the recovery clock frequency decreases, and controls the cutoff frequency of the filter 22 to be higher as the recovery clock frequency increases. The control unit 24 can determine the maximum cutoff frequency of the filter 22 that allows the first signal to pass through.

[0049] The control unit 24 determines the slew rate of the waveform of the second signal so that the harmonic components can be sufficiently attenuated by the filter 22. The control unit 24 controls the slew rate of the waveform of the second signal to be lower as the recovery clock frequency decreases, and controls the slew rate of the waveform of the second signal to be higher as the recovery clock frequency increases. The control unit 24 can determine the maximum slew rate of the waveform of the second signal so that the harmonic components can be sufficiently attenuated by the filter 22.

[0050] The control unit 24 determines the data rate of the second signal that the driver 21 can output at the above slew rate. The control unit 24 controls the data rate of the second signal to be lower as the recovery clock frequency decreases, and controls the data rate of the second signal to be higher as the recovery clock frequency increases. The control unit 24 can determine the maximum data rate of the second signal that the driver 21 can output at the above slew rate.

[0051] Based on these decisions, the control unit 24 controls the cutoff frequency of the filter 22 and controls the operation of the driver 21.

[0052] The control unit 24 may determine the cutoff frequency of the filter 22, as well as the slew rate and data rate of the waveform of the second signal output by the driver 21, based on the frequency information of the recovery clock output from the receiver 23 that received the first signal. However, it is preferable to determine these based on the frequency information of the recovery clock output from the receiver 23 that received the training pattern prior to receiving the first signal. Figure 5 is a flowchart showing an example of the operation of the bidirectional communication system 1 in the latter case.

[0053] When the power-down state of the bidirectional communication system 1 is released (step S1), the control unit 14 of the transmitting / receiving device 10 controls the training pattern generation unit 15 to output a training pattern, and the selection unit 16 to select and output the training pattern, causing the driver 11 to output a training pattern (step S2).

[0054] In the transceiver 20, the receiver 23 receives the training pattern output from the other transceiver 10, which has passed through the transmission path 30 and then through the filter 22. The receiver then performs frequency locking on this training pattern and outputs a recovery clock having a frequency matching the data rate of the first signal to the control unit 24 (step S3). At this time, it is preferable that the driver 21 is stopped. Alternatively, the cutoff frequency of the filter 22 may be set to the lowest value, and the driver 21 may be operating with the data rate and slew rate set to the lowest values.

[0055] The control unit 24, receiving the recovery clock output from the receiver 23, determines the maximum cutoff frequency of the filter 22 that can allow the first signal to pass through, and controls the cutoff frequency of the filter 22 based on this determination (step S4). The control unit 24 also determines the maximum slew rate of the waveform of the second signal that can be sufficiently attenuated by the filter 22, and the maximum data rate of the second signal that the driver 21 can output at the above slew rate, and controls the operation of the driver 21 based on these determinations (step S5). Through these controls, the cutoff frequency of the filter 22, as well as the slew rate and data rate of the waveform of the second signal output by the driver 21, are set to optimal values.

[0056] Once these settings are complete, the control unit 24 controls the driver 21 to notify the transceiver 10, which is the other transceiver, that the frequency lock on the training pattern by the receiver 23 has ended (step S6). At this time, the frequency lock termination notification signal output from the driver 21 is sent to the transceiver 10 via the transmission line 30 at the slew rate and data rate set in step S5.

[0057] In the transceiver 10, when the receiver 13 receives the frequency lock termination notification signal that has been sent from the transceiver 20 via the transmission line 30 and passed through the filter 12, it notifies the control unit 14 of this fact. Upon receiving this notification, the control unit 14 stops the generation and output of the training pattern by the training pattern generation unit 15, controls the selection unit 16 to select and output the first signal, and causes the driver 11 to output the first signal (step S7). In the transceiver 20, after the driver 21 sends the frequency lock termination notification signal to the transceiver 10, the receiver 23 begins receiving the first signal that has passed from the transceiver 10 via the transmission line 30 and passed through the filter 22.

[0058] At this point, the cutoff frequency of filter 22 is already optimally set in step S4, and the slew rate and data rate of the waveform of the second signal output by driver 21 are already optimally set in step S5. Therefore, filter 22 can allow the first signal to pass through while blocking the second signal, and can also block the harmonics of the second signal.

[0059] As described above, in this embodiment, in a bidirectional communication system 1 employing a frequency division scheme, the transceiver 20 can optimally set the cutoff frequency of the filter 22 for a desired data rate of the first signal according to the application, based on the first signal or training pattern sent from the transceiver 10 via the transmission line 30, and can also optimally set the slew rate and data rate of the waveform of the second signal output by the driver 21. Furthermore, a signal notifying the transceiver 10 that the settings have been completed in the transceiver 20 is transmitted via the transmission line 30 that transmits the first and second signals. In this embodiment, the transmission line 30 that transmits the first and second signals is used as the transmission line for setting various operating conditions of the transceiver 20. Therefore, in this embodiment, there is no increase in the number of transmission lines or connectors, and there are no problems of increased weight or cost. In addition, since this embodiment employs a frequency division scheme, it is superior to other bidirectional communication methods in terms of weight, cost, latency, EMI, and power consumption. [Explanation of symbols]

[0060] 1,1A...Bidirectional communication system, 10,10A...Transmitting / receiving device, 11...Driver, 12...Filter, 13...Receiver, 14...Control unit, 15...Training pattern generation unit, 16...Selection unit, 20,20A...Transmitting / receiving device, 21...Driver, 22...Filter, 23...Receiver, 24...Control unit, 30...Transmission line.

Claims

1. A transceiver that, through bidirectional communication with a counterpart transceiver via a transmission line, receives a first signal sent from the counterpart transceiver that has reached the input / output terminal, and sends a second signal having a data rate lower than the data rate of the first signal from the input / output terminal to the counterpart transceiver, A filter connected to the input / output terminals selectively passes the first signal and outputs it, and selectively attenuates the second signal, A receiver that receives the first signal output after passing through the filter, recovers and outputs data and clock based on this first signal, A driver that sends the second signal from the input / output terminal to the other transmitting / receiving device, A control unit controls the cutoff frequency of the filter and the data rate of the second signal output by the driver based on the frequency of the clock recovered and output by the receiver, A transmitting and receiving device equipped with the following features.

2. The receiver receives a training pattern from the other transmitting / receiving device before it begins receiving the first signal from the other transmitting / receiving device, performs frequency locking on this training pattern, and outputs a recovery clock having a frequency that matches the data rate of the first signal. The transmitting and receiving device according to claim 1.

3. The control unit controls the cutoff frequency of the filter to be lower as the recovery clock frequency decreases, and controls the cutoff frequency of the filter to be higher as the recovery clock frequency increases. The transmitting and receiving device according to claim 2.

4. The control unit controls the data rate of the second signal to be lower as the frequency of the recovery clock decreases, and controls the data rate of the second signal to be higher as the frequency of the recovery clock increases. The transmitting and receiving device according to claim 2.

5. The control unit controls the slew rate of the waveform of the second signal to be lower as the frequency of the recovery clock decreases, and controls the slew rate of the waveform of the second signal to be higher as the frequency of the recovery clock increases. The transmitting and receiving device according to claim 2.

6. The driver notifies the other transmitting / receiving device that the receiver has terminated the frequency lock on the training pattern. The transmitting and receiving device according to claim 2.

7. The receiver begins receiving the first signal from the other transceiver after the driver has notified the other transceiver that the frequency lock has ended. The transmitting and receiving device according to claim 6.

8. The filter includes a high-pass filter or a band-pass filter. The transmitting and receiving device according to claim 1.

9. A bidirectional communication system comprising a transmitting and receiving device according to any one of claims 1 to 8, and a counterpart transmitting and receiving device that performs bidirectional communication with the transmitting and receiving device via a transmission path.

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