Control device

Abstract

To provide a control device that can suppress the occurrence of signal waveform distortion within a threshold voltage range while enabling hot-swap.SOLUTION: A motherboard is formed with a main wiring 2 including a plurality of differential transmission lines 21 for transmitting a differential signal. A terminating resistor 22 is provided at both ends of each of the plurality of differential transmission lines 21, and connects the plurality of differential transmission lines 21 to each other. A plurality of daughter boards 4 are connected in parallel to each other via the main wiring 2. The line characteristic impedance Zdiff of each differential transmission line 21 is larger than a terminating resistance value Rterm which is the resistance value of the terminating resistor 22.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a control device. [Background technology]

[0002] Industrial control devices are usually equipped with multiple control boards, and signal communication is performed between each of the control boards. In order to achieve high data rates of, for example, 80 Mbps or higher for signal communication between control boards while also obtaining high noise resistance for the signal communication, a differential transmission method is more preferable than a single-ended transmission method. A communication method that uses a differential transmission method to connect multiple control boards so that they can communicate with each other is the MLVDS (Multi Low Voltage Differential Signaling) method.

[0003] In the MLVDS method, in order to suppress waveform distortion of the differential signal, it is recommended that multiple control boards are connected in a daisy chain structure, with each control board directly connected to the main wiring without using a stub. For this reason, the main wiring is drawn into the control board, and the main wiring is branched into a wiring that connects to the communication node within a few millimeters of the communication node in the control board, and a wiring that is drawn out to the outside of the control board. In addition, in order to suppress waveform distortion of the signal, it is recommended that the differential characteristic impedance of the main wiring and the termination resistance be matched to each other. Specifically, it is recommended that both the differential characteristic impedance and the termination resistance be 100 Ω.

[0004] On the other hand, for industrial control devices, there is a demand for hot swapping, which allows replacement of a control board while continuing operation, during maintenance or when a breakdown occurs.

[0005] However, in the above MLVDS system, the control board is directly connected to the main wiring without a stub, which means that hot swapping is not possible when replacing the control board. Even if hot swapping is not required, it is necessary to insert a dummy control board or the like when removing a control board in order to enable signal communication between other control boards, which is time-consuming.

[0006] In response to this, Patent Document 1 discloses a transmission device in which receivers, which are control boards capable of communicating by the MLVDS method, are connected in parallel to each other via main wiring. This transmission device includes two transmission lines for transmitting differential signals as main wiring, and a plurality of control boards each having two input / output terminals connected to the two transmission lines. This allows hot-swap of the control boards. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2014-127809 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, when hot-swap is performed in the transmission device described in Patent Document 1, the wiring from the communication node (specifically, the pin of the IC (Integrated Circuit) chip that constitutes the communication node) to the main wiring becomes a stub, and waveform distortion called ringing or shelf occurs in the differential signal. If this shelf occurs within the threshold voltage range, the waveform residence time of the differential signal in the threshold voltage range becomes long, and there is a risk that it will not be possible to ensure the timing margin of the eye mask (minimum setup and hold time). In addition, when the number of control boards increases, the load (especially the capacitive load) of the communication node of each control board causes the rise time / fall time of the signal waveform to slow down, resulting in a narrow eye pattern.

[0009] As described in Patent Document 1, the MLVDS method includes Type 1, whose threshold voltage range is −50 mV to 50 mV, and Type 2, whose threshold voltage range is 50 mV to 150 mV. In Type 2, the threshold voltage range has an offset of +100 mV, so that a low-level signal is output during an idle period, and malfunctions can be suppressed. However, since the threshold voltage range has an offset, the duty ratio of the signal is modulated, and DCD (Duty Cycle Distortion) jitter increases. Therefore, compared with Type 1, whose threshold voltage range is symmetrical with respect to 0 V, it is required to shorten the waveform residence time during which the differential signal resides in the threshold voltage range, especially when speeding up. Therefore, it is necessary to suppress the occurrence of shelves within the threshold voltage range, especially in Type 2.

[0010] An object of the present disclosure is to provide a control device capable of suppressing distortion of a signal waveform from occurring within a threshold voltage range while enabling hot swapping. [Means for solving the problem]

[0011] A control device according to one embodiment of the present disclosure includes a mother board on which a main wiring including a plurality of differential transmission paths for transmitting differential signals is formed, termination resistors provided at both ends of each of the plurality of differential transmission paths and connecting the plurality of differential transmission paths to each other, and a plurality of control boards connected in parallel to each other via the main wiring, wherein the characteristic impedance of each differential transmission path is greater than a termination resistance value which is the resistance value of the termination resistor. Effect of the Invention

[0012] According to the present invention, it is possible to suppress distortion of a signal waveform from occurring within a threshold voltage range while enabling hot swapping. [Brief description of the drawings]

[0013] [Figure 1]FIG. 2 is a perspective view illustrating a schematic configuration of a control device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram illustrating an example of a circuit topology of a control device according to an embodiment of the present disclosure. [Diagram 3] FIG. 2 is a diagram showing a circuit topology of a control device of a first comparative example. [Figure 4] FIG. 11 is a diagram showing a circuit topology of a control device of a second comparative example. [Diagram 5] FIG. 11 is a diagram showing an example of a signal waveform in a control device of a second comparative example. [Figure 6] FIG. 4 is a diagram illustrating an example of a signal waveform in a control device according to an embodiment of the present disclosure. [Figure 7] FIG. 2 is a diagram illustrating an example of an eye pattern in a control device according to an embodiment of the present disclosure. [Figure 8] FIG. 13 is a diagram illustrating another example of an eye pattern in the control device according to the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0015] Fig. 1 is a perspective view showing a schematic configuration of a control device according to an embodiment of the present disclosure. The control device 100 shown in Fig. 1 includes a motherboard 1 which is a parent substrate, main wiring 2 formed on the motherboard 1, a plurality of connectors 3 provided on the motherboard 1, and a plurality of daughterboards 4 which can be inserted into and removed from the connectors 3.

[0016] The main wiring 2 includes a plurality of (two in this embodiment) differential transmission lines 21 for transmitting differential signals. Termination resistors 22 are provided at both ends of each differential transmission line 21 to connect the differential transmission lines 21 to each other.

[0017] The connector 3 is a connection portion for connecting the mother board 1 and the daughter board 4 to each other. The multiple connectors 3 are connected to each other in parallel via the main wiring 2. Each connector 3 is connected to both of the two differential transmission paths 21 included in the main wiring 2. Also, the number of connectors 3 is not limited as long as there is a plurality of connectors 3.

[0018] The daughter board 4 is a control board (child board) that can be inserted into and removed from the connector 3, and when inserted into the connector 3, it is connected to the main wiring 2 via the connector 3. Therefore, a plurality of daughter boards 4 are connected in parallel to one another via the main wiring 2. The daughter board 4 has an MLVDS device 41 that is a communication unit that communicates with other daughter boards 4 via the main wiring 2 in the MLVDS system. The MLVDS device 41 is formed, for example, of an IC chip. As described above, there are a plurality of types of the MLVDS system that have different threshold voltage ranges, but here, unless otherwise specified, it is assumed that the threshold voltage range is Type 2, which has a range of 50 mV to 150 mV.

[0019] Fig. 2 is a diagram showing an example of a circuit topology of the control device 100. In Fig. 2, the main wiring 2 includes two differential transmission lines 21 as described above, and the ends of the lines are connected to each other via a termination resistor 22. In this embodiment, each differential transmission line 21 is about 400 mm long.

[0020] A plurality of connectors (represented as CN in FIG. 2) 3 are connected in parallel to each other via two differential transmission paths 21. In the example of FIG. 2, there are 19 connectors 3, and a daughter board 4 is inserted into each of the 19 connectors 3. However, it is not necessary to insert a daughter board 4 into all of the connectors 3. In this embodiment, the 19 daughter boards 4 may be distinguished and referred to as daughter boards 4_1 to 4_19 in order from the left in the drawing.

[0021] The daughter board 4 has an MLVDS device 41, an internal transmission path 42, and a damping resistor 43. The MLVDS device 41 is connected to the connector 3 via the internal transmission path 42. The damping resistor 43 is provided on the internal transmission path 42. In this embodiment, the length of the internal transmission path 42 is about 40 mm. Also, it is assumed that the length of the internal transmission path 42 is approximately equal to the length of the stub.

[0022] The line characteristic impedance Z, which is the characteristic impedance of the differential transmission line 21 diff and the resistance value of the termination resistor 22, R term are configured so as not to be matched to each other. In other words, the line characteristic impedance Z diff and the termination resistance value R term Specifically, the line characteristic impedance Z diff is the termination resistance value R term Also, the line characteristic impedance Z diff is preferably greater than 100 Ω, and the termination resistance R term It is desirable that the line characteristic impedance Z be smaller than 100Ω. diff 140Ω, termination resistance R term is set to 68 Ω.

[0023] The damping resistance value R dump is the line characteristic impedance Z diff In the example of Figure 2, the damping resistance R dump is set to 33 Ω. Note that there is a risk of distortion in the signal waveform due to the line characteristic impedance Zdiff and the termination resistance value Rterm not being matched, but when a stub is present as in this embodiment, distortion in the signal waveform due to the stub becomes dominant and is attenuated by the damping resistor 43, so there is no problem.

[0024] In the above-described control device 100, a generated voltage value (generation position) V, which is a voltage value at which a waveform distortion called a shelf occurs in a differential signal, is expressed by the following relational expression (1). V = V0 × (Z diff ) / (R0+R dump +Z diff ) · · · (1) Here, V0 is the voltage value of the driving power supply of the control device 100, and R0 is the output resistance of the MLVDS device 41. As shown in the relational expression (1), in order to increase the generated voltage value of the shelf and position the generated voltage value of the shelf outside the threshold voltage range, the line characteristic impedance Z diff and damping resistance R dump It is effective to make as small as possible. For simplicity, equation (1) assumes that there is no termination resistor. When a termination resistor is present, the generated voltage value cannot be expressed by a simple equation such as equation (1), but the basic tendency is the same as when there is no termination resistor.

[0025] For simplicity's sake, let's take a signal that does not have a termination resistor as an example. V0=3.3V, Z diff = 100Ω, R0 = 50Ω, R dump =Z diff If / 2=50 Ω, then the generated voltage value V is 3.3×0.5=1.65 V, and a shelf occurs near the midpoint of the amplitude, that is, near the threshold voltage range when converted into a differential voltage.

[0026] In contrast, V0=3.3V, Z diff = 140Ω, R0 = 50Ω, R dump = 33 Ω, the generated voltage value V is 3.3 × 0.63 = 2.07 V, which is higher than V0 / 2. Therefore, the generated voltage of the shelf can be made higher than around V0 / 2, and the occurrence of the shelf within the threshold voltage range can be suppressed.

[0027] Fig. 3 is a diagram showing a circuit topology of a control device of a first comparative example for this embodiment. In Fig. 3, components corresponding to the components of this embodiment shown in Fig. 1 and Fig. 2 are denoted by adding "a" to the reference numeral. For example, a component corresponding to the MLVDS device 41 is denoted as the MLVDS device 41a.

[0028] The control device 100a shown in Fig. 3 has a circuit topology that suppresses stubs. That is, in the control device 100a, the main wiring 2a is drawn into the daughter board 4a, and within a few mm of the MLVDS device 41a, it is branched into a wiring that connects to the MLVDS device 41a and a wiring that returns to the outside of the daughter board 4a. In other words, the main wiring 2a serves both as a lead-in wiring and a lead-out wiring for the daughter board 4a, and the daughter board 4a cannot be hot-plugged or plugged in.

[0029] Fig. 4 is a diagram showing a circuit topology of a control device of a second comparative example for this embodiment. In Fig. 4, components corresponding to the components of this embodiment shown in Fig. 1 and Fig. 2 are denoted by adding "b" to the reference numeral. For example, a component corresponding to MLVDS device 41 is denoted as MLVDS device 41b.

[0030] In the control device 100b shown in FIG. 4, a daughter board 4b is connected in parallel to a main wiring 2b, as in the control device 100 of the present embodiment. This allows hot swapping. However, in the control device 100b, the termination resistance value R term and line characteristic impedance Z diff The resistors are matched at 100 Ω. Furthermore, there is no resistor corresponding to the damping resistor 43 in the daughter board 4b.

[0031] Fig. 5 is a diagram showing an example of a signal waveform in the control device 100b of the second comparative example shown in Fig. 4. Fig. 5 shows a transmission signal waveform 51 and a reception signal waveform 52 when a signal is transmitted from the sixth daughter board 4b_6 to the seventh daughter board 4b_7. As shown in Fig. 5, in both the transmission signal waveform 51 and the reception signal waveform 52, ringing occurs due to the influence of the reflection of the signal from each daughter board 4b, and a shelf 53 enters a threshold voltage range 54.

[0032] 6 is a diagram showing an example of a signal waveform in the control device 100 of the present embodiment shown in FIG. 1 and FIG. 2. FIG. 6 shows a transmission signal waveform 61 and a reception signal waveform 62 when a signal is transmitted from the sixth daughter board 4_6 to the seventh daughter board 4_7. As shown in FIG. 6, in this embodiment, the ringing shown in FIG. 5 is suppressed in both the transmission signal waveform 61 and the reception signal waveform 62, and a shelf 63 appears as a change in the slope of a signal without aliasing. In addition, the generated voltage of the shelf 63 is located outside the threshold voltage range 64, and the shelf 63 does not enter the threshold voltage range 64.

[0033] 7 is a schematic diagram showing an example of an eye pattern and an eye mask in the control device 100 of this embodiment. FIG. 7 shows an eye pattern 73 in which a shelf 71 occurs inside a threshold voltage range 72, and an eye pattern 74 in which the shelf 71 occurs outside the threshold voltage range 72. As shown in the eye patterns 73 and 74 in FIG. 7, an eye width 74a in the case where the shelf 71 occurs outside the threshold voltage range 72 is longer than an eye width 73a in the case where the shelf 71 occurs inside the threshold voltage range 72. For this reason, the case where the shelf 71 occurs outside the threshold voltage range 72 is more advantageous in terms of securing a timing margin of the eye mask than the case where the shelf 71 occurs inside the threshold voltage range 72.

[0034] Figure 8 shows the line characteristic impedance Z diff 8 is a schematic diagram showing an eye pattern when only the line characteristic impedance Z diff is lower than that of 140 Ω. Therefore, the line characteristic impedance Z diff It can be seen that the higher the value, the more effective it is to position the occurrence position of the shelf 81 outside the threshold voltage range.

[0035] In addition, the termination resistance R termis the line characteristic impedance Z diff By setting the impedance at 68 Ω, which is smaller than the reference impedance, the range of change in amplitude according to the bit string of the signal is small, and jitter 82 can be suppressed to less than 0.1 ns in both the rising waveform and the falling waveform, and the generated voltage value of shelf 81 can be suppressed within a voltage range of about 20 mV.

[0036] As described above, according to this embodiment, the motherboard 1 is formed with the main wiring 2 including a plurality of differential transmission paths 21 for transmitting differential signals. The termination resistors 22 are provided at both ends of each of the differential transmission paths 21, and connect the differential transmission paths 21 to each other. The daughter boards 4 are connected in parallel to each other via the main wiring 2. The line characteristic impedance Z diff is the resistance value of the termination resistor 22, R term Therefore, since the daughter boards 4 are connected in parallel to each other via the main wiring 2, the daughter boards 4 can be hot-plugged. diff Since it is possible to increase the voltage value of the shelf in the differential signal, it is possible to suppress the shelf from occurring within the threshold voltage range. Also, it is possible to suppress the range of change in amplitude according to the bit string of the signal, and it is possible to suppress jitter.

[0037] In this embodiment, the line characteristic impedance Z diff is greater than 100 Ω, allowing the shelf to occur more reliably outside the threshold voltage.

[0038] In this embodiment, the termination resistance value R term Since the impedance is smaller than 100Ω, it is possible to suppress jitter more appropriately.

[0039] In this embodiment, a damping resistor 43 is provided in the internal transmission path 42 that connects the MLVDS 41 in the daughter board 4 and the main wiring 2. The damping resistance value R dumpis the line characteristic impedance Z diff In this case, it is possible to suppress the occurrence of a shelf within the threshold voltage range, while suppressing ringing occurring at the shelf.

[0040] In this embodiment, the damping resistance value R dump is 33 Ω or less. In this case, it is possible to more appropriately suppress ringing that occurs on the shelf.

[0041] Furthermore, in this embodiment, the MLVDS device 41a performs communication in the MLVDS format with a threshold voltage range of 50 mV to 150 mV. This makes it possible to achieve high speed communication even when the duty ratio of the signal is modulated.

[0042] Furthermore, in this embodiment, since a plurality of connectors 3 are provided to allow the daughter board 4 to be inserted and removed, the daughter board 4 can be easily inserted and removed while the power is on.

[0043] The above-described embodiments of the present disclosure are illustrative examples of the present disclosure, and are not intended to limit the scope of the present disclosure to only these embodiments. A person skilled in the art can implement the present disclosure in various other forms without departing from the scope of the present disclosure. [Explanation of symbols]

[0044] 1: motherboard, 2: main wiring, 3: connector, 4: daughter board, 21: differential transmission path, 22: termination resistor, 41: MLVDS device, 42: internal transmission path, 43: damping resistor, 100: control device

Claims

1. a mother board on which main wiring including a plurality of differential transmission paths for transmitting differential signals is formed; a termination resistor provided at each end of the plurality of differential transmission paths and connecting the plurality of differential transmission paths to each other; a plurality of control boards connected in parallel to each other via the main wiring; a characteristic impedance of each of the plurality of differential transmission paths is greater than a termination resistance value that is a resistance value of the termination resistor, Each control board has a communication unit that communicates with the other control boards via the main wiring using differential signals, an internal wiring that connects the communication unit and the main wiring, and a damping resistor provided on the internal wiring, A control device, wherein a damping resistance value of the damping resistor is smaller than half of the characteristic impedance.

2. The control device of claim 1 , wherein the characteristic impedance is greater than 100Ω.

3. The control device according to claim 1 , wherein the termination resistance value is less than 100Ω.

4. The control device according to claim 1 , wherein the damping resistance value is 33Ω or less.

5. The control device according to claim 1 , wherein the communication unit performs communication using a Multi Low Voltage Differential Signaling (MLVDS) method with a threshold voltage range of 50 mV to 150 mV.

6. The control device according to claim 1 , further comprising a plurality of connectors provided in parallel via the main wiring, the connectors enabling insertion and removal of the control board.

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