Signal transmission device

Abstract

To provide a signal transmission device capable of implementing reduction of noise and reduction of signal reflection on a signal line between the signal transmission device and the other device.SOLUTION: A signal transmission device includes: a circuit board; a connector which is provided in the circuit board and to / from which a cable for transmitting a differential signal with an external device is attachable / detachable; an integrated circuit mounted on the circuit board; a signal line, which is provided on the circuit board, for exchanging the differential signal between the integrated circuit and the connector; a common-mode choke coil, which is provided in the signal line, for suppressing noise outputted from the integrated circuit; and a re-timer IC provided between the common-mode choke coil and the connector in the signal line.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a signal transmission device.

Background Art

[0002] A controller IC such as a USB-IC may be mounted on a signal transmission device. For example, a USB-IC outputs a USB (Universal Serial Bus) signal. The USB signal is a differential signal compliant with the USB standard. The USB signal is input to a device outside the signal transmission device via a connector.

[0003] Here, in order to reduce the noise generated in the controller IC, a common mode choke coil (CMCC) may be provided. The common mode choke coil (hereinafter sometimes referred to as CMCC) is provided, for example, between the controller IC and the connector (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a signal transmission device, it is necessary to reduce noise and consider signal reflection in the signal line between the signal transmission device and another device.

[0006] The present invention has been made in view of the above, and an object thereof is to provide a signal transmission device capable of reducing noise and reducing signal reflection in the signal line between the signal transmission device and another device.

Means for Solving the Problems

[0007] A signal transmission device according to an aspect of the present disclosure includes a circuit board, a connector provided on the circuit board and detachable from a cable for transmitting a differential signal to an external device, an integrated circuit mounted on the circuit board, a signal line provided on the circuit board for transmitting and receiving the differential signal between the integrated circuit and the connector, a common mode choke coil provided on the signal line for suppressing noise output from the integrated circuit, and a retimer IC provided on the signal line between the common mode choke coil and the connector. Note that in the signal line, the retimer IC is connected directly in DC, and the common-mode choke coil is provided closest to the terminal that outputs the differential signal from the integrated circuit to the signal line, where "closest" means within a distance of half the wavelength corresponding to the band of the differential signal.

Effect of the Invention

[0008] According to the signal transmission device according to the present disclosure, it is possible to reduce noise and reduce signal reflection in a signal line between the device and other devices.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the signal transmission device of the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited by this embodiment. Also, the constituent elements of each embodiment include those that can be replaced and are easy for those skilled in the art, or those that are substantially the same. Each embodiment is an example, and partial replacement or combination of the configurations shown in different embodiments is possible. In the description of each of the following embodiments, the same reference numerals are given to the same or equivalent constituent parts as those in other embodiments, and the description thereof is simplified or omitted. The configurations described below can be combined as appropriate. Also, omissions, replacements, or changes of the configuration can be made without departing from the gist of the present disclosure.

[0011] (Comparative Example) For understanding the present disclosure, the comparative example will be described first.

[0012] FIG. 1 is a diagram showing the configuration of a main part of a signal transmission device 10a of a comparative example. In FIG. 1, the signal transmission device 10a includes a circuit board 1a, a controller IC 11, a connector 20, a CMCC 12, and a signal line 15. The controller IC 11, the connector 20, the CMCC 12, and the signal line 15 are mounted on the circuit board 1a.

[0013] The connector 20 is provided on the circuit board 1a. The connector 20 can attach and detach the cable 2. By connecting the cable 2 to the connector 20, an external device (not shown) can be electrically connected to the signal transmission device 10a. The cable 2 is, for example, a cable that transmits differential signals to an external device.

[0014] The controller IC 11 is an integrated circuit having a function as a controller that can input and output signals conforming to a predetermined standard. The controller IC 11 is mounted on the circuit board 1a. The controller IC 11 is an integrated circuit that exchanges differential signals with an external device via the connector 20 when an external device (not shown) is connected to the connector 20. The controller IC 11 is, for example, a USB-IC that can input and output USB signals. The controller IC 11 may be a CPU (Central Processing Unit) having a function as a controller.

[0015] The signal line 15 is provided on the circuit board 1a. The signal line 15 is a line for exchanging differential signals between the controller IC 11 and the connector 20. The CMCC 12 is provided on the signal line 15. The CMCC 12 suppresses the common-mode noise of the signal output from the controller IC 11 and transmitted through the signal line 15.

[0016] In the signal transmission device 10a shown in FIG. 1, the signal output from the controller IC 11 is transmitted through the signal line 15 and transmitted to an external device (not shown) via the connector 20 and the cable 2. Also, the signal output from an external device (not shown) is input to the signal transmission device 10a via the cable 2 and the connector 20. The signal input to the signal transmission device 10a is transmitted through the signal line 15 and input to the controller IC 11. The common-mode noise of the signal transmitted through the signal line 15 is reduced by the CMCC 12. For this reason, the common-mode noise flowing from the signal transmission device 10a to the cable 2 via the connector 20 is reduced by the CMCC 12.

[0017] Here, CMCC12 is provided between the controller IC11 and the connector 20. Therefore, for the signal output from the controller IC11, depending on the frequency band, it is reflected by CMCC12 as indicated by the arrow Y1. It is not preferable that the signal reflected as the arrow Y1 is input to each part of the signal transmission device 10a.

[0018] Also, for the signal output from an external device, after passing through the connector 20, depending on the frequency band, it is reflected by CMCC12 as indicated by the arrow Y2. The signal reflected as the arrow Y2 is input to the cable 2 after passing through the connector 20. It is not preferable that the signal reflected as the arrow Y2 is input to the external device through the cable 2.

[0019] FIG. 2 is a diagram showing an example of a common mode signal reflected on the cable 2 side in the configuration of FIG. 1. In FIG. 2, the horizontal axis represents the frequency [GHz], and the vertical axis represents Scc11 [dB] of the S parameter. Scc11 indicates the reflection characteristic of the common mode signal.

[0020] In FIG. 2, the signal range 100 is a range defined as an index for the quality of the signal according to a predetermined standard. The signal range 100 is, for example, a range that defines a common mode signal reflected on the USB connector side in the USB standard. Here, the CMCC12 for noise removal has the characteristic of reflecting the input common mode signal to the input side without passing it through. Therefore, due to the reflection characteristic of CMCC12, as shown by the arrow Y2, the common mode signal is reflected to the connector 20 side. Therefore, in the configuration of the comparative example shown in FIG. 1, there is a portion outside the signal range 100 in FIG. 2, and the index of the common mode return loss cannot be satisfied.

[0021] (Embodiment) Next, a signal transmission device according to an embodiment will be described.

[0022] FIG. 3 is a diagram showing the main part of the signal transmission device 10 according to the embodiment. As shown in FIG. 3, the signal transmission device 10 of this example includes a circuit board 1, a controller IC 11, a connector 20, a CMCC 12, a signal line 15, and a retimer IC 13. The difference from the comparative example described with reference to FIG. 1 is that a retimer IC 13 is added to the signal line 15. The retimer IC 13 is provided between the CMCC 12 and the connector 20 in the signal line 15. Note that the signal transmission device 10 is, for example, a notebook personal computer, a desktop personal computer, a game machine, or the like.

[0023] (Retimer IC) The retimer IC 13 once converts the input differential signal into a single-ended signal, further converts it into a differential signal, and outputs it. Therefore, the common-mode component of the input signal does not flow to the output signal side. At this time, the retimer IC 13 outputs the differential signal corresponding to the input differential signal in synchronization with another clock. That is, the retimer IC 13 regenerates the input differential signal in synchronization with another clock. The common-mode reflection signal by the CMCC 12 is canceled by the retimer IC 13. Therefore, no common-mode reflection signal is transmitted to the connector 20 side.

[0024] The retimer IC 13 does not amplify the input signal but has a function of completely reconstructing a new signal. Therefore, the signal output from the retimer IC 13 is not affected by the input signal.

[0025] FIG. 4 is a diagram showing a configuration example of the retimer IC 13. In FIG. 4, the retimer IC 13 includes a receiving unit (Rx) 121, a clock data recovery unit (CDR) 122, an elastic buffer 123, a clock generation unit (Local Clock) 124, and a transmitting unit (Tx) 125.

[0026] The receiving unit 121 converts the differential signal 110 into a single-ended signal 111. That is, the receiving unit 121 receives the differential signal 110 and outputs the single-ended signal 111.

[0027] The clock data recovery unit 122 receives the single-ended signal 111 and outputs the data 112 and the clock 113. That is, the clock data recovery unit 122 generates the data 112 and the clock 113 from the single-ended signal 111 output from the receiving unit 121.

[0028] The elastic buffer 123 receives the data 112 and the clock 113 generated by the clock data recovery unit 122. The elastic buffer 123 stores the data 112 at the timing of the clock 113.

[0029] The clock generation unit 124 generates a clock CK for reading the data 114 from the elastic buffer 123. The clock generation unit 124 generates a clock CK different from the clock 113.

[0030] The transmitting unit 125 converts the data 114 into a differential signal 115. That is, the transmitting unit 125 receives the data 114 read from the elastic buffer 123 and outputs the differential signal 115.

[0031] (Example of CMCC) FIG. 5 is an external view showing an example of CMCC. In FIG. 5, for example, the vertical length A of CMCC12 is 0.65 [mm], the horizontal length B is 0.5 [mm], and the height C is 0.3 [mm].

[0032] CMCC12 has four terminals T11, T12, T21, and T22. The terminal T11 and the terminal T12 are connected to the controller IC11 side of CMCC12, for example, in the signal line 15. The terminal T21 and the terminal T22 are connected to the connector 20 side of CMCC12, for example, in the signal line 15 in FIG. 1.

[0033] By providing CMCC12 on signal line 15, it is possible to suppress common-mode noise generated during the transmission of differential signals. Generally, the source of common-mode noise is controller IC11 that generates differential signals. Also, regarding noise radiation, it is common for the common-mode noise generated from controller IC11 to be transmitted on signal line 15 and then radiate noise from signal line 15. By reflecting the common-mode noise transmitted from controller IC11 to CMCC12 back to the controller IC11 side, the passing noise can be suppressed. Therefore, as shown in FIG. 3, by mounting CMCC12 between controller IC11 and retimer IC13 on signal line 15, it is possible to suppress the common-mode noise N radiated from signal line 15 (X mark in FIG. 3).

[0034] In signal line 15 of FIG. 3, CMCC12 is preferably provided in the immediate vicinity of terminals T1 and T2 that output differential signals from controller IC11 to signal line 15. If it is provided in the immediate vicinity of terminals T1 and T2, the effect of suppressing noise is significant. Here, in order to suppress the influence of noise on the 5 [GHz] communication band of the wireless communication standard, for example, within 3 [cm], which is half of about 6 [cm], which is one wavelength corresponding to 5 [GHz], is set as the immediate vicinity of terminals T1 and T2. Note that this "3 [cm]" is the result of wavelength shortening considering the relative dielectric constant 4.5 of FR-4 (Flame Retardant Type 4), which is a common substrate material. That is, on the substrate on which controller IC11 and CMCC12 are mounted, it is preferable to mount CMCC12 with a wiring length within 3 [cm] from terminals T1 and T2.

[0035] (Frequency characteristics of CMCC) Figures 6 and 7 are diagrams showing the frequency characteristics of the CMCC12 in FIG. 5. FIG. 6 is a diagram showing the frequency characteristics when a differential signal is input to the CMCC12 in FIG. 5. In FIG. 6, the horizontal axis represents the frequency [Hz], and the vertical axis represents Sdd11 [dB] of the S parameter. Also, FIG. 7 is a diagram showing the frequency when a common mode signal is input to the CMCC12 in FIG. 5. In FIG. 7, the horizontal axis represents the frequency [Hz], and the vertical axis represents Scc11 [dB] of the S parameter. The frequency f1 in FIG. 7 corresponds to 2.4 [GHz] of the wireless communication standard. The frequency f2 corresponds to 5 [GHz] of the wireless communication standard. In the frequency bands near these frequencies f1 and f2, the CMCC12 of this example has good reflection characteristics.

[0036] Returning to FIG. 3, when the CMCC12 is mounted between the retimer IC13 and the connector 20, the common mode signal is reflected toward the connector 20 as indicated by the arrow Y3. Here, the retimer IC13 is an IC that corrects the signal by newly regenerating the differential signal. Therefore, the signal output from the retimer IC13 is not affected by the reflected common mode signal reflected as indicated by the arrow Y3. Therefore, the CMCC12 is mounted between the controller IC11 and the retimer IC13 as shown in FIG. 3. The reflected common mode signal by the CMCC12 is canceled by the retimer IC13. Therefore, no reflected common mode signal is transmitted to the connector 20 side.

[0037] (Measurement of Noise) Figures 8 and 9 are diagrams for explaining the measurement of noise in the signal transmission device 10. In FIGS. 8 and 9, when the signal transmission device 10 and the external device 16 exchange the USB signal 200 via the cable 2, the noise radiated from the signal line 15 between the controller IC and the retimer IC is measured. In this example, the radiation level of the noise interfering with the 2.4 [GHz] band of the wireless communication standard was measured using the spectrum analyzer 18.

[0038] FIG. 8 shows the measurement situation when no CMCC is mounted on the signal line 15 between the controller IC 11 and the retimer IC 13. FIG. 9 shows the measurement situation when the CMCC 12 is mounted on the signal line 15 between the controller IC 11 and the retimer IC 13.

[0039] In FIGS. 8 and 9, the signal transmission device 10 was placed in the anechoic chamber 300, and the antenna 14 was provided in the signal transmission device 10. The antenna 14 was provided at a position 10 cm away from the substrate on which the controller IC was mounted. The antenna 14 is an antenna capable of receiving the radiation level of noise interfering with the 2.4 [GHz] band of the wireless communication standard. The cable C1 connected to the antenna 14 was connected to the preamplifier 17, and the signal amplified by the preamplifier 17 was input to the spectrum analyzer 18 through the cable C2. An external device 16 was connected to the connector 20 via the cable 2. The external device 16 is a storage device using an SDD (Solid State Drive) in this example.

[0040] FIG. 10 is a diagram showing an example of the evaluation regarding noise. In FIG. 10, the horizontal axis is the frequency [MHz], and the vertical axis is the noise level [dBm].

[0041] The solid line in FIG. 10 indicates the state (No communication) where no signal is output. The broken line in FIG. 10 indicates the state where the signal of USB4 is output without providing the CMCC as shown in FIG. 8 (No CMCC). The one-dot chain line in FIG. 10 indicates the state where the signal of USB4 is output with the CMCC provided as shown in FIG. 9 (with CMCC). As shown by the elliptical D of the broken line in FIG. 10, an improvement of about 4.5 [dBm] was confirmed regarding the 2.4 [GHz] band of the wireless communication standard. Therefore, as shown in FIG. 3, the noise N in the signal transmission device 10 can be reduced.

[0042] (Measurement of reflection characteristics) Figures 11 and 12 are diagrams for explaining the measurement of the reflection characteristics as viewed from the connector 20 side with respect to the signal transmission device 10. As shown in FIGS. 11 and 12, a jig 40 was connected to the connector 20, and the reflection characteristics were measured by a network analyzer 19. That is, for the signal reflected like the arrow Y4 in the connector 20, the common mode return loss, that is, Scc11 was measured.

[0043] FIG. 11 shows the measurement situation when no CMCC is mounted on the signal line 15 between the controller IC 11 and the retimer IC 13. FIG. 12 shows the measurement situation when CMCC 12 is mounted on the signal line 15 between the controller IC 11 and the retimer IC 13.

[0044] The jig 40 is a jig that converts from the connector 20 of the signal line 15 to a 50Ω coaxial line. In either case of FIGS. 11 and 12, the common mode signals Tx + and Tx− converted by the jig 40 were input to channels Ch1 and Ch3 of the network analyzer 19 by the cables C3 and C4. The network analyzer 19 measured the common mode return loss, that is, Scc11, as viewed from the connector 20 side.

[0045] FIG. 13 is a diagram showing an example of a common mode signal reflected on the cable 2 side in the configuration of FIG. 3. In FIG. 13, the horizontal axis represents the frequency [GHz], and the vertical axis represents the Scc11 [dB] of the S parameter. Different from the common mode signal 101 described with reference to FIG. 2, the common mode signal 102 is a signal that changes within the signal range 100. Therefore, the common mode signal 102 satisfies a predetermined standard.

[0046] As described above, in the signal transmission device 10, a CMCC 12 that suppresses noise interfering with the 2.4 [GHz] communication band of the wireless communication standard, for example, is mounted on the signal line 15 between the controller IC and the retimer IC. Thereby, while satisfying the standard of the common mode return loss, that is, Scc11, it is possible to suppress the radiation of noise interfering with the communication band of the wireless communication standard.

Description of Symbols

[0047] 1, 1a Circuit board 2 Cable 10, 10a Signal transmission device 11 Controller IC 13 Retimer IC 14 Antenna 15 Signal line 20 Connector 121 Receiver 122 Clock data recovery unit 123 Elastic buffer 124 Clock generation unit 125 Transmitter

Claims

1. A circuit board, a connector provided on the circuit board and detachable from a cable for transmitting a differential signal to / from an external device, an integrated circuit mounted on the circuit board, a signal line provided on the circuit board for transferring the differential signal between the integrated circuit and the connector, a common mode choke coil provided on the signal line for suppressing noise output from the integrated circuit, a retimer IC provided between the common mode choke coil and the connector in the signal line, wherein in the signal line, the retimer IC is connected directly, wherein the common mode choke coil is provided in the immediate vicinity of a terminal for outputting the differential signal from the integrated circuit to the signal line, wherein the immediate vicinity means a distance within half of the wavelength corresponding to the band of the differential signal, a signal transmission device.

2. The retimer IC of the signal transmission device according to claim 1, comprising: a receiving section for receiving the differential signal and outputting a single-ended signal; a clock data recovery section for generating data and a clock from the single-ended signal output from the receiving section; an elastic buffer for storing the data generated by the clock data recovery section at the timing of the clock; a clock generation section for generating a clock for reading data from the elastic buffer; and a transmitting section for inputting the data read from the elastic buffer and outputting a differential signal.

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