Signal transmission device

Abstract

This signal transmission device comprises: a transmission line (2) having a signal line (21) and a reference line (22); and a termination circuit (3). One end of the signal line (21) of the transmission line (2) is electrically connected to a signal output terminal (101) of a transmitter (100) that transmits an electrical signal, and the other end of the signal line (21) of the transmission line (2) is electrically connected to a signal input terminal (201) which is electrically connected to a constant power supply potential node (203) via a pull-up resistor (204) in a receiver (200) that receives the electrical signal from the transmitter (100). The reference line (22) has a first conductor (221) considered to be ground potential, a second conductor (222) that is DC-isolated from the first conductor (221), and a capacitor (22a) that connects the first conductor (221) and the second conductor (222). The termination circuit (3) is electrically connected to the other end of the signal line (21) of the transmission line (2) and applies a constant voltage, which is a voltage below the constant power supply voltage applied to the constant power supply potential node (203) of the receiver (200), to the other end of the signal line (21) of the transmission line (2).

Description

signal transmission device

[0001] The present disclosure relates to a signal transmission device including a transmission line having a signal line and a reference line connected between a signal output terminal of a transmitter and a signal input terminal of a receiver.

[0002] An input protection circuit for protecting a microcomputer from overvoltage is disclosed in Patent Document 1. The input protection circuit disclosed in Patent Document 1 is connected between an analog signal input terminal of the microcomputer and a ground line (ground potential). The input protection circuit disclosed in Patent Document 1 includes a first resistor and a second resistor connected in series between a power supply voltage and the ground line, and a transistor connected between the analog signal input terminal and the ground line, the on / off of which is controlled by applying a voltage divided by the first resistor and the second resistor to its base.

[0003] JP 2015-186008 A

[0004] On the other hand, as the data communication capacity increases, the operating frequency of electronic devices is also increasing, and transmission lines with a signal line and a reference line (ground conductor) are used for signal transmission. Also, in receivers with many input pins, a pseudo open drain (POD) has been proposed to reduce power consumption by pulling up the signal input terminal to which the signal line of the transmission line is connected to the power supply voltage.

[0005] One possible solution to potential fluctuations in signal lines in transmission lines is to apply the input protection circuit shown in Patent Document 1. However, in this case, the first and second resistors are connected in series between the power supply voltage and the ground line, which causes a problem of increased power consumption.

[0006] The present disclosure has been made in consideration of the above points, and aims to provide a signal transmission device that includes a transmission line having a reference line and a signal line one end of which is connected to a signal output terminal of a transmitter that transmits an electrical signal and the other end of which is connected to a signal input terminal of a receiver that receives a received signal from the transmitter, and that can maintain a constant midpoint potential, i.e., an offset voltage, in the signal line, and that can achieve both reduced power consumption and improved noise resistance of the receiver.

[0007] A signal transmission device according to the present disclosure comprises a transmission line having a signal line and a reference line, and a termination circuit, wherein one end of the signal line in the transmission line is electrically connected to a signal output terminal of a transmitter that transmits an electrical signal, and the other end of the signal line in the transmission line is electrically connected to a signal input terminal in a receiver that receives the electrical signal from the transmitter, the signal input terminal being electrically connected to a constant power supply potential node via a pull-up resistor, the reference line having a first conductor at ground potential, a second conductor that is DC-insulated from the first conductor, and a capacitor that connects the first conductor and the second conductor, and the termination circuit is electrically connected to the other end of the signal line in the transmission line, and applies a constant voltage to the other end of the signal line in the transmission line, the constant voltage being a voltage lower than the constant power supply voltage applied to the constant power supply potential node in the receiver.

[0008] According to the present disclosure, it is possible to keep the midpoint potential, i.e., the offset voltage, constant in the signal line of the transmission line, and further to achieve both reduced power consumption and improved noise resistance of the receiver.

[0009] It is a configuration diagram showing a signal transmission device according to embodiment 1. It is a configuration diagram showing a transmission line in the signal transmission device according to embodiment 1. It is a configuration diagram showing a termination circuit in the signal transmission device according to embodiment 1. It is a configuration diagram showing a termination circuit in the signal transmission device according to embodiment 2.

[0010] Embodiment 1 A signal transmission device 1 according to embodiment 1 will be described with reference to Figures 1 to 3. The signal transmission device 1 according to embodiment 1 transmits a transmission signal from a signal output terminal 101 of a transmitter 100 to a signal input terminal 201 of a receiver 200. The transmission signal from the transmitter 100 is a digital signal made up of an electrical signal.

[0011] The signal transmission device 1 according to the first embodiment is mounted on a printed wiring board together with a transmitter 100 and a receiver 200. The signal transmission device 1 according to the first embodiment transmits a signal from the transmitter 100 to the receiver 200 within the printed wiring board.

[0012] The transmitter 100 has many signal output terminals 101, and the receiver 200 has many signal input terminals 201, and a large number of signal transmission devices 1 are mounted on a printed wiring board in accordance with the number of signal output terminals 101 of the transmitters 100 and the number of signal input terminals 201 of the receivers 200. Since the large number of signal transmission devices 1 mounted on the printed wiring board each have the same configuration, one signal transmission device 1 is shown as a representative in Figure 1.

[0013] Before describing the signal transmission device 1 according to the first embodiment, we will explain the transmitter 100 and the receiver 200. The receiver 200 has a signal input terminal 201 that receives a transmission signal from the transmitter 100 as a received signal, a ground potential terminal 202 that is electrically connected to a ground potential node in the receiver 200, and a constant power supply potential node 203 to which a constant power supply voltage is applied.

[0014] The receiver 200 includes a pull-up resistor 204 and a receiver 205. The pull-up resistor 204 is electrically connected between a constant power supply potential node 203 and a signal input terminal 201. That is, the signal input terminal 201 is electrically connected to the constant power supply potential node 203 via the pull-up resistor 204. In short, the receiver 200 has the constant power supply potential node 203 internally as a constant power supply termination.

[0015] The input terminal of the receiver 205 is electrically connected to the signal input terminal 201. The receiver 205 demodulates the transmission signal from the transmitter 100 and converts it into a data signal. The receiver 200 is a DDR-SDRAM (Double-Data-Rate SDRAM), which is a type of high-speed memory. The receiver 200 is a semiconductor device made up of an IC, and is mounted on a printed wiring board.

[0016] The transmitter 100 has a signal output terminal 101 that outputs a transmission signal formed of an electrical signal, and a ground potential terminal 102 that is electrically connected to a ground potential node in the transmitter 100. The transmitter 100 includes a driver 103 and a transmission resistor 104. The output terminal of the driver 103 is electrically connected to the signal output terminal 101 via the transmission resistor 104.

[0017] The driver 103 modulates the data and outputs a transmission signal consisting of an electrical signal from the signal output terminal 101 to the signal line 21 of the transmission line 2 via a transmission resistor 104. When the receiver 200 is a DDR-SDRAM, the transmitter 100 is a controller such as a microcomputer or FPGA (Field Programmable Gate Array) for writing data to the DDR-SDRAM. The transmitter 100 is a semiconductor device consisting of an IC, and is mounted on a printed wiring board.

[0018] The signal transmission device 1 according to the first embodiment includes a transmission line 2, a termination circuit 3, and a control circuit 4. As shown in Figures 1 and 2, the transmission line 2 has a signal line 21 and a reference line 22. A transmission signal transmitted from a signal output terminal 101 of a transmitter 100 is applied to the signal line 21 with reference to the reference line 22, propagates along the transmission line 2, and is received by the receiver 200 at a signal input terminal 201 of the receiver 200.

[0019] One end of the signal line 21 is electrically connected to the signal output terminal 101 of the transmitter 100. The other end of the signal line 21 is electrically connected to the signal input terminal 201 of the receiver 200. The reference line 22 has a first conductor 221, a second conductor 222, a third conductor 223, a first capacitor 22a, and a second capacitor 22b.

[0020] The first conductor 221 is electrically connected to the ground potential end 102 of the transmitter 100. The third conductor 223 is electrically connected to the ground potential end 202 of the receiver 200. The second conductor 222 is a conductor layer that is DC-insulated from the first conductor 221 and the third conductor 223 and to which a potential different from the ground potential is applied. The second conductor 222 is a conductor layer that does not contribute to the power supply of the transmitter 100 and the receiver 200. The second conductor 222 is formed on a printed wiring board.

[0021] The first capacitor 22a insulates the first conductor 221 from the second conductor 222 in terms of direct current and electrically connects them in terms of alternating current. The second capacitor 22b insulates the third conductor 223 from the second conductor 222 in terms of direct current and electrically connects them in terms of alternating current. The first capacitor 22a and the second capacitor 22b are chip capacitors mounted on a printed wiring board.

[0022] Assuming that the first conductor 221 and the third conductor 223 are not electrically connected on the printed wiring board, the first conductor 221 and the third conductor 223 are electrically connected in an AC manner to the first capacitor 22a and the second capacitor 22b, respectively. If the first conductor 221 and the third conductor 223 are electrically connected on the printed wiring board, the third conductor 223 can be regarded as the first conductor 221, and the second capacitor 22b is not necessary.

[0023] If the receiver 200 is a DDR-SDRAM, the bus clock was 100 MHz when DDR-SDRAM was first released, but the bus clock has increased to 3200 MHz in DDR5-SDRAM, which was standardized in 2020. It is expected that the operating frequency will continue to increase with each generation.

[0024] To transmit such high-speed signals within a printed wiring board, impedance matching and isolation from other signal lines and power lines are required. Therefore, in the first embodiment, the signal line 21 in the transmission line 2 is a strip line or a microstrip line, and the first conductor 221 and the third conductor 223 are ground conductors formed opposite the signal line 21, thereby providing a transmission line for a high-speed signal line that ensures signal quality.

[0025] Furthermore, an increase in the number of conductive layers in the printed wiring board is suppressed even if a portion of the signal line 21 is formed facing the second conductor 222, which has a different potential from the first conductor 221 and the third conductor 223. Each of the first conductor 221 and the third conductor 223 may be formed from a single conductive layer, and the signal line 21 may be formed facing the first conductor 221 and the third conductor 223. Alternatively, each of the first conductor 221 and the third conductor 223 may be formed from two different conductive layers, and the signal line 21 may be sandwiched between the two conductive layers of the first conductor 221 and the third conductor 223 and positioned facing each other.

[0026] The first capacitor 22a is disposed at a position where the signal line 21 faces the first conductor 221 and the second conductor 222, that is, at a location or nearby where the signal line 21 straddles the first conductor 221 and the second conductor 222. The second capacitor 22b is disposed at a position where the signal line 21 faces the third conductor 223 and the second conductor 222, that is, at a location or nearby where the signal line 21 straddles the third conductor 223 and the second conductor 222.

[0027] In this way, the first capacitor 22 a electrically connects the first conductor 221 and the second conductor 222 in an AC manner, and in particular, the first capacitor 22 a is disposed at or near the location where the signal line 21 straddles the first conductor 221 and the second conductor 222, which provides the following advantages: The first capacitor 22 a can lower the power supply impedance and suppress parallel plate resonance, and further, the return current in the transmission line 2 that is generated near the boundary between the first conductor 221 and the second conductor 222 flows through the first capacitor 22 a to the first conductor 221, which is at ground potential, thereby contributing to eliminating impedance discontinuity. As a result, waveform distortion in the transmitted transmission signal due to impedance discontinuity can be suppressed, and the generation of radiation noise due to the return current can be suppressed.

[0028] Furthermore, the second capacitor 22b electrically connects the third conductor 223 and the second conductor 222 in an AC manner, and in particular, the second capacitor 22b is disposed at or near the location where the signal line 21 straddles the third conductor 223 and the second conductor 222, which provides the following advantages: The second capacitor 22b lowers the power supply impedance and suppresses parallel plate resonance. Furthermore, the return current in the transmission line 2, which is generated near the boundary between the third conductor 223 and the second conductor 222, flows through the second capacitor 22b to the third conductor 223, which is at ground potential, thereby contributing to the elimination of impedance discontinuity. As a result, waveform distortion in the transmitted transmission signal due to impedance discontinuity can be suppressed, and the generation of radiation noise due to the return current can be suppressed.

[0029] The termination circuit 3 is electrically connected to the other end of the signal line 21 of the transmission line 2, i.e., the end on the signal input terminal 201 side of the receiver 200, and applies a constant voltage, which is lower than the constant power supply voltage Vdd applied to the constant power supply potential node 203 of the receiver 200, to the other end of the signal line 21 of the transmission line 2. The constant power supply voltage Vdd applied to the constant power supply potential node 203 of the receiver 200 is the power supply voltage of the receiver 200.

[0030] The termination circuit 3 has a constant power supply potential node 32a for offset voltage to which a constant voltage lower than the constant power supply voltage applied to the constant power supply potential node 203 in the receiver 200 is applied. １ ~32a Ｎ and the other end of the signal line 21 of the transmission line 2. １ ~32b Ｎ A constant power supply potential node 32a for offset voltage having a series body of １ ~32a Ｎ and switch 32b １ ~32b Ｎ constitutes the variable power supply 32.

[0031] As shown in FIG. 3, the termination circuit 3 includes an offset voltage resistor 31, one end of which is electrically connected to the other end of the signal line 21 in the transmission line 2, and a terminal of the offset voltage resistor 31, one terminal of which is electrically connected to the other end of the offset voltage resistor 31, and the other terminal of which is applied to a constant power supply potential node 203 in the receiver 200 and supplies a constant voltage Vtt that is lower than the constant power supply voltage Vdd and is different from the constant power supply voltage Vtt. １ ~Vtt Ｎ A plurality of offset voltage constant power supply potential nodes 32a to which １ ~32a Ｎ A plurality of switches 32b electrically connected to each of the １ ~32b Ｎ Equipped with

[0032] Resistance value R of offset voltage resistor 31 ２ is determined to satisfy the following equation (1): (1 / R １ ) + (1 / R ２ ) = 1 / Z ０　　　　　　 (1) In the above formula (1), R １ is the resistance of the pull-up resistor 204 in the receiver 200, Z ０ is the resistance value of the transmitting resistor 104 in the transmitter 100 and is the characteristic impedance of the transmission line 2. That is, the resistance value Z ０ is the characteristic impedance Z of transmission line 2 ０ and the resistance value R １ and resistance value R ２ The combined resistance value R satisfies the above equation (1) from the viewpoint of impedance matching.

[0033] Switch 32b １ ~32b Ｎ is digitally controlled by the control circuit 4, and one switch 32b ｎ is selected and turned on. n represents one of 1 to N. １ ~32b Ｎ is a switch digitally controlled by the control circuit 4, such as an FET switch, a dedicated switch IC with N inputs and 1 output, or a multiplexer. １ ~32b ＮIn consideration of the mounting area, a dedicated switch IC or multiplexer with N inputs and one output is preferable.

[0034] Different constant voltages Vtt １ ~Vtt Ｎ is a constant voltage that is 1 / 2, 1 / 3, 1 / 4, ... of the constant power supply voltage Vdd. The constant voltage Vtt may be the ground potential.

[0035] The midpoint potential of the digital signal applied to the signal line 21 and input to the signal input terminal 201 of the receiver 200, i.e., the offset voltage Vref, indicates a value obtained by dividing the voltage by the pull-up resistor 204 and the offset voltage resistor 31 in the range between the constant power supply voltage Vdd applied to the constant power supply potential node 203 and the constant voltage Vtt applied to the offset voltage constant power supply potential node 32a.

[0036] Resistance value R of offset voltage resistor 31 ２ is the resistance value R of the pull-up resistor 204 in the receiver 200. １ When the offset voltage Vref is equal to the constant power supply voltage Vdd and the constant voltage Vtt, the offset voltage Vref is expressed by the following equation (2): ｎ Vref = (Vdd + Vtt ｎ ) / 2 (2) Vtt ｎ is the offset voltage constant power supply potential node 32a ｎ is a constant voltage applied to switch 32b ｎ is a constant voltage applied to the other end of the offset voltage resistor 31 when is selected.

[0037] The offset voltage Vref when N is 2 will be described below. ２ is the resistance value R of the pull-up resistor 204 in the receiver 200. １ If the characteristic impedance of the transmission line 2 is 40Ω, then the resistance value R ２ and resistance value R １ becomes 80 Ω.

[0038] Furthermore, the constant power supply voltage Vdd applied to the constant power supply potential node 203 is set to 1.2 V, and the constant power supply potential node 32a for offset voltage is set to 1.2 V. １ The constant voltage applied to the offset voltage constant power supply potential node 32a is set to 0.6 V. ２ The constant voltage applied to is set to 0.3V.

[0039] The control circuit 4 controls the switch 32b １ is selected, and switch 32b １ When the switch 32b is turned on, the constant power supply potential node 203 in the receiver 200, the pull-up resistor 204, the connection point with the signal line 21, the offset voltage resistor 31, and the switch 32b １ - Offset voltage constant power supply potential node 32a １ As a result, a series path is formed to the offset voltage Vref １ is set to a constant voltage of 0.9 V according to the following equation (3): (1.2 + 0.6) / 2 = 0.9 = Vref １　　　　　 (3)

[0040] On the other hand, the control circuit 4 controls the switch 32b ２ is selected, and switch 32b ２ When the switch 32b is turned on, the constant power supply potential node 203 in the receiver 200, the pull-up resistor 204, the connection point with the signal line 21, the offset voltage resistor 31, and the switch 32b ２ - Offset voltage constant power supply potential node 32a ２ As a result, a series path is formed to the offset voltage Vref ２ is set to a constant voltage of 0.75 V according to the following equation (4): (1.2 + 0.3) / 2 = 0.75 = Vref ２　　　　 (4)

[0041] That is, the control circuit 4 controls the switch 32b １ or switch 32b ２ By selecting either of these, the offset voltage can be set to Vref １ or Vref ２ For example, when the signal transmission device 1 starts operating, the offset voltage constant power supply potential node 32a ｎ The constant voltage to be applied to the

[0042] In the above example, when the operation starts, the control circuit 4 switches the switch 32b １ is selected, and the offset voltage constant power supply potential node 32a １ A constant voltage Vtt is applied to １ As a result, the offset voltage Vref １ is set to a constant voltage of 0.9V.

[0043] Offset voltage Vref １ is set to a constant voltage of 0.9 V, the offset voltage constant power supply potential node 32a ｎ When compared with the case where the potential is set to ground, the amount of current flowing through the pull-up resistor 204 and the offset voltage resistor 31 is halved, and the power consumption is also halved.

[0044] If there are many errors in the received signal input to the signal input terminal 201 of the receiver 200 during operation of the signal transmission device 1, the offset voltage constant power supply potential node 32a selected at the start of operation １ A constant voltage Vtt is applied to １ Lower constant voltage Vtt ２ In the above example, the control circuit 4 sets the switch 32b １ to switch 32b ２ The selection is changed to the offset voltage constant power supply potential node 32a １ A constant voltage Vtt is applied to ２ As a result, the offset voltage Vref ２ is set to a constant voltage of 0.75V.

[0045] Offset voltage Vref ２ By setting the offset voltage Vref to a constant voltage of 0.75V, ２ The difference between the constant power supply voltage Vdd (=1.2 V) applied to the constant power supply potential node 203 in the receiver 200 and the constant power supply voltage Vdd (=0.75 V) is 0.45 V, which allows a large noise margin for the received signal input to the signal input terminal 201 of the receiver 200. In other words, the noise resistance performance of the receiver 200 is improved.

[0046] On the other hand, the offset voltage Vref２ Even when the offset voltage constant power supply potential node 32a is set to a constant voltage of 0.75V, ｎ is set to the ground potential, the amount of current flowing through the pull-up resistor 204 and the offset voltage resistor 31 is reduced to about two-thirds, and the power consumption is also reduced to about two-thirds. Therefore, it is possible to achieve both a reduction in power consumption and an improvement in the noise resistance performance of the receiver 200.

[0047] In this way, the offset voltage Vref ２ offset voltage Vref １ Setting a lower constant voltage allows for a larger noise margin for the received signal input to the signal input terminal 201 of the receiver 200, thereby preventing errors in the received signal. If the receiver 200 has a built-in function for measuring bit errors or packet errors, the control circuit 4 uses the measurement results of bit errors or packet errors from the receiver 200. The control circuit 4 compares the measurement results of bit errors or packet errors with a threshold, and if the measurement results exceed the threshold, turns off the switch 32b in the above example. １ to switch 32b ２ Change the selection to

[0048] If the offset voltage Vref is increased to reduce power consumption, the noise margin will be smaller, and if the offset voltage Vref is decreased to increase the noise margin, the reduction in power consumption will be smaller. There is a trade-off between the reduction in power consumption and the noise margin.

[0049] In the above example, the offset voltage Vref is increased from the start of operation of the signal transmission device 1 to reduce power consumption, and when the measurement results of bit errors or packet errors during operation are equal to or greater than a threshold, the offset voltage Vref is lowered, and although the reduction in power consumption is small, the noise margin is increased, enabling stable signal transmission.

[0050] In short, in the above example, in consideration of the trade-off between the reduction in power consumption and the noise margin, the switch 32b １and switch 32b ２ By selecting the offset voltage constant power supply potential node 32a １ and the offset voltage constant power supply potential node 32a ２ This reduces power consumption and prevents reception errors of the received signal due to noise.

[0051] If it is known in advance that the noise environment during operation of the signal transmission device 1 will be favorable, the variable power supply 32 may function as a fixed power supply. That is, only one offset voltage constant power supply potential node 32a may be used as the variable power supply 32. In this case, the switch 32b and the control circuit 4 are not required.

[0052] When the variable power supply 32 is a fixed power supply, the resistance value R of the offset voltage resistor 31 is set to 0.05V. ２ is the resistance value R of the pull-up resistor 204 in the receiver 200. １ Same as (R ２ =R １ ), the offset voltage Vref is given by the following equation (5): Vref=(Vdd+Vtt) / 2 (5)

[0053] Therefore, when the signal transmission device 1 starts operating and during operation, the signal line 21 is supplied with a constant voltage Vtt and a resistance value R ２ A constant offset voltage Vref determined by the above equation is applied, enabling stable signal transmission. That is, taking into consideration the noise environment during operation of the signal transmission device 1 and the trade-off relationship between the amount of reduction in power consumption and the noise margin, a constant voltage to be applied to the offset voltage constant power supply potential node 32a is set that is expected to achieve the maximum reduction in power consumption while preventing reception errors of the received signal due to the noise environment during operation.

[0054] For example, power consumption can be reduced by setting the constant voltage Vtt applied to the offset voltage constant power supply potential node 32a to 1 / 2 of the constant power supply voltage Vdd applied to the constant power supply potential node 203 in the receiver 200, and setting the offset voltage Vref to 3 / 4 of Vdd. Note that if the constant voltage Vtt is set to ground potential, the offset voltage Vref will be 1 / 2 of Vdd.

[0055] The signal transmission device 1 according to the first embodiment includes a transmission line 2 having a signal line 21 and a reference line 22, which transmits a transmission signal from a signal output terminal 101 of a transmitter 100 to a signal input terminal 201 electrically connected to a constant power supply potential node 203 via a pull-up resistor 204 in a receiver 200. The reference line 22 includes first conductors 221 and 223 which are at ground potential, a second conductor 222 which is DC-insulated from the first conductors 221 and 223, and capacitors 22a and 22b which connect the first conductors 221 and 223 to the second conductor 222. Therefore, a return current in the transmission line 2 which is generated near the boundary between the first conductors 221 and 223 and the second conductor 222 flows through the capacitors 22a and 22b to the first conductors 221 and 223 which are at ground potential, and therefore the capacitors 22a and 22b contribute to eliminating impedance discontinuities.

[0056] The signal transmission device 1 according to the first embodiment further includes a termination circuit 3 at the other end of the signal line 21 in the transmission line 2, which applies a constant voltage that is lower than the constant power supply voltage applied to the constant power supply potential node 203 in the receiver 200. This makes it possible to keep the midpoint potential of the digital signal input to the signal input terminal 201 in the receiver 200, i.e., the offset voltage Vref, constant, while suppressing power consumption and improving the noise resistance performance of the receiver 200, thereby achieving stable signal transmission.

[0057] The termination circuit 3 in the signal transmission device 1 according to the first embodiment is configured to include an offset voltage resistor 31 having one end electrically connected to the other end of the signal line 21 in the transmission line 2, and a plurality of offset voltage constant power supply potential nodes 32a each having one terminal electrically connected to the other end of the offset voltage resistor 31 and having the other terminals applied to a constant power supply potential node 203 in the receiver and different constant voltages lower than the constant power supply voltage. ｎ A plurality of switches 32b electrically connected to each of the ｎ Therefore, the offset voltage Vref, which is a constant voltage, is increased from the start of operation of the signal transmission device 1 to reduce power consumption, and when it is necessary to increase the noise margin during operation, the offset voltage Vref, which is a constant voltage, is decreased to perform stable signal transmission.

[0058] In other words, the signal transmission device 1 of embodiment 1 can significantly reduce power consumption at the start of operation by changing the offset voltage Vref at the start of operation and when it is necessary to increase the noise margin during operation, and can also improve noise resistance performance while suppressing power consumption during operation.

[0059] Although the transmitter 100 is a controller such as a microcomputer or FPGA, and the receiver 200 is a DDR-SDRAM, the transmitter 100 and the receiver 200 are not limited to these, and the signal transmission device 1 of embodiment 1 can be applied to a transmission system between a transmitter and a receiver that transmits a digital signal from the transmitter to the receiver.

[0060] Furthermore, the switch 32b in the signal transmission device 1 according to the first embodiment １ ~32b Ｎ However, a mechanical analog switch may be used. In the case of using a mechanical analog switch, the control circuit 4 is not required.

[0061] Furthermore, although the signal transmission device 1 according to the first embodiment is intended for a signal transmission device mounted on a printed wiring board together with the transmitter 100 and the receiver 200, the signal transmission device 1 can also be applied to a signal transmission system in which the transmitter 100 and the receiver 200 are mounted on separate printed wiring boards, and the printed wiring board on which the transmitter 100 is mounted and the printed wiring board on which the receiver 200 is mounted are connected by a cable having a signal line and a reference line.

[0062] A cable connecting printed wiring boards is, for example, a shielded cable that has a conductor (core) for transmitting signals and a shielding material between the core and the sheath that surrounds the core. In a shielded cable, the core is the signal line and the shielding material is the reference line.

[0063] There are three types of signal transmission devices in which a printed wiring board (hereinafter referred to as a first board) on which a transmitter 100 is mounted and a printed wiring board (hereinafter referred to as a second board) on which a receiver 200 is mounted are connected by a cable. First, the relationship between the signal transmission devices in this case and the configuration diagrams shown in Figures 1 and 2 will be described.

[0064] The first substrate has a signal output terminal to which signal output terminal 101 of transmitter 100 is connected, and a ground potential terminal that is electrically connected to ground potential terminal 102 and is also electrically connected to a ground potential node in transmitter 100. The second substrate has a signal input terminal to which signal input terminal 201 of receiver 200 is connected, and a ground potential terminal that is connected to ground potential terminal 202 and is also electrically connected to the ground potential node in receiver 200.

[0065] In the first substrate, the line electrically connecting the signal output end 101 and the signal output terminal constitutes part of the signal line 21 of the transmission line 2. In the second substrate, the line electrically connecting the signal input end 201 and the signal input terminal constitutes part of the signal line 21 of the transmission line 2. The signal line in the cable electrically connects the signal output terminal on the first substrate and the signal input terminal on the second substrate, and constitutes the main part of the signal line 21 of the transmission line 2.

[0066] In the first board, the line electrically connecting the ground potential terminal and the ground potential node in the transmitter 100 corresponds to the first conductor 221 of the reference line 22. In the second board, the line electrically connecting the ground potential terminal and the ground potential node in the receiver 200 corresponds to the third conductor 223 of the reference line 22. The reference line in the cable corresponds to the second conductor 222 of the reference line 22.

[0067] Aspect 1. A line (corresponding to first conductor 221 of reference line 22) electrically connecting a ground potential terminal on the first board and a ground potential node on transmitter 100 and a reference line in the cable (corresponding to second conductor 222 of reference line 22) are insulated in terms of direct current by a capacitor (corresponding to first capacitor 22a) and electrically connected in terms of alternating current. One electrode of the capacitor (corresponding to first capacitor 22a) is connected to the ground potential terminal on the first board and the other electrode is connected to one end of the reference line in the cable, and the capacitor is mounted on the first board.

[0068] The line (corresponding to the third conductor 223 of the reference line 22) electrically connecting the ground potential terminal of the second board and the ground potential node of the receiver 200 and the reference line of the cable (corresponding to the second conductor 222 of the reference line 22) are insulated in terms of direct current by a capacitor (corresponding to the second capacitor 22b) and are electrically connected in terms of alternating current. One electrode of the capacitor (corresponding to the second capacitor 22b) is connected to the other end of the reference line of the cable, and the other electrode is connected to the ground potential terminal of the second board, and the capacitor is mounted on the second board.

[0069] Aspect 2. A line (corresponding to first conductor 221 of reference line 22) electrically connecting the ground potential terminal on the first board and the ground potential node on transmitter 100 and a reference line in the cable (corresponding to second conductor 222 of reference line 22) are insulated in terms of direct current by a capacitor (corresponding to first capacitor 22a) and electrically connected in terms of alternating current. One electrode of the capacitor (corresponding to first capacitor 22a) is connected to the ground potential terminal on the first board and the other electrode is connected to one end of the reference line in the cable, and the capacitor is mounted on the first board.

[0070] The line (corresponding to the third conductor 223 of the reference line 22) electrically connecting the ground potential terminal on the second substrate and the ground potential node on the receiver 200 is in DC conduction with the reference line in the cable (corresponding to the second conductor 222 of the reference line 22). In other words, the ground potential terminal on the second substrate and the other end of the reference line in the cable are directly connected.

[0071] Aspect 3. A line (corresponding to third conductor 223 of reference line 22) electrically connecting the ground potential terminal of the second board and the ground potential node of receiver 200 and a reference line of the cable (corresponding to second conductor 222 of reference line 22) are insulated in terms of direct current by a capacitor (corresponding to second capacitor 22b) and electrically connected in terms of alternating current. One electrode of the capacitor (corresponding to second capacitor 22b) is connected to the other end of the reference line of the cable, and the other electrode is connected to the ground potential terminal of the second board, and the capacitor is mounted on the second board.

[0072] The line (corresponding to the first conductor 221 of the reference line 22) electrically connecting the ground potential terminal on the first board and the ground potential node on the transmitter 100 and the reference line in the cable (corresponding to the second conductor 222 of the reference line 22) are in DC conduction. In other words, the ground potential terminal on the first board and one end of the reference line in the cable are directly connected.

[0073] Second Embodiment A signal transmission device 1 according to a second embodiment will be described with reference to Fig. 4. The signal transmission device 1 according to the second embodiment differs from the signal transmission device 1 according to the first embodiment in that the termination circuit 3 in the signal transmission device 1 according to the first embodiment uses a constant power supply potential node 32a for offset voltage to set the offset voltage. ｎ However, a Zener diode 32c is used to set the offset voltage in the termination circuit 3. ｎ 4 is different from the signal transmission device 1 according to the first embodiment in that it uses the same reference numerals as those in FIGS. 1 to 3, and is otherwise the same.

[0074] Similar to the signal transmission device 1 according to the first embodiment, the signal transmission device 1 according to the second embodiment transmits a transmission signal from a signal output terminal 101 of a transmitter 100 to a signal input terminal 201 of a receiver 200. Similar to the signal transmission device 1 according to the first embodiment, the signal transmission device 1 according to the second embodiment includes a transmission line 2, a termination circuit 3, and a control circuit 4. The transmission line 2 and the control circuit 4 are the same as the transmission line 2 and the control circuit 4 in the signal transmission device 1 according to the first embodiment, and therefore a description thereof will be omitted.

[0075] The termination circuit 3A includes an offset voltage resistor 31 and a switch 32b electrically connected between the other end of the signal line 21 of the transmission line 2 and the ground potential node. １ ~32b Ｎ and a Zener diode 32c whose anode is connected to the ground potential node side. １ ~32c Ｎ The switch 32b is a series circuit of the １ ~32b Ｎ and Zener diode 32c １ ~32c Ｎ These constitute the variable power supply 32A.

[0076] As shown in FIG. 4, the termination circuit 3 includes an offset voltage resistor 31, one end of which is electrically connected to the other end of the signal line 21 of the transmission line 2, and a plurality of switches 32b, one terminal of which is electrically connected to the other end of the offset voltage resistor 31. １ ~32b Ｎ and a plurality of switches 32b, each of which has a corresponding cathode. １ ~32b Ｎ and a plurality of Zener diodes 32c whose anodes are connected to the ground potential node. １ ~32c Ｎ Each Zener diode 32c １ ~32c Ｎ and switch 32b １ ~32b Ｎ form a series body, and N series bodies are connected in parallel between the other end of the offset voltage resistor 31 and the ground potential node.

[0077] Multiple Zener diodes 32c １ ~32c Ｎ Zener voltage Vz １ ~Vz Ｎ The offset voltage Vref applied to the signal line 21 is the constant power supply voltage Vdd applied to the constant power supply potential node 203 and the Zener diode 32c ｎ Zener voltage Vz ｎ 3 indicates a voltage divided by the pull-up resistor 204 and the offset voltage resistor 31 in the range of .

[0078] Resistance value R of offset voltage resistor 31 ２ is the resistance value R of the pull-up resistor 204 in the receiver 200. １ When the offset voltage Vref is equal to the constant power supply voltage Vdd and the Zener voltage Vz, the offset voltage Vref is expressed by the following equation (6): ｎ It becomes the intermediate potential between Vref and Vdd. ｎ ) / 2 (6)

[0079] As in the signal transmission device 1 according to the first embodiment, N is set to 2, and the conditions are the same. １ Zener voltage Vz １ to 0.6V, Zener diode 32c ２ Zener voltage Vz ２ is set to 0.3V.

[0080] The control circuit 4 controls the switch 32b １ is selected, and switch 32b １ When the switch 32b is turned on, the constant power supply potential node 203 in the receiver 200, the pull-up resistor 204, the connection point with the signal line 21, the offset voltage resistor 31, and the switch 32b １ Zener diode 32c １ - A series path to the ground potential node is formed. As a result, the offset voltage Vref １ is set to a constant voltage of 0.9V.

[0081] On the other hand, the control circuit 4 controls the switch 32b ２ is selected, and switch 32b ２ When the switch 32b is turned on, the constant power supply potential node 203 in the receiver 200, the pull-up resistor 204, the connection point with the signal line 21, the offset voltage resistor 31, and the switch 32b ２ Zener diode 32c ２ - A series path to the ground potential node is formed. As a result, the offset voltage Vref ２ is set to a constant voltage of 0.75V.

[0082] That is, the control circuit 4 controls the switch 32b １ or switch 32b ２By selecting either of these, the offset voltage can be set to Vref １ or Vref ２ When the signal transmission device 1 starts operating, the control circuit 4 controls the switch 32b １ is selected, and the Zener voltage Vz １ Zener diode 32c with a voltage of 0.6V １ As a result, the offset voltage Vref １ is set to a constant voltage of 0.9V.

[0083] If there are many errors in the received signal input to the signal input terminal 201 of the receiver 200 during operation of the signal transmission device 1, the control circuit 4 switches the switch 32b １ to switch 32b ２ The selection is changed to Zener voltage Vz １ Zener diode 32c with a voltage of 0.3V ２ As a result, the offset voltage Vref ２ is set to a constant voltage of 0.75V.

[0084] If it is known in advance that the noise environment during operation of the signal transmission device 1 will be favorable, the variable power supply 32 may function as a fixed power supply, as in the signal transmission device 1 according to the first embodiment. That is, only one Zener diode 32c may be used as the variable power supply 32. In this case, the switch 32b and the control circuit 4 are not required.

[0085] The signal transmission device 1 according to the second embodiment has the same effects as the signal transmission device 1 according to the first embodiment, and in addition, since the Zener diode 32c is used as a constant voltage source, the mounting area of ​​the termination circuit 3 is small.

[0086] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0087] The signal transmission device according to the present disclosure is applicable to a signal transmission device having a transmission line having a signal line and a reference line, which transmits a transmission signal from a signal output terminal of a transmitter to a signal input terminal of a receiver, and is particularly suitable for a signal transmission device which transmits a high-speed signal between a transmitter and a receiver and is mounted on the same printed wiring board on which the transmitter and receiver are mounted.

[0088] REFERENCE SIGNS LIST 1 signal transmission device, 2 transmission line, 21 signal line, 22 reference line, 221 first conductor, 222 second conductor, 223 third conductor, 22a first capacitor, 22b second capacitor, 3, 3A termination circuit, 31 offset voltage resistor, 32a １ ~32a Ｎ Offset voltage constant power supply potential node, 32b １ ~32b Ｎ Switch, 32c １ ~32c Ｎ Zener diode, 4 control circuit, 100 transmitter, 200 receiver.

Claims

1. A signal transmission device comprising: a transmission line having a signal line and a reference line; and a termination circuit; one end of the signal line of the transmission line is electrically connected to a signal output terminal of a transmitter that transmits an electric signal; and the other end of the signal line of the transmission line is electrically connected to a signal input terminal of a receiver that receives the electric signal from the transmitter, the signal input terminal being electrically connected to a constant power supply potential node via a pull-up resistor; the reference line has a first conductor that is at ground potential, a second conductor that is DC-insulated from the first conductor, and a capacitor that connects the first conductor and the second conductor; and the termination circuit is electrically connected to the other end of the signal line of the transmission line and applies a constant voltage to the other end of the signal line of the transmission line, the constant voltage being a voltage lower than the constant power supply voltage applied to the constant power supply potential node of the receiver.

2. The signal transmission device according to claim 1, wherein the termination circuit comprises a series circuit of an offset voltage resistor and a switch electrically connected between a constant power supply potential node for offset voltage to which a constant voltage lower than the constant power supply voltage applied to the constant power supply potential node in the receiver is applied and the other end of the signal line in the transmission line.

3. A signal transmission device according to claim 2, wherein the constant voltage applied to the offset voltage constant power supply potential node is half the voltage value of the constant power supply voltage applied to the constant power supply potential node in the receiver.

4. A signal transmission device according to claim 2, wherein the constant voltage applied to said offset voltage constant power supply potential node is 1 / 4 of the constant power supply voltage applied to said constant power supply potential node in said receiver.

5. The signal transmission device according to claim 1, wherein the termination circuit comprises an offset voltage resistor having one end electrically connected to the other end of the signal line in the transmission line, and a plurality of switches each having one terminal electrically connected to the other end of the offset voltage resistor and the other terminal electrically connected to a plurality of offset voltage constant power supply potential nodes to which different constant voltages lower than the constant power supply voltage are applied, the constant power supply potential node in the receiver.

6. A signal transmission device according to claim 5, wherein the number of the plurality of offset voltage constant power supply potential nodes and the number of the plurality of switches are each two, the constant voltage applied to one offset voltage constant power supply potential node is half the voltage value of the constant power supply voltage applied to the constant power supply potential node in said receiver, and the constant voltage applied to the other offset voltage constant power supply potential node is one-quarter the voltage value of the constant power supply voltage applied to the constant power supply potential node in said receiver.

7. A signal transmission device according to claim 6, further comprising a control circuit that can control, when the transmitter and the receiver start operating, to turn on a switch electrically connected to one of the offset voltage constant power supply potential nodes and to turn off a switch electrically connected to the other offset voltage constant power supply potential node, and can control, during operation of the transmitter and the receiver, to turn off a switch electrically connected to one of the offset voltage constant power supply potential nodes and to turn on a switch electrically connected to the other offset voltage constant power supply potential node.

8. The signal transmission device according to claim 1, wherein the termination circuit comprises a series circuit of an offset voltage resistor, a switch, and a Zener diode, the anode of which is connected to the ground node potential side, electrically connected between the other end of the signal line in the transmission line and a ground potential node.

9. A signal transmission device according to claim 8, wherein the Zener voltage of said Zener diode is applied to a constant power supply potential node in said receiver and has a voltage value that is half the constant power supply voltage.

10. A signal transmission device according to claim 8, wherein the Zener voltage of said Zener diode is applied to a constant power supply potential node in said receiver and has a voltage value of 1 / 4 of the constant power supply voltage.

11. The signal transmission device according to claim 1, wherein the termination circuit comprises a resistor for offset voltage, one end of which is connected to the other end of the signal line in the transmission line, and a plurality of series elements each comprising a Zener diode and a switch, the anode of which is connected to the ground potential side and electrically connected between the other end of the resistor for offset voltage and a ground potential node, and wherein the Zener voltages of the Zener diodes in the plurality of series elements are different from one another.

12. A signal transmission device according to claim 11, wherein the number of said plurality of series bodies is two, the Zener voltage of the Zener diode in one series body is applied to a constant power supply potential node in said receiver and has a voltage value that is 1 / 2 of the constant power supply voltage, and the Zener voltage of the Zener diode in the other series body is applied to a constant power supply potential node in said receiver and has a voltage value that is 1 / 4 of the constant power supply voltage.

13. A signal transmission device according to claim 12, further comprising a control circuit that controls the switch in one series body to be on and the switch in the other series body to be off when the transmitter and the receiver start operating, and that controls the switch in one series body to be off and the switch in the other series body to be on while the transmitter and the receiver are operating.

14. The signal transmission device according to claim 1, wherein the termination circuit comprises: an offset voltage resistor having one end connected to the other end of the signal line in the transmission line; a switch electrically connected between the other end of the offset voltage resistor and a constant power supply potential node for offset voltage to which is applied a constant voltage that is lower than the constant power supply voltage applied to a constant power supply potential node in the receiver; and a series body of a Zener diode and switch, the anode of which is connected to the ground potential side, electrically connected between the other end of the offset voltage resistor and the ground potential node.

15. A signal transmission device according to any one of claims 1 to 14, which is mounted together with the transmitter and receiver on a printed wiring board.

16. A signal transmission device according to claim 15, wherein the signal line of the transmission line is a strip line formed on the printed wiring board, and the first conductor of the reference line of the transmission line is a ground conductor formed on the printed wiring board and arranged opposite the signal line of the transmission line.

17. A signal transmission device according to any one of claims 1 to 14, wherein the capacitor is disposed at a position where the signal line is disposed opposite the first conductor and the second conductor.

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