JP5672277B2 - Electronic equipment - Google Patents

Description

  The present invention relates to an electronic device including a connector for housing a printed wiring board on which an LSI is mounted in a resin casing and electrically connecting the printed wiring board to the printed wiring board with a cable from the outside of the resin casing.

  When an in-vehicle electronic device operates, an unintended radio wave may be radiated from a printed wiring board or a power cable (radiation noise). If there is this radiation noise, for example, radio broadcast radio wave reception by an antenna mounted on the vehicle body is disturbed, and problems such as so-called radio noise occur. In the vehicle-mounted electronic device, the radiation noise is generated mainly due to the common mode current due to the impedance imbalance in the power supply / GND wiring.

  For example, Japanese Patent No. 4624415 (Patent Document 1) and International Publication No. WO 2009/096203 (Patent Document) describe a mechanism for generating a common mode current in the in-vehicle electronic device and a technique for reducing common mode radiation noise caused by the common mode current. 2), and IEICE Transactions C Vol.J89-C (2006) No.11 pp.854-865 (Non-Patent Document 1) and IEICE TRANS. COMMUN., Vol.E93-B No.7 JULY 2010 pp.1788-1796 (Non-Patent Document 2).

  FIG. 7 is a diagram for explaining analysis of common mode radiation noise according to Non-Patent Document 1. (A), (b) is a figure showing the approximate equivalent circuit with respect to the power supply system of the printed circuit board (PCB) and wire harness which mounted the microcomputer (CMOS driver). Moreover, (c) is a figure showing the equivalent circuit with respect to the (b) circuit in -100MHz.

(A) shows an important element extracted in examining reduction of a common mode current generated by a current fluctuation of a power supply system in an electronic device to which a wire harness is connected. (B) is a circuit approximating the circuit of (a), and Vd is a power source for generating a high-frequency current. L _V and L _G represent inductances from the microcomputer to the bypass capacitor on the PCB power line and GND line, respectively. C _V and C _G represent the parasitic capacitance between the power line and the GND line of the PCB and the reference GND, respectively. Also, _{C b} represents a bypass capacitor mounted between the power supply -GND printed circuit _board, Z V, _{Z G,} respectively represent the impedance of the power supply line and the GND line of the wire harness.

In the following frequencies 100 MHz, it can be handled bypass capacitor _{C b} as short-circuit of (b) is a circuit of an approximation (c). In the circuit of (c), V _C is a common mode voltage at a position where the wire harness is connected, and I _C is a common mode current flowing through the wire harness. When the circuit of (c) is analyzed, the condition for finally causing the common mode voltage V _{C to} be 0 and the common mode current I _C not being generated is expressed by the following Equation 1.
(Number _{1) L V C V -L G} C G = 0

Patent No. 4624415 International Publication No. WO2009 / 096203

IEICE Transactions C Vol.J89-C No.11 pp.854-865, (2006) IEICE TRANS.COMMUN., Vol.E93-B No.7 JULY 2010 pp.1788-1796

  According to Non-Patent Document 1, common mode noise can be minimized by satisfying Equation 1 described above. Therefore, in order to reduce common mode noise, it is not always necessary to provide a common mode choke as conventionally performed near the connector. Further, if a large coil or a large capacitor is provided, the common mode noise is not reduced proportionally. There is an appropriate combination of inductance and capacitance for reducing common mode noise, and when Equation 1 is satisfied, common mode noise can be reduced over a wide frequency range.

  For example, in Patent Document 1, an inductor is connected in series to either one of the power supply / GND wiring so as to satisfy Formula 1. In Patent Document 2, an inductor is connected and a conductive plate that generates a parasitic capacitance with respect to the power supply wiring / GND wiring is arranged on the package substrate so that Formula 1 is satisfied. In addition, the present inventors can easily satisfy the above-described Expression 1 by inserting a capacitive element between at least one of the high potential wiring and the low potential wiring of the printed wiring board without using an inductor. An inexpensive electronic device with a configuration has been invented and a patent application is pending (Japanese Patent Application No. 2011-004044).

  On the other hand, Equation 1 described above is composed of the parasitic inductance due to the wiring pattern of the printed wiring board or LSI and the parasitic capacitance between the wiring pattern and the reference GND, as described with reference to FIGS. Yes. Therefore, in order to satisfy Equation 1 and reduce common mode noise, for example, as in Patent Documents 1 and 2, an inductor is added or a parasitic capacitance is generated to repeatedly design and prototype an electronic device. The value of the additional inductor and the value of the generated parasitic capacitance necessary to satisfy the above are determined.

  However, even if an electronic device that satisfies Equation 1 is completed at the prototype stage, Equation 1 may not be satisfied when the electronic device is attached to a vehicle. In particular, in many electronic devices adopting a resin casing instead of a metal casing in recent years, the metal shape around the mounting position serving as the reference GND directly affects Formula 1, and Formula 1 is expressed at the prototype stage. Satisfactory reduction of common mode noise may make little sense at the stage of mounting an electronic device on a vehicle.

  As an example of an electronic apparatus using such a resin casing, in an HVAC (Heating Ventilation & Air Conditioning) unit of an in-vehicle air conditioner system, an electronic apparatus in which an electronic circuit board for driving a servo motor is incorporated in a resin casing of a connector ( A so-called smart connector is employed. In the HVAC unit, a plurality of smart connectors are attached around the housing, and the housing of the HVAC unit is also made of resin. Therefore, in this case, the automobile body is considered to be the reference GND shown in FIG. 7A. However, the automobile body has a complicated shape, and the reference GND is also determined by the mounting position of the smart connector on the housing. It will change.

  Accordingly, the present invention is an electronic device including a connector for accommodating a printed wiring board mounted with an LSI inside a resin casing and electrically connecting the printed wiring board from the outside of the resin casing to the printed wiring board with a cable. An object of the present invention is to provide an electronic device that can be adjusted so as to satisfy a conditional expression for reducing common mode noise even if the reference GND changes depending on the position, and that is simple in configuration and inexpensive.

An electronic device according to the present invention is an electronic device including a connector for accommodating a printed wiring board mounted with an LSI inside a resin casing and electrically connecting the printed wiring board to the printed wiring board from the outside of the resin casing with a cable. In the vicinity of the connector, a bypass capacitor is inserted between the high potential wiring and the low potential wiring of the printed wiring board connected to the LSI. Further, an island-shaped conductor pattern is formed on the printed wiring board, and an output terminal of the LSI is connected to the island-shaped conductor pattern. A plurality of combinations of island-shaped conductor patterns and output terminals are formed on a printed wiring board, and the output signal of the output terminal is in a high state by internal setting of the LSI or external communication with the LSI. Or it can be switched to the Low state, and the island-like conductor pattern connected to the output terminal can be selected from either the state connected to the high potential wiring or the state connected to the low potential wiring by switching the output signal. It is characterized in that it is configured .

  The LSI in the above electronic device is generally a noise source. By a bypass capacitor inserted between the high potential wiring and the low potential wiring of the printed wiring board near the connector, the high potential wiring and the low potential wiring are used. The normal mode noise flowing in the opposite direction is removed. On the other hand, common mode noise generated between the high potential wiring and the low potential wiring and the reference GND flows through the high potential wiring and the low potential wiring in the same direction and cannot be removed by the bypass capacitor.

According to the examination results of the generation mechanism of the common mode noise obtained so far, the common mode noise is caused by the potential difference (average potential difference) ΔV between the reference potential (reference GND potential) and the cable (wire harness) potential. A common mode current is generated and noise electromagnetic waves are radiated from the cable. Further, occurrence of the potential difference ΔV is due to the parasitic capacitance C _V, C _G against parasitic inductance L _V, L _G and reference GND of the high potential wiring and a low potential wiring of the high potential wiring and a low potential wiring, the The conditional expression for minimizing the common mode noise by setting the potential difference ΔV to 0 is the following expression 1 described in the background art.
(Number _{1) L V C V -L G} C G = 0

However, by setting the parasitic inductance L _V high potential wire and a low potential wiring in the design _stage, L _G and the parasitic capacitance C _V, the C _G to a desired value is generally difficult. Therefore, the left-hand side of the equation in Equation _{1 (L V C V -L G} C G) is generally becomes a value of> 0 or <0. Therefore, in order to satisfy Equation 1 and reduce common mode noise, an inductor is added or a parasitic capacitance is generated to repeatedly design and prototype an electronic device, and an additional inductor required to satisfy Equation 1 And the value of the generated parasitic capacitance are determined.

  On the other hand, even if an electronic device that satisfies Equation 1 is completed at the prototype stage, Equation 1 may not be satisfied if the electronic device is attached to a device that is actually used. In particular, in many electronic devices that employ a resin casing instead of a metal casing in recent years, the metal shape around the mounting position serving as the reference GND directly affects Formula 1, and finally Formula 1 at the prototype stage. In some cases, the reduction of common mode noise obtained by satisfying the above is almost meaningless when the electronic device is attached to a device that actually uses the electronic device.

  Therefore, in the electronic device, a plurality of combinations of island-shaped conductor patterns formed on the printed wiring board and LSI output terminals connected to the island-shaped conductor patterns are formed on the printed wiring board.

  In the electronic device employing the resin casing, the island-like conductor pattern connected to the output terminal of the LSI can function as a parasitic capacitance by paired with the reference GND.

By setting the output signal of the connected output terminal to either the high state or the low state according to the internal setting of the LSI , the island-like conductor pattern connected to the output terminal is connected to the high potential wiring , respectively. It can be a state or a state connected to a low potential wiring .

In addition, the output signal of the output terminal can be switched to a high state or a low state by communication from the outside to the LSI. By switching the output signal, the island-shaped conductor pattern connected to the output terminal is changed to a high potential wiring. A connected state or a state connected to a low-potential wiring can also be used . In this case, by switching the output signal of the output terminal to which the island-shaped conductor pattern is connected to the high state or the low state by communication from the outside to the LSI, the island-shaped conductor pattern is connected to the high potential wiring. Or a state connected to a low potential wiring can be selected.

In the electronic device, since the combination of the island-shaped conductor pattern and the output terminal having such a function is constituted by a plurality of sets of printed wiring boards, the electronic device is attached to an actually used device. Therefore, it is possible to select the connection destination of each island-like conductor pattern that functions as a parasitic capacitance and adjust the capacitance value so that the relationship of the above formula 1 holds as much as possible. If N sets (N: plural) of the combination of the island-like conductor pattern and the output terminal are configured, ^2N adjustments to Formula 1 are possible. The island-like conductor pattern in the electronic device functions as a parasitic capacitance paired with the reference GND as described above, and corrects the parasitic capacitance of the high potential wiring or the low potential wiring. It may be a small thing.

  As described above, after the electronic device is attached to a device that is actually used, the value on the left side of Equation 1 is brought close to 0, and the potential of the cable (the bypass capacitor that short-circuits the high potential wiring and the low potential wiring in a high frequency manner). The potential difference ΔV between the potential of the connection point) and the reference GND can be brought close to zero. As a result, the electronic device is attached to an arbitrary position of the device that is actually used, and even if the reference GND changes depending on the attachment position, the common mode noise generated by the LSI that is the noise source is canceled in the resin casing, It is possible to prevent common mode noise from being transmitted to the cable outside the resin casing.

  In the above-described electronic device, adjustment to satisfy Formula 1 is performed by setting the output signal of each output terminal to a high state or a low state for a combination of island-shaped conductor patterns and output terminals configured on a printed wiring board. Just a simple one. Further, even when the same electronic device is attached at a different position of the device that is actually used and reused, it is only necessary to appropriately change the output signal of each output terminal to the High state or the Low state.

  On the other hand, as another method of adjusting so that the relationship of Formula 1 is satisfied after being attached to a device to be actually used, for example, a method using trimming can be considered. In other words, by forming conductor patterns to be connected to the high-potential wiring and low-potential wiring in a large area in advance, repeatedly checking the noise generation status and performing trimming of the conductor pattern, and finding the optimum value is there. However, such a method using trimming not only takes time for adjustment, but also cannot be reused by changing the mounting position of the electronic device.

  As described above, the electronic device appropriately adjusts the capacitance value of the parasitic capacitance with respect to the reference GND for reducing common mode noise by communication from the outside, and is attached to a device that actually uses the electronic device. After that, noise reduction can be realized without attaching and detaching. As a result, noise reduction can be realized even under different impedance environments such as the prototype stage and the mounting stage.

  As described above, the electronic apparatus includes a connector for housing a printed wiring board on which an LSI is mounted in a resin casing and electrically connecting the printed wiring board to the printed wiring board from the outside of the resin casing with a cable. Even if the reference GND changes depending on the mounting position, the electronic device can be adjusted so as to satisfy the conditional expression for reducing the common mode noise, and the electronic device can be configured simply and inexpensively.

  Accordingly, the above-described electronic device is suitable as an on-vehicle electronic device in which a large number of resin housings have been adopted in recent years in place of the metal housing, and the complicated body shape of the automobile becomes the reference GND. The electronic device may be configured such that the resin casing also serves as a connector housing. As an example of this, for example, when the electronic device is a drive device for a servo motor that controls the wind direction of an air conditioner, an electronic control unit (ECU) that controls the overall operation of the air conditioner with a configuration in which a resin housing also serves as a connector housing. Connected to the bus harness.

It is the figure which showed typically the electronic device 10a which is an example of this invention, (a) is the top view which showed the external appearance of the printed wiring board 2a accommodated in the electronic device 10a, (b) It is sectional drawing of the electronic device 10a. It is the figure which expanded the inside and periphery of LSI1a shown in FIG. 1, and was shown typically. This is a result of testing the reduction of common mode noise by switching the output signal of the output terminal to the high state or the low state and switching the connection state of the island-like conductor pattern by communication from the outside to the LSI. It is a figure which shows a part of external appearance in the HVAC unit of a vehicle-mounted air conditioner system, and is a figure which showed the use condition of the electronic apparatus. FIG. 5 is an exploded view of a conventional electronic device as an example of the electronic device 10 of FIG. 4. (A) is the perspective view which showed the resin housing | casing 3 which also serves as the housing of a connector, (b) is the top view which expanded and showed the printed wiring board 2 accommodated in the inside of the resin housing | casing 3. FIG. is there. It is the figure which showed an example of the electronic device based on this invention used similarly to the electronic device 10 of FIG. (A) is the top view which showed typically the principal part of the electronic device 10b, (b) is the top view which showed the printed wiring board 2b before mounting an electronic component. Moreover, (c) is a circuit diagram of the principal part of the electronic device 10b. It is a figure explaining the analysis of the common mode radiation noise by a nonpatent literature 1. (A), (b) is a figure showing the approximate equivalent circuit with respect to the power supply system of the printed circuit board (PCB) and wire harness which mounted the microcomputer (CMOS driver). Moreover, (c) is a figure showing the equivalent circuit with respect to the (b) circuit in -100MHz.

  Embodiments of an electronic device according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram schematically showing an electronic device 10a which is an example of the present invention. FIG. 1A is a top view showing an appearance of a printed wiring board 2a accommodated in the electronic device 10a. b) is a cross-sectional view of the electronic device 10a. In addition, the cross section of the electronic device 10a shown to (b) respond | corresponds to the cross section in the dashed-dotted line II in (a) about the printed wiring board 2a in the state accommodated in the resin housing | casing 3a.

  FIG. 2 is an enlarged view schematically showing the inside and the periphery of the LSI 1a shown in FIG.

  The electronic device 10a shown in FIG. 1 accommodates a printed wiring board 2a on which an LSI 1a is mounted in a resin casing 3a, and electrically connects the printed wiring board 2a from the outside of the resin casing 3a with a cable (not shown). It is an electronic device provided with the connector 4a. In the electronic device 10a, as shown in (a), between the power supply wiring VCC, which is a high potential wiring of the printed wiring board 2a connected to the LSI 1a, and the ground wiring GND, which is a low potential wiring, near the connector 4a. The bypass capacitor BC1 shown in the circuit model of FIG. 7 is inserted.

  In the electronic device 10a, as shown in FIGS. 1A and 2, island-shaped conductor patterns Pa to Pd are formed on the printed wiring board 2a, and the output terminals Sa to Sd of the LSI 1a are connected to the respective islands. The conductor patterns Pa to Pd are connected. As described above, the electronic device 10a shown in FIG. 1 includes a plurality of combinations of the island-shaped conductor patterns Pa to Pd and the output terminals Sa to Sd of the LSI 1a connected to the island-shaped conductor patterns Pa to Pd. 4 sets in the example of the apparatus 10a), and the printed wiring board 2a is configured.

  The LSI 1a in the electronic device 10a of FIG. 1 is generally a noise source, and the power supply wiring is provided by the bypass capacitor BC1 inserted between the power supply wiring VCC and the ground wiring GND of the printed wiring board 2a near the connector 4a. Normal mode noise flowing in the opposite direction is removed by VCC and ground wiring GND. On the other hand, common mode noise generated between the power supply wiring VCC and the ground wiring GND and the reference GND flows in the same direction through the power supply wiring VCC and the ground wiring GND and cannot be removed by the bypass capacitor BC1.

As described in FIG. 7 and the background art, according to the examination result of the generation mechanism of the common mode noise obtained so far, the common mode noise includes the reference potential (reference GND potential) and the cable (wire harness). A noise electromagnetic wave is radiated from the cable by a common mode current generated by a potential difference (average potential difference) ΔV of the potential and flowing through the cable. Further, occurrence of the potential difference ΔV is parasitic capacitance _{C V} for reference GND of the parasitic inductance _L V high potential wire and a low potential wiring, _{L G} and the high potential wiring (power supply wiring VCC) and a low potential wire (ground line GND) , C _G , and the conditional expression for minimizing the common mode noise by setting the potential difference ΔV to 0 is the following Expression 1 described in the background art.
(Number _{1) L V C V -L G} C G = 0

However, by setting the parasitic inductance L _V high potential wire and a low potential wiring in the design _stage, L _G and the parasitic capacitance C _V, the C _G to a desired value is generally difficult. Therefore, the left-hand side of the equation in Equation _{1 (L V C V -L G} C G) is generally becomes a value of> 0 or <0. Therefore, in order to satisfy Equation 1 and reduce common mode noise, an inductor is added or a parasitic capacitance is generated to repeatedly design and prototype an electronic device, and an additional inductor required to satisfy Equation 1 And the value of the generated parasitic capacitance are determined.

  On the other hand, even if an electronic device that satisfies Equation 1 is completed at the prototype stage, Equation 1 may not be satisfied if the electronic device is attached to a device that is actually used. In particular, in many electronic devices that employ a resin casing instead of a metal casing in recent years, the metal shape around the mounting position serving as the reference GND directly affects Formula 1, and finally Formula 1 at the prototype stage. In some cases, the reduction of common mode noise obtained by satisfying the above is almost meaningless when the electronic device is attached to a device that actually uses the electronic device.

  Therefore, in the electronic device 10a illustrated in FIG. 1, the combination of the island-shaped conductor patterns Pa to Pd formed on the printed wiring board 2a and the output terminals Sa to Sd of the LSI 1a connected to the island-shaped conductor patterns Pa to Pd. However, a plurality of sets of printed wiring boards 2a are configured.

  In the electronic device 10a employing the resin casing 3a, the island-like conductor patterns Pa to Pd connected to the output terminals Sa to Sd of the LSI 1a can be paired with the reference GND to function as parasitic capacitance. it can.

  By setting the output signals of the connected output terminals Sa to Sd to either the high state or the low state according to the internal setting of the LSI 1a, the island-like conductor patterns Pa to Pd are respectively connected to the high potential wiring. A connected state or a state connected to the low potential wiring may be realized.

  However, as shown in FIG. 2, the electronic device 10a can switch the output signals of the output terminals Sa to Sd to a high state or a low state by communication from the outside to the LSI 1a using the reception line Rx. The island-like conductor patterns Pa to Pd connected to the output terminals Sa to Sd can be selected from either the state connected to the high potential wiring or the state connected to the low potential wiring by switching the output signal. It is preferable that it is comprised. In this case, by switching the output signal of the output terminal to which the island-shaped conductor pattern is connected to the high state or the low state by communication from the outside to the LSI, the island-shaped conductor pattern is connected to the high potential wiring. Or a state connected to a low potential wiring can be selected.

  For example, in the example of FIG. 2, the output signal of the output terminal Sa is taken out from the connection point A of the transistors PT and NT constituting the CMOS inverter. If the gate control signal of the CMOS inverter is set to High by communication from the outside to the LSI 1a, the transistor NT is turned on and the transistor PT is turned off, so that the output signal at the output terminal Sa is in the low state (the potential of the low potential wiring). Thus, the island-shaped conductor pattern Pa is connected to the low potential wiring. Conversely, when the gate control signal is set to Low, the transistor NT is turned OFF and the transistor PT is turned ON, so that the output signal at the output terminal Sa becomes High (the potential of the high potential wiring), and the island conductor pattern Pa becomes high. It is connected to the potential wiring.

  In the electronic device 10a illustrated in FIG. 1, a plurality of combinations of the island-shaped conductor patterns Pa to Pd and the output terminals Sa to Sd having the functions as described above are configured in the printed wiring board 2a. As a result, the electronic device 10a selects the connection destinations of the island-like conductor patterns Pa to Pd functioning as parasitic capacitances so that the relationship of Formula 1 is established as much as possible even after the electronic device 10a is attached to a device that is actually used. Thus, the capacitance value can be adjusted. Note that the island-shaped conductor patterns Pa to Pd in the electronic device 10a function as a parasitic capacitance paired with the reference GND as described above, and correct the parasitic capacitance of the high potential wiring or the low potential wiring. The capacity value may be small.

For example, the parasitic inductance _L V of the left side of Equation 1, _{L G} and the parasitic capacitance _C V, relationship for _{C G (L V C V -L} G C G) is> 0, the one of the plurality of sets, The output signals of several output terminals are set to the Low state, and the corresponding several island-like conductor patterns are connected to the low potential wiring. As a result, the island-shaped conductor pattern can be made to function as a parasitic capacitance having an appropriate capacitance value C _A , so that L _V C _V− L _G (C _G + C _A ) = 0 can be obtained. Conversely, when the relational expression _{(L V C V -L G C} G) <0 , among the plurality of sets, and set the output signal of several output a High state, the corresponding number of The island-like conductor pattern is connected to the high potential wiring. Thus, L _V (C _V + C _A ) −L _G C _G = 0 can be approximated by causing the island-shaped conductor pattern to function as a parasitic capacitance having an appropriate capacitance value C _A. In this way, if N combinations (N: plural) of the combination of the island-like conductor pattern and the output terminal are configured, ^2N adjustments to Formula 1 are possible.

  FIG. 3 shows the result of testing the reduction of the common mode noise by switching the output signal of the output terminal to the high state or the low state and switching the connection state of the island-like conductor pattern by communication from the outside to the LSI described above. .

In the test, H8S2134 (manufactured by Renesas Electronics) LSI is used, and the area of the island-like conductor pattern connected to the power supply potential is switched by communication from the outside to the LSI, and common mode noise is measured. In the example of FIG. 3, when the area of the island-like conductor pattern connected to the power supply potential is switched to 550 [mm ² ] by communication from the outside to the LSI, the noise is reduced most.

  As described above, the electronic device 10a illustrated in FIG. 1 has the value of the left side of Equation 1 close to 0 after being attached to the device to be actually used, and the potential of the cable (high-potential wiring and low-potential wiring are increased in frequency. The potential difference ΔV between the potential of the connection point of the bypass capacitor that is short-circuited) and the potential of the reference GND can be brought close to zero. As a result, even when the electronic device 10a is attached to an arbitrary position of the device that is actually used and the reference GND changes depending on the attachment position, common mode noise generated by the LSI 1a that is a noise source is generated in the resin casing 3a. It is possible to cancel and prevent common mode noise from being transmitted to the cable outside the resin casing 3a.

  In the electronic device 10a, the adjustment so as to satisfy Formula 1 is performed for each of the output terminals Sa to Sd with respect to combinations of the island-shaped conductor patterns Pa to Pd and the output terminals Sa to Sd that are configured in a plurality on the printed wiring board 2a. The output signal is simply set to the High state or the Low state. Further, even when the same electronic device 10a is attached and reused at a different position of the device that is actually used, it is only necessary to appropriately change the setting of the output signals of the output terminals Sa to Sd to the High state or the Low state. .

  On the other hand, as another method of adjusting so that the relationship of Formula 1 is satisfied after being attached to a device to be actually used, for example, a method using trimming can be considered. In other words, by forming conductor patterns to be connected to the high-potential wiring and low-potential wiring in a large area in advance, repeatedly checking the noise generation status and performing trimming of the conductor pattern, and finding the optimum value is there. However, such a method using trimming not only takes time for adjustment, but also cannot be reused by changing the mounting position as in the electronic device 10a.

  As described above, the electronic device 10a illustrated in FIG. 1 appropriately adjusts the capacitance value of the parasitic capacitance with respect to the reference GND for reducing common mode noise by communication from the outside, and actually uses the electronic device. Noise reduction can be realized without attaching or detaching after attaching to the device. As a result, noise reduction can be realized even under different impedance environments such as the prototype stage and the mounting stage.

  As described above, the electronic device 10a illustrated in FIG. 1 houses the printed wiring board 2a on which the LSI 1a is mounted inside the resin casing 3a, and electrically connects the printed wiring board 2a with the cable from the outside of the resin casing 3a. An electronic device provided with a connector 4a for connection, which can be adjusted to satisfy a conditional expression for reducing common mode noise even if the reference GND changes depending on the mounting position, and has a simple configuration and is inexpensive It has become.

  Therefore, the above-described electronic device is suitable as an in-vehicle electronic device in which a large number of resin casings are employed in recent years instead of the metal casing, and the complex body shape of the automobile becomes the reference GND.

  In the electronic device described above, the resin casing may also serve as the connector housing.

  As such an example, there is an electronic device shown in FIGS.

  FIG. 4 is a diagram showing a part of the appearance of the HVAC unit of the in-vehicle air conditioner system, and is a diagram showing a usage state of the electronic device 10.

  FIG. 5 is an example of the electronic device 10 of FIG. 4 and is an exploded view of a conventional electronic device. FIG. 5A is a perspective view showing the resin casing 3 also serving as a connector housing, and FIG. 5B is an enlarged view of the printed wiring board 2 accommodated in the resin casing 3. It is a top view.

  As shown in FIG. 4, in the HVAC unit of the in-vehicle air conditioner system, an electronic device 10 using a resin casing is connected to a bus harness H of an electronic control unit (ECU) that performs overall control of the operation of the air conditioner. Attached to the outer wall of the housing adjacent to the servo motor M. The electronic device 10 is a drive device for a servo motor M that controls the wind direction of an air conditioner, and has the following structure.

  As shown in FIG. 5, the electronic device 10 includes an electronic device (so-called smart device) in which a printed wiring board 2 on which an LSI 1 for driving a servo motor is mounted is incorporated in a resin casing 3 of a connector having connection terminals 4. In the connector), the resin housing 3 that accommodates the printed wiring board 2 also serves as a connector housing.

  As shown in FIG. 4, in the HVAC unit, a plurality of smart connectors are attached around the housing. The housing of the HVAC unit is also made of resin. Therefore, in this case, the automobile body is considered to be the reference GND shown in FIG. 7A. However, the automobile body has a complicated shape, and the reference GND is also determined by the mounting position of the smart connector on the housing. It will change.

  FIG. 6 is a diagram showing an example of an electronic device according to the present invention, which is used in the same manner as the electronic device 10 of FIG. FIG. 6A is a top view schematically showing the main part of the electronic device 10b, and FIG. 6B is a top view showing the printed wiring board 2b before the electronic component is mounted. Moreover, (c) is a circuit diagram of the principal part of the electronic device 10b.

  The electronic device 10b shown in FIG. 6 is similar to the electronic device 10a shown in FIG. 1, and, as shown in FIG. 6A, the printed wiring board 2b on which the LSI 1b is mounted is accommodated inside the resin casing 3b shown by a broken line. To do. In the electronic device 10b, near the connection terminal 4b of the connector, the circuit shown in FIG. 7 is provided between the power supply wiring VCC, which is the high potential wiring of the printed wiring board 2b connected to the LSI 1b, and the ground wiring GND, which is the low potential wiring. The bypass capacitor BC2 shown in the model is inserted.

  In the electronic device 10a, island-shaped conductor patterns Pe to Pg are formed on the printed wiring board 2b, and the output terminals Se to Sg of the LSI 1b are connected to the respective island-shaped conductor patterns Pe to Pg. As described above, the electronic device 10a shown in FIG. 6 includes a plurality of combinations of the island-shaped conductor patterns Pe to Pg and the output terminals Se to Sg of the LSI 1b connected to the island-shaped conductor patterns Pe to Pg (the electronic device of FIG. 6). In the example of the apparatus 10b, three sets) are configured on the printed wiring board 2b. In the electronic device 10b employing the resin casing 3b, the island-shaped conductor patterns Pe to Pg connected to the output terminals Se to Sg of the LSI 1b are paired with the reference GND shown in FIG. , Can function as a parasitic capacitance.

  As shown in FIG. 6C, the output signals of the output terminals Se to Sg of the LSI 1b are taken out from the CMOS inverter CM indicated by a triangle symbol. The CMOS inverter CM may have the same configuration as the transistors PT and NT constituting the CMOS inverter in FIG. By setting the gate control signal of the CMOS inverter CM to High or Low by external communication with the LSI 1b, the island-like conductor patterns Pe to Pg are connected to the high potential wiring or to the low potential wiring. You can switch to the state.

  Accordingly, even if the electronic device 10b shown in FIG. 6 is attached to an arbitrary position of the HVAC unit shown in FIG. 4 and the reference GND changes depending on the attachment position, the common mode noise generated by the LSI 1b as the noise source is resinated. It is possible to cancel within the housing 3b and prevent the common mode noise from being transmitted to the cable outside the resin housing 3b.

  As shown in FIG. 6B, a part of the island-shaped conductor pattern Pf is formed immediately below the LSI 1b. As described above, the island-like conductor patterns Pe to Pg that are connected to the HVAC unit and switch the connection state by communication from the outside and function as a parasitic capacitance paired with the reference GND are formed immediately below the LSI 1b. May be. As a result, the area occupied by the island-like conductor patterns Pe to Pg can be reduced and the size can be reduced.

  As described above, in each of the electronic devices according to the present invention exemplified by the electronic devices 10a and 10b, the printed wiring board on which the LSI is mounted is accommodated in the resin casing, and the cable is provided from the outside of the resin casing with a cable. An electronic device having a connector for electrical connection to the printed wiring board, which can be adjusted to satisfy a conditional expression for reducing common mode noise even if the reference GND changes depending on the mounting position, and has a simple configuration An inexpensive electronic device can be obtained.

  Note that, among the high potential wiring and the low potential wiring in the electronic device described above, typically, the high potential wiring is an LSI power supply wiring, and the low potential wiring is an LSI ground wiring. However, the present invention is not limited to this. For example, the high potential wiring may be a high wiring of an LSI that controls CAN communication, and the low potential wiring may be a low wiring of the LSI.

  Further, the number of combinations of island-shaped conductor patterns and output terminals connected to the island-shaped conductor patterns may be an arbitrary number of 2 or more. As the number of combinations increases, finer adjustment that satisfies Equation 1 is possible.

10, 10a, 10b Electronic device 1, 1a, 1b LSI
Sa to Sg Output terminals 2, 2a, 2b Printed wiring board Pa to Pg Island-like conductor pattern BC1, BC2 Bypass capacitor 3, 3a, 3b Resin housing 4, 4a, 4b Connector (connection terminal)

Claims (7)

A printed wiring board (2a, 2b) on which the LSI (1a, 1b) is mounted is accommodated inside the resin casing (3a, 3b), and is electrically connected to the printed wiring board by a cable from the outside of the resin casing. An electronic device (10a, 10b) comprising connectors (4a, 4b),
Near the connector, bypass capacitors (BC1, BC2) are inserted between the high potential wiring (VCC) and the low potential wiring (GND) of the printed wiring board connected to the LSI,
An island-shaped conductor pattern (Pa to Pg) is formed on the printed wiring board,
The output terminals (Sa to Sg) of the LSI are connected to the island-shaped conductor pattern,
The combination of the output terminals to be connected to the island-shaped conductor patterns and island-shaped conductor pattern, a plurality of sets, Ri Na is configured on the printed wiring board,
The output signal of the output terminal can be switched to a high state or a low state by internal setting of the LSI or communication from the outside to the LSI.
Island conductor pattern connected to the output terminal, the switching of the output signal, that Do is configured to be selected from any of the conditions the high connected potential wiring connected state or in the low potential wiring An electronic device characterized by that. The electronic device according to claim 1 , wherein the island-shaped conductor pattern is formed immediately below the LSI. The electronic device according to claim 1 , wherein the high potential wiring is a power supply wiring of the LSI, and the low potential wiring is a ground wiring of the LSI. A printed wiring board (2a, 2b) on which the LSI (1a, 1b) is mounted is accommodated inside the resin casing (3a, 3b), and is electrically connected to the printed wiring board by a cable from the outside of the resin casing. An electronic device (10a, 10b) comprising connectors (4a, 4b),
Near the connector, bypass capacitors (BC1, BC2) are inserted between the high potential wiring (VCC) and the low potential wiring (GND) of the printed wiring board connected to the LSI,
An island-shaped conductor pattern (Pa to Pg) is formed on the printed wiring board,
The output terminals (Sa to Sg) of the LSI are connected to the island-shaped conductor pattern,
The combination of the output terminals to be connected to the island-shaped conductor patterns and island-shaped conductor pattern, a plurality of sets, Ri Na is configured on the printed wiring board,
The high potential wiring, the a LSI power supply wiring, the low potential wiring, the electronic device according to claim ground wiring der Rukoto of the LSI.   The electronic device according to claim 1, wherein the electronic device is for vehicle use.   6. The electronic device according to claim 1, wherein the resin casing (3b) also serves as a housing for the connector (4b). The electronic device is
Servo motor (M) drive device that controls the air direction of the air conditioner,
The electronic apparatus according to claim 6, wherein the electronic apparatus is connected to a bus harness (H) of an electronic control unit (ECU) that performs overall control of the operation of the air conditioner.

Images