JP7264679B2 - coupling circuit - Google Patents

Description

The present invention relates to a coupling circuit that combines a direct current and a high frequency alternating current used in a light emitting element or a light receiving element in an optical signal transmission circuit that handles high frequency signals of the gigahertz class or higher. In particular, for providing a coupling circuit with a simple configuration in which a direct current and a high-frequency alternating current that are required to be applied to a light-emitting element are combined with a conductor such as a circuit board pattern and, if necessary, a resistor. Regarding technology.

In order to convert a high-frequency electric signal of gigahertz class or higher into a good optical signal, a DC current as an appropriate bias current is applied to a light-emitting element such as a laser to emit light at a constant output. A light signal must be generated by superimposing two alternating currents to produce a light intensity.

For this purpose, a coupling circuit of DC and AC components, generally called a bias-tee, is used. Bias tees generally consist of many inductors and capacitors and tend to be expensive and bulky.

For example, in Patent Document 1, regarding the inductors required for the high-pass filter in the bias tee, only the high-frequency coil and the mid-range coil are used, and the low-frequency coil is eliminated. On the other hand, for low frequencies, a low-pass filter circuit is newly configured to apply a bias corresponding to low frequency components to the driven element.

JP 2007-241142 A

According to Patent Literature 1, although the number of inductors used in the high-pass filter is reduced, the inductors for high frequencies and mid frequencies remain. As for the low frequency range, a new detection circuit including an operational amplifier or the like is required, which raises concerns about an increase in circuit size and cost.
Accordingly, an object of the present invention is to provide means for solving such problems.
That is, one of the objects of the present invention is to satisfactorily couple a direct current and a high frequency alternating current using only a conductor such as a transmission line pattern on a circuit board and a terminating resistor without requiring an inductor or a capacitor.

In order to solve the above problems, the present invention employs the following configuration.
That is, the coupling circuit according to claim 1 is
a parallel running portion in which the first conductor and the second conductor run in parallel at a predetermined interval;
a third conductor forming a ground for an electrical signal transmitted by the first conductor;
a fourth conductor connected to the third conductor, forming a ground for an electrical signal transmitted by the second conductor, and being connected to the first conductor in the parallel running portion; In a coupling circuit in which an electrical signal is transmitted between the second conductors,
In the parallel running portion, the first electrical signal transmitted by the first conductor is transmitted through the second conductor in the same direction as the transmission direction of the first conductor, or the first electrical signal transmitted through the conductor of is transmitted through the first conductor in the same direction as the transmission direction of the second conductor;
A second electrical signal having a frequency different from that of the first electrical signal is applied to the second conductor.

According to the above configuration, the number of mounting parts such as resistors, inductors, capacitors, operational amplifiers, etc. can be reduced, so that not only the cost of parts and mounting can be reduced, but also the size of the device can be significantly reduced. Moreover, according to the present invention, it is possible to cope with a device having a low power supply impedance simply by forming an inductor with a circuit pattern.

In order to solve the above problems, the invention according to claim 2 is the coupling circuit according to claim 1,
The first conductor and the third conductor are connected to the terminal end of the first conductor located on the side opposite to the one end of the first conductor to which the first electrical signal is applied. A terminating resistor having a value within ±20% of a characteristic impedance value formed with the third conductor is connected between the terminating portion and the third conductor.

The terminal end of the first conductor is normally open since it is not connected to a device involved in the transmission and reception of the first electrical signal and the second electrical signal. However, according to the above configuration, the end portion of the first conductor can be matched with the characteristic impedance of the first conductor. Therefore, the influence of reflection of the first electric signal transmitted by the first conductor is reduced, and the frequency characteristics when the first electric signal is transmitted are improved.

In order to solve the above problems, the invention according to claim 3 is the coupling circuit according to claim 1 or 2, wherein the shorter the parallel running parts of the first conductor and the second conductor, The coupling peak frequency of the first electrical signal is increased, and the coupling peak frequency is the most attenuated in the amplitude of the first electrical signal transmitted between the first conductor and the second conductor. It is characterized by a small frequency.

According to the above configuration, it is possible to change the coupling peak frequency of the first electrical signal transmitted through the parallel running portion. In particular, the shorter the length of the parallel running portion, the higher the coupling peak frequency. Therefore, in a coupling circuit that handles high frequencies, this method can be used as an effective method for reducing the size of the coupling circuit.

In order to solve the above problems, the invention according to claim 4 provides the coupling circuit according to any one of claims 1 to 3, wherein the parallel running of the first conductor and the second conductor is provided. The narrower the distance between the first conductor and the second conductor in the section, the lower the coupling peak frequency of the first electrical signal. It is characterized by being the frequency at which attenuation of the amplitude of the first electric signal transmitted between the conductors is the smallest.

According to the above configuration, it is possible to change the coupling peak frequency of the first electrical signal transmitted through the parallel running portion. In particular, when it is necessary to keep the distance between the conductors in the parallel section narrow, manufacturing variability increases. Fluctuations in peak frequency can be kept low.

In order to solve the above problems, the invention according to claim 5 provides the coupling circuit according to any one of claims 1 to 4, wherein the first conductor and the third conductor are formed. the characteristic impedance formed by the second conductor and the third conductor; and the characteristic impedance of an external transmission line through which the first electric signal connected to the coupling circuit is transmitted. It is characterized in that the variation between them is within ±20%.

According to the above configuration, since the variation in the characteristic impedance is defined, it is possible to maintain good frequency characteristics of the first electrical signal passing through the parallel running portion. Also, fluctuations in the coupling peak frequency can be kept low.

In order to solve the above problems, the invention according to claim 6 provides the coupling circuit according to any one of claims 1 to 5,
further comprising a circuit board;
the first conductor and the second conductor are wiring configured on the surface of the circuit board;
The third conductor and the fourth conductor are characterized by being a ground plane formed on the back surface of the circuit board.

According to the above configuration, since the coupling circuit can be realized by the circuit board and the circuit pattern, it is possible to reduce the number of mounting parts such as inductors, capacitors, and operational amplifiers, thereby not only reducing the parts cost and the mounting cost but also significantly miniaturizing the device. becomes possible.

In order to solve the above problems, the invention according to claim 7 provides the coupling circuit according to any one of claims 1 to 6, wherein the second conductor to which the second electrical signal is input is An inductor formed by spiraling the second conductor is formed in the input section, and the impedance of the inductor at the frequency of the first electrical signal is formed by the second conductor and the fourth conductor. It is characterized by being within ±20% of the measured characteristic impedance.

According to the above configuration, even if a power supply device with low output impedance or the like is connected, it is possible to maintain good frequency characteristics with respect to high-frequency AC signals simply by forming an inductor with a circuit pattern.

In order to solve the above problems, the invention according to claim 8 provides the coupling circuit according to any one of claims 1 to 7,
Port 1 is one end of the first conductor, port 2 is the other end of the first conductor, port 3 is one end of the second conductor, and port 3 is the second conductor. Assuming that the other end is a port 4, the first electrical signal input to the port 1 is output from the port 4, or the first electrical signal input to the port 4 is output from the port 1. and the second electrical signal is output from the port 3 to the port 4;
The port 1, the port 3, and the port 4 are each provided with a connector for transmitting and receiving the first electrical signal and the second electrical signal to/from an external device.

According to the above configuration, even in the configuration in which the connectors for transmitting and receiving the first electric signal and the second electric signal are mounted on the coupling circuit, the mounted parts such as resistors, inductors, capacitors, and operational amplifiers can be reduced. Not only can the cost and mounting cost be reduced, but the device can be made significantly smaller.

In order to solve the above problems, the invention according to claim 9 provides the coupling circuit according to any one of claims 1 to 8, wherein the first conductor to the second conductor or the Attenuation of the coupling peak frequency due to transmission of the first electrical signal transmitted from the second conductor to the first conductor is within 1 dB, and the coupling peak frequency is between the first conductor and the second conductor. is the frequency at which attenuation of the amplitude of the first electric signal transmitted between the conductor and the first electric signal is the smallest.

According to the above configuration, it is possible to obtain a substantially flat characteristic with an insertion loss of about 1 dB in at least a range of about ±1 GHz with respect to the target frequency.

In order to solve the above problems, the invention according to claim 10 is the coupling circuit according to any one of claims 1 to 9, wherein the second electric signal is a direct current, and the first electric signal is 6 GHz or higher.

According to the above configuration, it is possible to provide the configuration of the coupling circuit suitable for the frequency band expected to be used in the fifth generation wireless communication.

According to the present invention, mounting parts such as inductors, capacitors, and operational amplifiers can be reduced, so not only can the parts cost and mounting cost be reduced, but also the size of the device can be significantly reduced. Moreover, according to the present invention, it is possible to cope with a device having a low power supply impedance simply by forming an inductor with a circuit pattern.

1 is a diagram showing the basic concept of a coupling circuit realized by a circuit board; FIG. 1B is a diagram showing an example of frequency characteristics of a transmitted signal and a reflected signal in the coupling circuit of FIG. 1A; FIG. FIG. 4 is a diagram showing some of the parameters of the coupling circuit; FIG. 2B is a diagram showing changes in the coupling peak frequency when the coupling transmission line spacing of the parameters of FIG. 2A is changed; FIG. 2B is a diagram showing the change in coupling peak frequency when the coupling transmission line spacing for the parameters of FIG. 2A is 0.7 mm; FIG. 2B is a diagram showing the change in coupling peak frequency when the coupling transmission line spacing for the parameters of FIG. 2A is 1.0 mm; FIG. 2B is a diagram showing the change in coupling peak frequency when the coupling transmission line spacing for the parameters of FIG. 2A is 2.0 mm; FIG. 2B is a diagram showing changes in the coupling peak frequency when the coupling transmission line length of the parameters in FIG. 2A is changed; 2B is a diagram showing an example of a coupling circuit in which a coaxial connector is mounted on the coupling circuit of FIG. 2A and a terminating resistor is mounted on port 2; FIG. 3B is a diagram showing an example of frequency characteristics of a transmitted signal and a reflected signal of the coupling circuit of FIG. 3A; FIG. 3B is a diagram showing an example of a configuration in which a low output impedance power supply device is input to port 3 in the coupling circuit of FIG. 3A; FIG. 4B is a diagram showing an example of frequency characteristics of a transmitted signal and a reflected signal of the coupling circuit of FIG. 4A; FIG. 4B is a diagram showing an example of a configuration in which an inductor is formed in the input section of port 3 in the coupling circuit of FIG. 4A; FIG. 5B is a diagram showing an example of frequency characteristics of a transmitted signal and a reflected signal of the coupling circuit of FIG. 5A; FIG. 5B is a diagram showing an example of a configuration in which the terminating resistor of port 2 is removed and port 2 is opened in the coupling circuit of FIG. 5A; FIG. 6B is a diagram showing an example of frequency characteristics of a transmitted signal and a reflected signal of the coupling circuit of FIG. 6A; FIG. 5B is a plan view of the coupling circuit of FIG. 5A; FIG. 5B illustrates an example of a port 4 connector and a port 2 terminating resistor mounting area of the coupling circuit of FIG. 5A; FIG. 5B illustrates an example of a mounting area for a Port 1 connector of the coupling circuit of FIG. 5A; FIG. 5B is a diagram illustrating an example of an area where an inductor formed above the mounting area of the port 3 connector of the coupling circuit of FIG. 5A is formed; FIG. 5B illustrates an example of a mounting area for a port 3 connector of the coupling circuit of FIG. 5A; FIG. It is drawing for demonstrating a prior art.

(Summary of features of coupling circuits formed on circuit boards)
The configuration of the coupling circuit (1000) of this embodiment includes two copper foil patterns (copper foil pattern 1 (100) and copper foil pattern 2 (copper foil pattern 1 (100) and copper foil pattern 2 ( 200)), a ground 500 provided as a plane on the back surface of the circuit board 300, and a terminating resistor (not shown) mounted on the port 2 (320). However, a configuration in which no terminating resistor is mounted on port 2 (320) can also be used as a basic configuration. Also, in the following description of this embodiment, an example of a coupling circuit for driving a light emitting element (not shown) connected to port 4 (340) will be described in detail. Port 2 (320) and Port 4 (340) are described below.

Port 1 (310) is an input section for high-frequency AC signals in copper foil pattern 1 (100). Basically, a transmission line such as a coaxial cable with a characteristic impedance of 50Ω is connected. A high-frequency AC signal supplied to the copper foil pattern 1 (100) is transmitted through the transmission path.

Port 2 (320) is the termination of copper pattern 1 (100). A terminating resistor of 50Ω may or may not be mounted between the terminating portion and the ground 500 provided on the back surface of the circuit board 300 . In order to explain the basic operation, FIG. 1A numerically illustrates the case where the terminating resistor is mounted.

Port 3 (330) is an input part for DC signals such as bias current supplied to the light emitting element in copper foil pattern 2 (200). Port 3 (330) is basically connected to a low-output-impedance power supply or the like (not shown), which will be described later. FIG. 1A illustrates a case where a device (not shown) having an output impedance of 50Ω is connected in order to explain the basic operation.

Port 4 (340) outputs a copper foil in which a high-frequency AC signal transmitted from copper foil pattern 1 (100) to copper foil pattern 2 (200) is superimposed on the DC signal input from port 3 (330). It is an output part in pattern 2 (200), and is a port to which a driven device such as a light emitting element is connected.

The parallel running portion 350 is a section in which the copper foil pattern 1 (100) and the copper foil pattern 2 (200) run side by side at a predetermined distance. In parallel running portion 350, a high-frequency AC signal input from port 1 (310) to copper foil pattern 1 (100) passes through copper foil pattern 2 (100). The high frequency AC signal is progressively transmitted in the direction from port 3 (330) to port 4 (340), which is the same direction as the high frequency AC signal goes from port 1 (310) to port 2 (320). This transmission utilizes the phenomenon that the AC signal component is coupled from the copper foil pattern 1 (100) to the copper foil pattern 2 (200).

The most efficiently coupled frequencies depend on the length of the parallel running portion 350, the distance between the copper foil pattern 1 (100) and the copper foil pattern 2 (200) in the parallel running portion 350, and the distance between the inside and outside of the circuit board 300. It changes depending on parameters such as the characteristic impedance of the transmission line. Hereinafter, the length of the parallel running portion 350 may be referred to as the coupling transmission line length, and the interval between the copper foil pattern 1 (100) and the copper foil pattern 2 (200) in the parallel running portion 350 may be referred to as the coupling transmission line spacing. .

FIG. 1B shows a transmitted signal transmitted from port 1 (310) to port 4 (340) and a reflected signal from port 1 (310) to port 1 (310) when a high-frequency AC signal is input to port 1 (310). shows the frequency characteristics of the reflected signal. The example of FIG. 1B shows the most efficient coupling around 7.2 GHz, with the least amplitude attenuation of the transmitted signal. Hereinafter, the frequency at which the attenuation of the amplitude of the high-frequency AC signal transmitted between the copper foil pattern 1 (100) and the copper foil pattern 2 (200) is the smallest is referred to as the coupling peak frequency.

As noted above, the coupling peak frequency can be arbitrarily selected by varying parameters including coupling line spacing and coupling line length. According to these configurations and actions, it can be seen that the function of the bias tee can be realized only with the circuit pattern and the terminating resistor without providing an inductor or a capacitor separately.

(Specific specifications of coupling circuit)
FIG. 2A is a diagram showing some of the parameters of the coupling circuit. L is the length of the coupled transmission line, and corresponds to the length of copper foil pattern 1 (100) and copper foil pattern 2 (200) in FIG. 2A. Gap is the distance between the coupled transmission lines, and corresponds to the distance between the copper foil pattern 1 (100) and the copper foil pattern 2 (200) in FIG. 2A. W is the width of the transmission line, and corresponds to the width of copper foil pattern 1 (100) and copper foil pattern 2 (200) in FIG. 2A. In FIG. 2A, copper foil pattern 1 (100) and copper foil pattern 2 (200) have the same width. t is the thickness of the circuit board. Table 1 shows specific values for the parameters of the coupling circuit of FIG. 2A.

2B is a diagram showing the change in coupling peak frequency when the coupling transmission line spacing is varied in the coupling circuit of FIG. 2A having the parameter values of Table 1. FIG. The horizontal axis of FIG. 2B indicates the coupling transmission line spacing [mm], and the vertical axis of FIG. 2B indicates the coupling peak frequency [GHz]. In FIG. 2B, when the coupling transmission line spacing is changed from 2 mm to 0.2 mm, the coupling peak frequency changes from approximately 12 GHz to approximately 6 GHz. That is, the coupling peak frequency becomes lower as the coupling transmission line spacing becomes narrower.

FIG. 2C shows a transmission signal transmitted from port 1 (310) to port 4 (340) when a high-frequency AC signal is input to port 1 (310) when the coupling transmission line spacing in FIG. 2B is 0.7 mm. and the frequency characteristic of the reflected signal reflected from port 1 (310) to port 1 (310). The horizontal axis of FIG. 2C indicates the frequency [GHz], and the vertical axis indicates the amplitude [dB] of the transmitted signal and the reflected signal. Since the reflected signal is reduced to about -20 dB or less, it is shown that the effect on the transmitted signal is small. In the example of FIG. 2C, there is a coupling peak frequency near 7.0 GHz, indicating that the coupling peak frequency is the maximum value.

FIG. 2D shows a transmission signal transmitted from port 1 (310) to port 4 (340) when a high-frequency AC signal is input to port 1 (310) when the coupling transmission line spacing in FIG. 2B is 1.0 mm. and the frequency characteristic of the reflected signal reflected from port 1 (310) to port 1 (310). The horizontal axis of FIG. 2D indicates the frequency [GHz], and the vertical axis indicates the amplitude [dB] of the transmitted signal and the reflected signal. Since the reflected signal is reduced to about -20 dB or less, it is shown that the effect on the transmitted signal is small. In the example of FIG. 2D, there is a coupling peak frequency near 7.8 GHz, indicating that the coupling peak frequency is the maximum value.

FIG. 2E shows a transmission signal transmitted from port 1 (310) to port 4 (340) when a high-frequency AC signal is input to port 1 (310) when the coupling transmission line spacing in FIG. 2B is 2.0 mm. and the frequency characteristic of the reflected signal reflected from port 1 (310) to port 1 (310). The horizontal axis of FIG. 2E indicates the frequency [GHz], and the vertical axis indicates the amplitude [dB] of the transmitted signal and the reflected signal. Since the reflected signal is reduced to about -20 dB or less, it is shown that the effect on the transmitted signal is small. In the example of FIG. 2E, there is a coupling peak frequency near 12.0 GHz, indicating that the coupling peak frequency is a local maximum.

FIG. 2F is a diagram showing the change in coupling peak frequency when the coupling transmission line length is varied in the coupling circuit of FIG. 2A having the parameter values of Table 1; The horizontal axis of FIG. 2F indicates the coupling transmission line length [mm], and the vertical axis of FIG. 2F indicates the coupling peak frequency [GHz]. In FIG. 2F, when the coupling transmission line length is changed from approximately 175 mm to approximately 25 mm, the coupling peak frequency changes from approximately 5 GHz to approximately 43 GHz. That is, the shorter the coupling transmission line length, the higher the coupling peak frequency.

According to the above configuration example, a coupling circuit of 10 GHz or higher can be configured simply by using a general glass-epoxy circuit pattern within about 10 cm.

(Concrete example of coupling circuit with coaxial connector mounted)
In Figures 3A, 4A, 5A and 6A, a coaxial connector mounting area has been added to the edge of the circuit board to better match the actual usage, and is intended for the 28 GHz band expected to be used in the fifth generation wireless communication. A configuration example is shown. Parameter values for circuit board 300 and coupling circuit 1000 of FIGS. 3A, 4A, 5A and 6A are shown in Table 2.

(Example 1)
FIG. 3A shows the implementation of a coaxial connector in a coupling circuit having the parameter values of Table 1. FIG. The characteristic impedance of copper foil pattern 1 (100) and copper foil pattern 2 (200) in FIG. 3A is about 50Ω. A coaxial connector 311 is mounted on port 1 (310) for inputting a high-frequency AC signal. The characteristic impedance of coaxial connector 311 is about 50Ω. The coaxial connector 311 is connected to a coaxial cable having a characteristic impedance of about 50Ω for transmitting high-frequency AC signals. The mounting area of port 1 is referred to as area A101 (360), and details of area A101 (360) are shown in FIG. 7C. As shown in FIG. 7C, coaxial connector 311 is mounted across port 1 connector mounting area 1 (361) and port 1 connector mounting area 2 (362). Copper foil pattern 1 (100) extends to the edge of circuit board 300 between port 1 connector mounting area 1 (361) and port 1 connector mounting area 2 (362).

A terminating resistor 321 with an impedance of 50Ω is mounted on port 2 (320) for the purpose of suppressing reflection of high-frequency AC signals. The terminating resistor 321 is mounted so as to connect between the copper foil pattern 1 (100) and the ground on the back surface of the circuit board 300. FIG. Details of the area where the termination resistor 321 is mounted are shown in FIG. 7B. A terminating resistor 321 is mounted in the terminating resistor mounting area 383 of FIG. 7B. A terminal resistor 321 is connected to the port 2 (320), which is the terminal of the copper foil pattern 1 (100) adjacent to the right side of the terminal resistor mounting area 383 in FIG. 7B. 7B is connected to the rear surface of the circuit board 100 via a through hole or the like. The impedance of the terminating resistor 321 has a value within ±20% of the value of the characteristic impedance of the copper foil pattern 1 (100).

Port 3 (330) functions as a DC input for inputting a DC signal to copper foil pattern 2 (200). A DC signal is generally connected to a power supply device having a low output impedance. In FIG. 3A, the output impedance of the device connected to port 3 is set to about 50Ω. Therefore, since it matches the characteristic impedance of the copper foil pattern 2 (200), the effect on the high-frequency AC signal transmitted through the copper foil pattern 2 (200) is reduced. That is, in the case of this embodiment, the flatness of the transmitted signal transmitted through the copper foil pattern 2 (200) is maintained with respect to the frequency change.

Port 4 (340) is equipped with a coaxial connector 341 for outputting a superimposed signal obtained by superimposing a transmission signal of a high-frequency AC signal and a DC signal input to port 3 (330). The characteristic impedance of coaxial connector 341 is about 50Ω. A coaxial cable having a characteristic impedance of about 50Ω for transmitting superimposed signals is connected to the coaxial connector 341 . A light emitting element such as a laser diode is connected to the other end of the coaxial cable. The DC signal is used to define the bias level of the light emitting element, and the transmission signal can also be used as a carrier signal for carrying information or as an information signal. The implementation area for port 4 (340) is included in part of area A103 (380) and the details of area A101 (360) are shown in FIG. 7C as previously described. As shown in FIG. 7C, coaxial connector 341 is mounted across port 4 connector mounting area 1 (381) and port 4 connector mounting area 2 (382). Copper foil pattern 2 (200) extends to the edge of circuit board 300 between Port 4 connector mounting area 1 (381) and Port 4 connector mounting area 2 (382).

3A, 4A, 5A and 6A, the characteristic impedance of copper foil pattern 1 (100), the characteristic impedance of copper foil pattern 2 (200), and the coaxial Variation between cable characteristic impedances is within ±20%.

Furthermore, the characteristic impedance of the copper foil pattern 1 (100) in FIGS. 1A and 2A, the characteristic impedance of the copper foil pattern 2 (200), and the characteristic impedance of the transmission line connected to the copper foil pattern 1 (100) Variation is within ±20%.

FIG. 3B shows a transmission signal when a high-frequency AC signal is input to port 1 (310) of the coupling circuit in FIG. 3A, a DC signal is input to port 3 (330), and a superimposed signal is output from port 4 (340). and frequency characteristics of reflected signals. The transmitted signal is the transmitted component of the high frequency ac signal measured at port 4 (340), and the reflected signal is the reflected component of the high frequency ac signal measured at port 1 (310). The horizontal axis of FIG. 3B is the frequency [GHz], and the vertical axis is the amplitude [dB] of the transmitted signal and the reflected signal. The coupling peak frequency of the transmission signal is around 28.0 GHz, and the transmission signal is most efficiently obtained at the target frequency of 28.0 GHz. Although the transmitted signal is attenuated by about 1 dB, the attenuation amount is less than about 1 dB by optimizing the structure and suppressing variations in manufacturing the structure.

According to the above configuration example, even when a general coaxial connector is mounted on a glass-epoxy circuit board, it is expected to be used in fifth-generation wireless communication by using a circuit pattern configuration within about 5 cm. A coupling circuit can be configured simply in the vicinity of 28.0 GHz.

(Example 2)
FIG. 4A also illustrates the implementation of a coaxial connector in a coupling circuit having the parameter values of Table 1. FIG. The characteristic impedance of copper foil pattern 1 (100) and copper foil pattern 2 (200) in FIG. 4A is about 50Ω. Also, port 1 (310), port 2 (320) and port 4 (340) have the same configuration as in FIG. 3A. A coaxial connector 311 is connected to port 1 (310), a terminating resistor 321 is connected to port 2 (320), and a coaxial connector 341 is mounted to port 4 (340). To avoid duplication of description, refer to the description of FIG. 3A for Port 1 (310), Port 2 (320) and Port 4 (340).

Port 3 (330), which differs from the configuration of FIG. 3A, is described below. Port 3 (330) functions as a DC input for inputting a DC signal. A DC signal is generally connected to a power supply having a low output impedance. Therefore, the configuration shown in FIG. 4A is such that the output impedance of the device connected to the port 3 (330) is lowered to 1Ω. In this case, an impedance mismatch is given to the AC component, so that the flatness of the frequency characteristic is degraded. FIG. 4B shows how the flatness of the frequency characteristic deteriorates.

FIG. 4B shows a transmission signal when a high-frequency AC signal is input to port 1 (310) of the coupling circuit in FIG. 4A, a DC signal is input to port 3 (330), and a superimposed signal is output from port 4 (340). and frequency characteristics of reflected signals. The transmitted signal is the transmitted component of the high frequency ac signal measured at port 4 (340), and the reflected signal is the reflected component of the high frequency ac signal measured at port 1 (310). The horizontal axis of FIG. 4B is the frequency [GHz], and the vertical axis is the amplitude [dB] of the transmitted signal and the reflected signal. The coupling peak frequency of the transmission signal is around 28.0 GHz, and the transmission signal is most efficiently obtained at the target frequency of 28.0 GHz. Also, the transmitted signal is attenuated by about 1 dB, which can be optimized to less than about 1 dB. Compared with the transmitted signal in FIG. 3B, the transmitted signal of about 20 GHz or less and the transmitted signal of about 40 GHz or more show deterioration in the flatness of the frequency characteristics. maintained.

According to the above configuration example, even if a DC signal is generally supplied by a power supply device with low output impedance, it is expected to be used in fifth-generation wireless communication by using a circuit pattern configuration within about 5 cm28. A coupling circuit in the vicinity of .0 GHz can be configured simply.

(Example 3)
FIG. 5A also shows the implementation of a coaxial connector in a coupling circuit having the parameters of Table 1. FIG. The characteristic impedance of copper foil pattern 1 (100) and copper foil pattern 2 (200) in FIG. 5A is about 50Ω. Also, port 1 (310), port 2 (320) and port 4 (340) have the same configuration as in FIG. 3A. A coaxial connector 311 is connected to port 1 (310), a terminating resistor 321 is connected to port 2 (320), and a coaxial connector 341 is mounted to port 4 (340). To avoid duplication of description, refer to the description of FIG. 3A for Port 1 (310), Port 2 (320) and Port 4 (340).

Port 3 (330), which differs from the configuration of Figures 3A and 4A, is described below. Port 3 (330) functions as a DC input for inputting a DC signal. A DC signal is generally connected to a power supply having a low output impedance. Therefore, the configuration shown in FIG. 5A is such that the output impedance of the device connected to the port 3 (330) is reduced to 1Ω, as in FIG. 4A. In this case, as explained in FIG. 4A, an impedance mismatch is given to the AC component, so that the flatness of the frequency characteristic is degraded. However, in FIG. 5A, in order to improve the flatness of the frequency characteristics, an inductor 400 is formed in the DC input section of port 3 (330) to improve the flatness of the frequency characteristics.

The area where the inductor 400 is formed at the DC input part of port 3 (330) is called area C101 (390), and the details of area C101 (390) are shown in FIG. 7D. As shown in FIG. 7D, the formation of the inductor 400 with a spiral circuit pattern increases the impedance in the high frequency region. As a result, in the copper foil pattern 2 (200), only the impedance mismatch of the high frequency component is improved without affecting the DC component, and the flatness of the frequency response characteristic is improved.

The radius of the inductor 400 shown in FIG. 7D is approximately 5 mm, and the distance from the winding start to the winding end of the circuit pattern is approximately 4 mm. The target impedance near 28.0 GHz is about 50Ω, and it is possible to form a self-inductance of about 0.37 nH. Further, no ground plane is formed on the back surface of the circuit board 300 corresponding to the region where the inductor 400 is formed in the area C101 (390). Moreover, the impedance of the inductor 400 at the frequency of the high-frequency AC signal transmitted through the copper foil pattern 1 (100) is within ±20% of the characteristic impedance of the copper foil pattern 2 (200).

FIG. 5B shows a transmission signal when a high-frequency AC signal is input to port 1 (310) of the coupling circuit in FIG. 5A, a DC signal is input to port 3 (330), and a superimposed signal is output from port 4 (340). and frequency characteristics of reflected signals. The transmitted signal is the transmitted component of the high frequency ac signal measured at port 4 (340), and the reflected signal is the reflected component of the high frequency ac signal measured at port 1 (310). The horizontal axis of FIG. 5B is the frequency [GHz], and the vertical axis is the amplitude [dB] of the transmitted signal and the reflected signal. The coupling peak frequency of the transmission signal is around 28.0 GHz, and the transmission signal is most efficiently obtained at the target frequency of 28.0 GHz. Also, the transmitted signal is attenuated by about 2 dB, which can be reduced to less than 1 dB with the optimization described above. Compared to the transmitted signal in FIG. 4B, the transmitted signal of about 20 GHz or less and the transmitted signal of about 40 GHz or more have improved flatness of the frequency characteristics, and the flatness of the frequency characteristics near the target frequency of 28.0 GHz is also improved. Improved.

According to the above configuration example, even if a DC signal is generally supplied by a power supply device with low output impedance, by using the configuration of the circuit pattern within about 5 cm including the inductor 400 formed by the circuit pattern, it is possible to achieve a frequency of around 28.0 GHz. The coupling circuit in can be configured simply. In other words, stable coupling characteristics can be realized without requiring additional mounting components such as inductors and capacitors, even after considering the shape for actual use, the impedance of the connection destination, and the like. In this way, it is possible to obtain a substantially flat frequency characteristic with an insertion loss of about 1 dB in at least a range of about ±1 GHz with respect to the target frequency of 28 GHz.

(Example 4)
FIG. 6A also shows the implementation of a coaxial connector in a coupling circuit having the parameters of Table 1. FIG. The characteristic impedance of copper foil pattern 1 (100) and copper foil pattern 2 (200) in FIG. 6A is about 50Ω. Port 1 (310), port 3 (330) and port 4 (340) have the same configuration as in FIG. 5A. A coaxial connector 311 is connected to port 1 (310), and a coaxial connector 341 is mounted to port 4 (340). A coaxial connector 331 is connected to port 3 (330) to form an inductor 400. FIG. Terminating resistor 321 is not connected to port 2 (320). Therefore, port 2 (320) is open. That is, the coupling circuit in FIG. 6A differs from the coupling circuit in FIG. 5A in that port 2 (320) is in an open state. To avoid duplication of description, please refer to the descriptions of FIGS. 3A and 5A for port 1 (310), port 3 (330) and port 4 (340).

FIG. 6B shows a transmission signal when a high-frequency AC signal is input to port 1 (310) of the coupling circuit in FIG. 6A, a DC signal is input to port 3 (330), and a superimposed signal is output from port 4 (340). and frequency characteristics of reflected signals. The transmitted signal is the transmitted component of the high frequency ac signal measured at port 4 (340), and the reflected signal is the reflected component of the high frequency ac signal measured at port 1 (310). The horizontal axis of FIG. 5B is the frequency [GHz], and the vertical axis is the amplitude [dB] of the transmitted signal and the reflected signal. The coupling peak frequency of the transmitted signal is around 28.0 GHz, and the transmitted signal is most efficiently obtained at the target frequency of 28.0 GHz. However, since the port 2 (320) is in an open state, the level of the reflected signal rises as a whole. However, with respect to the target frequency of 28 GHz, a substantially flat characteristic can be obtained with an insertion loss of about 2.5 dB in at least a range of about ±1 GHz. Also, the insertion loss can be reduced to less than 1 dB by optimizing the basic shape, such as variations in manufacturing and the spacing of the coupling transmission lines of the parallel running portion 350 .

According to the above configuration example, even if the terminating resistor 321 of the port 2 (320) is removed, there is almost no influence such as deterioration on the transmission characteristics of high frequency components, and by using the configuration of the circuit pattern within about 5 cm, 28 A coupling circuit in the vicinity of .0 GHz can be configured simply. In other words, stable coupling characteristics can be realized without requiring additional mounted components such as resistors, inductors, and capacitors, even after considering the shape for actual use, the impedance of the connection destination, and the like. In this way, it is possible to obtain a substantially flat frequency characteristic with an insertion loss of about 1 dB in at least a range of about ±1 GHz with respect to the target frequency of 28 GHz.

(Mounting area for coaxial connectors, etc.)
FIG. 7A is a plan view of the coupling circuit of FIG. 5A. In the plan view of FIG. 7A, area A101 (360) where coaxial connector 311 is mounted on port 1 (310), area A102 (370) where coaxial connector 331 is mounted on port 3 (330), and inductor 400 are Included is area C101 (390) that is formed. Furthermore, the plan view of FIG. 7A includes an area A103 (380) where a coaxial connector 341 is mounted on port 4 (340) and a terminating resistor 321 is mounted on port 2 (320). Between the area A101 (360) and the area A103 (380), the parallel running part 350 extends over a length of 37 mm. In the parallel running portion 350, copper foil pattern 1 (100) and copper foil pattern 2 (200) with a width of 0.2 mm run in parallel with a coupling transmission line interval of 0.2 mm.

FIG. 7B is an enlarged view of area A103 (380). In area A103 (380), coaxial connector 341 mounted on port 4 (340) is mounted across port 4 connector mounting area 1 (381) and port 4 connector mounting area 2 (382). Copper foil pattern 2 (200) extends to the edge of circuit board 100 between Port 4 connector mounting area 1 (381) and Port 4 connector mounting area 2 (382). A terminating resistor 321 connecting between port 2 ( 320 ) and the ground 500 is mounted in a terminating resistor mounting area 383 .

FIG. 7C is an enlarged view of area A101 (360). In area A101 (360), coaxial connector 311 mounted on port 1 (310) is mounted across port 1 connector mounting area 1 (361) and port 1 connector mounting area 2 (362). Copper foil pattern 1 (100) extends to the edge of circuit board 100 between port 1 connector mounting area 1 (361) and port 1 connector mounting area 2 (362). Copper foil pattern 2 (200) is bent toward area C101 (390) where inductor 400 is formed. In FIG. 7C, the copper foil pattern 2 (200) is bent almost at a right angle to area C101 (390).

FIG. 7D is an enlarged view of area C101 (390) where inductor 400 is formed. Inductor 400 is formed by spirally wiring copper foil pattern 2 (200). The radius of the inductor 400 shown in FIG. 7D is approximately 5 mm, and the distance from the winding start to the winding end of the copper foil pattern 2 (200) is approximately 4 mm. The target impedance near 28.0 GHz is about 50Ω, and it is possible to form a self-inductance of about 0.37 nH. Further, no ground plane is formed on the back surface of the circuit board 300 corresponding to the region where the inductor 400 is formed in the area C101 (390). Therefore, through holes are formed at the winding start and the winding end of the copper foil pattern 2 (200), and by providing the circuit pattern on the back surface of the circuit board 300, the winding start and the winding end of the copper foil pattern 2 (200) are connected. It is

FIG. 7E is an enlarged view of area A102 (370). In area A102 (370), the coaxial connector 331 mounted on port 3 (330) is mounted across port 3 connector mounting area 1 (371) and port 3 connector mounting area 2 (372). Copper foil pattern 2 (200) extends to the edge of circuit board 100 between Port 3 connector mounting area 1 (371) and Port 3 connector mounting area 2 (372).

In the above embodiments, the variation in characteristic impedance of each component is within ±20%. In addition, the impedance of the terminating resistor 321 and the inductor 400 at the frequency of the high-frequency AC signal that transmits the copper foil pattern 1 (100) or the coupling peak frequency is included within ±20% of the characteristic impedance variation of each component.

As described above, the coupling circuit of FIG. 5A in which the coaxial connectors 311, 331, 341 and the terminating resistor 321 are mounted is suitable for inductors, capacitors, etc., even in consideration of the shape for actual use and the impedance of the connection destination. Stable coupling characteristics can be achieved without the need for additional mounting parts. That is, it is possible to obtain a substantially flat frequency characteristic with an insertion loss of about 1 dB in at least a range of about ±1 GHz with respect to the target frequency of 28 GHz.

(Modification 1)
In the above-described embodiment, the device connected to port 4 (340) of circuit board 300 is assumed to be a light-emitting element. The principles of the embodiment described above can be applied. That is, when a light receiving element is connected to port 4 (340), a high-frequency AC signal is input to port 4 (340) as an output signal of the light receiving element, is transmitted through parallel running section 350, and the transmitted signal is transmitted to port 4 (340). 1 (310). The characteristics of the transmitted signal and the reflected signal in the parallel running portion 350 in this case are shown in FIGS. 3B, 4B, 5B and 6B. Also, since the DC signal input to port 3 (330) is used as a signal that defines the bias of the light receiving element, the DC signal is output from port 4 (340).

(Modification 2)
In the above-described embodiment, the configuration in which the copper foil pattern 1 (100) and the copper foil pattern 2 (200) are wired on the circuit board 300 has been described. However, the present invention is not limited to printed circuit boards, and may be applied to electric wires, molded interconnect devices (MIDs), etc., as long as the copper foil patterns are in close proximity to each other. In the case of electric wires, two electric wires running in parallel correspond to the parallel running portions 350 of the copper foil pattern 1 (100) and the copper foil pattern 2 (200), and a ground electric wire is provided outside the two electric wires. Two more can be arranged.

(Modification 3)
In the embodiment described above, the configuration in which only one parallel running portion 350 is provided has been described. However, a plurality of parallel running portions 350 may be provided, and signals of different frequencies may be used as transmission signals in the respective parallel running portions 350 . As described with reference to FIG. 2B, if the coupling transmission line spacing is different in each parallel section 350, the coupling peak frequency is also different. In addition, as explained in FIG. 2F, if the coupling transmission line length is different in each parallel section 350, the coupling peak frequency is also different. Also, even if the values of other parameters other than the coupling transmission line spacing and the coupling transmission line length in Table 1 are changed, the coupling peak frequency also changes. It is also possible to employ a configuration in which a plurality of parallel running portions 350 with these parameters changed is provided in the coupling circuit 1000 .

(Modification 4)
In the above-described embodiment, the case where the terminating resistor 321 is mounted on the port 2 (320) has been mainly described, but the basic configuration is such that the terminating resistor 321 is not mounted on the port 2 (320) as shown in FIG. 6A. It is also possible to That is, in the coupling circuits of FIGS. 3A and 4, it is also possible to adopt a configuration in which the termination resistor 321 is not mounted on the port 2 (320). Even in this case, considering the shape for actual use, the impedance of the connection destination, etc., it is necessary to realize stable coupling characteristics without the need for additional mounting parts such as resistors, inductors, and capacitors. can be done. That is, even if the port 2 (320) is not equipped with the terminating resistor 321, it is possible to obtain a substantially flat frequency characteristic with an insertion loss of about 1 dB in a range of at least about ±1 GHz with respect to the target frequency of 28 GHz. .

(Modification 5)
In the above-described embodiment, the electrical signal applied to port 3 (330) is described as a direct current, but in this embodiment, the electrical signal applied to port 3 (330) is not limited to direct current. That is, any frequency different from the frequency of the high-frequency AC signal applied to port 1 (310) or port 4 (340) can be set as the frequency of the electrical signal applied to port 3 (330). .

Although the embodiments have been described in detail with reference to the drawings, the present invention is not limited by the contents described in the above embodiments. In addition, the components described above include components that can be easily assumed by those skilled in the art and components that are substantially the same. Furthermore, the configurations described above can be combined as appropriate. In addition, various omissions, substitutions, or changes in configuration can be made without departing from the gist of the present invention.

INDUSTRIAL APPLICABILITY The present invention is extremely useful in optical signal transmission circuits that handle high-frequency signals of the gigahertz class or higher, and is extremely useful for coupling circuits for direct current and high-frequency alternating current used in light-emitting elements or light-receiving elements.

100... Copper foil pattern 1 (first conductor)
200... Copper foil pattern 2 (second conductor)
300 circuit board 310 port 1
311 Port 1 connector 320 Port 2
321 terminating resistor 330 port 3
331 Port 3 connector 340 Port 4
341 Port 4 connector 350 Parallel running portion 360 Area A101
361 Port 1 connector mounting area 1
362 Port 1 connector mounting area 2
370 Area A102
371 Port 3 connector mounting area 1
372 Port 3 connector mounting area 2
380 Area A103
381 Port 4 connector mounting area 1
382 Port 4 connector mounting area 2
383 Terminating resistor mounting area 390 Area C101
400... Inductor 500... Ground (third conductor, fourth conductor)
1000 ... Coupling circuit

Claims (9)

a parallel running portion in which the first conductor and the second conductor run in parallel at a predetermined interval;
a third conductor forming a ground for an electrical signal transmitted by the first conductor;
a fourth conductor connected to the third conductor, forming a ground for an electrical signal transmitted by the second conductor, and being connected to the first conductor in the parallel running portion; In a coupling circuit in which an electrical signal is transmitted between the second conductors,
In the parallel running portion, the first electrical signal transmitted by the first conductor is transmitted through the second conductor in the same direction as the transmission direction of the first conductor, or the first electrical signal transmitted through the conductor of is transmitted through the first conductor in the same direction as the transmission direction of the second conductor;
a second electrical signal having a frequency different from that of the first electrical signal is applied to the second conductor ;
The first conductor and the third conductor are connected to the terminal end of the first conductor located on the side opposite to the one end of the first conductor to which the first electrical signal is applied. and a terminating resistor having a value within ±20% of the value of the characteristic impedance formed with the third conductor is connected between the terminating portion and the third conductor. The shorter the parallel-running portion of the first conductor and the second conductor, the higher the coupling peak frequency of the first electrical signal. 2. A coupling circuit according to claim 1, wherein the attenuation of the amplitude of said first electrical signal transmitted between said two conductors is the frequency at which it is least attenuated. The coupling peak frequency of the first electrical signal decreases as the distance between the first conductor and the second conductor in the parallel running portion of the first conductor and the second conductor becomes narrower. wherein said coupling peak frequency is the frequency at which amplitude attenuation of said first electrical signal transmitted between said first electrical conductor and said second electrical conductor is least attenuated. 3. The coupling circuit according to 2 . A characteristic impedance formed by the first conductor and the third conductor, a characteristic impedance formed by the second conductor and the third conductor, and a characteristic impedance connected to the coupling circuit 4. The coupling circuit according to any one of claims 1 to 3 , wherein a variation between characteristic impedances of an external transmission line through which said first electrical signal is transmitted is within ±20%. further comprising a circuit board;
the first conductor and the second conductor are wiring configured on the surface of the circuit board;
5. The coupling circuit according to claim 1, wherein the third conductor and the fourth conductor are ground planes formed on the back surface of the circuit board. An inductor formed by spiraling the second conductor is formed at an input portion of the second conductor to which the second electric signal is input, and the impedance of the inductor at the frequency of the first electric signal is , within ±20% of the characteristic impedance formed by the second conductor and the fourth conductor . Port 1 is one end of the first conductor, port 2 is the other end of the first conductor, port 3 is one end of the second conductor, and port 3 is the second conductor. Assuming that the other end is a port 4, the first electrical signal input to the port 1 is output from the port 4, or the first electrical signal input to the port 4 is output from the port 1. and the second electrical signal is output from the port 3 to the port 4;
6. Connectors for transmitting/receiving said first electric signal and said second electric signal to/from an external device are mounted on said port 1, said port 3 and said port 4, respectively. A coupling circuit according to any one of Claims 1 to 3. Attenuation of the coupling peak frequency due to transmission of the first electrical signal transmitted from the first conductor to the second conductor or from the second conductor to the first conductor is within 1 dB. and said coupling peak frequency is a frequency at which amplitude attenuation of said first electric signal transmitted between said first conductor and said second conductor is smallest. 8. A coupling circuit according to any one of Claims 1 to 7 . 9. The coupling circuit according to any one of claims 1 to 8 , wherein the second electrical signal is direct current and the frequency of the first electrical signal is 6 GHz or higher.

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