KR101688142B1 - Mobile Communication Terminal - Google Patents

Abstract

The present invention relates to a mobile communication terminal improved in SAR characteristics, and more particularly, to a mobile communication terminal including a circuit board on which a ground plane is formed; An antenna disposed on one surface of the circuit board; And at least one pad formed on one surface of the circuit board so that the antenna can be connected thereto, wherein the ground surface is formed in a first region excluding a region where the antenna is disposed on the circuit board; And a second ground extending from the first ground, the second ground being disposed in a second area surrounding the pad, the second ground being spaced apart from the pad, wherein the second ground is absorbed by the human body The present invention provides a mobile communication terminal which can secure stable communication quality to a user by allowing the user to use the mobile communication terminal with ease by reducing the amount of harmful electromagnetic waves and keeping the total radiation power of the antenna to be almost the same.

Description

The present invention relates to a mobile communication terminal,

The present invention relates to a SAR reduction structure of a mobile communication terminal.

A mobile communication terminal is a portable device having one or more functions that can carry a voice and video call function, a function to input and output information, and a function to store data.

As the functions are diversified, the mobile communication terminal has complicated functions such as, for example, shooting of an event or a moving picture, reproduction of a music or video file, reception of a game, reception of a broadcast, etc., Player).

In order to implement complex functions in multimedia devices, various new attempts have been made in terms of hardware or software. For example, a user interface environment is provided for a user to easily and conveniently search for or select a function.

The mobile communication terminal includes radio frequency (RF) components to transmit and receive radio signals. However, because electromagnetic waves generated by RF components may be harmful to the human body, a method for reducing the electromagnetic waves is being developed. Therefore, in order to quantify the influence of electromagnetic waves on the human body, a specific absorption ratio (SAR) is introduced, and only a mobile communication terminal below a reference value is recommended to be produced and used.

The SAR abatement system according to the related art is capable of preventing the human body from being exposed to electromagnetic waves emitted from the cellular phone body by performing double shielding against electromagnetic waves generated in the inside of the cellular phone or by providing two or more antennas separated by the electromagnetic wave shielding membrane, Only the antenna relatively far from the human body is operated in the air so as to cut off the electromagnetic wave toward the human body during the call standby or to shield the electromagnetic wave by only the case which forms the outer shape of the mobile phone without providing any additional shield Have been proposed. However, such measures are insignificant and can not expect a safe level of electromagnetic wave shielding effect.

In recent years, it has been proposed to attach and use an electromagnetic wave shielding pad for absorbing harmful electromagnetic waves on the surface of the mooring portion of a cellular phone. However, this not only hurts the appearance of the mobile phone, but also has a small effect.

In addition, the total radiated power (TRP) of the antenna by modifying the antenna pattern was reduced to achieve the desired performance. However, there are problems such as an increase in the development cost due to the modification of the antenna pattern, an increase in the labor cost, and an increase in the material cost due to the modification of the injection object.

On the contrary, there has been an attempt to reduce the SAR by conducting conductor sputtering on the instrument case, but there is a problem such as an additional operation of the deposition work and a deviation in the management of the resistance value.

The present invention has been made in view of the above points, and it is an object of the present invention to reduce the absorption rate of electromagnetic waves in the maximum value range of the absorption rate of electromagnetic waves through the correction of the ground pattern around the antenna and to keep the total radiation power of the antenna almost constant, have.

To achieve the above object, a mobile communication terminal according to the present invention includes: a circuit board having a ground plane; An antenna disposed on one surface of the circuit board; And at least one pad formed on one surface of the circuit board so that the antenna can be connected thereto, wherein the ground surface is formed in a first region excluding a region where the antenna is disposed on the circuit board; And a second ground extending from the first ground and disposed in a second region surrounding the pad while being spaced apart from the pad.

The ground excluding region between the second ground and the pad may be formed in a U-shaped slot, and the pad may be a signal pad.

The pad may include a signal pad to which a signal is supplied to the antenna, and a ground pad shorted to the ground, and the ground may be a first ground.

The ground plane may include at least two different layers of the circuit board, and each layer may be connected via a via hole formed in the circuit board.

The pad may be formed to have a plurality of sides, and a side of the plurality of sides remote from the first ground may exclude the formation of the second ground.

The circuit board may be disposed inside the terminal separate from the main board on which the circuit components of the terminal are disposed.

Wherein the U-shaped slot comprises: a first slot formed by disposing the second ground with a gap having a predetermined width and width on the left side of the lower end of the signal pad; A second slot formed by disposing the second ground with a gap having a predetermined width and width at a center of a lower end of the signal pad; And a third slot formed by disposing the second ground with a gap having a predetermined width and width on the right side of the lower end of the signal pad.

According to the mobile communication terminal of the present invention, since the ground is extended to the periphery of the feeding pad of the antenna, the total radiation power of the antenna is kept substantially constant while the absorption rate of electromagnetic waves is reduced in the maximum value range of the electromagnetic wave absorption rate .

The user can safely use the mobile communication terminal by significantly reducing the amount of harmful electromagnetic waves absorbed into the human body from the main body of the terminal and the antenna and by keeping the total radiated power of the antenna almost equal, There is an effect.

FIG. 1 is a block diagram illustrating a functional structure of a mobile communication terminal according to the present invention.
2 is a front view showing a configuration of a power supply structure of a mobile communication terminal according to the present invention,
FIG. 3 is a current distribution diagram showing a current density distribution and a point at which the absorption rate of electromagnetic waves is maximum in the mobile communication terminal before and after the U-shaped slot is provided,
FIG. 4 is a front view showing a shape of an electromagnetic wave absorptance reduction power feeding structure equipped with a U-shaped slot installed in a mobile communication terminal according to the present invention,
5 is a current density distribution diagram showing the current density distribution of the circuit board before and after the U-shaped slot is provided.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram illustrating a functional structure of a general mobile communication terminal 100.

The mobile communication terminal 100 includes an antenna 110 for radiating an electromagnetic signal of a high frequency band into a free space in the form of an electromagnetic wave, an RF (Radio Frequency) band signal from the antenna 110 to a high frequency circuit A feeding part 120 for transmitting an RF band signal from the circuit to the antenna 110, a low noise amplifying part for receiving the RF band signal from the feeding part 120 and frequency-converting the RF band signal into an IF (intermediate frequency) band A desired IF band signal is generated or the IF band signal is frequency-converted into an RF band and an RF band signal obtained by low noise amplification is supplied to the feeder 120

A frequency conversion unit for frequency converting the IF band signal into a baseband frequency band that can be processed by a central processing unit (CPU), converting the analog signal to a digital signal, and generating a beat stream A terminal modem 160 that interfaces with the analog baseband processor 140, the RF / IF circuitry 130 and the analog baseband processor 140 and processes a defined protocol, A memory and a peripheral circuit 150 for storing variables and states of the program, a real-time processing operating system and a terminal call processing software program, and a memory and peripheral circuit 150 for interfacing with the terminal modem 160, A codec 170 for performing a function of a speaker, an output means 181 such as a speaker and an input means 182 such as a microphone. It comprises a input and output unit 180 for.

The present invention relates to the structure of the feeder 120 of the mobile communication terminal 100 and is designed to reduce the Specific Absorption Rate (SAR) while maintaining the total radiated power (TRP) The structure of the feeding part will be described with reference to FIG. 2 as follows.

A ground plane 220 is formed in a predetermined region of the front and rear surfaces of the circuit board 200 of the mobile communication terminal. An antenna (not shown) for transmitting and receiving a high frequency signal is disposed at an upper end 210 of the front surface of the circuit board 200. Since about 90% of the antenna area is excluded from the ground plane 220, the radiation pattern of the antenna has an almost constant isotropical beam pattern in the horizontal axis direction.

The upper end 210 of the front surface of the circuit board 200 includes at least one pad 230 to which the antenna can be connected.

A first ground 221 is formed at a lower end of the front surface of the circuit board 200 in a first region excluding a region where the antenna is disposed on the circuit board 200. A second ground 222 extends from the first ground 221 and is spaced apart from the pad 230 in a second area surrounding the pad.

The ground plane 220 includes at least two different layers of the circuit board 200 and the layers may be connected to each other via a via hole 224 formed in the circuit board 200. Referring to FIG. 2, the ground plane 220 includes the first ground 221, the second ground 222, and the back ground 223 formed on the rear surface. The back ground 223 is electrically connected to the first ground 221 or the second ground 222 through the via hole 224. The via hole 224 is formed in a hole having a predetermined diameter at a predetermined position in the photoetching process of the circuit board 200 and is plated to form a through- So that the first and second grounds 221 and 222 and the back ground 223 on the rear surface are electrically connected to each other.

 The pad 230 is formed to have a plurality of sides, and the side of the plurality of sides remote from the first ground 221 is not formed with the second ground 222. The pad 230 includes a signal pad 231 through which the signal is fed to the antenna and a ground pad 232 short-circuited to the ground.

 The ground plane 220 electrically short-circuited by the ground pad 232 is preferably the first ground 221 formed at the lower end of the front surface of the circuit board. When the ground pad 220 is electrically connected to the second ground 222 and is short-circuited, the interference of the high-frequency signal between the signal pad 231 and the ground pad 232 increases, It is difficult to control the electromagnetic wave absorption rate reduction performance.

The ground pad 232 may be electrically connected to the ground through a micro strip line 233 to be short-circuited. The microstrip line 233 has a structure in which a ground plane is formed on the back surface and a signal line is formed on the front surface to transmit electromagnetic signals. The microstrip line 233 has a structure in which the ground pad 232 is connected to the first ground plane 221 It does not necessarily require a signal line or a ground surface on the back surface of the circuit board 200 for shorting. It is preferable that the microstrip line 233 is implemented with a high impedance in which the length of the microstrip line 233 is shorter than the wavelength (λ _g ) in the operating frequency band and the width of the line is thin.

The ground exclusion region between the second ground 222 and the pad 230 may be formed as a U-shaped slot 240. The pad 230 in which the U-shaped slot 240 is formed must be the signal pad 231. This is because the current density around the signal pad 231 is increased by changing the structure of the ground plane 220 around the signal pad 231 having the strongest current intensity.

Qualitatively, most of the electromagnetic energy in the microstrip line is guided in the dielectric between the signal line on the circuit board and the ground plane, but there are some components that emit in free space, loss. However, if the ground plane is appropriately placed around the signal line, a larger amount of electromagnetic energy is guided and transmitted in the dielectric, and the amount of loss is reduced. This is consistent with the fact that the stripline form with the ground plane on both sides of the microstrip line open on one side is less radiating to free space.

 Therefore, by disposing the second ground 222 around the signal pad 231, the current loss around the signal pad 231 can be minimized, so that the current density around the signal pad 231 increases. According to Energy Conservation's Law, the current density should be weakened in a region relatively different according to the increase of the current density around the signal pad 231.

It is required that the total radiation power (TRP) of the antenna is kept constant and the absorption rate of electromagnetic waves is reduced by forming the U-shaped slot 240. Therefore, the U-shaped slot 240 should be designed and configured as follows. The U-shaped slot 240 includes a first slot portion 241 formed by disposing the second ground 222 with a gap having a predetermined width and width on the left side of the lower end of the signal pad 231; A second slot portion 242 formed by disposing the second ground 222 with a gap having a predetermined width and width at the center of the lower end of the signal pad 231; And a third slot portion 243 formed by disposing the second ground 222 with a gap having a predetermined width and width on the right side of the lower end of the signal pad 231. Next, the first slot portion 241, the second slot portion 242, and the third slot portion 243 are formed in order to design an optimal power feeding structure for reducing the absorption rate of electromagnetic waves while maintaining the total radiated power of the antenna constant. The width and the width of each of the first and second electrodes may be independent of each other.

Also, factors affecting the performance of the antenna correspond to the area of the area where the back ground 223 is formed in addition to the slot 240. The area of the back ground 223 may be the same as the area of the first ground 221 or wider or narrower than the area of the first ground 221. As shown in FIG. 2, the vertical length of the area indicated by the dotted line corresponds to the vertical length of the rear ground 223. If the vertical length of the back ground 223 is longer than the vertical length of the first ground 221, the performance of the antenna is affected. Particularly, when the vertical length of the back ground 223 extends to the area of the second slot 242, the performance of the antenna is further increased. The longitudinal length of the back ground 223 is set to be greater than the longitudinal length of the second slot 242 in order to robustly design the antenna so that performance of the antenna is not affected by the error of the longitudinal length of the back ground 223. [ As shown in Fig.

The specific absorption rate (SAR), which has been recognized as the most effective parameter to define the interaction between electromagnetic waves and human body, can be defined as follows using the pointing vector theorem for the electromagnetic field which changes in sinusoidal form .

Where σ is the tissue conductivity at the radar frequency [S / m], ρ is the tissue density [kg / m ³ ], and E _i is the field strength [V / m] in the internal tissue. As described above, the electromagnetic wave absorptivity is proportional to the square of the field strength in the tissue because the conductivity and the density are constant in the same tissue, and thus is inversely proportional to the square of the distance in the tissue from the source. Therefore, in a mobile communication terminal, a region in which the current intensity is strongest is not necessarily coincident with a region around the signal pad 221 but having a maximum electromagnetic wave absorption rate. This is because the distance between the minimum distance and the maximum current density is different when the user touches the face when actually using the mobile communication terminal.

3 is a current distribution diagram showing a current density distribution and a point of maximum electromagnetic wave absorption rate of the mobile communication terminal before and after the U-shaped slot 240 formed by the arrangement of the second ground 222 is provided.

3 (a) and 3 (b), it is confirmed that the current distribution is maximum around the signal pad 231 of the terminal both before and after the U-shaped slot 240, 240), it is hard to confirm that it is increased from (b) to (a). However, it can be seen that the current density is slightly reduced in the maximum hot spot area 320. FIG. 3 (c) shows the absorption rate of the electromagnetic wave absorbed by the human body at a position corresponding to the position of the terminal. At the same time, the signal pad 421 and the maximum electromagnetic wave absorption rate region 320 are displayed as the maximum current density region 310 on the surface of the terminal. FIG. 3 (d) shows a color corresponding to the decibel (dB) value of the current distribution values in FIGS. 3 (a) and 3 (b).

In FIG. 3C, when the user uses the terminal, it can be seen that the maximum electromagnetic wave absorptivity region 320 is located at a lower angle than the maximum current density region 310 of the terminal, As described above, when the user actually uses the mobile communication terminal, the distance between the minimum distance and the maximum current density is different from each other. The point at which the electromagnetic wave absorption rate obtained by applying the human-like model and the mobile communication terminal model is maximum is located slightly below the signal pad 231 as shown in FIG. 3C.

FIG. 4 illustrates a shape of a U-shaped slot 440 mounted on a mobile communication terminal according to the present invention. 4 (a) is a power supply structure including parts for mounting the circuit board 200 and a mobile communication terminal, (b) is a front view of the circuit board 200, and (c) Fig. Conventionally, a main board including various signal processing and high frequency circuits, and the circuit board 200 including the antenna and the pad 230 are implemented in one substrate. However, in recent years, the motherboard substrate and the circuit board 200 are separated from each other in response to sliming and downsizing. Therefore, in the power supply structure according to the present invention, not only the circuit board 200 is implemented on a board integrated with the circuit components of the mobile communication terminal, but also disposed inside the terminal separately from the main board on which the components are disposed And the like.

5 is a current density distribution diagram showing a current density distribution of the circuit board 200 before and after the U-shaped slot 240 is provided. 5 (a) is a current density distribution diagram without a slot, (b) is a current density distribution diagram with a slot, and (c) is a graph of current density according to whether or not the U-shaped slot 240 is provided. 5, it is difficult to confirm that the current density around the feed pad 221 is increased due to the current density distribution considering the mobile communication terminal. However, compared to FIG. 5 (b) Is increased. In FIG. 5 (c), the current density increases when the U-shaped slot is provided, and the maximum value increases by 4 dB from -5 dB to -9 dB. Therefore, it can be expected that the current density is relatively decreased in the maximum absorption region due to the energy conservation law.

Table 1 shows the total radiation power and the absorption rate of the antenna when the circuit board 200 is inserted into the mobile communication terminal before and after the U-shaped slot 240 of FIG. 4 is inserted.

Total radiated power of antenna The value of the absorption rate of electromagnetic waves Conventional technology 28.5 dBm 1.9 mW / g In case of U slot 28.4 dBm 1.63 mW / g

As shown in Table 1, when the U-shaped slot 240 is provided, it can be seen that the total radiation power of the antenna is kept almost constant while the value of the absorption rate of electromagnetic waves is reduced by about 0.3 mW / g, have.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

Claims (11)

A circuit board on which a ground plane is formed;
An antenna disposed on one surface of the circuit board; And
And at least one pad formed on one side of the circuit board so that the antenna can be connected,
A first ground formed on a first region of the circuit board excluding a region where the antenna is disposed; And
And a second ground extending from the first ground and disposed in a second region surrounding the pad while being spaced apart from the pad,
A ground excluded region between the second ground and the pad is formed in a U-shaped slot shape,
Wherein the pad comprises a signal pad to which a signal is fed to the antenna,
The U-
Wherein the second ground is formed by a gap having a predetermined width and width at the center of the lower end of the signal pad. delete The method according to claim 1,
And the pad includes a ground pad short-circuited to the first ground. The method according to claim 1,
Wherein the ground plane includes at least two different layers of the circuit board, and the layers are connected to each other through a via hole formed in the circuit board. The method according to claim 1,
Wherein the pad is formed to have a plurality of sides, and a side of the plurality of sides farther from the first ground is excluded from forming the second ground. The method according to claim 1,
Wherein the circuit board is disposed inside the terminal separately from a main board on which circuit components of the terminal are disposed. The method according to claim 1,
The U slot
A first slot formed by disposing the second ground with a gap having a predetermined width and width on the left side of the lower end of the signal pad;
A second slot formed by disposing the second ground with a gap having a predetermined width and width at a center of a lower end of the signal pad; And
And a third slot formed by disposing the second ground with a gap having a predetermined width and width on the right side of the lower end of the signal pad. delete delete The method of claim 3,
Wherein the ground pad is electrically short-circuited through the first ground and the microstrip line. 8. The method of claim 7,
Wherein the width and the width of the first slot portion, the second slot portion, and the third slot portion are independent of each other.

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