Patent Publication Number: US-11662837-B2

Title: Stylus pen

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation Application of U.S. 5 patent application Ser. No. 16/790,853 filed on Feb. 14, 2020, which claims priority to and benefits of Korean Patent Application No. 10-2019-0017373, filed in the Korean Intellectual Property Office on Feb. 14, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present disclosure relates to a stylus pen. 
     (b) Description of the Related Art 
     Various terminals such as mobile phones, smart phones, tablet PCs, laptop computers, digital broadcasting terminals, PDAs (personal digital assistants), PMPs (portable multimedia players), and navigation devices include touch sensors. 
     In such a terminal, a touch sensor may be disposed on a display panel displaying an image, or may be disposed in an area of a terminal body. As a user interacts with the terminal by touching the touch sensor, the terminal may provide the user with an intuitive user interface. 
     The user may use a stylus pen for sophisticated touch input. The stylus pen may be classified into an active stylus pen and a passive stylus pen depending on whether a battery and an electronic component are provided therein. 
     The active stylus pen may have better basic performance as compared with the passive stylus pen and provide additional functions (pen pressure, hovering, and buttons), but the pen itself is expensive and requires a power source to charge the battery, so there are not many users except for some advanced users. 
     The passive stylus pen is inexpensive and requires no battery compared to the active stylus pen, but has difficult touch recognition as compared to the active stylus pen. However, recently, techniques of an inductive resonance type of an EMR (Electro Magnetic Resonance) method and a capacitive resonance method have been proposed in order to implement a passive stylus pen capable of sophisticated touch recognition. 
     The EMR method is superior in writing/drawing quality, which is a key feature of the stylus pen, but is thicker and more expensive since a separate EMR sensor panel and an EMR driving IC must be added in addition to the capacitance touch panel. 
     The capacitive resonance method uses a general capacitance touch sensor and a touch controller IC to support the pen touch by increasing the performance of the IC without additional cost. 
     In the capacitive resonance method, the amplitude of a resonance signal must be large for the touch sensor to more accurately identify the touch by the stylus pen, and thus a frequency of the driving signal transferred from the touch sensor to the stylus pen is almost equal to a resonance frequency of a resonance circuit built in the stylus pen. However, depending on the conventional capacitive resonance method, even when the resonance frequency and the frequency of the drive signal coincide with each other, attenuation of signal transmission becomes very large due to very small capacitance formed between a touch sensor that outputs the drive signal and a pen tip that receives the drive signal, thereby making signal transmission difficult. As a result, despite a long attempt by many touch controller IC vendors, there are no companies that have succeeded in mass production because sufficient output signals are not obtained. 
     Therefore, how to design the internal resonance circuit and pen structure is a very important factor in manufacturing capacitive resonant stylus pens that can produce maximum output signals. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present exemplary embodiments have been made in an effort to provide a capacitive resonant stylus pen capable of generating sufficient output signals. 
     For achieving the objects or other objects, an exemplary embodiment of the present invention provides a stylus pen including: 
     a body; a conductive tip configured to be exposed from an inside of the body to an outside thereof; an inductor unit including a ferrite core disposed in the body and a coil connected to the conductive tip and wound in multiple layers over at least a portion of the ferrite core; and a capacitor unit disposed in the body to be electrically connected to the inductor unit to form a resonance circuit. 
     Herein, the ferrite core may have permittivity of 1000 F/m or less, and the coil has a form where adjacent winding layers are alternately wound, and the coil is a wire covering two or more insulated wires. 
     In addition, the ferrite core may include nickel, and the coil may be formed of a litz wire. 
     It may further include a ground portion that can be electrically connected to the user, it may further include a bobbin surrounding at least a portion of the ferrite core, and the coil may be wound over at least a portion of the bobbin. 
     It may further include a conductive blocking member configured to surround at least a portion of the resonance circuit. The blocking member may include one slit for blocking generation of eddy currents, and opposite ends of the blocking member may be spaced apart by the slit in a first direction in which an eddy current is formed. 
     Another exemplary embodiment of the present invention provides a stylus pen including: a body; a conductive tip configured to be exposed from an inside of the body to an outside thereof; a resonance circuit disposed in the body to be connected to the conductive tip and to resonate an electrical signal transferred from the conductive tip; and a ground portion configured to be capable of being electrically connected to a user. 
     Herein, the resonance circuit may include: an inductor unit configured to include a ferrite core disposed in the body and a coil electrically connected to the conductive tip and wound in multiple layers over at least a portion of the ferrite core; and a capacitor unit disposed within the body to be electrically connected to the ground portion and the conductive tip. In this case, the ferrite core may have permittivity of 1000 F/m or less, the coil is zigzag wound so that adjacent winding layers are inclined, and the coil may be a wire covering two or more insulated wires. 
     In addition, the ferrite core may include nickel, and the coil may be formed of litz wire. 
     In this case, the resonance circuit may be formed to include two or more inductor units and one capacitor unit connected in series. In addition, the resonance circuit may include two or more LC resonance circuits that are connected in series. 
     It may further include a conductive blocking member configured to surround at least a portion of the resonance circuit. The blocking member may include one slit for blocking generation of eddy currents, and opposite ends of the blocking member may be spaced apart by the slit in a first direction in which an eddy current is formed. 
     The effects of the stylus pen according to the present disclosure will be described as follows. 
     According to at least one of the exemplary embodiments of the present disclosure, a sufficient output signal may be generated even with a thin diameter by presenting the structure of the resonance circuit of the optimal capacitive resonant stylus pen. 
     According to at least one of the exemplary embodiments of the present disclosure, it is possible to provide a stylus pen that is robust against external factors. 
     The additional range of applicability of the present disclosure will become apparent from the following detailed description. However, since various modifications and alternatives within the spirit and scope of the present disclosure may be clearly understood by those skilled in the art, it is to be understood that a detailed description and a specific exemplary embodiment of the present invention are provided only by way of example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a schematic view showing a stylus pen and a touch sensor. 
         FIG.  2    illustrates a stylus pen and a touch sensor in detail. 
         FIG.  3    illustrates an inductor unit of the stylus pen in detail. 
         FIG.  4    illustrates inductance and Q values depending on frequency changes. 
         FIG.  5    and  FIG.  6    respectively illustrate an enamel wire and a litz wire. 
         FIG.  7 A  and  FIG.  7 B  illustrate a multi-layer winding method. 
         FIG.  8    to  FIG.  10    illustrate graphs showing results of comparative experiments. 
         FIG.  11    illustrates another example of the inductor unit. 
         FIG.  12    and  FIG.  13    are graphs illustrating the magnitude of a resonance signal depending on the structure of the inductor unit. 
         FIG.  14    and  FIG.  15    illustrate other examples of the resonance circuit. 
         FIG.  16    illustrates an equivalent circuit showing an effect of parasitic capacitance of a user&#39;s hand. 
         FIG.  17    illustrates a schematic view showing a stylus pen of an LLC structure. 
         FIG.  18 A  to  FIG.  18 D  illustrate various examples of a blocking member. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     To clearly describe the present invention, parts that are irrelevant to the description are omitted, and like numerals refer to like or similar constituent elements throughout the specification. 
     In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. When referring to a part as being “on” or “above” another part, it may be positioned directly on or above the other part, or another part may be interposed therebetween. In contrast, when referring to a part being “directly above” another part, no other part is interposed therebetween. 
       FIG.  1    illustrates a schematic view showing a capacitive resonant stylus pen and a touch sensor. As illustrated in  FIG.  1   , a stylus pen  10  and a touch sensor  20  may be close to each other. 
     The stylus pen  10  may include a conductive tip  11 , a resonance circuit  12 , a ground portion  18 , and a body  19 . 
     The conductive tip  11  is connected with the resonance circuit  12 . All or part of the conductive tip  11  may be formed of a conductive material (e.g., a metal, graphite, a conductive rubber, a conductive fabric, a conductive silicon, etc.). In addition, the conductive tip  11  may have a form in which a portion of the conductive tip  11  is exposed to an outside of a non-conductive housing while being present inside the non-conductive housing, but it is not limited thereto. 
     The resonance circuit  12  may resonate with a driving signal that is inputted from the touch sensor  20 . For example, the resonance circuit  12  may be an LC resonance circuit, and may resonate with a driving signal that is received from the touch sensor  20  through the conductive tip  11 . The driving signal may be a Tx signal that is transferred to the touch electrode (channel). For example, the driving signal may include a signal (e.g., a sine wave, a square wave, etc.) having a frequency corresponding to the resonance frequency of the stylus pen  10  so as to allow the stylus pen  10  to generate a resonance signal by capacitive coupling or electromagnetic resonance. 
     The resonance circuit  12  may output a resonance signal caused by resonance to the conductive tip  11  during a period in which a driving signal is inputted and during a partial period thereafter. The resonance circuit  12  is disposed in the body  19  to be connected to the ground portion  18 . The ground portion  18  may be grounded by a body of a user who contacts an outer surface of the body  19 . 
     The body  19  may accommodate elements of the stylus pen  10 . In  FIG.  1   , the body  19  is illustrated in a form in which a horn portion and a pillar portion are integrally combined, but the two portions may be separated. It may have a cylindrical shape, a polygonal shape, a column shape having at least part of a shape of a curved surface, an entasis, a frustum of a pyramid, a circular truncated cone, or the like, but it is not limited thereto. Since the body  19  is empty inside, the body  19  may accommodate the conductive tip  11 , the resonance circuit  12 , and the ground portion  18  therein. 
     The touch sensor  20  may include a channel electrode  21  and a window  22  disposed at an upper portion of the channel electrode  21 . The channel electrode  21 , the conductive tip  11 , and the window  22  may constitute capacitor Cx. 
       FIG.  2    illustrates a schematic view showing a stylus pen and a touch sensor in detail. 
     First, as illustrated in  FIG.  2   , the stylus pen  10  includes a conductive tip  11 , a capacitor unit  13 , an inductor unit  14 , a ground portion  18 , and a body  19 . The capacitor unit  13  and the inductor unit  14  constitute the resonance circuit  12  of  FIG.  1   . 
     The conductive tip  11  may be connected to the capacitor unit  13  and/or the inductor unit  14  through a conductive connection member, and the conductive connecting member may be a wire, a pin, a rod, a bar, or the like, but it is not limited thereto. In addition, the conductive connection member may include a coil of the inductor unit  14 . 
     The capacitor unit  13  may include a plurality of capacitors connected in parallel. The capacitors may have different capacitances, and may be trimmed in a manufacturing process. 
     The inductor unit  14  may be disposed adjacent to the conductive tip  11 . The inductor unit  14  includes a ferrite core and a coil that is wound around the ferrite core. 
     The capacitor unit  13  and the inductor unit  14  are connected in parallel, and a resonance signal is generated in response to a driving signal through LC resonance of the capacitor unit  13  and the inductor unit  14 .  FIG.  3    illustrates a schematic view showing an inductor unit of a stylus pen in detail. 
     Referring to  FIG.  3   , the inductor unit  14  includes a ferrite core  15  and a coil  16  that is wound around the ferrite core  15 . 
     In this case, the inductance of the inductor unit  14  is determined by the following Equation 1. 
     
       
         
           
             
               
                 
                   L 
                   = 
                   
                     
                       µ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         SN 
                         2 
                       
                     
                     l 
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     As can be seen from Equation 1, the inductance is proportional to the permeability of the ferrite core  15 , a cross-sectional area of the coil  16 , and a square of a number of turns, and is inversely proportional to a winding length of the coil  16 . 
     A design of the inductor unit  14  is very important in the resonance circuit  12  accommodated in the capacitive resonant stylus pen. In particular, in the design of the inductor unit, inductance L and a Q value are very important parameters as illustrated in  FIG.  4   . Herein, the Q value is an amount representing a coil characteristic as a resonance circuit element, and is given by an equation Q=2πfL/R. In addition, L and R indicate the inductance and resistance of the coil, respectively, and f indicates the frequency. The higher the Q value, the sharper the resonance characteristic. 
     In the design of the capacitive resonant stylus pen, L may have a sufficiently large self-resonance frequency relative to a frequency to be used, and the Q value may have a maximum at a frequency to be used. To satisfy this, it is necessary to optimize a material of the ferrite core, a wire type of the coil, and a winding scheme. There is also a need for a method that can obtain a high output signal while maintaining the diameter of a thin pen. 
     In the following exemplary embodiments, a design method of a capacitive resonant stylus pen that is most optimized among materials of a plurality of ferrite cores, wire types of coils, and a winding scheme will be described. 
     1. Ferrite Core Material 
     In an example, manganese (Mn) and nickel (Ni) were used as a ferrite core material. 
     2. Wire Type 
     In the example, an enameled wire and a litz wire were used as the wire type of the coil used. 
     As illustrated in  FIG.  5   , an enameled wire  100  is an electric wire made by coating an insulating enamel  102  on a surface of a copper wire  101  and heating it to a high temperature, and is used for winding and wiring of electrical devices, communication devices, and electrical instruments. In the example, an enameled wire having a total thickness T of 0.2 mm, an electric wire diameter Φ of 0.18 mm, and a coating thickness t of 0.01 mm was used. 
     As illustrated in  FIG.  6   , a litz wire  200  is a special insulated wire that is made by twisting several strands of a thin insulated wire  100  (e.g., an enameled wire) having a diameter of about 0.1 mm as one wire and applying an insulating coating  201  made of nylon or the like thereon. The litz wire  200  may reduce a skin effect by increasing a surface area, and is used for coils of high frequency circuits and the like. 
     In the example, a litz wire having a total thickness T of 0.2 mm, an electric wire diameter Φ of 0.06 mm, and a covering thickness t of 0.007 mm was used. 
     3. Winding Scheme 
     In the example of the present invention, a winding scheme of a multilayer winding structure is used in order to obtain a sufficient inductance value (that is, a sufficient number of turns) in a limited space of a stylus pen. Specifically, as shown in  FIG.  7 A  and  FIG.  7 B , two kinds of multi-layer winding schemes were used. 
     The winding scheme of  FIG.  7 A  is a simplest winding scheme, and is a sequential layer winding scheme in which an upper layer is wound after winding of a lower layer that is disposed immediately therebelow is finished. In this case, the scheme of  FIG.  7 A  is a scheme in which winding of a layer starts at a point where winding of a previous layer that is disposed immediately therebelow ends, and is hereinafter referred to as a U-type winding scheme. 
     The winding scheme of  FIG.  7 B  is an alternate layer winding scheme in which adjacent winding layers are alternately wound, such that windings of adjacent layers are wound in a zigzag form. Hereinafter, this is referred to as a zigzag winding scheme. This zigzag winding scheme may minimize a voltage difference between the windings of adjacent layers, thereby reducing winding self-capacitance. In this case, the winding self-capacitance, which is a kind of parasitic capacitance, is a parameter representing electric field energy stored in the winding. 
     Comparative Experiment 1 (Comparison of Characteristic Values for Each Material 
     A material of the ferrite core was changed to manganese, nickel, and magnesium, and the Q value was measured in a state where an enameled wire was used as a wire type of coil and was wound by a U type of winding scheme. 
     As a result of the measurement, there was little difference between the characteristics of the Q values for each material of cores, and a measured Q value was not enough to be implemented as a product. 
     Comparative Experiment 2 (Comparison of Characteristic Values for Each Type of Windings) 
     Q values were respectively measured for the Inductors 1 and 2 produced using the enameled wire and the litz wire in a state in which the ferrite core was wound with manganese (Mn) by the U type of winding scheme. 
       FIG.  8    illustrates Q values of Inductors 1 and 2 measured while changing frequencies through an E4980A precision LCR meter manufactured by KEYSIGHT TECHNOLOGIES. 
     In  FIG.  8   , a indicates a waveform showing a change in the Q value with respect to the frequency of Inductor 1 (manganese core/enameled wire/U-type winding scheme), and b indicates a waveform showing a change of the Q value with respect to the frequency of the Inductor 2 (manganese core/litz wire/U-type winding scheme). 
     The Q value has almost a maximum at a frequency (frequency f1) around 400 kHz in the Inductor 2 manufactured by the Litz wire, and the Q value has almost a maximum at a frequency (frequency f2) around 150 kHz in the Inductor 1 manufactured by the enameled wire. 
     As a result of comparing a and b of  FIG.  8   , it can be seen that the maximum Q value of the Inductor 2 is about 1.5 times higher than the maximum Q value of the Inductor 1. Accordingly, it can be seen that the litz wire is superior to the enameled wire as the coil of the inductor forming the resonance circuit of the stylus pen. 
     However, the maximum Q value of Inductor 2 measured in Comparative Experiment 2 was about ½ of a target value Q target  required for commercialization. 
     Comparative Experiment 3 (Comparison of Characteristic Values for Each Winding Scheme) 
     Q values were measured for the inductors 3 to 5 manufactured by changing the wire type to the enameled wire and the litz wire and the winding scheme to the U type and the zigzag type in a state where the ferrite core was made of manganese (Mn). 
       FIG.  9    illustrates Q values of Inductors 3 to 5 measured while changing frequencies through an E4980A precision LCR meter manufactured by KEYSIGHT TECHNOLOGIES. 
     In  FIG.  9   , a indicates a waveform showing a change in the Q value with respect to the frequency of Inductor 3 (manganese core/enameled wire/U-type winding scheme), b indicates a waveform showing a change of the Q value with respect to the frequency of Inductor 4 (manganese core/enameled wire/zigzag winding scheme), and c indicates a waveform showing a change of the Q value with respect to the frequency of Inductor 5 (manganese core/litz wire/zigzag winding scheme) 
     As can be seen from the waveform c of  FIG.  9   , the Q value has almost a maximum at a frequency (frequency f3) around 300 kHz in Inductor 5 manufactured by the litz wire/zigzag winding scheme. The Q value has almost a maximum at a frequency (frequency f2) around 150 kHz in Inductor 4 manufactured by the enameled wire/zigzag winding scheme and Inductor 3 manufactured by the enameled wire/U-type winding scheme. 
     In addition, as a result of comparing a, b, and c of  FIG.  9   , it can be seen that the maximum Q value of Inductor 5 is about 1.5 times higher than the maximum Q value of the Inductor 4 and is twice or more higher than the maximum Q value of Inductor 3. Accordingly, it can be seen that the zigzag type is superior to the U-type as the winding scheme of the inductor forming the resonance circuit of the stylus pen. 
     However, the maximum Q value of Inductor 5 (manganese core/litz wire/zigzag winding scheme) measured in Comparative Experiment 2 was about ¾ of a target value Q target  required for commercialization. 
     Comparative Experiment 4 (Comparison of Characteristic Values for Each Core Material) 
     In this example, manganese and nickel were used as a ferrite core material, and it is known that permeability of nickel is generally 200-300, and the permeability of manganese is generally 3000-5000. 
     Since the manganese used in this example is approximately 15 times higher in permeability than nickel, assuming that the coils have same cross-sectional area and length, the number of turns of manganese is reduced by approximately four times that of nickel to obtain the same inductance value. Accordingly, only from the viewpoint of the number of turns, it can be seen that is more effective to use manganese than nickel. 
     On the other hand, since the inductor unit  14  has a complicated structure including a coil wound around the core, parasitic capacitance is additionally generated. Since the Q value decreases due to such parasitic capacitance, an amplitude of the resonance signal may be reduced. 
     The parasitic capacitance generated in the inductor unit  14  may occur between the wound coils and between the core and the coil, and as described above, the parasitic capacitance between the wound coils may be reduced by adopting the zigzag winding scheme. 
     Meanwhile, in this example, a core material having lower permittivity than that of manganese was tested in order to reduce the parasitic capacitance between the core and the coil, and the test result confirmed that the nickel core was an optimal material for the ferrite core. 
     An important physical property in manganese and nickel, which are mainly used as a ferrite core element, is permeability, which has an important effect on an inductance value as shown in Equation 1. However, in manganese and nickel as ferrite elements, the permittivity is a physical property of little concern, and in fact, nickel does not have relevant information in the data sheet provided by the manufacturer. 
     In this example, the permittivity of manganese and nickel was measured using E4980A precision LCR meter of KEYSIGHT TECHNOLOGIES in order to confirm the permittivity of manganese and nickel, and the measurement results are shown in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Manganese permittivity 
                 Nickel permittivity 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Measurement 1 
                 2400 
                 — 
               
               
                 Measurement 2 
                 8300 
                 2 
               
               
                   
               
            
           
         
       
     
     Measurements 1 and 2 were measured using the same E4980A precision LCR meter of KEYSIGHT TECHNOLOGIES, where Measurement 1 represents the permittivity that is automatically calculated by measurement software. According to Measurement 1, although the permittivity of manganese is 2400, the permittivity of nickel is not measured. 
     Measurement 2 is a method of calculating the dielectric constant by measuring capacitance, area, and distance between ferrite cores, and according to Measurement 2, the permittivity of manganese is 8300 and the permittivity of nickel is 2. 
     There is a big difference in the result of permittivity between Measurement 1 and Measurement 2, and in the case of Measurement 2, it was confirmed that errors were considerable depending on capacitance, area, distance, and the like. However, as results of Measurement 1 and Measurement 2, it can be seen that nickel has permittivity of at least 1/1000 or more relative to manganese. 
     In Comparative Experiment 4, Q values were measured for Inductors 6 and 7 manufactured by changing the winding type to the U type and the zigzag type with the ferrite core made of nickel and using the litz wire as the wire type. 
       FIG.  10    illustrates Q values of Inductors 6 and 7 measured while changing frequencies through an E4980A precision LCR meter manufactured by KEYSIGHT TECHNOLOGIES. 
     In  FIG.  9   , a indicates a waveform showing a change in the Q value with respect to the frequency of Inductor 6 (nickel core/litz wire/U-type winding scheme), and b indicates a waveform showing a change of the Q value with respect to the frequency of the Inductor 7 (nickel core/litz wire/zigzag winding scheme). 
     As can be seen from the waveform b of  FIG.  10   , the Q value has almost a maximum at a frequency (frequency f5) around 400 kHz in Inductor 7 manufactured by the nickel core/litz wire/zigzag winding scheme. The Q value has almost a maximum at a frequency (frequency f6) around 200kHz in Inductor 6 manufactured by the nickel core/litz wire/U-type winding scheme. As a result of comparing a and b of  FIG.  11   , it can be seen that the maximum Q value of Inductor 7 is about two times higher than the maximum Q value of Inductor 6. 
     The maximum Q value of Inductor 7 (nickel core/litz wire/zigzag winding scheme) measured in Comparative Experiment 4 almost reaches a target value Q target  required for commercialization. 
     In Comparative Experiments 1 to 4 described above, inductors were manufactured and tested for Q values by changing the material of the ferrite core, the wire type of the coil, and the winding scheme, and test results show that the highest Q value is obtained when the inductor unit of the capacitive resonant stylus is designed by winding of the nickel core, the litz wire, and the zigzag winding scheme. In addition, it can be seen that the maximum Q value of the inductor manufactured by this combination reaches the target value Q target  for commercialization. 
     Meanwhile, in the present exemplary embodiment, the nickel core is used as the ferrite core and the litz wire is used as the wire type of the core, but similar results may be obtained when a material with permittivity of 1000 or less is used as the ferrite core instead of the nickel core, and a single wire wrapped with two or more insulated strands is used instead of the litz wire. 
     In the present exemplary embodiment, as described below, a method of increasing the distance between the core and the coil by providing a bobbin between the core and the coil may be used in order to further reduce the parasitic capacitance between the core and the coil, in addition to using nickel having lower permittivity than manganese. 
     Referring to  FIG.  11   , the inductor unit  14  includes a ferrite core  15 , a bobbin  141  surrounding at least a portion of the ferrite core  15 , and a coil  16  wound on at least a portion of the bobbin  141 . The bobbin  141  may be fixed by being closely adhered to the ferrite core  15  by a force caused by the winding of the coil  16 . The bobbin  141  may include the same material as that of the body  19  or a different material, and may include, e.g., a plastic or metal having an insulating surface. Specifically, polyphenylene sulfide (PPS), liquid crystalline polyester (LCP), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), a phenolic resin, or the like may be used for the bobbin  141 . 
     As such, when the bobbin  141  covers the ferrite core  15  and the bobbin  141  is wound as the coil  16 , a distance between the ferrite core  15  and the coil  16  increases, so that a value of a parasitic capacitance Cp 2  in  FIG.  11    may be set to be smaller than a value of a parasitic capacitance Cp 1  in  FIG.  3   . 
     Referring to  FIG.  12   , when the inductor unit  14  includes only the ferrite core  15  and the coil  16 , a maximum amplitude of the resonance signal is measured to be about 2 V (+1 V to −1 V). Referring to  FIG.  13   , when the inductor unit  14  includes the ferrite core  15 , the bobbin  141 , and the coil  16 , the maximum amplitude of the resonance signal is measured to be about 4 V (+2 V to −2 V). That is, when at least a portion of the ferrite core  15  is surrounded in the bobbin  141  and the coil  16  is wound on the bobbin  141 , it is confirmed that the amplitude of the resonance signal is larger. 
     Meanwhile, in the case of using nickel as the ferrite core to design the optimum inductor unit according to the present exemplary embodiment, as described above, nickel has a 1/15 times lower permeability than manganese, and thus the number of turns of nickel must be increased to approximately four times that of manganese to achieve the same inductance. Accordingly, the nickel must be larger in diameter than manganese to achieve the same inductance as manganese. 
     In the present exemplary embodiment, a method of using a plurality of inductors is proposed to achieve a high output signal while reducing a diameter of the stylus pen. 
       FIG.  14    illustrates an equivalent circuit in which two inductors of thin diameter are connected in series and a capacitor is connected in parallel between opposite ends of the two inductors. Hereinafter, this type of resonance circuit is referred to as an ‘LLC resonance circuit’. In  FIG.  14   , it is illustrated that two inductors are connected in series, but the exemplary embodiment is not limited thereto, and three or more inductors may be connected in series. According to the LLC resonance circuit, since the inductance L is twice as large as that of the resonance circuit having one inductor and capacitor (hereinafter referred to as an ‘LC resonance circuit’), the capacitance may be reduced to half. That is, the LLC resonance may be made to be thinner than the LC resonance circuit, but is more sensitive to an influence on the capacitance. 
     Meanwhile,  FIG.  15    illustrates an equivalent circuit in which two LC resonance circuits are connected in series (hereinafter referred to as an “LCLC resonance circuit”), where two resonance signals are combined and outputted. In  FIG.  15   , it is illustrated that two LC resonance circuits are connected in series, but the exemplary embodiment is not limited thereto, and three or more LC resonance circuits may be connected in series. 
     According to the LCLC resonance circuit, since resonance frequencies of the two resonance circuits must be the same, the resonance frequency of each resonance circuit must be tuned to be the same in a manufacturing process. 
     As described above, in spite of an increase in the number of windings generated by using nickel as a ferrite core, when two or more inductors are used as illustrated in  FIG.  14    and  FIG.  15   , a stylus pen having a thin diameter may be manufactured by suppressing an increase in the diameter of the inductor unit. 
     Meanwhile, as illustrated in  FIG.  14   , when the LLC resonance circuit is used, a stylus pen having a structure described in the following may be adopted to minimize an effect on the capacitance reduced by half. 
     In  FIG.  2   , the stylus pen  10  is held by a user&#39;s finger or the like, and in this case, parasitic capacitance Cf may be formed by a finger and an internal conductor (coil or capacitor) of the stylus pen  1 . 
       FIG.  16    illustrates an equivalent circuit showing an effect of the parasitic capacitance Cf by a user&#39;s hand. Referring to  FIG.  16   , a resonance frequency of the stylus pen  10  is changed by the parasitic capacitance Cf ( 40 ). Then, a frequency of the driving signal  30  and a resonance frequency of the stylus pen  10  do not coincide, and thus a magnitude of the signal that is outputted from the stylus pen  10  decreases. In this case, an influence of the parasitic capacitance Cf ( 40 ) is greater in the LLC circuit illustrated in  FIG.  14    than in the LC resonance circuit or the LCLC resonance circuit. This is because, when designed with the same resonance frequency, capacitance of the LLC resonance circuit is ½ smaller than that of the LC resonance circuit or the LCLC resonance circuit. 
     Hereinafter, a stylus pen for preventing a change in resonance frequency due to a user&#39;s grip will be described with reference to  FIG.  17   . 
       FIG.  17    illustrates a schematic view showing a stylus pen of an LLC structure. 
     As illustrated in  FIG.  17   , the stylus pen  10  includes a conductive tip  11 , a capacitor unit  13 , two inductor units  14  and  14 ′, a blocking member  17 , a ground portion  18 , and a body  19 . 
     The inductor units  14  and  14 ′ include ferrite cores  15  and  15 ′ and coils  16  and  16 ′ wound around the ferrite cores  15  and  15 ′, respectively. In this case, the two inductor units  14  and  14 ′ are connected in series. 
     The blocking member  17 , which is a conductive member surrounding the capacitor unit  13  and the inductor units  14  and  14 ′, may prevent parasitic capacitance from being generated by a user&#39;s hand. 
     In this case, the blocking member  17  may be designed such that opposite ends of the blocking member  17  may be spaced apart along a direction ED of an eddy current in order to minimize an influence of the eddy current generated in the stylus pen. 
     In this regard, the blocking member  17  will be described in detail with reference to  FIG.  18 A  to  FIG.  18 D . 
     As illustrated in  FIG.  17   , a clockwise current flows through the coils  16  and  16 ′ by a driving signal transferred from the conductive tip  11 , and a magnetic field is generated by the currents flowing through the coils  16  and  16 ′. In this case, an eddy current is generated in a counterclockwise direction that is opposite to the current direction of the coils by a change in the magnetic field generated by the currents of the coils, and thus the eddy current in the counterclockwise direction flows in the blocking member  17 . 
     Referring to  FIG.  18 A , the blocking member  17  includes one slit GP for blocking generation of eddy currents. The slit GP extends along a direction PD that is perpendicular to the eddy current (counterclockwise in  FIG.  18   ). Opposite ends  17   a  and  17   b  of the blocking member  17  are spaced apart by the slit GP. In exemplary embodiments, the slit GP may have a width of 0.03 mm or more along the direction ED of the eddy current. 
     Although the slit GP has been described as extending along the direction PD that is perpendicular to the eddy current, the slit GP may extend along the direction inclined at a predetermined angle (more than 0 degrees and less than 90 degrees) to the direction PD. The opposite ends  17   a  and  17   b  of the blocking member  17  are spaced apart along the direction ED of the eddy current. Accordingly, since the eddy current cannot flow along the blocking member  17 , generation of the eddy current is interrupted. 
     Referring to  FIG.  18 B , the blocking member  17  includes a plurality of first blocking units  171 . The first blocking units  171  extend along the direction PD that is perpendicular to the eddy current, and are spaced apart from each other along the direction ED of the eddy current. Similarly, since the blocking member  17  includes the plurality of first blocking units  171  spaced apart from each other along the direction ED of the eddy current, no eddy current can flow along the blocking member  17 , thereby blocking the generation of the eddy current. Although the first blocking units  171  have been described as extending along the direction PD that is perpendicular to the eddy current, the first blocking units  171  may extend along the direction inclined at a predetermined angle (more than 0 degrees and less than 90 degrees) to the direction PD. 
     Referring to  FIG.  18 C , the blocking member  17  includes a plurality of second blocking units  172 . The second blocking units  172  are spaced apart along the direction PD that is perpendicular to the eddy current, and opposite ends of each of the second blocking units  172  are spaced apart from each other along the direction ED of the eddy current. Similarly, since the opposite ends of each of the second blocking units  172  included in the blocking member  17  are spaced along the direction ED of the eddy current, no eddy current can flow along the blocking member  17 , thereby blocking the generation of the eddy current. 
     Referring to  FIG.  18 D , the blocking member  17  includes a plurality of third blocking units  173 . The third blocking units  173  are spaced apart from each other along the direction PD that is perpendicular to the eddy current and the direction ED of the eddy current. Similarly, since the third blocking units  173  included in the blocking member  17  are spaced along the direction ED of the eddy current, no eddy current can flow along the blocking member  17 , thereby blocking the generation of the eddy current. 
     Although the present exemplary embodiment has been described above, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the present invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent range of the present invention are included in the scope of the present invention. 
     DESCRIPTION OF SYMBOLS 
       10  stylus pens,  11  conductive tip,  12  resonance circuit,  13  capacitor unit 
       14  inductor unit,  15  ferrite core,  16  coil,  17  blocking element,  18  ground portion 
       19  body,  20  touch sensor,  30  driving signal,  40  parasitic capacitance,  100  enameled wire 
       101  copper wire,  102  enamel,  141  bobbin,  200  litz wire,  201  insulating coating