Abstract:
A tunable passive device is disclosed. It includes a plurality of passive elements and at least a switch. The passive elements are stacked along the same direction, and connected with each other via the switch. By changing open/close conditions of the switch(es) and selecting specific passive elements that a current can pass, a responsive value of the tunable passive device is obtained.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention generally relates to a passive device, and in particular relates to a tunable passive device.  
       BACKGROUND OF THE INVENTION  
       [0002]     Capacitors, resistors and inductors are three kinds of major passive devices. Functionally, capacitors store electrical charge and release electrical power in certain time interval; resistors adjust voltage and current in circuits; inductors work as filters, chargers and dischargers. The three ones usually cooperate to achieve electronic control functions. Most electronic and electrical products use the passive devices in the fields of information, communication, consumer electronics and other industries. Passive devices become essential components in 3C industries and are required more and more as electronic technologies and products being developed.  
         [0003]     In order to control the quality of electrical circuits, the requirements of qualified passive devices become more important. Especially the passive devices of capacitors and inductors that generate frequency response highly influence the working frequency and power transmission. Some components, such as electronically tunable filters and voltage-controlled oscillators (VCOs), applied in wireless communication or micro-electromechanical systems (especially in energy storage and communication modules of bioelectrical systems) usually work for high frequencies, such as 13.56 MHz. The applications require components of high inductance or high capacitance, which usually have larger dimensions that cannot meet the requirements of system microminiaturization. Therefore, tunable passive devices applicable in aforesaid circuits are required to have higher densities of inductance or capacitance and larger tunable range in order to reduce the space requirement and increase the flexibility of circuit design.  
         [0004]     Conventional tunable passive devices are mainly of unitary capacitor or inductor tunable by adjustment of inductive areas for different capacitances or inductances.  
         [0005]     For example, a tunable capacitor is tuned by changing the clearance of two electrode plates. However, restrained by a “pull in” effect of electrodes, the tunable range is limited. That is, when the clearance of electrode plates is reduced to one third of an original clearance, the “pull in” effect makes the electrode plate contact to each other. Therefore, a practical minimum space is two third of original clearance, and theoretically allows a tunable range of 50%, which is rather small for application. Another method is to apply an actuator for displacing the relative position of two parallel electrode plates and adjusting the overlapping area for changing the capacitance. The tuning range is still limited to the displacement of the actuator and electrode plates and unsatisfied for the needs of higher capacitance to area ratios.  
         [0006]     Tunable inductors are further difficult to be made. As disclosed in U.S. Pat. No. 6,184,755, the inductance is adjusted by controlling the spacing of two inductive elements and changing their induction. However, the inductance change is not linear to the spacing change. Also, the inductive elements are not easy to be fabricated, and the inductances are not large enough.  
         [0007]     U.S. Pat. No. 6,249,206 provides a laminated ferrite chip inductor array, in which the array is composed in that multiple layers of ferrite sheets printed with U-shaped patterns of internal conductors are piled in such a manner that the U-shaped patterns of the internal conductors on adjacent sheets are opposed as faced one another. However, the inductance to area ratio of the laminated inductor array is still limited and a higher inductance cannot be obtained.  
       SUMMARY OF THE INVENTION  
       [0008]     The object of the invention is to provide a tunable passive device, in which plurality of passive elements are stacked. In accompany with a tunable structure, the tunable passive device has advantages of higher inductance and larger tuning range.  
         [0009]     A tunable passive device according to the invention includes a plurality of passive elements and at least a switch. The passive elements are stacked and spaced along a same direction, and connected with each other via the switch. By changing open/close conditions of the switch or switches and selecting specific passive elements that a current can pass, a responsive value of the tunable passive device is obtained.  
         [0010]     The passive elements are capacitors or inductors. The switches for connecting the stacks are made by current micro electromechanical systems (MEMS) technologies. These are well-developed technologies. Therefore, the passive devices of the invention integrate current available elements and inventive constructions to improve the functions. The devices can be practically made by semiconductor fabrication process nowadays.  
         [0011]     Furthermore, the tunable passive devices of the invention can be made of array element stacks. The tunable passive device includes a plurality of passive element array and at least a main switch. The passive element arrays are stacked and spaced along the same direction, and connected with each other via the main switch. By changing open/close conditions of the main switch or switches and selecting specific passive elements that a current can pass, a responsive value of the tunable passive device is obtained. Also, there are sub-switches in the passive element arrays for selectively changing the connections among passive elements. Therefore, multiple stages of responsive values can be adjusted. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention will become more fully understood from the detailed description given hereinbelow. However, this description is for purposes of illustration only, and thus is not limitative of the invention, wherein:  
         [0013]      FIG. 1  is a first embodiment of the invention applied to a tunable inductor;  
         [0014]      FIGS. 1A and 1B  are functional views of a tunable inductor of the invention;  
         [0015]      FIG. 2  is a second embodiment of the invention applied to a tunable inductor;  
         [0016]      FIG. 2A  is a functional view of a tunable inductor of the invention;  
         [0017]      FIG. 3  is a third embodiment of the invention applied to a tunable capacitor; and  
         [0018]      FIG. 4  is a fourth embodiment of the invention applied to a tunable passive array device. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     As shown in  FIG. 1 , a first embodiment of the invention is applied to a tunable inductor. The tunable inductor includes a first coil  11 , a second coil  12 , a third coil  13 , a first switch  21  and a second switch  22 . The second coil  12  is stacked on top of the first coil  11  and serially connected through the first switch  21 . The third coil  13  is stacked on top of the second coil  12  and serially connected through the second switch  22 . Each of the switches  21  and  22  has selectable first contact  23  and second contact  24 . When the first contact  23  is connected, it is in a “close” condition. When the second contact  24  is connected, it is in an “open” condition. The invention adjusts the inductance by the switch conditions. As shown in  FIG. 1 , the switches  21  and  22  are all in “open” conditions so that current flow only through the first coil  11  and gets a single coil inductance.  
         [0020]     The inductance of the first, second and third coils  11 ,  12 ,  13  can be the same. While, through changing the connection conditions of the switches  21  and  22 , different inductance can be obtained. For example, as shown in  FIG. 1A , the first and second switches  21  and  22  are all in “close” conditions so that the first, second and third coils  11 ,  12  and  13  are connected serially through contacts  23  of the switches  21  and  22 , and three times of inductance is obtained.  
         [0021]     Then, in  FIG. 1B , the first switch  21  is in “close” condition, while the second switch  22  is in “open” condition. A current can pass the first coil  11  and the second coil  12  and get two times of inductance of a single coil. Similarly, when the first switch  21  is in “open” condition, and the second switch  22  is in “close” condition, a current can pass the second coil  12  and the third coil  13  and get the same result of two times of inductance.  
         [0022]     Further, because coil inductance has a direction corresponding to the clockwise or counterclockwise of the current passing the coil. In the aforesaid first embodiment, the coils  11 ,  12  and  13  are applied with the same direction of current. However, any of the coils can be arranged to connect to different direction of current, and the inductance can be finely tuned by the mutual induction.  
         [0023]     As shown in  FIG. 2 , a second embodiment of the invention is applied to a tunable inductor. The inductor includes a first coil  11 , a second coil  12  and a switch  21 . The second coil  12  is stacked on top of the first coil  11  and serially connected through the switch  21 . Through wiring arrangement, a current can pass the first coil  11  counterclockwise; while, the current can pass the second coil  12  clockwise. Supposed the first coil  11  has an inductance L 1 ; the second coil  12  has an inductance L 2 ; and L 1 &gt;L 2 . However, in  FIG. 2 , the switch  21  is in “open” condition, a current only passes the first coil  11  and gets a single coil inductance L 1 .  
         [0024]     The function of the tunable inductor is shown in  FIG. 2A . The switch  21  is in “close” condition so that a current first passes the first coil  11  counterclockwise, then passes the second coil  12  clockwise. Because the current directions are different, the mutual inductance M of the two coils is negative. Therefore, the total inductance is L 1 +L 2 −M. The tunable inductor is thus tuned by changing a part of the current directions of the coils.  
         [0025]      FIG. 3  is a third embodiment of the invention applied to a tunable capacitor. The tunable capacitor includes a first laminated capacitor  31 , a second laminated capacitor  32 , a third laminated capacitor  33 , a first switch  41  and a second switch  32 . The second laminated capacitor  32  is connected in parallel to the first laminated capacitor  31  through the first switch  41 . The third laminated capacitor  33  is connected in parallel to the second laminated capacitor  32  through the second switch  42 . By changing the connection conditions of the switches  41  and  42 , different numbers of laminated capacitors are connected to provide different capacitance outputs.  
         [0026]     As described above, the tunable passive elements (capacitors or inductors) are connected in parallel or in serial so as to get several times of capacitance or inductance. By changing the connection or switch conditions, the correspondent capacitance or inductance can be changed.  
         [0027]     Further, the tunable passive elements can be connected through element arrays so as to achieve a larger range of tuning.  FIG. 4  shows a fourth embodiment of the invention applied to a tunable inductor having a plurality of inductor arrays. The tunable inductor includes a first inductor array  51 , a second inductor array  52  and a main switch  71  connected between the two arrays. The first inductor array  51  is composed of four coils  61  on a same plane. The second inductor array  52  is also composed of four coils  61  on a same plane and stacked on top of the first inductor array  51 . The second inductor  52  connects serially to the first inductor array  51  through the main switch  71  and forms a tunable inductor.  
         [0028]     Each of the inductor arrays  51  and  52  includes several sub-switches for multiple stages of inductance tuning. As shown in  FIG. 4 , each of the first inductor array  51  and the second inductor array  52  includes first, second and third coils  61  and three sub-switches  72 . The first, second and third coils  61  are serially connected by the three sub-switches  72 . By controlling the connection conditions of the sub-switches  72 , the inductances of the first and second inductor arrays  51  and  52  are adjustable. Further, by controlling the connection condition of the main switch  71 , the total inductance of the first and second inductor arrays  51  and  52  is tuned.  
         [0029]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.