Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0107435 filed in the Korean Intellectual Property Office on Oct. 24, 2007, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   (a) Field of the Invention 
   The present invention relates to a switch, a negative resistance cell, and a differential voltage controlled oscillator using the same. More particularly, the present invention relates to a switch, a negative resistance cell, and a differential voltage controlled oscillator using the same for minimizing generation of a parasitic component. 
   (b) Description of the Related Art 
   A differential voltage controlled oscillator (DVCO) is a device for changing and outputting an oscillation frequency corresponding to an applied voltage, and is generally used for an analog voice synthesizer and a mobile communication terminal. 
   The DVCO used for the voice synthesizer generates sine waves, sawtooth waves, pulse waves, square waves, and triangular waves to generate various sound signals. The DVCO used for the mobile communication device is used for the phase locked loop (PLL) module to function as a local oscillator for allocating channels and converting frequencies into the radio frequency (RF) or the intermediate frequency (IF). 
   Also the DVCO is an essential constituent element for the wired/wireless transmitting/receiving system, and study on improving the performance of the DVCO is ongoing. 
   However, regarding the general DVCO, performance improvement and downsizing are limited since it is difficult to reduce the parasitic component and the realized area that are caused by the transistor structure and the length of the connection lines between elements by more than a predetermined level, and hence, methods for solving the problem are needed. 
   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 invention has been made in an effort to provide a switch, a negative resistance cell, and a differential voltage controlled oscillator using the same for minimizing the parasitic components and the realization area. 
   In one aspect of the present invention, a differential voltage controlled oscillator includes: a resonator for generating an oscillation frequency corresponding to an input voltage; a first output terminal and a second output terminal, respectively coupled to a first terminal and a second terminal of the resonator, for outputting the oscillation frequency; and a negative resistance cell driven in correspondence to the oscillation frequency. The negative resistance cell includes a switch, and the switch includes: a first signal line extended in a first direction; a second signal line formed to be parallel with the first signal line; a source electrode formed between the first and second signal lines; a first gate electrode arranged to be parallel with the source electrode and coupled to the first signal line; a second gate electrode provided to the opposite side of the first gate electrode with respect to the source electrode, and coupled to the second signal line; a first drain electrode provided to the opposite side of the source electrode with respect to the first gate electrode, and coupled to the second signal line; and a second drain electrode provided to the opposite side of the source electrode with respect to the second gate electrode, and coupled to the first signal line. 
   In another aspect of the present invention, a differential voltage controlled oscillator includes: a resonator for generating an oscillation frequency corresponding to an input voltage; a first output terminal and a second output terminal, respectively coupled to a first terminal and a second terminal of the resonator, for outputting the oscillation frequency; and a negative resistance cell driven in correspondence to the oscillation frequency. The negative resistance cell includes a switch, and the switch includes: a first signal line extended in a first direction; a second signal line formed to be parallel with the first signal line; and a first gate electrode to a fourth gate electrode, a first source electrode to a third source electrode, and a first drain electrode to a fourth drain electrode formed between the first signal line and the second signal line. 
   The electrodes are formed in the order of the first gate electrode, the first drain electrode, the second gate electrode, the first source electrode, the third gate electrode, the second drain electrode, the fourth gate electrode, the second source electrode, the fifth gate electrode, the third drain electrode, the sixth gate electrode, the third source electrode, the seventh gate electrode, the fourth drain electrode, and the eighth gate electrode. 
   In another aspect of the present invention, provided is a negative resistance cell included in a resonator for generating an oscillation frequency corresponding to an input voltage, and a differential voltage controlled oscillator for outputting the oscillation frequency through a first output terminal and a second output terminal and including a switch that is driven corresponding to the oscillation frequency. The switch includes: a first signal line extended in a first direction; a second signal line formed to be parallel with the first signal line; a source electrode formed between the first and second signal lines; a first gate electrode arranged to be parallel with the source electrode and coupled to the first signal line; a second gate electrode provided to the opposite side of the first gate electrode with respect to the source electrode, and coupled to the second signal line; a first drain electrode provided to the opposite side of the source electrode with respect to the first gate electrode, and coupled to the second signal line; and a second drain electrode provided to the opposite side of the source electrode with respect to the second gate electrode, and coupled to the first signal line. 
   In another aspect of the present invention, provided is a negative resistance cell included in a resonator for generating an oscillation frequency corresponding to an input voltage, and a differential voltage controlled oscillator for outputting the oscillation frequency through a first output terminal and a second output terminal and including a switch driven corresponding to the oscillation frequency. The switch includes: a first signal line extended in a first direction; a second signal line formed to be parallel with the first signal line; and a first gate electrode to a fourth gate electrode, a first source electrode to a third source electrode, and a first drain electrode to a fourth drain electrode formed between the first signal line and the second signal line. 
   The electrodes are formed in the order of the first gate electrode, the first drain electrode, the second gate electrode, the first source electrode, the third gate electrode, the second drain electrode, the fourth gate electrode, the second source electrode, the fifth gate electrode, the third drain electrode, the sixth gate electrode, the third source electrode, the seventh gate electrode, the fourth drain electrode, and the eighth gate electrode. 
   In another aspect of the present invention, a switch includes: a first signal line extended in a first direction; a second signal line formed to be parallel with the first signal line; a source electrode formed between the first and second signal lines; a first gate electrode arranged to be parallel with the source electrode and coupled to the first signal line; a second gate electrode provided to the opposite side of the first gate electrode with respect to the source electrode, and coupled to the second signal line; a first drain electrode provided to the opposite side of the source electrode with respect to the first gate electrode, and coupled to the second signal line; and a second drain electrode provided to the opposite side of the source electrode with respect to the second gate electrode, and coupled to the first signal line. 
   In another aspect of the present invention, a switch includes: a first signal line extended in a first direction; a second signal line formed to be parallel with the first signal line; and a first gate electrode to a fourth gate electrode, a first source electrode to a third source electrode, and a first drain electrode to a fourth drain electrode formed between the first signal line and the second signal line 
   The electrodes are formed in the order of the first gate electrode, the first drain electrode, the second gate electrode, the first source electrode, the third gate electrode, the second drain electrode, the fourth gate electrode, the second source electrode, the fifth gate electrode, the third drain electrode, the sixth gate electrode, the third source electrode, the seventh gate electrode, the fourth drain electrode, and the eighth gate electrode. 
   According to the present invention, the switch, the negative resistance cell, and the differential voltage controlled oscillator using them for minimizing parasitic components and realization area are realized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of a differential voltage controlled oscillator  1000  according to an exemplary embodiment of the present invention. 
       FIG. 2  is a detailed schematic diagram of a negative resistance cell  10  included in a general differential voltage controlled oscillator. 
       FIG. 3  is a detailed schematic diagram of a negative resistance cell  20  included in a general RF differential voltage controlled oscillator. 
       FIG. 4  is a detailed schematic diagram of a negative resistance cell  100  according to an exemplary embodiment of the present invention. 
       FIG. 5  shows a structure of a minimum unit cell included in a negative resistance cell  100  according to an exemplary embodiment of the present invention shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. 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. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
   Throughout this specification and the claims that follow, when it is described that an element is “coupled” to another element, the element may be “directly coupled” to the other element or “electrically coupled” to the other element through a third element. 
   Throughout this 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. In addition, the terms “-er”, “-or”, and “module” described in the specification mean units for processing at least one function and operation and can be implemented by hardware components or software components and combinations thereof. 
     FIG. 1  is a schematic diagram of a differential voltage controlled oscillator  1000  according to an exemplary embodiment of the present invention. 
   As shown in  FIG. 1 , the differential voltage controlled oscillator  1000  includes a negative resistance cell  100  and an LC tank  200 . 
   The negative resistance cell  100  includes a switch formed by cross-coupled transistors  110  and  120 . For reference, in  FIG. 1 , the transistor  110  and the transistor  120  are respectively shown to be formed as a transistor, and differing from this, they can be formed by a plurality of transistors coupled in parallel. 
   A drain  110   d  of the transistor  110  is coupled to an output terminal Out 1  through a node N 1 , and a source  110   s  thereof is grounded. A gate  110   g  of the transistor  110  is coupled to a node N 2 . 
   A drain  120   d  of the transistor  120  is coupled to an output terminal Out 2  through a node N 2 , and a source  120   s  is grounded. A gate  120   g  of the transistor  120  is coupled to the node N 1 . 
   A first terminal of the LC tank  200  is coupled to the node N 1 , and a second terminal is coupled to the node N 2 . The LC tank  200  is formed by coupling an inductor (not shown) and a capacitor (not shown) in parallel, and here, capacitance of the capacitor is changed according to an input voltage, and an oscillation frequency is changed corresponding to the voltage. 
   The negative resistance cell  100  of the differential voltage controlled oscillator  1000  according to the exemplary embodiment of the present invention will now be described with reference to drawings. A negative resistance cell included in the general differential voltage controlled oscillator will now be described with reference to  FIG. 2  and  FIG. 3 . 
     FIG. 2  is a detailed schematic diagram  26  a negative resistance cell  10  included in a general differential voltage controlled oscillator. 
   As shown in  FIG. 2 , the negative resistance cell  10  included in the differential voltage controlled oscillator is formed by a switch including a transistor  11  and a transistor  12 . 
   A drain  11   d  of the transistor  11  is coupled to a node N 11  coupled to an LC tank (not shown), and a source  11   s  is grounded through a source common connector ( 11   s - 1 ). 
   A drain  12   d  of the transistor  12  is coupled to a node N 12  coupled to the LC tank (not shown), and a source  12   s  is grounded through a source common connector ( 12   s - 1 ). 
   A gate  11   g  of the transistor  11  is coupled to the node N 12 , and a gate  12   g  of the transistor  12  is coupled to the node N 11 . 
   The drains  11   d  and  12   d  of the transistors  11  and  12  have a junction with an active area. Also, while not shown in  FIG. 2 , the sources  11   s  and  12   s  of the transistors  11  and  12  obviously have a junction with the active area. 
   As shown in  FIG. 2 , the transistor  11  and the transistor  12  of the negative resistance cell  10  included in the general differential voltage controlled oscillator are formed to be symmetrical with each other. Therefore, the node N 11  and the node N 12  must be formed to be superimposed with each other, and parasitic resistance, parasitic inductance, and parasitic capacitance components that are caused by the superimposition structure are substantially increased, which cannot be ignored. As shown in  FIG. 2 , as the transistors  11  and  12  are formed, a mismatch caused by a gradient in the process for generating the two transistors  11  and  12  may occur. 
   Particularly, when the negative resistance cell  10  shown in  FIG. 2  is used to manufacture the differential voltage controlled oscillator that is operable in the RF area, the oscillation frequency and frequency tuning range are substantially limited by the parasitic component and the mismatch, and phase noise performance is deteriorated. 
   Also, the negative resistance cell  10  shown in  FIG. 2  substantially generates an undesired parasitic component as the lengths of the node N 11  and the node N 12  are increased. 
   A large parasitic component generated in the negative resistance cell  10  deteriorates the Q factor of the LC tank ( 200  in  FIG. 1 ) to thus deteriorate the phase noise performance. The large parasitic component generated in the negative resistance cell  10  limits the frequency bandwidth of the oscillation frequency output by the general differential voltage controlled oscillator to be not greater than a predetermined level. Also, the large parasitic component generated in the negative resistance cell  10  limits the variable range of the output frequency of the LC tank ( 200  in  FIG. 1 ). In order to realize an RF differential voltage controlled oscillator for outputting the RF oscillation frequency, a negative resistance cell  20  for reducing generation of the parasitic component compared to the negative resistance cell  10  shown in  FIG. 2  is shown in  FIG. 3 . 
     FIG. 3  is a detailed schematic diagram of a negative resistance cell  20  included in a general RF differential voltage controlled oscillator. 
   As shown in  FIG. 3 , the negative resistance cell  20  included in the general RF differential voltage controlled oscillator is formed by a switch including a transistor  21  and a transistor  22 . 
   A drain  21   d  of the transistor  21  is coupled to a node N 21  coupled to an LC tank (not shown), and a source  21   s  thereof is grounded. 
   A drain  22   d  of the transistor  22  is coupled to a node N 22  coupled to the LC tank (not shown), and a source  22   s  thereof is grounded. 
   A gate  21   g  of the transistor  21  is coupled to the drain  22   d  of the transistor  22 , and a gate  22   g  of the transistor  22  is coupled to the drain  21   d  of the transistor  21 . 
   The drains  21   d  and  22   d  of the transistors  21  and  22  have a junction with the active area. Also, while not shown in  FIG. 3 , the sources  21   s  and  22   s  of the transistors  21  and  22  have a junction with the active area. 
   The negative resistance cell  20  shown in  FIG. 3  arranges the two transistors  21  and  22  asymmetrically so that the gate  21   g  of the transistor  21  is coupled to the drain  22   d  of the transistor  22  and the gate  22   g  of the transistor  22  is coupled to the drain  21   d  of the transistor  21 . That is, the negative resistance cell  20  shown in  FIG. 3  includes no superimposition structure, differing from the negative resistance cell  10  shown in  FIG. 2 , and thus generates a lesser parasitic component compared to the negative resistance cell  10  shown in  FIG. 2 . Because of the reduction of the parasitic component, the negative resistance cell  20  shown in  FIG. 3  improves the Q factor of the LC tank ( 200  in  FIG. 1 ) compared to the negative resistance cell  10  shown in  FIG. 2 , and thus acquires improved phase noise performance. The negative resistance cell  20  shown in  FIG. 3  can realize the output frequency bandwidth of the differential voltage controlled oscillator to be greater than that of the negative resistance cell  10  shown in  FIG. 2 . Also, the negative resistance cell  20  shown in  FIG. 3  increases the change of the capacitance of the capacitor corresponding to the voltage input to the capacitor included in the LC tank ( 200  in  FIG. 1 ) compared to the negative resistance cell  10  shown in  FIG. 2 , and hence, it realizes the improved broadband characteristic. 
   However, it is required for the negative resistance cell  20  shown in  FIG. 3  to increase the number of the drains  21   d  and  22   d  by one for the respective transistors  21  and  22  compared to the negative resistance cell  10  shown in  FIG. 2  in order to couple the drain and the source of the two transistors  21  and  22  that are arranged asymmetrically. Also, because of the nodes N 21  and N 22 , a parasitic capacitance component is generated between the gate  21   g  of the transistor  21  and the drain  21   d  of the transistor  21  and between the gate  22   g  of the transistor  22  and the drain  22   d  of the transistor  22 . Also, the negative resistance cell  20  shown in  FIG. 3  may generate a mismatch caused by a gradient because of the asymmetric structure of the two transistors  21  and  22 . The gradient may differentiate the lengths of the connection metal lines between the two transistors  21  and  22  and the LC tank (not shown), and hence, the symmetry between the transistor  21  and the transistor  22  with reference to the LC tank cannot be guaranteed. This asymmetry worsens the phase noise performance, and deteriorates the performance of the differential voltage controlled oscillator. 
   A negative resistance cell  100  that is suitable for realizing the RF differential voltage controlled oscillator by minimizing the parasitic component compared to the negative resistance cells  10  and  20  shown in  FIG. 2  and  FIG. 3 , and for minimizing the realization area according to an exemplary embodiment of the present invention, will now be described with reference to  FIG. 4 . 
     FIG. 4  is a detailed schematic diagram of a negative resistance cell  100  according to an exemplary embodiment of the present invention. 
   As shown in  FIG. 4 , the negative resistance cell  100  is formed by a switch including a transistor  120  arranged symmetrically, and a transistor  110  arranged symmetrically to the right and left of the transistor  120 . The negative resistance cell  100  shown in  FIG. 4  has a common-centroid structure for the transistor  110  and the transistor  120 . The negative resistance cell  100  shown in  FIG. 4  will now be described. 
   The node N 1  and the node N 2  are formed as parallel signal lines. The gate  110   g , drain  110   d , and source  110   s  of the transistor  110  are provided between the node N 1  and the node N 2 . The gate  120   g , drain  120   d , and source  120   s  of the transistor  120  are provided between the node N 1  and the node N 2 . The electrodes are formed in the order of gate  110   g , drain  110   d , the gate  110   g , the source  110   s  of the transistor  110 , the gate  120   g , the drain  120   d , the gate  120   g , the source  120   s , the gate  120   g , the drain  120   d , the gate  120   g  of the transistor  120 , the source  110   s , the gate  110   g , the drain  110   d , and the gate  110   g  of the transistor  110 . 
   The drains  110   d  and  120   d  of the transistors  110  and  120  have a junction with the active area. Also, while not shown in  FIG. 4 , the sources  110   s  and  120   s  of the transistors  110  and  120  have a junction with the active area. 
   The negative resistance cell  100  shown in  FIG. 4  is formed so that the transistor  110  and the transistor  120  respectively share the sources  110   s  and  120   s , and the sources are grounded through the common source connector (S). Accordingly, the number of sources is reduced by 1 compared to the general negative resistance cell  10  shown in  FIG. 2 . Also, the general negative resistance cell  20  shown in  FIG. 3  has a structure that requires 3 drains for 4 gates, and the negative resistance cell  100  according to the exemplary embodiment of the present invention requires 2 drains for 4 gates. That is, the negative resistance cell  100  has fewer drains than the general negative resistance cell  20  by 2, and hence, the parasitic component, that is, the parasitic capacitor component generated between the drains  110   d  and  120   d  and the sources  110   s  and  120   s , is reduced. Because of the reduction of the parasitic components, the negative resistance cell  100  improves the Q factor of the LC tank ( 200  in  FIG. 1 ) compared to the general negative resistance cell  20  shown in  FIG. 3 , and thus realizes improved phase noise performance. Also, the negative resistance cell  100  increases the change of capacitance of the capacitor corresponding to the input voltage of the capacitor included in the LC tank ( 200  in  FIG. 1 ) compared to the general negative resistance cell  20  shown in  FIG. 3 , and thus realizes the improved broadband characteristic. 
   Also, the negative resistance cell  100  shown in  FIG. 4  forms a structure in which the node N 1  coupled to the gate  110   d  of the transistor  110  is completely symmetrical with the node N 2  coupled to the gate  120   d  of the transistor  120 , differing from the general negative resistance cell  20  shown in  FIG. 3 . That is, the transistors  110  and  120  are formed in the linear symmetric format with respect to the common source  120 S. Because of the common-centroid structure, the negative resistance cell  100  can minimize generation of the parasitic component and generation of a mismatch caused by a gradient, and thus improves phase noise performance. 
   In  FIG. 4 , the transistor  120  is shown to be formed nearer to the common source  120   s  that is the axis of the linear symmetry than the transistor  110 , and differing from this, the transistor  110  can be formed nearer to the common source  120   s  than the transistor  120 . Also, the gate  110   g  and  120   g  of the transistors  110  and  120  are coupled to the nodes N 1  and N 2 . In detail, the gap between the node N 1  and the node N 2  is formed to be within the range of the lengths of the gates  110   g  and  120   g  of the transistors  110  and  120 , and hence, the heat and the realization area of the parasitic component can be reduced compared to the negative resistance cells  10  and  20  included in the general differential voltage controlled oscillator shown in  FIG. 2  and  FIG. 3 . 
   The transistors  110  and  120  included in the negative resistance cell  100  according to the exemplary embodiment of the present invention shown in  FIG. 4  are applicable to other elements having the cross coupled transistor structure in addition to the differential voltage controlled oscillator  1000  according to the exemplary embodiment of the present invention. 
     FIG. 5  is a structure of a minimum unit cell included in a negative resistance cell  100  according to an exemplary embodiment of the present invention shown in  FIG. 4 . Here, a minimum unit cell represents a switch including transistors  110  and  120  driven in correspondence to two different control signals, and the negative resistance cell  100  can be formed with one minimum unit cell. 
   As shown in  FIG. 5 , the transistor  110  and the transistor  120  of the minimum unit cell included in the negative resistance cell  100  according to the exemplary embodiment of the present invention share a common source. The minimum unit cell structure shown in  FIG. 5  will now be described in detail. 
   The node N 1  and the node N 2  are formed as parallel signal lines. The gate  110   g  of the transistor  110  is provided in parallel to the common source, and is coupled to the node N 2 . The drain  100   d  of the transistor  110  is provided to the opposite side of the common source with respect to the gate  110   g , and is coupled to the node N 1 . The gate  120   g  of the transistor  120  is provided to the opposite side of the gate  110   g  of the transistor  110  with respect to the common source, and is coupled to the node N 1 . The drain  120   d  of the transistor  120  is provided to the opposite side of the common source with respect to the gate  120   g , and is coupled to the node N 2 . 
   The drains  110   d  and  120   d  of the transistors  110  and  120  have a junction with the active area. Also, while not shown in  FIG. 5 , the sources  110   s  and  120   s  of the transistors  110  and  120  have a junction with the active area. 
   Here, the common source is coupled to the common source connector (S) and is then grounded. Further, the gate  110   g  of the transistor  110  and the drain  120   d  of the transistor  120 , and the gate  120   g  of the transistor  120  and the drain  110   d  of the transistor  110 , are set to not be superimposed with each other. Hence, the length of the connection line for forming the minimum unit cell is minimized. 
   The minimum unit cell structure shown in  FIG. 5  can be selected as the standard cell for the library provided by the general semiconductor process. When the minimum unit cell structure shown in  FIG. 5  is used as the standard cell, the extended form of the standard cell can be realized as the same format as the negative resistance cell  100  according to the exemplary embodiment of the present invention shown in  FIG. 4 , and can also be realized as a format that is different from the negative resistance cell  100  according to the exemplary embodiment of the present invention shown in  FIG. 4 . The negative resistance cell  100  minimizes the switch structure, minimizes the number of drains  110   d  and  120   d  and sources  110   s  and  110   s  of the transistors  110  and  120 , and is formed in the common-centroid structure for solving the mismatch during the process. Accordingly, the negative resistance cell  100  improves the Q factor of the LC tank  200  to improve phase noise performance, and improves the performance of the differential voltage controlled oscillator  1000  for outputting the RF band oscillation frequency. Also, the negative resistance cell  100  increases the change of capacitance of the capacitor corresponding to the input voltage of the capacitor included in the LC tank  200 , and realizes the improved broadband characteristic. Therefore, the negative resistance cell  100  allows the realization of the differential voltage controlled oscillator  1000  for outputting the RF broadband oscillation frequency. 
   The transistors  110  and  120  shown in  FIG. 4  and  FIG. 5  can be realized with various types of switches including a complimentary metal oxide semiconductor (CMOS) and a bipolar junction transistor (BJT). 
   The above-described embodiments can be realized through a program for realizing functions corresponding to the configuration of the embodiments or a recording medium for recording the program in addition to through the above-described device and/or method, which is easily realized by a person skilled in the art. 
   While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Technology Category: h