Abstract:
A multilayer chip-type triplexer is provided. It uses four-session matching transmission lines to integrate three band-pass filters at different frequency bands for simplifying triplexer design. A band-pass filter may be composed of a two-stage combline band-pass filter. The transmission zero generated by the two-stage combline band-pass filter is to increase the isolation and performance of the triplexer. The triplexer uses low-loss materials to reduce the insertion loss of the circuit Moreover, a multilayer structure is adopted to minimize the size of the triplexer. The triplexer is applicable to multiband radio-frequency modules, and meets the multimodule requirement for wireless communication products.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to a triplexer, and especially to a multilayer chip-type triplexer. 
   BACKGROUND OF THE INVENTION 
   With the advance of wireless communication technology, plenty of convenient wireless communication systems have been developed. These systems include global system for mobile communication (GSM), personal communication service (PCS), and wireless local area network (WLAN), etc. The radio-frequency (RF) modules adopted in conventional single-band systems are not sufficient for current wireless communication systems that essentially emphasize multiple functions. The multi-band or even multi-mode modules have become the future trend of the RF modules. 
   The structures of a matching circuit (e.g., inductors or transmission lines) associated with filters of different frequency bands are similar to the duplexer designs disclosed in U.S. Pat. Nos. 6,707,350, 6,414,567, and 6,411,178. In U.S. Pat. No. 6,707,350, the band-pass filter of a duplexer uses a direct input structure. The band-pass filter structure of a duplexer disclosed in U.S. Pat. No. 6,414,567 consists of three resonator These resonators are coupled through capacitive coupling, and inductors are used for the design of the matching circuit. In another U.S. Pat. No. 6,411,178, the band-pass filter structure of a disclosed duplexer comprises three resonators, and its matching circuit adopts a serial combination of capacitors and inductors. 
   The major function of a triplexer is to separate a received signal into different frequency bands with good isolation. Conventional triplexers are designed with low-pass and high-pass filters or plural band-pass filters. The former design has the advantage of low insertion loss and good isolation but its drawback is a large distortion outside the allowed frequency band. The latter design has the advantage of good selectivity among various frequency bands but its design is quite complicated. The complexity of the design results from a requirement of many stages for band-pass filters. Furthermore, it has a high insertion loss. 
   SUMMARY OF THE INVENTION 
   The present invention has been made to overcome the drawback of high design complexity for the aforementioned conventional triplexers which contain plural band-pass filters. It provides a chip-type triplexer capable of reducing the design complexity. 
   The triplexer of the present invention is designed to locate the center frequencies of three different frequency bands to 900 MHz, 1800 MHz, and 2400 MHz. In order to improve signal isolation and impedance matching, the first band-pass filter in 900 MHz frequency band is designed to allow transmission zero at a frequency of 2000 MHz. The second band-pass filter in 1800 MHz frequency band is designed to allow transmission zero at a frequency of 2400 MHz. The third band-pass filter in 2400 MHz frequency band is designed to allow transmission zero at a frequency between 1800 MHz and 1900 MHz. 
   The three band-pass filters of the present invention are designed separately, and then the second band-pass filter and the third band-pass filter are combined into a duplexer through a matching circuit Finally, the first band-pass filter is incorporated into the duplexer through another matching circuit to form a triplexer. The matching circuit can be implemented with matching transmission lines. 
   According to the chip-type triplexer of the present invention, four matching transmission lines are used to integrate three two-stage combline-type band-pass filters located at different bands. The three band-pass filters can be three stand-alone two-stage combline-type band-pass filters. The two-stage combline-type band-pass filters have low insertion loss. In addition, they can produce transmission zeros at low pass-band skirt and at high pass-band skirt respectively, through controlling the coupling coefficients (e.g., electric coupling or magnetic coupling) of the transmission lines. A J-inverter between the two resonators of the two-stage combline-type band-pass filter can become an equivalent of a π-type capacitor or inductor. Therefore, it behaves like an inductive coupling when used with a low-frequency combline-type band-pass filter or a capacitive coupling when used with a high-frequency combline-type band-pass filter. 
   The first band-pass filter and the second band-pass filter each adopts a two-stage combline-type band-pass filter which is capable of producing transmission zero at high passband skirt. The third band-pass filter adopts a two-stage combline-type band-pass filter which is capable of producing transmission zero at low passband skirt. 
   Every matching transmission line has two terminals, the first terminal and the second terminal. The first band-pass filter is electrically connected to the second terminal of the first matching transmission line. The second band-pass filter is electrically connected to the second terminal of the second matching transmission line. The third band-pass filter is electrically connected to the second terminal of the third matching transmission line. The first terminal of the third matching transmission line, the first terminal of the second transmission line, and the first terminal of the fourth transmission line are electrically connected together. The first terminal of the first transmission line and the second terminal of the fourth transmission line are electrically connected to the input port of the antenna. 
   The adoption of capacitive coupling at the input port of a combline-type band-pass filter can improve the insertion loss at low frequencies. However, there is a side effect of introducing extra loss at other frequencies. Therefore, the second band-pass filter must be isolated from the third band-pass filter when they are designed. To enhance the isolation between the second band-pass filter and the first band-pass filter, a capacitive coupling is adopted for the second band-pass filter. A direct input method is chosen for the third band-pass filter. Moreover, there are two input capacitors disposed in the second band-pass filter. 
   The chip-type triplexer of the present invention has a multilayer structure. The multilayer structure consists of seventeen layers, a first layer to a seventeenth layer from top to bottom. Each layer comprises a primary surface plane. 
   Four matching transmission lines and thirty-one metallic sheets are formed on the primary surface planes of the seventeen-layer structure. The multilayer chip-type triplexer is obtained by connecting nineteen metallic sheets to the matching transmission metallic lines and sheets on each layer through via-holes. 
   An electromagnetic simulation indicates that the multilayer chip-type triplexer of the present invention has very good isolation and selectivity. 
   In summary, the band-pass filters of the present invention at various frequencies bands are first designed independently, and then matching circuit is applied to integrate these band-pass filters. The complexity of circuit design is hence reduced. The matching circuit uses a structure of matching transmission line to simplify the design flow and reduce the design time. Moreover, the triplexer of the present invention consists of a multilayer circuit structure and its matching transmission lines surround multiple substrate layers. Therefore, the area of the circuit layout is greatly reduced to meet the requirement of small form factor for future wireless communication products. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows the equivalent circuit of an embodiment of the present invention. 
       FIG. 2  shows the block diagram of an embodiment of the present invention. 
       FIG. 3  shows the equivalent circuit of two-stage combline-type band-pass filter adopted in an embodiment of the present invention. 
       FIG. 4A  depicts an equivalent circuit of the band-pass filter shown in  FIG. 3 , in which a transmission zero at low pass-band skirt is produced through controlling the coupling coefficients of the transmission lines. 
       FIG. 4B  depicts another equivalent circuit of the band-pass filter shown in  FIG. 3 , in which a transmission zero at high pass-band skirt is produced through controlling the coupling coefficients of the transmission lines. 
       FIG. 5  shows a perspective view of the multiplayer structure of an embodiment of the present invention. 
       FIG. 6  shows the layout structure of each circuit layer of an embodiment of the present invention. 
       FIG. 7  shows an electromagnetic simulation result of an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows the equivalent circuit of an embodiment of the multilayer chip-type triplexer according to the present invention.  FIG. 2  depicts the block diagram of the embodiment shown in  FIG. 1 . As can be seen from  FIG. 2 , the three band-pass filters  201 - 203  can be first designed independently, and then the second matching circuit  212  and the third matching circuit  213  are applied to integrate the second band-pass filter  202  and the third band-pass filter  203  into a duplexer. The duplexer is further integrated with the fourth matching circuit  214  and the first matching circuit  211  to form a triplexer  200 . 
   Referring to  FIG. 1  again, every matching transmission line has two terminals, the first terminal and the second terminal. The second terminal of the third matching transmission line M 3  is electrically connected with the third band-pass filter  103  through the sixth node N 6 . The second terminal of the second matching transmission line M 2  is electrically connected with the second band-pass filter  102  through the third node N 3 . The second terminal of the first matching transmission line M 1  is electrically connected with the first band-pass filter  101  through the first node N 1 . The first terminal of the third matching transmission line M 3 , the first terminal of the second matching transmission line M 2 , and the first terminal of the fourth matching transmission line M 4  are electrically connected together through the second node N 2 . The first terminal of the first transmission line M 1  and the second terminal of the fourth transmission line M 4  are electrically connected to the input port P 1  of the antenna. 
   The two-stage combline-type band-pass filter  300  shown in  FIG. 3  has low insertion loss. Through controlling the coupling coefficients (e.g., electric coupling or magnetic coupling) of the transmission lines, it can produce transmission zero at low pass-band skirt as the two-stage combline-type band-pass filter  401  shown in  FIG. 4A , and at high pass-band skirt as the two-stage combline-type band-pass filter  402  shown in  FIG. 4B , respectively. The first band-pass filter  101  and the second band-pass filter  102  each uses a two-stage combline band-pass filter  402 . The third band-pass filter  103  uses a two-stage combline band-pass filter  401 . 
   The first band-pass filter  101  has two identical resonators which are connected in parallel. The first resonator is formed by connecting a transmission line T 11  and a capacitor C 11  in parallel, and the second resonator is formed by connecting a transmission line T 12  and a capacitor C 12  in parallel. One terminal of each resonator is grounded, and the other terminal is electrically connected to each other through a coupling inductor L 1 . The second band-pass filter  102  also has two identical resonators which are connected in parallel. The first resonator is formed by connecting a transmission line T 21  and a capacitor C 21  in parallel, and the second resonator is formed by connecting a transmission line T 22  and a capacitor C 22  in parallel. One terminal of each resonator is grounded, and the other terminal is electrically connected to each other through a coupling inductor L 2 . The third band-pass filter  103  has two identical resonators which are connected in parallel. The first resonator is formed by connecting a transmission line T 31  and a capacitor C 31  in parallel, and the second resonator is formed by connecting a transmission line T 32  and a capacitor C 32  in parallel. One terminal of each resonator is grounded, and the other terminal is electrically connected to each other through a coupling capacitor C 3 . inductor L 2 . The third band-pass filter  103  has two identical resonators which are connected in parallel. The first resonator is formed by connecting a transmission line T 31  and a capacitor C 31  in parallel, and the second resonator is formed by connecting a transmission line T 32  and a capacitor C 32  in parallel. One terminal of each resonator is grounded, and the other terminal is electrically connected each other through a coupling capacitor C 3 . 
   Referring to the combline band-pass filter of the triplexer  100  shown  FIG. 1 , an input method using capacitive coupling is adopted in the design of the second band-pass filter. Two identical input capacitors C 20   a  and C 20   b  are disposed between nodes N 3  and N 4  and between node N 5  and output port P 3  of the second band-pass filter. The first band-pass filter  101  and the third band-pass filter  103  use a direct input method. 
     FIG. 5  shows a perspective view of the multiplayer structure of an embodiment of the present invention.  FIG. 6  shows the layout structure of each circuit layer of an embodiment of the present invention. Every black dot shown in each layout pattern in  FIG. 6  represents a connecting via going from top surface to bottom surface. 
   Referring to  FIG.5 , the multilayer chip-type triplexer  500  has a plural-layer structure. From top to bottom, these layers are a first layer  501 , a second layer  502 , a third layer  503 , a fourth layer  504 , a fifth layer  505 , a sixth layer  506 , a seventh layer  507 , an eighth layer  508 , a ninth layer  509 , a tenth layer  510 , an eleventh layer  511 , a twelfth layer  512 , a thirteenth layer  513 , a fourteenth layer  514 , a fifteenth layer  515 , a sixteenth layer  515 , and a seventeenth layer  517 . Each layer contains a primary surface plane. 
   The primary surface plane of the first layer  501  comprises an antenna input port P 1 , an output port P 2  of a first band-pass filter, an output port P 3  of a second band-pass filter, an output port P 4  of a third band-pass filter, a fourth matching transmission metallic line  501   a , a second matching transmission metallic line  501   b , and a third matching transmission metallic line  501   c.    
   A first metallic sheet  503   a  is formed on the primary surface plane of the third layer  503 . 
   A second metallic sheet  504   a  is formed on the primary surface plane of the fourth layer  504 . 
   A third metallic sheet  505   a , a fourth metallic sheet  505   b , and a fifth metallic sheet  505   c  are formed on the primary surface plane of the fifth layer  505 . 
   A sixth metallic sheet  506   a  is formed on the primary surface plane of the sixth layer  506 . 
   A seventh metallic sheet  507   a , an eighth metallic sheet  507   b , and a first matching transmission metallic line  507   c  are formed on the primary surface plane of the seventh layer  507 . 
   A ninth metallic sheet  508   a , a tenth metallic sheet  508   b , and an eleventh metallic sheet  508   c  are formed on the primary surface plane of the eighth layer  508 . 
   A twelfth metallic sheet  509   a , a thirteenth metallic sheet  509   b , a fourteenth matching transmission metallic line  509   c , and a fifteenth metallic sheet  509   d  are formed on the primary surface plane of the ninth layer  509 . 
   A sixteenth metallic sheet  510   a  and a seventeenth metallic sheet  510   b  are formed on the primary surface plane of the tenth layer  510 . 
   An eighteenth metallic sheet  511   a , a nineteenth metallic sheet  511   b , and a twentieth metallic sheet  511   c  are formed on the primary plane of the eleventh layer  511 . The eighteenth metallic sheet comprises a first part  511   a   1  and a second part  511   a   2 . 
   A twenty-first metallic sheet  512   a , a twenty-second metallic sheet  512   b , and a twenty-third metallic sheet  512   c  are formed on the primary plane of the twelfth layer  512 . The twenty-third metallic sheet comprises a first part  512   c   1  and a second part  512   c   2 . 
   A twenty-fourth metallic sheet  513   a  and a twenty-fifth metallic sheet  513   b  are formed on the primary plane of the thirteenth layer  513 . The twenty-fourth metallic sheet comprises a first part  513   a   1  and a second part  513   a   2 . 
   A twenty-sixth metallic sheet  514   a  and a twenty-seventh metallic sheet  514   b  are formed on the primary plane of the fourteenth layer  514 . The twenty-sixth metallic sheet comprises a first part  514   a   1  and a second part  514   a   2 . 
   A twenty-eighth metallic sheet  515   a  and a twenty-ninth metallic sheet  515   b  are formed on the primary plane of the fifteenth layer  515 . 
   A thirtieth metallic sheet  516   a  is formed on the primary plane of the sixteenth layer  516 . 
   A thirty-first metallic sheet  517   a  is formed on the primary plane of the seventeenth layer  517 . 
   In order to implement transmission lines which have magnetic coupling effects, ground planes are disposed on thick layers and these ground planes are connected through via-holes The first metallic sheet  503   a , the second metallic sheet  504   a , the fifth metallic sheet  505   c , the sixth metallic sheet  506   a , the ninth metallic sheet  508   a  the fifteenth metallic sheet  509   d , the seventeenth metallic sheet  510   b , the twentieth metallic sheet  511   c , the twenty-first metallic  512   a , the twenty-fifth metallic sheet  513   b , the twenty-ninth metallic sheet  515   b , and the thirty-first metallic sheet  517   a  are all grounded metallic sheets. 
   The first terminal of the third matching transmission metallic line  501   c  and the first terminal of the second matching transmission metallic line  501   b  are electrically connected to the first terminal of the fourth matching transmission metallic line  501   a . The connecting point is the second node N 2  shown in  FIG. 1 . 
   The first through-hole connecting metallic sheet  521  penetrates the primary surfaces of the first layer  501 , the second layer  502 , the third layer  503 , the fourth layer  504 , the fifth layer  505 , and the sixth layer  506  to electrically connect the antenna input port P 1  with the first terminal of the first matching transmission metallic line  507   c . The fourth through-hole connecting metallic sheet  524  penetrates the primary surfaces of the seventh layer  507 , the eighth layer  508 , the ninth layer  509 , the tenth layer  510 , and the eleventh layer  511  to electrically connect the second terminal of the first matching transmission metallic line  507   c  with the second part  512   c   2  of the twenty-third metallic sheet  512   c . The connecting point is the first node N 1  shown in  FIG. 1 . The second part  512   c   2  of the twenty-third metallic sheet  512   c , the fifteenth metallic sheet  509   d , the twentieth metallic sheet  511   c , and the twenty-fifth metallic sheet  513   b  form an equivalent capacitor as the C 11  shown in  FIG. 1 . The first part  512   c   1  of the twenty-third metallic sheet  512   c  is the transmission line T 11  of the first band-pass filter shown in  FIG. 1 . The second through-hole connecting metallic sheet  522  penetrates the primary surfaces of the ninth layer  509 , the tenth layer  510 , and the eleventh layer  511  to electrically connect the fifth metallic sheet  509   d  with the first part  512   c   1  of the twenty-third metallic sheet  512   c . The connecting point is the ground terminal of the T 11  shown in  FIG. 1 . The second part  514   a   2  of the twenty-sixth metallic sheet  514   a , the twenty-fifth metallic sheet  513   b , the twenty-ninth metallic sheet  515   b , and the thirty-first metallic sheet  517   a  form an equivalent capacitor as the C 12  shown in  FIG. 1 . The first part  514   a   1  of the twenty-sixth metallic sheet  514   a  is the transmission line T 12  of the first band-pass filter shown in  FIG. 1 . The third through-hole connecting metallic sheet  523  penetrates the primary surfaces of the fourteenth layer  514 , the fifteenth layer  515 , and the sixteenth layer  516  to electrically connect the thirty-first metallic sheet  517   a  with the first part  514   a   1  of the twenty-sixth metallic sheet  514   a . The connecting point is the ground terminal of the T 12  shown in  FIG. 1 . The first part  512   c   1  of the twenty-third metallic sheet  512   c  and the first part  514   a   1  of the twenty-sixth metallic sheet  514   a  form an inductive coupling effect between top and bottom elements, which results in a coupling inductor L 1  of the first band-pass filter shown in  FIG. 1 . The tenth through-hole connecting metallic sheet  530  penetrates the primary surfaces of the first layer  501 , the second layer  502 , the third layer  503 , the fourth layer  504 , the fifth layer  505 , the sixth layer  506 , the seventh layer  507 , the eighth layer  508 , the ninth layer  509 , the tenth layer  510 , the eleventh layer  511 , the twelfth layer  512 , and the thirteenth layer  513  to electrically connect the second part  514   a   2  of the twenty-sixth metallic sheet  514   a  with the output port P 2  of the first band-pass filter. 
   The fourteenth through-hole connecting metallic sheet  534  penetrates the primary surface of the first layer  501 , the second layer  502 , the third layer  503 , the fourth layer  504 , the fifth layer  505 , the sixth layer  506 , the seventh layer  507 , the eighth layer  508 , the ninth layer  509 , the tenth layer  510 , the eleventh layer  511 , the twelfth layer  512 , the thirteenth layer  513 , and the fourteenth layer  514  to electrically connect the second terminal of the second matching transmission metallic line  501   b  with the twenty-eighth metallic sheet  515   a . The connecting point is the third node N 3  shown in  FIG. 1 . The twenty-eighth metallic sheet  515   a , the second part  513   a   2  of the twenty-fourth metallic sheet  513   a , and the thirtieth metallic sheet  516   a  form an equivalent capacitor as the input capacitor C 20   a  shown in  FIG. 1 . The sixteenth through-hole connecting metallic sheet  536  penetrates the primary surfaces of the thirteenth layer  513 , the fourteenth layer  514 , and the fifteenth layer  515  to electrically connect the thirtieth metallic sheet  516   a  with the second part  513   a   2  of the twenty-fourth metallic sheet  513   a.    
   The first part  513   a   1  of the twenty-fourth metallic sheet  513   a  is the transmission line T 21  of the second band-pass filter shown in  FIG. 1 . The eighteenth through-hole connecting metallic sheet  538  penetrates the primary surfaces of the thirteenth layer  513 , the fourteenth layer  514 , the fifteenth layer  515 , and the sixteenth layer  516  to electrically connect the thirty-first metallic sheet  517   a  with the first part  513   a   1  of the twenty-fourth metallic sheet  513   a . The connecting point is the ground terminal of T 21  shown in  FIG. 1 . The second part  513   a   2  of the twenty-fourth metallic sheet  513   a  and the twenty-first metallic sheet  512   a  form an equivalent capacitor. The thirtieth metallic sheet  516   a  and the thirty-first metallic sheet  517   a  form another equivalent capacitor. These two capacitors define an equivalent capacitor C 21 , as shown in  FIG. 1 . The first part  511   a   1  of the eighteenth metallic sheet  511   a  is the transmission line T 22  of the second band-pass filter shown in  FIG. 1 . The seventeenth through-hole connecting metallic sheet  537  penetrates the primary surfaces of the eighth layer  508 , the ninth layer  509 , and the tenth layer  510  to electrically connect the first part  511   a   1  of the eighteenth metallic sheet  511   a  with the ninth metallic sheet  508   a . The connecting point is the ground terminal of T 22  shown in  FIG. 1 . The first part  513   a   1  of the twenty-fourth metallic sheet  513   a  and the first part  511   a   1  of the eighteenth metallic sheet  511   a  form an inductive coupling effect between top and bottom elements, which results in a coupling inductor L 2  of the first band-pass filter shown in  FIG. 1 . The second part  511   a   2  of the eighteenth metallic sheet  511   a  and the twenty-first metallic sheet  512   a  form an equivalent capacitor. The twelfth metallic sheet  509   a  and the ninth metallic sheet  508   a  form another equivalent capacitor. These two capacitors define an equivalent capacitor C 22 , as shown in  FIG. 1 . The fifteenth through-hole connecting metallic sheet  535  penetrates the primary surfaces of the ninth layer  509  and the tenth layer  510  to electrically connect the second part  511   a   2  of the eighteenth metallic sheet  511   a  with the first part  509   a   1  of the twelfth metallic sheet  509   a . The sixteenth metallic sheet  510   a , the twelfth metallic sheet  509   a , and the second part  511   a   2  of the eighteenth metallic sheet  511   a  form an equivalent capacitor as the first input capacitor C 20   b  shown in  FIG. 1 . The nineteenth through-hole connecting metallic sheet  539  penetrates the primary surfaces of the first layer  501 , the second layer  502 , the third layer  503 , the fourth layer  504 , the fifth layer  505 , the sixth layer  506 , the seventh layer  507 , the eighth layer  508 , and the ninth layer  509  to electrically connect the seventeenth metallic sheet  510   b  with the output port P 3  of the second band-pass filter. 
   The eleventh through-hole connecting metallic sheet  531  penetrates the primary surfaces of the first layer  501 , the second layer  502 , the third layer  503 , the fourth layer  504 , the fifth layer  505 , the sixth layer  506 , the seventh layer  507 , and the eighth layer  508  to electrically connect the second terminal of the third matching transmission metallic line  510   c  with the thirteenth metallic sheet  509   b . The connecting point is the sixth node N 6  shown in  FIG. 1 . The twenty-second metallic sheet  512   b  is the transmission line T 31  of the third band-pass filter shown in  FIG. 1 . The ninth through-hole connecting metallic sheet  529  penetrates the primary surfaces of the ninth layer  509 , the tenth layer  510 , and the eleventh layer  511  to electrically connect the thirteenth metallic sheet  509   b  with the twenty-second metallic sheet  512   b . The thirteenth through-hole connecting metallic sheet  533  penetrates the primary surfaces of the twelfth layer  512  and the thirteenth layer  513  to electrically connect the twenty-second metallic sheet  512   b  with the twenty-seventh metallic sheet  514   b . The thirteenth metallic sheet  509   b , the seventeenth metallic sheet  510   b , the seventh metallic sheet  507   a , the sixth metallic sheet  506   a , the third metallic sheet  505   a , the second metallic sheet  504   a , and the sixth metallic sheet  506   a  form an equivalent capacitor which is the capacitor C 31  of the third band-pass filter shown in  FIG. 1 . The eighth metallic sheet  511   b  is the transmission line T 32  of the third band-pass filter shown in  FIG. 1 . The tenth metallic sheet  508   b , the seventh metallic sheet  507   a , and the thirteenth metallic sheet  509   b  form an equivalent capacitor. The fourteenth metallic sheet  508   c , the eighth metallic sheet  507   b , and the fourteenth metallic sheet  509   c  form another equivalent capacitor. These two capacitors define an equivalent coupling capacitor C 3  of the third band pass filter, as shown in  FIG. 1 . The seventh through-hole connecting metallic sheet  527  penetrates the primary surfaces of the fifth layer  505 , the sixth layer  506 , the seventh layer  507 , and the eighth layer  508  to electrically connect the fourteenth metallic sheet  509   c  with the fourth metallic sheet  505   b . The fourteenth metallic sheet  509   c , the seventeenth metallic sheet  510   b , the eighth metallic sheet  507   b , the sixth metallic sheet  506   a , the fourth metallic sheet  505   b , the second metallic sheet  504   a , and the sixth metallic sheet  506   a  form an equivalent capacitor which is the capacitor C 32  of the third band-pass filter shown in  FIG. 1 . The eighth through-hole connecting metallic sheet  528  penetrates the primary surfaces of the fifth layer  505  and the sixth layer  506  to electrically connect the third metallic sheet  505   a  with the seventh metallic sheet  507   a . The fifth through-hole connecting metallic sheet  525  penetrates the primary surfaces of the ninth layer  509  and the tenth layer  510  to electrically connect the fourteenth metallic sheet  509   c  with the nineteenth metallic sheet  511   b . The twelfth through-hole connecting metallic sheet  532  penetrates the primary surface of the tenth layer  510  to electrically connect the nineteenth metallic sheet  511   b  with the seventeenth metallic sheet  510   b . The sixth through-hole connecting metallic sheet  526  penetrates the primary surfaces of the first layer  501 , the second layer  502 , the third layer  503 , the fourth layer  504 , the fifth layer  505 , the sixth layer  506 , the seventh layer  507 , and the eighth layer  508  to electrically connect the fourteenth metallic sheet  509   c  with the output port P 4  of the third band-pass filter. 
     FIG. 7  shows an electromagnetic simulation result of an embodiment of the present invention. As shown in  FIG. 7A  for three different frequency bands, the insertion loss is smaller than 2.5 dB and the reflection loss is greater than 15 dB. The first band-pass filter at 900 MHz has a transmission zero at 2000 MHz. The second band-pass filter at 1800 MHz has a transmission zero at 2400 MHz. The third band-pass filter at 2400 MHz has a transmission zero between 1800 MHz and 1900 MHz. This means that the isolation is good among different frequency bands.  FIG. 7B  also shows that the isolation is greater than 20 dB among different frequency bands. The above results can be applied to the design of multimode RF modules. 
   In summary, the multilayer chip-type triplexer of the present invention provides the advantage of integrating multiple frequency bands. It can be widely applied in the industry. 
   Although the present invention has been described with reference to the embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.