Abstract:
A wireless communication module is proposed, in which an LTCC substrate is employed. The LTCC substrate comprises at least a first layer and a second layer. At least first and second communication elements are deposited on the first layer, and a matching network is embedded in the second layer. The matching network couple the first and second communication elements to provide matched impedance, such that radio frequency signals are transmitted without distortion. Specifically, the first layer is the surface of the LTCC substrate, whereas the second layer is a depth inside the LTCC substrate. The matching network comprises at least one inductance or capacitance buried in the second layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of Taiwan Patent Application No. 96143435, filed on Nov. 16, 2007, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to wireless communications, and in particular, to a wireless communication module having matching networks implemented on a Low-Temperature Cofired Ceramics (LTCC) substrate. 
         [0004]    2. Description of the Related Art 
         [0005]      FIG. 1  shows a conventional receiver comprising a plurality of wireless communication modules. The receiver is implemented based on printed circuit board (PCB) architecture. As the demand for wireless communication grows, various different wireless communication modules or systems such as 3.5G, GPS, WiFi and Bluetooth may be integrated in one mobile device such as a cell phone or a PDA. As shown in  FIG. 1 , there are multiple receivers  110   a  to  110   d  sharing one antenna  102 , and their functionalities are switched by a system switch  106 . Each receiver may be designed to process a plurality of channels. For example, the receiver  110   a  comprises a plurality of RF modules  115   a  to  115   n  each handling a different channel. One of the RF modules  115   a  to  115   n  is enabled by a channel switch  112  to receive the RF signal sent from the system switch  106 . An RE module  115   a  may comprise a low noise amplifier (LNA)  104 , a band pass filter (BPF)  116  and an antenna  102 . The LNA  104  amplifies the RF signal sent from the system switch  106 , and the BPF  116  filters the output from the LNA  104  to eliminate unwanted noise terms. Thereafter, the mixer  120  down converts the filtered signals to generate an intermediate signal or a baseband signal and outputs the signals for further processes such as digitalization in an ADC (not shown). The RF module  115   a  may further comprise many other essential components that can be found in prior arts, so detailed descriptions are not provided herein. 
         [0006]    In conventional architecture, impedance mismatch between the BPF  116  and the mixer  120  may degrade quality of signal transmission, thus, conventionally, a matching network  118  is deployed between the BPF  116  and the mixer  120  to compensate for impedance mismatch. The same problem occurs between the BPF  116  and LNA  104 , so a matching network  114  is also required to match their impedances. Generally speaking, impedance mismatch exists between any two elements in the RF modules  115   a  to  115   n , so matching networks are essential components in such an architecture. 
         [0007]    In the receiver  110   a , all the RF modules  115   a  to  115   n  are deposited on the surface of a PCB  111  using discrete components. The PCB  111  may be a multi-layered structure such as FR4. Due to natural limitations of materials, when all components are deposited together, circuit complexity, weight and area size are increased, and consequently, system stability and performance are influenced. As market requirements continue to trend toward more compact and light weighted products, the area size issue for a PCB  111  has become a technical bottleneck to be solved. 
         [0008]    Additionally, a matching network is typically formed by inductors and capacitors which are market offered components, and only specific parameters are available. A matching network implemented by the components of specific parameters is not flexible enough to fully compensate various impedance mismatches. For these reasons, an enhanced architecture for a circuit board is desirable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    An exemplary embodiment of a wireless communication module is implemented based on an LTCC substrate comprising at least first and second layers. First and second communication units are deposited at the first layer, and a matching network is deposited at the second layer, coupled to the first and second units to match impedances therebetween. In this way, signals are correctly transmitted to and from the first and second communication units. The first layer is at the surface of the LTTC substrate, and the second layer is at a depth inside the LTCC substrate. The matching network comprises at least an inductor or a capacitor embedded in the second layer. 
         [0010]    In one embodiment, the first and second communication units are selected from an LNA, a bandpass filter and a down conversion mixer. Alternatively, the first and second communication units may be selected from a power amplifier, a bandpass filter and an up conversion mixer. 
         [0011]    Another embodiment provides a wireless communication device, employing the same structure, comprising a plurality of receivers coupled to the antenna. At least one of the receivers is deposited on the LTCC substrate, comprising a plurality of RF modules each associated with a channel, and one of the RF modules comprises a first communication unit and a second communication unit deposited at the first layer, and a matching network deposited at the second layer. 
         [0012]    Further embodiments are transmitters and receivers employing the same structure. A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0014]      FIG. 1  shows a conventional communication device implemented based on a conventional PCB architecture; 
           [0015]      FIG. 2  shows an embodiment of a communication device implemented on an LTCC substrate; 
           [0016]      FIG. 3  is a cross-sectional view of the embodiment according to  FIG. 2 ; 
           [0017]      FIG. 4   a  shows an embodiment of a matching network  410 ; and 
           [0018]      FIG. 4   b  shows an embodiment of a matching network  420 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0020]    Low-Temperature Cofired Ceramics (LTCC) is a substrate material for circuit boards with electrodes made by silver, gold or copper. Passive elements such as capacitor, resistors, filters, matching networks and couplers can be buried inside the LTCC substrate using a parallel printed coating process in a 900 degrees centigrade debinding oven to organize an integrated ceramic product. 
         [0021]    LTCC technologies have been widely adopted because ceramic has similar material features with silicon, and is particularly suitable to be combined with integrated circuits. Area size is significantly reduced as well as the costs, and passive components are buried in a three-dimensional high density structure, so the modules made therefrom can be easily packaged. LTCC integrated components can be flexibly made into various substrate based or active/passive component embedded products, so the applicable product type covers a wide range comprising component, substrate or module. Because the LTCC substrate uses ceramic as the dielectric material which features high-Q and high frequency range, it is particularly adaptable for high frequency communication applications. 
         [0022]      FIG. 2  shows an embodiment of a communication device based on the LTCC architecture. The communication device mainly comprises a transmitter and a receiver. There may be a plurality of receivers ( 210   a  to  210   d ) each specifically designed for different communication applications such as WCDMA, GPS, WiFi or Bluetooth. Symmetrically, there may be a plurality of transmitters ( 230   a  to  230   d ) in the communication device. In the embodiment, the transmitters and receivers share one common antenna  102 . An RF switch  103  selectively switches the communication device between a transmitting mode and a receiving mode. In the receiving mode, an incoming RF signal is sent to one of the receivers  210   a  to  210   d  via a system switch  106 . Conversely, in the transmitting mode, an outbound RF signal is issued from one of the transmitters  230   a  to  230   d , and is sent to the RF switch  103  via the system switch  107  before transmission through the antenna  102 . 
         [0023]    In each of the receivers, there may be more than one RF modules for handling signals from different channels. As an example, the receiver  210   a  may comprise four RF modules  215   a  to  215   d , and a channel switch  112  selectively enabling one of the RF modules to receive RF signals from the system switch  106 . The channel switch  112  may not be an essential component in the embodiment, and the four RF modules may be able to operate concurrently. The RF modules  215   a  to  215   d  are made by LTCC substrates. Specifically, all the RF modules  215   a  to  215   d  may be deposited on one LTCC substrate. The LTCC substrate comprises at least two layers, the surface  221  and a depth inside  222 . General communication components such as an LNA  104   a , BPF  216   a  and mixer  218   a  are deposited on the surface  221 , and all the matching networks  212   a  and  214   a  are buried in the depth inside  222 . The matching network  212   a  is dedicated to compensate impedance mismatches between the LNA  104   a  and the BPF  216   a , and the matching network  214   a  is particularly adapted between the BPF  216   a  and the mixer  218   a . The communication components are not limited by  FIG. 2 , and any communication component that can be found in prior arts such as a variable gain amplifier (VGA) or a LPF is suitable for the structure disclosed in the embodiment. A matching network is an essential element between any two communication components, so any communication device with matching networks buried in the depth inside  222  belongs to the scope of the invention. 
         [0024]    As to the transmitters, there may also be a plurality of RF modules implemented in one transmitter. As an example, the transmitter  230   a  comprises a plurality of RF modules  225   a  to  225   d , each handling a different channel. In some applications, the transmitter  230   a  may use an RF switch  113  to selectively enable one of the RF modules  225   a  to  225   d  and output an outbound RF signal sent therefrom. Based on the LTCC structure, all the RF modules  225   a  to  225   d  are deposited on the same LTCC substrate, with components individually deposited at a surface  251  and a depth inside  252 . General communication components such as a power amplifier  105   a , BPF  236   a  and mixer  238   a  are deposited on the surface  251 , and all the matching networks  232   a  and  234   a  are buried in the depth inside  252 . In the embodiment, the matching network  232   a  is designed to match impedances between the power amplifier  105   a  and the BPF  236   a , and the matching network  234   a  is designed to match impedances between the BPF  236   a  and the mixer  238   a.    
         [0025]      FIG. 3  is a cross-sectional view of the embodiment according to  FIG. 2 , in which the RF modules  215   a ,  215   b  and  215   c  of  FIG. 2  are shown. The RF modules  215   a ,  215   b  and  215   c  are deposited on the same LTCC substrate  300 . In the RF module  215   a , the LNA  104   a , BPF  216   a  and mixer  218   a  are deposited on the surface  221  of the LTCC substrate  300 . Conversely, the matching network  212   a  and  214   a  are buried in the depth inside  222 . The matching network  212   a  is buried in a depth between the LNA  104   a  and BPF  216   a , coupled to both to compensate for their impedance mismatches. Likewise, the matching network  214   a  is embedded under somewhere between the BPF  216   a  and mixer  218   a , compensating impedance mismatches therebetween. Note that the same structure is applicable for RF modules  215   b  and  215   c , so further description is omitted. From the cross-sectional view, multiple RF modules from different receivers can also be arranged on the same LTCC substrate. Since the matching network  212   a ,  212   b ,  212   c ,  214   a ,  214   b , and  214   c  are buried inside the LTCC substrate, area size of the RF module  215   a ,  215   b  and  215   c  is efficiently reduced. The structure introduced in  FIG. 3  is also applicable for the transmitters  230   a  to  230   d , and the embodiment is similar to what was described previously. 
         [0026]      FIG. 4   a  shows an embodiment of a matching network  410 . In the depth insides  222  and  252  as shown in  FIG. 2 , the structures of matching networks  212   a  and  232   a  are illustrated as the matching network  410 , in which a inductor  402  and a capacitor  404  are deployed. The technique to bury the inductor  402  and capacitor  404  into the depth inside  222 , is deemed as a prior art of the LTCC processes. With the LTCC technique, the inductor  402  and capacitor  404  can be accurately made with parameters of any required value. While a conventional architecture can only use inductors and capacitors of fixed values, the embodiment of the invention benefits from accuracy of impedance matching. 
         [0027]      FIG. 4   b  shows an embodiment of a matching network  420 . The matching network  420  is a differential pair, particularly applicable for the matching network  214   a  and  234   a  deposited in the depth insides  222  and  252  of  FIG. 2 . The matching network  420  comprises three inductors, in which the inductor  406  is parallel to the inductor  412 , and the inductor  408  couples to both as a bridge. RF modules of different channels may require different parameters for impedance matching, and the inductors buried in the LTCC substrate can be accurately designed to achieve perfect impedance matching. 
         [0028]    The major concept of the invention is to bury matching networks of RF modules into the LTCC substrate of a wireless communication device, such that components on the surface can be overlapped to reduce area size. Based on the architecture, parameters of matching networks can be accurately implemented as required, surpassing the limitations of conventional fixed value components. Accuracy is efficiently increased while cost is significantly reduced. Although the embodiment in  FIG. 2  introduces a plurality of transmitters and receivers implemented together, the invention is not limited thereto. A single transmitter or receiver may also use the LTCC based architecture, with matching networks buried in the LTCC substrate. The communication protocol may include a wide variation such as WCDMA, CMDA2000, EV-DO&amp;EV-DV, EDGE, GPRS. GSM, WiFi, WiMAX, A-GPS, GPS, BT, RFID, UWB, SDR, DVHB, DAB, FM, and etc. 
         [0029]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.