Patent Publication Number: US-9900706-B2

Title: Microstrip filter and microphone device using same

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates to filter technologies, and more particularly, to a microstrip filter and a microphone device using the microstrip filter. 
     BACKGROUND 
     With development of wireless communication technologies, wireless communication apparatuses such as mobile phones, tablet computers, or the like, become more and more widely. Filters are used in the wireless communication devices for removing some unwanted frequency components from electrical signals to obtain frequency bands as desired. For example, a microstrip filter may be applied in a microphone device of the wireless communication apparatus for filtering noise components. 
     A typical microstrip filter is designed in a printed circuit board (PCB) in form of a buried capacitor or buried resistor. However, the above-mentioned microstrip filter has a high manufacturing cost and normally needs to occupy unduly large space in the wireless communication device, and moreover, a buried-resistor type microstrip filter is liable to suffer breakdown during an electro-static discharge (ESD) test of the PCB. In other words, the above-mentioned microstrip filter may be inapplicable to the microphone device of the wireless communication apparatus. 
     Therefore, it is desired to provide a microstrip filter and a microphone device using the microstrip filter which can overcome the aforesaid problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiment can be better understood with reference to the following drawings. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a planar, schematic view of a microstrip filter according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic view of a microphone device using the microstrip filter of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described in detail below with reference to the attached drawings and the embodiment thereof. 
     Referring to  FIG. 1 , a microstrip filter  100  according to an embodiment of the present disclosure is shown. The microstrip filter  100  may be applicable to a microphone device or other electronic device in a wireless communication apparatus. The microstrip filter  100  includes a substrate  11 , a first spiral metal line  12 , a second spiral metal line  13 , a first signal transmitting terminal  14  and a second signal transmitting signal  15 . 
     The substrate  11  may be a printed circuit board (PCB) substrate with two opposite surface, namely, a first surface and a second surface. The first spiral metal line  12  is formed on the first surface of the substrate  11 , and the second spiral metal line  13  is formed on the second surface of the substrate  11 . At least part of the first spiral metal line  12  overlaps the second spiral metal line  13 , as illustrated in  FIG. 1 . 
     The first signal transmitting terminal  14  is arranged at an end of the first spiral metal line  12 , and is electrically connected to the first spiral metal line  12 . The second signal transmitting terminal  15  is arranged at an end of the second spiral metal line  13 , and is electrically connected to the second spiral metal line  13 . Moreover, the first signal transmitting terminal  14  and the second signal transmitting terminal  15  are respectively located at two opposite edges of the substrate  11 . 
     In the present embodiment, both of the first spiral metal line  12  and the second spiral metal line  13  may be spiral copper lines, which are respectively formed by performing patterning process on copper foil layers of the substrate  11 . For example, a first copper foil layer and a second copper layer may be provided on the first surface and the second surface of the substrate  11 , and the first spiral metal line  12  and the second spiral metal line  13  may be formed by etching the first copper foil layer and the second copper foil layer respectively. 
     Because the second spiral metal line  13  is at least partly overlapped by the first spiral metal line  12 , the first spiral metal line  12  and the second spiral metal line  13  are coupled to each other and cooperatively form a filter capacitor. A capacitance of the filter capacitor can be designed to enable the microstrip filter  100  to have a desired frequency passband by adjusting an overlaying area of the first spiral metal line  12  and the second spiral metal line  13  or adjusting a thickness of the substrate  11 . For example, each of the first spiral metal line  12  and the second spiral metal line  13  may be designed to have an appropriate line width, an appropriate line pitch, or an appropriate shape. 
     For example, in the present embodiment as illustrated in  FIG. 1 , the first spiral metal line  12  and the second spiral metal line  13  are both configured as a rectangular spiral with a same line width and a same line pitch, and the first spiral metal line  12  and the second spiral metal line  13  are symmetrical to each other about an central axis of the substrate  11 . In other embodiment, the first spiral metal line  12  and the second spiral metal line  13  may alternatively have different line widths or different line pitches. 
     In the microstrip filter  100  according to the present disclosure, the filter capacitor is provided therein by forming the first spiral metal line  12  and the second spiral metal line  13  on the substrate  11 . Therefore, the microstrip filter  100  has a simple structure which can reduce a manufacturing cost thereof. Furthermore, because the spiral configuration of the first spiral metal line  12  and the second spiral metal line  13  can enable the microstrip filter  100  to occupy a smaller space, and thus meeting miniaturization requirement of a microphone device in which the microstrip filter  100  is applied. 
     Based on the above-described microstrip filter  100 , the present disclosure further provides a microphone device  200  as illustrated  FIG. 2 . The microphone device  200  includes a shell  21 , a circuit board  22 , a transducer  23 , an integrated circuit (IC) chip  24  and the microstrip filter  100 . 
     The shell  21  covers the circuit board  22  to form an accommodating space for accommodating the transducer  23  and the IC chip  24 . The transducer  23  and the IC chip  24  are both installed on the circuit board  22 , and are electrically connected with each other. The circuit board  22  may be a multi-layer circuit board, and the microstrip filter  100  is integrated into the circuit board  22  as a circuit layer of the circuit board  22 . As such, the microstrip filter  100  does not need to take up an extra space in the microphone device  200 , which is good for the miniaturization of the microphone device  200 . 
     The first signal transmitting terminal  14  of the microstrip filter  100  is electrically connected to the IC chip  24 , and the second signal transmitting terminal  15  of the microstrip filter  100  is grounded via the circuit board  22 . The IC chip  24  may be configured for performing signal processing on an electrical signal outputted by the transducer  23 , and an output signal of the IC chip  24  is further filtered by the microstrip filter  100 . The microstrip filter  100  provides a low impedance path for removing high frequency noise of the output signal to ground and allowing other frequency components to transmit through. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present embodiment have been set forth in the foregoing description, together with details of the structures and functions of the embodiment, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.