KR20100134324A - Band pass filter and band reject filter - Google Patents

Abstract

PURPOSE: A band pass filter and a band reject filter is provided to form a band reject filter for the band of 2.4GHz by using the band pass filter. CONSTITUTION: A band reject filter comprises a bandpass filter(140) and a 90 degree hybrid coupler(120). The bandpass filter passes the signal of the predetermined frequency band. The 90 degree hybrid coupler is connected to the bandpass filter. The 90 degree hybrid coupler is composed of two port devices.

Description

Band pass filter and band cut filter {BAND PASS FILTER AND BAND REJECT FILTER}

The present invention relates to a band cut filter for suppressing signals of a desired frequency band or a band pass filter for passing only signals of a desired frequency band.

Many kinds of electronic devices, such as communication devices and multimedia devices, have a band cut filter and / or a band pass filter as analog elements. The band cut filter performs a function of suppressing signals of a frequency band, and the band pass filter performs a function of passing only signals of a desired frequency band.

Meanwhile, according to the convergence trend of mobile terminals, communication methods of various functions coexist in one device. Coexistence of these different communication methods requires minimizing mutual interference. For example, the WiFi communication in the 2.4GHz band and the 2.3GHz Wibro data communication cause mutual interference at the terminal due to the frequency characteristics adjacent to each other, which causes a call drop due to a decrease in the sensitivity of the data communication. You can.

In particular, in the case of a convergence terminal performing wireless communication using the adjacent frequencies as described above, the use of a band pass filter and / or a band cut filter is inevitably important.

However, in recent electronic devices, especially portable terminals, there are frequent changes in addition of functions, and it is necessary to meet different frequency allocation policies in each country. Accordingly, the frequency characteristics of the band pass filter and / or the band cut filter, which should be provided in the portable terminal, are changed from time to time and variously required.

From the point of view of a real product developer, designing filters having different characteristics from time to time will inevitably reduce the efficiency and speed of product development, and if the development speed of new products is slow, the risk of being ignored in the market increases.

The present invention seeks to provide a band pass filter or a band cut filter which can be easily designed according to the characteristics desired by the product developer.

A band cut filter according to an embodiment of the present invention includes a band pass filter for passing a signal of a predetermined frequency band; And a 90 degree hybrid coupler coupled to the band cut filter.

A band pass filter according to another embodiment of the present invention, a band cut filter for suppressing a signal of a predetermined frequency band; And a 90 degree hybrid coupler coupled to the band cut filter.

By implementing the band pass filter or the band cut filter of the present invention according to the above configuration, there is an advantage of reducing the filter design burden of the product developer.

In the case of a terminal in which Wibro (m-WiMAX) and Wi-Fi (WiFi) coexist, adjacent band blocking using a filter is required to minimize mutual interference. However, Wi-Fi communication and WiBro communication have considerably adjacent frequency bands. Therefore, when activating any one function, the use band of the function to be inactivated should be cut off, and the SAW (Surface Acoustic Wave) or FBAR (Film Bulk Acoustic Wave Resonator) having a sufficiently high Q value due to adjacent frequency characteristics is applied. Filters should be applied.

For example, in the case of the Mobile WiMAX module, a filter having a high Q band blocking characteristic for blocking the Wi-Fi band is required. In this case, the 2.4 GHz band pass SAW filter is used to implement the 2.4 GHz band rejection characteristic, thereby reducing mutual interference by removing the Industrial Scientific Medical (ISM) band.

1 illustrates a band cut filter according to an embodiment of the present invention for suppressing passage of signals of a predetermined frequency band.

The illustrated band cut filter includes a band pass filter 140 for passing a signal of a predetermined frequency band; And a 90 degree hybrid coupler 120 connected to the band pass filter 140.

The 90 degree hybrid coupler 120 is a two port device (ie, a four terminal device) and the band pass filter 140 has two terminals. As shown, two terminals (a, b) of the band pass filter 140 are connected to the output ports (C, D) of the 90-degree hybrid coupler 120.

The two terminals A and B constituting the input port of the 90 degree hybrid coupler 120 serve as two terminals of the band cut filter. That is, two terminals A and B which form an input port of the 90 degree hybrid coupler 120 are connected to a portion where the band cut filter is connected in the electronic circuit.

Next, the concept of the 90 degree hybrid coupler 120 of FIG. 1 is shown. The signal input from the A terminal is output to the C terminal and the D terminal, which is output as a signal delayed by 90 degrees from the D terminal. In addition, the signal input from the B terminal is output to the C terminal and D terminal, which is output as a signal that is 90 degrees out of phase from the C terminal. On the contrary, the signal input from the C terminal is output to the A terminal and the B terminal, which is output as a signal that is 90 degrees out of phase from the B terminal. In addition, a signal input from the D terminal is output to the A terminal and the B terminal, which is output as a signal delayed by 90 degrees from the A terminal.

2A and 2B show embodiments of the 90 degree hybrid coupler 120 of FIG. 1. The illustrated 90 degree hybrid coupler may have the form of a ladder-shaped micro strip or four parallel micro strips, and function as a 90 degree hybrid coupler in a band of several GHz or more. In the kHz band, a 90-degree hybrid coupler in the form of a transmission strip can also be implemented, but the volume is so large that it is not practical. In the kHz band, 90-degree hybrid couplers can be implemented using passive components such as inductors and capacitors.

Hereinafter, the principle of the band cut filter according to the spirit of the present invention will be described.

The signal input to the A terminal is transmitted to the C terminal and the D terminal, the signal of the band other than the specific band is reflected by the band pass filter 140. The reflected signal is transferred from the C terminal and the D terminal to the A terminal and the B terminal. Among the reflected signals, the signal of the D terminal is delayed by 90 degrees compared to the signal of the C terminal. Finally, the signal inputted to the A terminal first and reflected by the C terminal and the signal input to the A terminal and reflected by the D terminal are output to the A terminal, and both signals cancel each other because they have a 180 degree phase difference. This is because a phase delay of 180 degrees is generated by the 90 degree hybrid coupler 120 when the signal input to the A terminal and reflected from the D terminal is output to the A terminal.

On the other hand, a signal input to the terminal A first and reflected at the C terminal and the signal input to the first A terminal and reflected at the D terminal is finally output to the B terminal, and both signals are combined without being outputted with a phase difference. This is because both signals experienced the same 90-degree phase delay by the 90-degree hybrid coupler.

As a result, only signals of a band other than the specific frequency band among the signals applied to the A terminal are output to the B terminal, which is the same as the function of the band cut filter for the specific frequency band.

3 illustrates one embodiment of a band pass filter 140 that may be applied to the band cut filter of FIG. 1. The band pass filter shown is one of the general band pass filters, and can be replaced with other known band pass filters.

4 is a graph illustrating a relationship between a band pass filter and a band cut filter to be used in the present invention.

The characteristics of the 2.4 GHz band pass filter have a characteristic of a bandwidth of 50 MHz at 2.4 GHz as shown in the left figure. If a 90 degree hybrid coupler is combined, it can be seen that it has the characteristics of a band cut filter with a bandwidth of 50 MHz at 2.4 GHz as shown in the figure on the right.

5 illustrates a band pass filter according to an embodiment of the present invention for passing only signals of a predetermined frequency band.

The illustrated band pass filter includes a band cut filter 240 for suppressing a signal of a predetermined frequency band; And a 90 degree hybrid coupler 220 connected to the band cut filter.

The 90 degree hybrid coupler 220 is a two port element (ie, four terminals), and the band cut filter 240 has two terminals a and b. As illustrated, two terminals a and b of the band cut filter 240 are connected to the output ports C and D of the 90 degree hybrid coupler 220.

The two terminals A and B constituting the input port of the 90 degree hybrid coupler 220 serve as two terminals of the band pass filter. That is, two terminals A and B which form an input port of the 90 degree hybrid coupler 220 are connected to a portion where the band pass filter is connected in the electronic circuit. Embodiments of the 90 degree hybrid coupler 220 are the same as those of FIGS. 2A and 2B.

An embodiment of the band cut filter 240 constituting the band pass filter of FIG. 5 is shown in FIG. 6. Since the operating principle of the band pass filter of FIG. 5 can be easily inferred from the description of FIG. 1, detailed description thereof will be omitted.

Using the technique according to the spirit of the present invention described above, it is possible to easily convert the RF bandpass filter, which is generally widely used, into a band cut filter (or vice versa). This greatly reduces the filter design burden on the circuit manufacturer during the design process. For example, since the band pass filter required for the 2.4 GHz band is known in various structures, without the development of a separate band cut filter, to implement a cut filter for the 2.4 GHz band using a known band pass, using the Wi-Fi band The signal of can be removed. As a result, it is easy to design a convergence system with Wi-Fi / WiBro.

Although the technical spirit of the present invention has been described in detail according to the above embodiment, it should be noted that the above embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

1 is a block diagram illustrating a band cut filter in accordance with an embodiment of the present invention.

2A and 2B are plan views illustrating embodiments of a 90 degree hybrid coupler that may be used to implement the band cut filter of FIG.

3 is a circuit diagram illustrating one embodiment of a band pass filter that may be used to implement the band cut filter of FIG.

4 is a characteristic transformation graph for explaining the principle of the band pass filter according to the spirit of the present invention.

5 is a block diagram illustrating a band pass filter in accordance with another embodiment of the present invention.

FIG. 6 is a circuit diagram illustrating one embodiment of a band cut filter that may be used to implement the band pass filter of FIG. 5. FIG.

Claims (6)

A band pass filter for passing a signal of a predetermined frequency band; And 90 degree hybrid coupler connected to the band pass filter Band cut filter comprising a. The method of claim 1, The 90 degree hybrid coupler is a four terminal device, And a band pass filter connected to two output terminals of the 90 degree hybrid coupler. The method of claim 1, And said 90 degree hybrid coupler has a microstrip structure. A band cut filter for suppressing a signal of a predetermined frequency band; And 90 degree hybrid coupler connected to the band cut filter Band pass filter comprising a. The method of claim 4, wherein The 90 degree hybrid coupler is a four terminal device, And a band pass filter connected to two output terminals of the 90 degree hybrid coupler. The method of claim 4, wherein And said 90 degree hybrid coupler has a microstrip structure.

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