KR20000025853A - Apparatus for preventing an inner noise in a surface acoustic wave filter - Google Patents

Abstract

PURPOSE: An inner noise preventing apparatus of a surface acoustic wave filter is provided to improve a characteristic of the surface acoustic wave filter by forming a plurality of grooves at a bottom plane of the filter and coating a conductive metal film at the grooves and the bottom plane. CONSTITUTION: An inner noise preventing apparatus of a surface acoustic wave filter comprises a substrate(10) and a scratching part(30). On a top of the substrate(10) are formed a plurality of terminals(20) which comprises an input terminal(21), an output terminal(22) and a filter circuit. The scratching part(30) has a plurality of grooves which are formed at a bottom of the substrate(10) so as to have a triangle shape and are spaced apart from each other. A prevention material is installed in order to prevent a signal hit at a groove and at a bottom from being reflected inside again.

Description

Internal noise suppression device of surface acoustic wave filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal noise preventing device of a surface acoustic wave filter for preventing a part of a signal from being radiated inside and acting as a noise to a system in the process of applying an electric signal at an input side and transmitting a signal to an output side. By forming grooves at predetermined intervals on the bottom surface of the substrate on which the surface acoustic wave filter is installed and applying a sound absorbing material to the groove portion or applying a conductive metal film on the bottom surface of the substrate to minimize or minimize the signal radiated therein, The present invention relates to an internal noise preventing device of a surface acoustic wave filter capable of improving the characteristics of the surface acoustic wave filter and minimizing noise.

In recent years, with the rapid development of mobile communication and electronic devices, the performance and service functions of internal parts have been expanded more widely and widely, and at the same time, the use of mobile communication has increased.

In general, a circuit for selectively passing a frequency to express or measure a task or action in a system such as a mobile communication using a continuously varying physical quantity such as current or voltage, and can be a signal of a specific frequency band. Surface acoustic waves (SAWs) in the manufacture of analog filters to transmit without loss and to block signals of other unnecessary frequency bands, as well as to remove noise outside of a predetermined band or to separate frequencies into separate multiplexed signals. A filter is used.

The surface acoustic wave represents a state of waves transmitted along the surface of the substrate, and has a feature of rapidly attenuating in the depth direction. The SAW filter uses this feature as a frequency selective device.

That is, the SAW device temporarily forms a metal electrode on a highly insulative substrate and applies a piezoelectric twist to the substrate surface. This action causes a physical wave. Since the wave speed transmitting the SAW element surface is slower than the electromagnetic wave, it is used as a filter to temporarily delay an electric signal or pass only a specific frequency signal.

The SAW filter is a ceramic container that protects a semiconductor device or a function, and is formed in a package form that protects an internal circuit from a harmful environment and provides a means for dissipating heat generated therein and connecting it to the outside.

The SAW filter package thus formed is formed by Surface Mounted Technology (hereinafter referred to as SMT), and is suitably used for devices requiring wide band transmission such as CDMA cellular phones, wireless LANs, and video devices. do.

1 is a diagram schematically illustrating a configuration of a surface acoustic wave filter and a signal flow thereof according to the prior art.

Referring to the surface acoustic wave filter according to the prior art with reference to Figure 1, generally, the surface acoustic wave filter is a wafer (3) having a predetermined thickness (0.5 mm) as a piezoelectric element, and the aluminum on the wafer (3) It is made of an interdigital transducer (Interdigital Transducer) to form a metal film, such as a material to convert an electrical signal is applied to the input side to a mechanical signal;

An input IDT in which an IDT group is formed by interconnecting a plurality of IDTs to an input side to which an electrical signal is applied, and an output IDT in which an IDT group is formed to output a converted mechanical signal by interconnecting a plurality of IDTs to an output side; The remaining IDTs, except for the input / output IDTs, are formed not to be connected to each other.

Looking at the signal flow passing through the surface acoustic wave filter according to the prior art configured as described above in detail as follows.

First, a wafer 3 and a circuit constituting a SAW filter are provided on the wafer 3, and a plurality of terminals 4 are formed to be connected to each other. The terminal 4 has an input terminal ( 4a) and output terminal 4b are included.

Next, when an electrical input signal S1 is applied to the input terminal 4a from the outside, the input signal S1 is transmitted to the output terminal 4b through the surface or the inside of the wafer 3, most of the time. The input signal S1 proceeds along the surface of the wafer 3 and is transmitted to the output terminal 4b.

However, at least 10% of the input signal S1 is radiated into the wafer 3 by the bulk wave B1 and transmitted to the other terminals 2c, 2d, and 2e, not the output terminal 4b. This will cause noise in the system.

Here, the bulk wave (B1) refers to a portion of the input signal (S1) is radiated into the system, the bulk wave (B1) has a direct effect on the output IDT (2b), the other IDT (2) has an indirect effect.

Therefore, in the related art, the bulk wave B1 is a noise that prevents normal signal transmission between the input terminal 4a and the output terminal 4b, that is, a portion of the input signal S1 is radiated to the inside, so that the wafer 3 Due to the reflection on the bottom surface of the, it affects the terminals 4 other than the output terminal (4b) there is a problem that can interfere with the characteristics of the SAW filter can act as noise in the system.

The present invention has been made to solve the above problems of the prior art, the object of the present invention is due to the bulk wave of the electrical signal is input at the input stage of the SAW filter and the input signal is radiated to the inside while proceeding to the output stage In order to prevent normal signal transmission between input and output terminals of the SAW filter, a plurality of grooves are formed at predetermined intervals on the bottom surface of the SAW filter, and a signal hitting the groove portion or the bottom surface is reflected back to the inside. The present invention provides an internal noise preventing device of a surface acoustic wave filter capable of improving the performance of a system by minimizing or minimizing a bulk wave by applying a sound absorbing material or a conductive metal film to prevent it from becoming.

1 is a view showing the configuration and signal flow of the surface acoustic wave filter according to the prior art,

2 is a view illustrating a signal flow in a form in which a sound absorbing material is applied to a scratching part of an internal noise preventing device of a surface acoustic wave filter according to the present invention;

FIG. 3 is a diagram illustrating a signal flow in a form in which a conductive metal film is added to FIG. 2.

<Explanation of symbols on main parts of the drawings>

10: board 20: terminal

21, 22: input and output terminal 30: scratching unit

31: sound absorbing material 32: conductive metal film

S: input signal S1, S2: internal wave and surface wave

According to a first feature of the surface acoustic wave filter of the present invention for solving the above problems, a predetermined thickness is provided on a substrate having a predetermined thickness and a circuit connection between the substrate and the surface acoustic wave filter. A plurality of connecting portions formed at intervals and a plurality of connecting portions formed at regular intervals on the bottom surface of the substrate so that a part thereof is radiated to the inside during signal transmission from the input side to the output side connection portion along the surface of the substrate so as not to interfere with the signal transmission. And a reflection blocking portion provided with a prevention material for preventing a signal from hitting the groove or the bottom surface of the substrate and being reflected back to the inside while the groove is formed.

In addition, according to the second aspect of the present invention, the anti-reflective material is provided with a sound absorbing material is applied to the groove portion to remove the signal radiated into the substrate.

Lastly, according to the third aspect of the present invention, the anti-reflective material may further include a conductive metal film applied to the bottom surface of the substrate to ground the signal to remove the signal radiated into the substrate. do.

Hereinafter, an embodiment of an internal noise preventing device of a surface acoustic wave filter according to the present invention will be described with reference to the accompanying drawings.

2 is a view illustrating a signal flow in a form in which a sound absorbing material is applied to a scratching part of an internal noise protection device of a surface acoustic wave filter according to the present invention, and FIG. 3 is a signal flow in a form in which a conductive metal film is added to FIG. 2. This is the figure shown.

2 and 3, in order to connect the substrate 10 having a predetermined thickness, a circuit of a surface acoustic wave filter (hereinafter referred to as a SAW filter) and the substrate 10 to the upper portion of the substrate 10. It includes a plurality of terminals 20 including the input terminal 21 and the output terminal 22, and the scratching portion 30 is formed with a plurality of grooves at regular intervals in the form of a triangle on the bottom surface of the substrate 10 It is configured by.

In particular, when the signal hits the bottom surface or the groove of the substrate 10, the scratching part 30 is further provided with a preventive material in order to prevent the signal is reflected back.

Here, when the electrical input signal (S) is applied from the input terminal 21 is made of an internal wave (S1), that is, a bulk wave 10% or more of the portion of the input signal (S) is reflected inside, the internal The remaining portion except for the wave S1 is formed by the surface wave S2 traveling along the surface of the substrate 10.

In this case, when the input signal S is transmitted to the input terminal 21, most of the input signal S is normally transmitted to the output terminal 22 in the form of surface wave S2. However, the internal wave S1 except for the surface wave S2 is reflected in various forms inside the substrate 10 having a predetermined thickness to affect other terminals 20 including the output terminal 22. Can cause noise in the system.

Therefore, in order to minimize or almost eliminate such internal noise, the sound absorbing material 31 is applied to the groove of the scratching part 30 as an anti-reflective material, or in some cases, the lower portion of the substrate 10 is electrically conductive. The metal film 32 may be further applied to allow the internal wave S1 to be removed or grounded.

Looking at the operation of the internal noise protection device of the surface acoustic wave filter according to the present invention configured as described above are as follows.

First, when the input signal (S) is applied from the input terminal 21, the input signal (S) in the form of a surface wave (S2) traveling along the surface of the substrate 10, the output terminal 22 in the input terminal 21. Will be delivered. However, at least 10% of the input signal S is radiated in the form of an internal wave S1, that is, a bulk wave, into the substrate 10 having a predetermined thickness.

The internal wave S1 is reflected inside the substrate 10 in various forms, and each terminal as well as the output terminal 22 during the normal transmission of the signal from the input terminal 21 to the output terminal 22. Will affect (20). Therefore, the scratching part 30 having the grooves formed in the triangular shape on the bottom surface of the substrate 10 suppresses unnecessary reflection.

In addition, the scratching part 30 is coated with a sound absorbing material 31 to further suppress the reflection of the internal wave S1, thereby absorbing the internal wave S1 hitting the groove portion to absorb the internal wave S1. Can be effectively reduced, and furthermore, as shown in FIG. 4, when the conductive metal film 32 is additionally applied to the bottom surface of the substrate 10, the internal wave S1 is grounded. There is little or no bulk wave acting as noise in the system.

The internal noise preventing device of the surface acoustic wave filter according to the present invention configured as described above is a bulk wave in which a part of the input signal is radiated to the inside while an input signal is applied from the input terminal of the SAW filter and the signal is transmitted to the output terminal. In order to prevent normal signal transmission between the input and output terminals of the SAW filter, a plurality of grooves are formed on the bottom surface of the SAW filter at predetermined intervals, and at the same time, a signal hitting the groove portion or the bottom surface is returned to the inside. In order to prevent reflection, the sound absorbing material or the conductive metal film is coated to minimize or minimize the bulk wave, thereby improving the SAW filter characteristics.

Claims (3)

A substrate having a constant thickness, a plurality of connecting portions formed at predetermined intervals on top of the substrate for circuit connection between the substrate and the surface acoustic wave filter, and part of which is a signal transmission from the input side to the output side connection portion along the surface of the substrate Is formed inside a plurality of grooves on the bottom surface of the substrate at regular intervals so that the radiation is prevented from interfering with the signal transmission, and a prevention material for preventing a signal hitting the groove or the bottom surface of the substrate from being reflected back to the inside An internal noise preventing device of a surface acoustic wave filter comprising a reflection shield installed. The method of claim 1, The anti-noise material of the surface acoustic wave filter is characterized in that the sound absorbing material is added to the groove portion to remove the signal radiated into the substrate. The method according to claim 1 or 2, The anti-reflective material of the anti-reflective part is formed by applying a conductive metal film to the bottom surface of the substrate to ground the signal to remove the signal radiated into the substrate. Device.