KR100312494B1 - Inter-digital transducer having step electrode pad - Google Patents

Abstract

PURPOSE: An inter-digital transducer having a step electrode pad is provided to prevent a passing band of an undesired frequency in an approximation process to a structure of a withdrawal inter-digital transducer. CONSTITUTION: The first electrode pad(32A) is connected with an input line. The second electrode pad(32B) is connected with a ground voltage source(GND). A step pad(32C) generates a null point. A multitude of relay electrode bar(32D) is connected with the step pad(32C), the first electrode pad(32A) or the second electrode pad(32B). A multitude of signal electrode bar(32E) and a multitude of ground electrode bar(32F) are arranged on the first and the second electrode pads(32A,32B) and the step pad(32C). A filtering characteristic is improved by forming a filter coefficient using a multi-level withdrawal inter-digital transducer.

Description

Inter-Digital Transducer with Electrode Pad of Stairs

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Surface Acoustic Wave ("SAW") filters, and more particularly to an Inter-Digital Transducer, which converts an SAW into an electrical signal or an SAW. "IDT").

A typical SAW filter converts an electrical signal into a SAW and then converts the SAW into an electrical signal in order to detect only a desired frequency component from the electrical signal. The SAW filter is divided into an Apodization IDT method and a Withdrawal IDT method according to a converter for converting an electrical signal to SAW. These two IDT type SAW filters show significant differences in filtering characteristics and conversion gains.

In fact, the apodization IDT method SAW filter is composed of the apodization IDT 12 and the withdrawal IDT 14 opposed to each other with the blocking bar 10 interposed therebetween as shown in FIG. The apodization IDT 12 converts only an electrical signal of a specific frequency band into a SAW. To this end, the apodization IDT 12 includes a first electrode pad 12A connected to the input line 11, a second electrode pad 12B connected to the ground voltage source GND, and these electrode pads 12A, It consists of the first signal electrode bars 12C and the first base electrode bars 12D arranged between 12B. The first signal electrode bars 12C and the first base electrode bars 12D are long in the center of the electrode pads 12A and 12B and toward both sides of the electrode pads 12A12B to form a gain waveform that varies with frequency. Will be shortened. The first signal electrode bars 12C are commonly connected to the first electrode pad 12A, and the first base electrode bars 12D are commonly connected to the second ground pad 12B. In this way, the formed first signal electrode bars 12C and the first base electrode bars 12D may generate SAW by attracting or pushing each other on the first electrode pad 12A according to an electrical signal of a specific frequency band. . The generated SAW proceeds to the withdrawal wall IDT 14. Withdrawal IDT 14 converts the SAW into an electrical signal. To this end, the withdrawal IDT 14 includes a third electrode pad 14A connected to the output line 13, a fourth electrode pad 14B connected to the ground voltage source GND, and these electrode pads 14A, The second base electrode bars 14C and the second signal electrode bars 14D arranged between 14B) are formed. Unlike the first signal electrode bars 12C, the second signal electrode bars 14D have the same length, but the density of the second signal electrode bars 14D varies according to the area of the third electrode pad 14A. In detail, the second signal electrode bars 14D may be installed in the center of the third electrode pad 14A and become smaller toward both sides of the third electrode pad 14A, depending on the size of the gain according to the frequency. Meanwhile, the second base electrode bars 14C have the same length as the second signal electrode bars 14D, but have a density opposite to that of the second signal electrode bars 14D. In detail, the second base electrode bars 14C are installed at a small portion in the center of the fourth electrode pad 14B according to the magnitude of the gain according to the frequency, and are installed toward both sides of the fourth electrode pad 14B. The density of the second signal electrode bars 14D and the second base electrode bars 14C depends on the normalized gain value generated by normalizing the gain according to the frequency. The second signal electrode bars 14D and the second base electrode bars 14C are sensitive to the SAW from the apodization IDT 12 and thus have a specific frequency on the output line 13 connected to the third electrode pad 14A. The electrical signal of the band appears. In this way, the apodization IDT 12 has a very good filtering characteristic in the SAW filter using the apodization IDT 12, which responds only to an electrical signal of a specific frequency, on the input side. This is based on that the apodization IDT 12 is implemented in an analog synthesis scheme that can implement the filter coefficients in a 1: 1 ratio. However, in such a SAW filter, the conversion efficiency is very low due to the signal electrode bars and the base electrode bars whose length varies depending on the gain. In addition, the apodization IDT 12 includes apodization loss and diffraction loss in addition to bidirectional loss, metallic loss, and mismatch loss of a general delay line filter. It appears to be a problem.

FIG. 2 illustrates a withdrawal wall IDT SAW filter, which is composed of an input side withdrawal IDT 16 and an output side withdrawal IDT 14 opposed to an input side and an output side with a blocking bar 10 interposed therebetween. have. This withdrawal IDT type SAW filter reduces conversion of apodization and diffraction as compared to the apodization IDT 12 as shown in FIG. Has the disadvantage that the filtering characteristics are poor. In detail, in the SAW filter using the withdrawal wall IDT 16 on the input side, the electrical signal is converted into the SAW by the signal electrode bars and the base electrode bars having the same length, and thus the conversion efficiency becomes very high. However, the signal electrode bars and the base electrode bars of the same length are sensitive not only to the electrical signals of the specific frequency band but also to the electrical signals of the peripheral frequency band of the specific frequency band, so that the withdrawal IDT 16 of the SAW filter is used. The filtering frequency characteristic is markedly inferior to that of the SAW filter used at the input side of the apodization IDT. This problem occurs by default, withdrawal IDT (16) is implemented by the digital synthesis method (approximately using 1 and 0) to match the integral value of the filter coefficients, so that the passband at an unwanted frequency It is easy to occur. In addition, in the conventional SAW filter, although not shown in the drawing, a sound absorbing agent is applied to absorb the SAW leaking to the back of the input side and the output side IDT and thereby minimize the deterioration of the characteristics. However, since the sound absorbing agent is applied on the back of the input side and the output side IDT, it becomes a factor to limit the thinning of the SAW filter, and since the absorption efficiency is not satisfactory, the reflected wave is generated from the sound absorbing agent and the output side passes through the IDT on the input side. The phase difference is generated in the signal detected by the IDT.

Therefore, there is a need for a method capable of minimizing deterioration of filtering characteristics by reflected waves by improving IDT which can improve frequency response characteristics and conversion efficiency by reducing losses due to approximate loss of withdrawal IDT. .

Accordingly, it is an object of the present invention to provide an inter-digital converter having stepped electrode pads to prevent passbands of unwanted frequencies that occur when approximating with a withdrawal IDT structure.

It is another object of the present invention to provide an inter-digital converter having a stepped electrode pad that facilitates the design of an accurate filter by reducing an error generated when approximating the withdrawal IDT structure.

It is still another object of the present invention to provide an inter-digital converter having a stepped electrode pad to improve conversion efficiency by reducing apodization loss generated when implementing a filter with an apodization IDT structure.

It is still another object of the present invention to provide an inter-digital converter having a stepped electrode pad which improves the efficiency of the sound absorbing agent by sufficiently securing the distribution area of the sound absorbing agent for absorbing reflected waves.

1 and 2 schematically show a conventional SAW filter.

3 is a diagram schematically showing a sonic transformation having stepped electrode patterns according to a first embodiment of the present invention;

4 is a characteristic diagram showing the aperture size of a withdrawal inter-digital transducer (IDT) with zero-crossing of filter coefficients.

FIG. 5A schematically illustrates a sonic transformation having stepped electrode patterns according to a second exemplary embodiment of the present invention. FIG.

FIG. 5B schematically illustrates a sonic transformation having stepped electrode patterns according to a third exemplary embodiment of the present invention. FIG.

<Description of Symbols for Main Parts of Drawings>

12: apodization IDT 12A, 32A, 42A, 52A: first electrode pad

12B, 32B, 42B, 52B: second electrode pad 12C, 14D: signal electrode bar

12D, 14C, 32F: Base electrode bar 14,16: Withdrawal IDT

14A: third electrode pad 14B: fourth electrode pad

32C, 42C, 52C: Stair pad 32D, 42D, 52D: Relay electrode bar

34,36: Sound Absorbers

In order to achieve the above object, an inter-digital converter having a stepped electrode pad of the present invention is divided on an arbitrary piezoelectric substrate and a portion where a null point occurs in a filter coefficient, and is formed on the piezoelectric substrate by forming a step in each region. And a patterned stepped electrode pad and an electrode bar pattern connected to the stepped electrode pad to convert electrical signals into surface acoustic waves.

Other objects and advantages of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, with reference to Figures 3 to 5 attached to an embodiment of the present invention will be described in detail.

3 shows an inter-digital converter having a stepped electrode pad according to a first embodiment of the present invention. 3 illustrates an input side IDT for converting an electrical signal into a surface acoustic wave in an inter-digital converter having a stepped electrode pad of the present invention.

In the configuration of FIG. 3, the inter-digital converter having the stepped electrode pads of the present invention includes a first electrode pad 32A connected to an input line 31 and a second electrode pad connected to a ground voltage source GND. 32B, stepped pads 32C separated into portions in which null points occur, and forming stepped steps, stepped pads 32C, first electrode pads 32A, or second electrode pads. The relay electrode bars 32D connected to the 32B, the signal electrode bars 32E and the base electrode bars 32F arranged on the first and second electrode pads 32A and 32B and the stepped pads 32C. It consists of).

To obtain the desired filter characteristics, first, the filter coefficients of order N are found by using a finite impulse response method, which is one of digital design methods. Then, the obtained N + 1 filter coefficients are implemented using affirmation or withdrawal IDT. The stepped pads 32C may be divided into portions in which null points are generated in a filter coefficient having a sink function form as shown in FIG. 4, so that the first and second electrode pads 32A, approx. 32B) between the center and the narrower to both sides. With this structure, the signal electrode bars 32E and the base electrode bars 32F connected to the first electrode pad 32A, the second electrode pad 32B, or the stepped pads 32C are nulled in the filter coefficient. The point is generated as a multi-step withdrawal IDT to approximate the gain waveform that varies with frequency. Therefore, the inter-digital converter having a stepped electrode pad of the present invention is divided into null points of filter coefficients, and is composed of a multi-step withdrawal wall consisting of signal electrode bars 32E and base electrode bars 32F that are shortened from both sides to the center portion. It consists of IDT. In contrast to the conventional withdrawal IDT structure, the withdrawal IDT of the related art approximates each value of the sink function to two levels of 0 and 1, resulting in a drop in filtering characteristics, but in the present invention, between 0 and 1 Since the filter has a withdrawal IDT structure having an intermediate level (for example, a level of 0.5), filtering characteristics are improved. In detail, when the filter coefficient has a shape as shown in FIG. 4, N + 1 coefficients have M zero crossing points. These filter coefficients are classified into M-1 regions with zero crossing and the maximum value in each region is calculated. As the approximation is performed using the maximum values 1, a, b, and c of each region, a multi-step withdrawal IDT is formed. Accordingly, by implementing the filter coefficients using the multi-stage withdrawal IDT, the present invention improves the filtering characteristics and reduces the apodization loss and the diffraction loss generated when the conventional apodization IDT structure is implemented. Can improve.

5A and 5B show the second and third embodiments of the present invention.

Referring to FIG. 5A, an inter-digital converter having a stepped electrode pad according to a second embodiment of the present invention includes a multi-stage withdrawal IDT divided by a null point of a filter coefficient, and a first or second electrode pad at an input end thereof. And a sound absorbing agent 34 applied over the relay electrode bars 42D connected between the 42A and 42B and the stepped pads 42C.

The sound absorbing agent 34 is applied to this area because a spare area exists between the first electrode pad 42A or the second electrode pad 42B and the stepped pads 42C. Since the sound absorbing agent 34 is applied to both sides in close proximity to the stepped pads 42C, the sound absorbing material 34 can improve the sound absorbing efficiency.

In the configuration of FIG. 5B, the inter-digital converter having the stepped electrode pads according to the third embodiment of the present invention has a first electrode pad 52A, a second electrode pad 52B, and relay electrode bars 52D at an input terminal. It is provided with a sound absorbing agent 36 is applied to remove. In this case, it has a simpler structure than the second embodiment of the present invention shown in FIG. 5A and a sound absorbing agent 36 is applied to the input terminal. At this time, the upper stepped pads 52C at the input end are connected to each other so that the signal voltage can be supplied from the input line, and are connected to the first electrode pad 52A, and the lower stepped pads 52C are at the bottom. They are connected to each other so that the voltage GND can be supplied, and are connected to the second electrode pad 52B.

As can be seen in the second and third embodiments of the present invention, the inter-digital transducers having the stepped electrode pads of the present invention take the structure of a multi-stage withdrawal IDT to absorb sound absorbers 34 and 36 in the free space. By coating, the reflected wave can be minimized to improve the filter characteristics.

As described above, the inter-digital converter having a stepped electrode pad according to the present invention can prevent the passband of the frequency generated when approximating the conventional withdrawal IDT structure.

The inter-digital transducer with stepped electrode pads of the present invention provides the ease of designing an accurate filter by reducing errors.

The inter-digital converter having the stepped electrode pad of the present invention can improve conversion efficiency by reducing apodization loss and diffraction loss generated when a filter is implemented with a conventional apodization IDT structure.

The inter-digital converter having the stepped electrode pad of the present invention can improve the performance of the filter by sufficiently securing the distribution area of the sound absorbing agent for absorbing the reflected wave.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (6)

Signal electrode pads supplied with a specific signal voltage by being stepped to form a step to have an opening approximated to an absolute maximum value of the frequency filter coefficients in each region divided by a portion where a null point occurs in the frequency filter coefficients. A base electrode pad patterned in steps so as to be symmetrical with the signal electrode pad and supplied with a base voltage, and a signal electrode bar pattern positioned between the signal electrode pad and the base electrode pad and connected to the signal electrode pad; A surface acoustic wave formed between the signal electrode pad and the base electrode pad and connected to the base electrode pad, and the signal electrode pad, the base electrode pad, the signal electrode pattern, and the base electrode bar pattern. Comprising a piezoelectric substrate for transmitting the signal electrode bar pattern and the base electrode The pattern having a step-like internal electrode pad, characterized in that for converting a signal from the signal electrode pad in the surface acoustic wave-digital converter. The inter-digital converter having a stepped electrode pad according to claim 1, wherein the signal electrode bar pattern and the base electrode bar pattern are capable of inverting the surface acoustic wave into the electrical signal. The inter-digital converter having a stepped electrode pad according to claim 1, wherein the signal electrode bar pattern and the base electrode bar pattern have different lengths in units of the region. The method of claim 1, wherein the signal electrode pad and the base electrode pad are disposed between the first electrode pad to which the specific signal voltage is supplied, the second electrode pad to which the base voltage is supplied, and the first and second electrode pads. A relay pad patterned to form a step so as to have a height approximated to an absolute maximum value of the frequency filter coefficient for each of the regions, the first electrode pad and the relay pad, and the second electrode pad and And a relay electrode bar pattern for connecting the relay pad to supply the specific signal voltage and the ground voltage to the relay pad. The display device of claim 1, wherein the signal electrode pad and the base electrode pad are connected to a first electrode pad supplied with the specific signal voltage, a second electrode pad supplied with the base voltage, and the first and second electrode pads. And a relay pad patterned to form a step to have a height approximated to an absolute maximum value of the frequency filter coefficient for each region. The inter-digital converter having a stepped electrode pad according to claim 1, further comprising a sound absorbing agent applied adjacent to the stepped signal electrode pad and the base electrode pad to absorb leakage of the surface acoustic wave.