KR20100112262A

KR20100112262A - Balanced surface acoustic wave filter

Info

Publication number: KR20100112262A
Application number: KR1020090030683A
Authority: KR
Inventors: 박병훈
Original assignee: 주식회사 쏘닉스
Priority date: 2009-04-09
Filing date: 2009-04-09
Publication date: 2010-10-19

Abstract

Balanced surface acoustic wave filter according to an embodiment of the present invention is a sub-coupled ladder-type SAW IEF in which at least one or more IEs are connected in series and parallel alternately, the IE is two identical IDT and disposed on the piezoelectric plate And two identical grating reflectors disposed in the elastic channel having a desired resonant frequency, wherein the two pairs of busbars of the two identical IDTs are connected outside the elastic channel.

According to this configuration, a larger number of series and parallel IE electrodes can be provided between a pair of grating reflectors to provide a good impedance to reduce insertion loss, and the IE structure is a "reflector + IDT + IDT + reflector" structure. Compared with the conventional balanced surface acoustic wave filter, which is composed of repeating "reflector + IDT + reflector" structure, the structure size can be reduced as a whole, and it is designed to have no interacting IE, so that it can provide stable operation and long life, while miniaturizing can do.

Description

Balanced Surface Acoustic Wave Filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balanced surface acoustic wave filter (hereinafter, referred to as a balanced SAW filter). In particular, the present invention relates to a balanced type using only a ladder type SAW element capable of providing a stable operation and a long life, and miniaturization. The present invention relates to a balanced surface acoustic wave filter that provides input and output characteristics.

In general, a SAW device is used as a filter that forms a comb-shaped transducer with a metal electrode on a piezoelectric substrate and passes an electric field to delay electromagnetic waves or pass only a specific frequency signal.

The SAW filter has an interdigital transducer (IDT) installed at each of the input terminal and the output terminal. When an electrical signal is applied to the piezoelectric object at the input terminal, the SAW filter is converted into a mechanical signal. By converting the output, a specific frequency band is passed and the remaining frequency bands are blocked.

In particular, a balanced SAW filter is an in-phase filter designed so that the phases of the input signal and the output signal are the same in the vicinity of the center frequency and have almost the same amplitude, and the phases of the input signal and the output signal are approximately 180 ° different from the center frequency. Includes a designed reverse phase filter.

Balun for converting the output signal of the SAW filter into a balanced form in order to provide a balanced input / output characteristic in the case of a MMIC (Monolithic Microwave Integrated Circuit) and a mixer that require such a balanced input / output characteristic. Since there is a problem in that the size of the filter element is increased, there has been a problem to reduce the size of the SAW filter element by forming a function for converting input / output characteristics into a balanced form inside the SAW filter.

Such a balanced surface acoustic wave filter mainly has a configuration in which a plurality of IDTs are arranged horizontally, and thus, in-phase and reversed phases can be easily replaced, and thus, a hybrid type or amplitude balance composed of or including a DMS-type surface acoustic wave filter. ) And phase balance were studied as.

However, the particular importance of the performance of the balanced filter, one having passed through the attenuation has in the insertion loss and pass-band in the above history. These amplitude balance and phase balance are collectively called balance characteristics.

The amplitude balance is defined by the difference between the signal amplitude output from the output terminal (first balanced output terminal) of the in-phase filter and the signal amplitude output from the output terminal (second balanced output terminal) of the inverse filter, and this value is zero. If it is close to, the amplitude balance is judged to be good, and the amplitude balance unit is usually dB.

On the other hand, the phase balance is defined as the phase difference between the phase of the signal output from the first balanced output terminal and the signal output from the second balanced output terminal, and when this value is close to 180 °, it is determined that the phase balance is good.

This balance characteristic is frequency dependent, and the balanced filter is evaluated by how much the amplitude balance is close to 0dB and the phase balance is close to 180 ° in the pass band.

However, the DMS (Double Mode SAW) filter has the advantage of having a good attenuation in a specific A frequency region outside the pass band and hardly outputting unwanted frequencies, but with a high insertion loss, attenuation in a specific frequency B region outside the pass band. There is a problem that the filtering characteristics are greatly degraded due to poor.

Therefore, the present invention has been made to solve such a problem, and an object of the present invention is a ladder type so that attenuation degree is good outside all pass bands for a specific frequency band, low insertion loss in the pass band, and the overall size is reduced. It is to provide a balanced surface acoustic wave filter formed by cascading SAW IEF filters.

According to one embodiment of the invention, there is a larger number of series and parallel IE electrodes between a pair of grating reflectors to provide a good impedance to reduce the insertion loss, the IE structure is "reflector + IDT + IDT + Compared with the conventional balanced surface acoustic wave filter, which is composed of a "reflector" structure and a "reflector + IDT + reflector" structure, the structure can be reduced overall and designed to have no interactive IE, thereby providing stable operation and long life. It can be miniaturized while being able to do it.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

1 is a schematic circuit diagram of a balanced SAW IEF according to an embodiment of the present invention, and FIG. 2 schematically shows half of the geometry of a 1220 MHz balanced IEF according to an embodiment of the present invention.

As shown in FIG. 1, in a balanced SAW IEF 100 according to an embodiment of the present invention, two pairs of serial SAW IE (Impedance Element) IE 110 and parallel SAW IE 120 are connected in a ladder form. The balanced input voltage is applied to the serial SAW IE 110 and the parallel SAW IE 120, and the serial SAW IE 110 and the parallel SAW IE 120 do not form an IE as they interact with. Are arranged symmetrically so that independent resonance frequencies are provided.

As shown in FIG. 2, a balanced SAW IEF 100 according to an embodiment of the present invention has a SAW IE structure, for example, a SAW resonator structure having a configuration of “RFLT + IDT + IDT + RFLT”. It can be seen that it is a ladder type SAW filter.

The serial SAW IE 110 and the parallel SAW IE 120 each comprise two identical IDTs 103, 104 and two arranged in one elastic channel 102 having a desired resonant frequency on the piezoelectric plate 101. The same grating reflectors (RFLT) 105, 106. The busbars 107, 108 of the serial SAW IE 110 may be connected to the balanced ports of the balanced SAW IEF.

Balanced SAW IEF according to an embodiment of the present invention includes two identical arms (103, 104) and busbars (107, 108), between the serial SAW IE (110) and parallel SAW IE (120) Does not include IE as interacting otherwise.

In addition, the in-phase electrode fingers 103a and 104a may be connected between the serial SAW IE 110 and the parallel SAW IE 120 to be connected to the balanced port.

An input grounding metal pattern 109 connecting between at least one input ground terminal of the serial SAW IE 110 and the parallel SAW IE 120 and an output ground terminal thereof, and the bus bars 107 and 108 It may be connected to the metal pattern 109.

When there are a plurality of parallel SAW IEs 120, their connection points may be grounded 109a using a metal pattern. As such, when the metal pattern is used, the balance characteristic may be improved by providing a value of the common ground inductance close to zero.

An interdigital transducer (IDT) 103, 104 disposed on the surface of the piezoelectric plate 101, the interdigital transducer comprises an electrode finger 103 ', 104' made of a metal strip, and the electrode fingers 103 ', 104. ') Are coupled to conductive busbars 107 and 108, and the grating reflectors 105 and 106 are disposed in the elastic channels of the IDTs 103 and 104.

The electrodes of the grating reflectors 105, 106 may be short circuited and connected to one of the busbars 107, 108 of the IDT 103, 104.

Electrical terminals may be connected to the bus bars 107 and 108, and electrical terminals may be connected to two electrode fingers 103a and 104a of the in-phase of the electrode fingers 103 ′ and 104 ′.

That is, the elasticity across the electrode fingers 103 'and 104' of the IDTs 103 and 104 with a piezoelectric effect when a voltage is applied to the busbars 107 and 108 through the electrical terminal by this configuration. It can be seen that the surface acoustic wave is generated in both directions along the channel 102.

The aperture of the IDTs 103 and 104 is W, and the electrode period is P.

The grating reflectors 105, 106 are configured as a periodic system of planar electrodes disposed in the elastic channels 102 of the IDTs 103, 104, and the electrodes of the IDTs 103, 104 and the grating reflectors 105. 106 electrodes are made in parallel.

Meanwhile, two electrode fingers 103a and 104a in phase of the electrode fingers 103 'and 104' are also formed in parallel with the electrodes of the IDTs 103 and 104.

According to an embodiment of the present invention, the distance between the centers of the neighboring electrode fingers 103 'and 104' of the IDTs 103 and 104 connected to the input balanced electrical terminals is equal to 1.5 times the electrode period of the IDTs 103 and 104. The distances 103 and 104 between the centers of neighboring electrodes connected to the output balanced electrical terminals are equal to the electrode period of 0.5 times the IDT.

In addition, the present invention may be opposite to each other without being limited thereto.

As described above, if the distance between the centers of neighboring electrodes of the IDTs 103 and 104 connected to the input balanced electrical terminals is equal to 1.5 times the electrode period of the IDTs, the high voltage is applied because the maximum voltage is applied through the larger gap. It is advantageous to obtain.

In the balanced IE, as described above, the distance between the centers of the neighboring electrodes of the IDT connected to the input balanced electrical terminal is not 1.5 times the electrode period of the IDT, but the center of the neighboring electrodes connected to the output balanced electrical terminals. Although the distance can be operated even if the electrode period is not 0.5 times the IDT, in this case, since the electrode structures of the IDTs 103 and 104 will not be synchronized, the balance characteristic will be weaker than when the resonance and impedance states are synchronized.

As described above, the series SAW impedance element 110 and the parallel SAW IE 120 may be cascaded as a resonator structure to generate various resonance frequencies and reverse resonance frequencies.

As shown in FIG. 2, the balanced voltage applied to the input balanced electrical terminals is a periodic charge distribution (_ + _ + _ + _ +) to the electrodes in the electrode balanced IEs 103 and 104 of both arms. And the charge distribution generates (_ _ _ _) or (++++) at the electrode fingers 103a, 104a connected to the output balanced electrical terminals between the two IDTs 103, 104 It can be seen.

According to one embodiment of the invention, the total number of electrodes in the resonator is equal to the total number of electrodes in both arms of both IDTs 103 and 104. The impedance of each arm is equal to the two calculated impedances.

On the other hand, insertion loss refers to an output reduction for an input when passing through a filter or a specific circuit for a certain purpose, and the serial IE 110 has a low impedance Z and the parallel IE 120 is high in a predetermined passband. It can be seen that when the impedance Y has a small insertion loss when the input signal input through the bus bars 107 and 108 is output through the electrode fingers 103a and 104a.

[Equation 1]

As a result, it can be seen that the insertion loss of the surface acoustic wave IEF (Impedance Element Filter) 100 decreases when the impedance of the series resonator of the resonance frequency decreases or the impedance of the parallel resonator increases.

According to an embodiment of the present invention, two identical IDTs are disposed between the pair of grating reflectors 105 and 106 using the fact that the admittance of the IDT is equal to the parabolic function of the number of electrode fingers. By using the electrode fingers (103a, 104a) as an output terminal, it can be configured to have more than twice the number of electrode fingers in one elastic channel 102 compared to the prior art.

According to this configuration, since two IEs must be connected in a line to each arm, a conventional balanced IEF having a problem that the area occupied by the resonator must be quadrupled to obtain the same impedance, for example, two 'RFLT + IDT + RFLT' It is possible to provide a smaller size to obtain the same impedance as compared to the case of repeating the arrangement of '.

Fig. 3 shows an impedance simulation graph of the IE when the number of electrode fingers is 180 and when the number is 90.

Referring to FIG. 3, it can be seen that insertion loss is reduced due to better impedance distribution when the number of electrode fingers is larger in the serial SAW IE 110 and the parallel SAW IE 120.

In this case, the resistance loss can also be small.

4 is a graph illustrating a 1220 MHz balanced IEF frequency response according to an embodiment of the present invention.

1212MHz balanced IEF according to an embodiment of the present invention shows a low insertion loss even when both the input impedance and the output impedance is 200Ω, it can be seen that the insertion loss value more than twice lower than the conventional balanced IEF. have.

As such, according to an embodiment of the present invention, the 1220 MHz balanced IEF exhibits a smaller insertion loss, as shown in FIG. 2, wherein the grating reflector is electrically connected to the bus bar, and in-phase of the electrode fingers is in phase. This is because the number of electrodes is increased by using the electrode fingers as the output terminals.

5A illustrates a balanced bridge circuit diagram of a 1220 MHz balanced IEF in accordance with an embodiment of the present invention. 5B is a geometric layout of the balanced bridge filter of FIG. 5A.

5A and 5B, two balanced IEFs 231 and 232 may be included and used as a balanced bridge filter.

This balanced bridge filter comprises two balanced IEs 231 and 232 having a center frequency F1 or F2, the period of the IDT electrode being determined by the desired frequencies.

[Equation 2]

P = V / F1,2 (V is SAW speed)

As shown in FIG. 5B, in the balanced bridge SAW filter according to the exemplary embodiment of the present invention, a bus bar on one side of the elastic channel is directly connected to a balance input terminal, and a bus bar on the other side of the elastic channel is connected to a balanced output terminal. A first balanced IE arranged in parallel with the first balanced IE, and a bus bar at one side of the elastic channel is directly connected to a balanced output terminal, and a bus bar at the other side of the elastic channel is connected to a balanced input terminal. And a second balanced IE.

According to this configuration, since it has only two elastic channels, it can occupy twice as much space as the conventional balanced bridge filter.

FIG. 6 is a frequency response graph of a 1150 MHz balanced bridge filter composed of two balanced bridge filters of FIGS. 5A and 5B.

Even in this case, it can be seen that the balanced IEF according to an embodiment of the present invention exhibits low insertion loss and low resistance loss.

At this time, the resistance loss of the SAW filter can be reduced by making the metal thin films of the common bus bars 107 and 108 larger than the electrode thicknesses of the IDTs 231 and 232 and the great reflectors 241 and 242.

It is not preferable to increase the electrode thickness of the IDTs 231 and 232 and the grating reflectors 105 and 106 as the electrode thickness of the busbars 107 and 108, because a high process deviation may occur in the sensitive parameters of the SAW device. .

1 is a schematic circuit diagram of a balanced SAW IEF according to an embodiment of the present invention,

2 schematically illustrates half of the geometry of a 1220 MHz balanced IEF in accordance with one embodiment of the present invention.

Fig. 3 shows an impedance simulation graph of IE when the number of electrode fingers is 180 and when the number is 90, respectively.

Claims

At least two IEs are made by cascading ladder type SAW IEFs connected in series and parallel alternately,

The IE comprises two identical grating reflectors disposed in an elastic channel having two identical IDTs and a desired resonant frequency disposed on a piezoelectric plate, wherein two pairs of busbars of the two identical IDTs are connected outside the elastic channel. Balanced surface acoustic wave filter.

The method of claim 1,

Surface acoustic wave filter of one pair of the two pair of bus bar is grounded.

The method of claim 2,

The two pairs of busbars are balanced surface acoustic wave filters connected in a metal pattern.

The method of claim 2,

Balanced surface acoustic wave filter, wherein one of the two identical grating reflectors is electrically connected to a busbar.

The method of claim 3, wherein

And a desired resonant frequency band of said elastic channel is 1220 MHz.

The method according to any one of claims 1 to 5,

Balanced surface acoustic wave filter having a distance of 1.5 times the electrode period between the center of the adjacent electrode of the IDT on one side of the elastic channel, the distance between the center of the neighboring electrode of the IDT on the other side of the elastic channel has an electrode period of 0.5 times .

The method of claim 6,

A bus bar on one side of the elastic channel is directly connected to a balanced input terminal, and a bus bar on the other side of the elastic channel is connected to a balanced output terminal; A balanced surface acoustic wave filter comprising a second balanced IE having a bus bar at one side of the elastic channel connected directly to a balanced output terminal and a bus bar at the other side of the elastic channel connected to a balanced input terminal.

The method of claim 7, wherein

Balanced surface acoustic wave filter with eight IEFs.

The method of claim 7, wherein

The bus bar is a balanced surface acoustic wave filter having a thickness of a thin metal film than the IDT electrode and the electrode of the grating reflector.

The method of claim 1,

Balanced surface acoustic wave filter, the electrical terminal is connected to the two electrode fingers of the in-phase of the electrode of the busbar or the IDT.