Transmission and reception switching device using thin film piezoelectric resonator

[Technical Field to which the Invention Belongs] The present invention belongs to the technical field of communication equipment, and particularly relates to a transmission / reception switch using a thin film piezoelectric resonator.

[0002] [Problems to be Solved by Conventional Techniques and Inventions] The RF circuit portion of a cellular telephone is always required to be miniaturized. Recently, in order to increase the mounting density in equipment, there is a strict demand for height reduction especially for the RF circuit unit, and therefore, the components constituting the RF circuit unit are also required to have a low height. In addition, each component is required to be composed of a single component as much as possible so that it can be manufactured at low cost. In particular, the transmission / reception switch, which is one of the components constituting the RF circuit unit, is required to have a withstand power, and it is necessary not to cause destruction or deterioration of characteristics with respect to the power supply.

[0003] Currently, this transmission / reception switch uses a ceramic filter or a SAW (surface acoustic wave) filter. Ceramic filters can be monolithic and are inexpensive, but the loss of the resonator is large, and a dimension of about 23 x 7 x 5 mm is required to cover it, which fully meets the demand for height reduction. I can't. On the other hand, although the SAW filter is small, it has a problem in withstand power at high frequencies, and may fail if a surge occurs in the output power of transmission. Further, in order to improve the characteristics, it is possible to configure a circuit in which an electronic switch is used in combination, but in that case, the circuit configuration becomes complicated and expensive.

[0004] In view of such circumstances, Japanese Patent Application Laid-Open No. 2001-24476 describes the use in applications such as CDMA-PCS devices in which the transmission band and the reception band are less separated and a higher power level is required. A transmit / receive switch that enables it has been proposed. This transmission / reception switch is composed of three parts: a transmission band filter, a reception band filter, and a 90-degree phase shifter. The 90 degree phase shifter is separate from the thin film piezoelectric resonator (abbreviated as FBAR) that composes each filter, and consists of passive components of the inductor and capacitor. is there. Therefore, it is difficult to make the transmission / reception switch described in Japanese Patent Application Laid-Open No. 2001-24476 monolithic, and it is difficult to sufficiently reduce the cost. It is also possible to form a 90-degree phase shifter for this transmission / reception switch with a transmission line, but in that case, a length of at least a dozen mm is required, which requires a considerably larger space than a filter. Not suitable for miniaturization.

[0005] The present invention has been made in view of the above circumstances, and the structure of the connection portion between the transmission filter and the reception filter can be miniaturized, and the transmission filter and the reception filter are monolithic. It is an object of the present invention to provide a small and inexpensive transmission / reception switching device having good power withstand power by enabling the conversion.

[Means for Solving the Problems] According to the present invention, a transmission port, a reception port, and a transmission / reception shared port are used to achieve the above object; between the transmission port and the transmission / reception shared port. A transmission band that includes a first ladder-type circuit that is connected to and includes a first series element consisting of a thin film piezoelectric resonator and a first divergence element consisting of a thin film piezoelectric resonator. With a filter; a second ladder type connected between the receiving port and the transmitting / receiving shared port and provided with a second series element composed of a thin film piezoelectric resonator and a second shunt element composed of a thin film piezoelectric resonator. In a transmission / reception switch that includes a circuit and includes a reception band filter having a reception / passage frequency band that does not overlap with the transmission / passage frequency band, the transmission / reception shared port, the first shunt element, and the said. It is provided with at least one adjusting thin film piezoelectric resonator connected between the second shunt element, and the resonance frequency of the adjusting thin film piezoelectric resonator is the transmission passing frequency band and the receiving passing frequency band. A transmission / reception switch, characterized in that it is set between the two, is provided.

[0007] In one aspect of the present invention, the adjusting thin film piezoelectric resonator is connected between the transmission / reception shared port and the ground, and the first shunt element and the second shunt element are It is connected to the ground.

[0008] In one aspect of the present invention, the transmission pass frequency band is lower than the reception pass frequency band, and the resonance frequency of the adjustment thin film piezoelectric resonator is the upper limit frequency of the transmission pass frequency band and the reception pass frequency band. It is set between the lower limit frequency of.

[0009] In one aspect of the present invention, the transmission band filter includes at least one inductor that enhances the attenuation characteristics on the higher frequency side than the transmission pass frequency band. In one aspect of the invention, the inductor is connected in parallel to some of the first series elements. In one aspect of the invention, one end of the inductor is connected to the transmit port.

[0010] In one aspect of the present invention, the reception band filter includes at least one capacitor that enhances the attenuation characteristic on the low frequency side of the reception pass frequency band. In one aspect of the invention, the capacitors are connected in parallel to some of the second series elements. In one aspect of the invention, one end of the capacitor is connected to the receiving port.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] FIG. 1 is a block diagram showing a configuration of an embodiment of a transmission / reception switching device of the present invention. In FIG. 1, the transmission / reception switch 100 includes a transmission band filter 110, a reception band filter 130, and a thin film piezoelectric resonator 150 for adjustment. One end of the transmit band filter 110 is connected to the first port (transmit port) 102, and one end of the receive band filter 130 is connected to the second port (receive port) 104. The other end of the transmission band filter 110 and the other end of the reception band filter 130 are connected to a third port (antenna port as a transmission / reception shared port) 106. The conditioning thin film piezoelectric resonator 150 has one end connected to the antenna port 106 (ie, the other end of the transmit band filter 110 and the other end of the receive band filter 130) and the other end connected to ground. Has been done. The transmit port 102 is connected to the transmit circuit, the receive port 104 is connected to the receive circuit, and the antenna port 106 is connected to the transmit / receive antenna ANT.

FIG. 2 is a circuit configuration diagram of the transmission / reception switch 100 of the present embodiment. The thin film piezoelectric resonator 150 for adjustment is arranged so as to connect the transmission band filter 110 and the reception band filter 130. The transmission band filter 110 and the reception band filter 130 both include a plurality of thin film piezoelectric resonators (FBARs).

[0014] Here, the thin film piezoelectric resonator will be briefly described.

[0015] FIG. 3 is a schematic plan view of the thin film piezoelectric resonator, and FIG. 4 is a sectional view thereof XX. The thin film piezoelectric resonator 10 has a substrate 16 having a through hole 14 that vertically penetrates between an upper surface and a lower surface to form an air gap, and an end that forms a through hole opening on the upper surface of the substrate 16. It has a piezoelectric stack 22 in a form in which a peripheral portion is supported by an edge and suspended. The piezoelectric stack 22 is composed of a piezoelectric layer 12 and electrode layers 18 and 20 bonded to both upper and lower surfaces thereof. Terminals 26 and 28 are attached to the electrode layers 18 and 20, respectively, and a power supply is connected to the terminals 26 and 28, respectively. In the piezoelectric resonator stack 22, the piezoelectric layer 12 expands and contracts in the direction indicated by the arrow 24 in response to the voltage applied between the electrode terminals 26 and 28.

[0016] The piezoelectric layer 12 has a piezoelectric material that can be produced as a thin film such as zinc oxide (ZnO) or aluminum nitride (AlN). The electrode layers 18 and 20 may be made of, for example, gold (Au), molybdenum (Mo), or aluminum (Al). The substrate 16 is, for example, silicon (Si), SiO.₂ , GaAs, or a material such as glass.

The piezoelectric resonator stack 22, which is composed of a laminate of the piezoelectric layer 12 and the electrode layers 18 and 20, is suspended at its peripheral edge, and both of its main surfaces are exposed to air or other ambient gas or vacuum. I'm in contact. In this case, the piezoelectric resonator stack 22 forms a sound resonator with a high Q. The AC signal applied to the electrode layers 18 and 20 via the terminals 26 and 28 has a frequency equal to the speed of sound in the piezoelectric resonator stack 22 divided by twice the weighted thickness of the stack 22. .. That is, f_r = c / 2t₀ (Here, f_r Is the resonant frequency, c is the speed of sound in stack 22, and t₀ Is the weighted thickness of the stack 22), the AC signal causes the piezoelectric resonator stack 22 to resonate. Since the speed of sound in the layers constituting the stack 22 is different for each material constituting each layer, the resonance frequency of the piezoelectric resonator stack 22 is not the physical thickness but the speed of sound in the piezoelectric layers 12 and the electrode layers 18 and 20. It is determined by the weighted thickness considering their physical thickness.

FIG. 5 is a schematic cross-sectional view of a thin film piezoelectric resonator different from that of FIGS. 3 and 4. This example is similar to that of FIGS. 3 and 4 except that the acoustic impedance transducer 30 is used instead of the air gap formed by the through hole 14. Such thin-film piezoelectric resonators are described in, for example, WE Newell's "Face-Mounted Piezoelectric Resonators" paper (Proceedings of the IEEE, pp.575-581, June 1965).

FIG. 6 shows an element equivalent circuit of the thin film piezoelectric resonator 10 as described above. The series resonance of the resonator is equivalent inductance (L)_m ) And equivalent capacitance (C)_m ). The impedance of the series resonant frequency of this resonator is low (ie, ideally, the resonator acts like a shunt with no loss at all). At frequencies lower than this series resonance frequency, the impedance of the thin film piezoelectric resonator 10 is capacitive. Higher than this series resonance frequency and equivalent capacitance (C₀ ), The impedance of the thin film piezoelectric resonator 10 is inductive at frequencies lower than the parallel resonance frequency. Also, at frequencies higher than the parallel resonance frequency, the impedance of the thin film piezoelectric resonator 10 has capacitance again, at the parallel resonance frequency the impedance of the resonator becomes high, and in an ideal system without loss, the impedance becomes infinite, similar to an open circuit. ing. In the present invention, by utilizing the change in impedance before and after the series resonance frequency of the thin film piezoelectric resonator 150 for adjustment, the configuration of the transmission / reception switch is made simple and compact as described below.

[0020] The transmission band filter 110 and the reception band filter 130 will be described in more detail with reference to FIG. 2 again.

[0021] The transmission band filter 110 is connected so as to form a ladder type circuit by a series resonance element 111,113,115 composed of a thin film piezoelectric resonator and a shunt resonance element 112,114 composed of a thin film piezoelectric resonator (2 + 1/2). ) Stage band filter. Ladder circuits are a common technique for forming band filters using piezoelectric resonators. The series resonant elements 111,113,115 are connected between the first port (transmission port) 102 and the third port (antenna port) 106. The shunt resonance element 112 connects between the ground and the node 117 between the series resonance elements 111 and 113. The shunt resonance element 114 connects the ground and the node 118 between the series resonance elements 113 and 115.

The reception band filter 130 is a three-stage band filter connected so as to form a ladder type circuit by a series resonance element 131,133,135 composed of a thin film piezoelectric resonator and a shunt resonance element 132,134,136 composed of a thin film piezoelectric resonator. .. The series resonant elements 131,133,135 are connected between the second port (reception port) 104 and the third port (antenna port) 106. The shunt resonance element 132 connects the ground and the node 137 between the series resonance elements 131 and 133. The shunt resonance element 134 connects the ground and the node 138 between the series resonance elements 133 and 135. The shunt resonance element 136 connects the ground and the second port (reception port) 104.

[0023] The adjusting thin film piezoelectric resonator 150 is connected to a third port at one end (that is, at the connection portion between the series resonance element 111 of the transmission band filter 110 and the series resonance element 131 of the reception band filter 130. (Connected), and the other end is connected to ground.

[0024] The adjusting thin film piezoelectric resonator 150 functions as a shunt resonator added to the ladder type circuit of the transmission band filter 110 on one surface, whereby a three-stage transmission band filter characteristic can be obtained. In a telephone, the transmission pass frequency band is usually set lower than the reception pass frequency band. For example, in the case of a CDMA-PCS telephone, the transmission pass frequency band is 1.85 to 1.91 GHz, and the receive pass frequency band is 1.93 to 1.99 GHz. Therefore, the transmission band filter 110 is required to have a steep and large attenuation at a frequency higher than the pass band. By obtaining the three-stage transmission band filter characteristics, it is possible to approach the characteristics in line with such requirements, and it is possible to reduce the size of the transmission / reception switch.

[0025] The thin-film piezoelectric resonator 150 for adjustment functions as a shunt resonator added to the ladder type circuit of the reception band filter 130 on the other side, whereby the reception band filter characteristics of the (3 + 1/2) stage are obtained. Is obtained. The reception band filter 130 requires steep and large attenuation at frequencies lower than the pass band. By obtaining the reception band filter characteristics of the (3 + 1/2) stage, it is possible to approach the characteristics in line with such requirements, and the transmission / reception switch can be miniaturized.

[0026] The series resonance frequency of the thin film piezoelectric resonator 150 for adjustment is larger than the upper limit of the transmission pass frequency band of the transmission band filter 110 (1.91 GHz in the case of a CDMA-PCS phone) and the receive pass frequency band of the receive band filter 130. By setting an appropriate value smaller than the lower limit of (1.93 GHz in the case of a CDMA-PCS phone), the transmission / reception switch 100 is operated without the transmission band filter 110 and the reception band filter 130 being affected by each other. Can be done. This is because the transmission pass frequency band is lower than the series resonance frequency of the resonator 150, so that the resonator 150 exhibits capacitiveity in the circuit in the transmission pass frequency band, and the reception band filter 130 does not exist as if it acts like an LPF. Behave as if. Also, since the receive pass frequency band is higher than the series resonance frequency of the resonator 150, the resonator 150 exhibits inductiveness in the circuit in the receive pass frequency band, and ignores the existence of the transmission band filter 110 by an action like HPF. Behave as if you were. Therefore, due to the presence of the resonator 150, the transmission signal applied to the first port (transmission port) 102 flows from the first port (transmission port) 102 to the third port (antenna port) 106. It has almost no effect on the second port (receive port) 104 and the receive band filter 130. Further, due to the presence of the resonator 150, the received signal coming from the third port (antenna port) 106 is received without being affected by the transmission band filter 110 or the first port (transmission port) 102. It passes through the band filter 130 and reaches the second port (receive port) 104. Therefore, it operates stably as a transmission / reception switch.

FIG. 7 shows an example of the transmission / reception characteristic Tt and the reception / passage characteristic Rt of the transmission / reception switch 100 having the thin film piezoelectric resonator 150 for adjustment as described above.

[0028] Since the thin film piezoelectric resonator 150 can be easily monolithic together with the thin film piezoelectric resonator constituting the transmission band filter 110 and the thin film piezoelectric resonator constituting the reception band filter 130, transmission / reception switching can be performed in this sense as well. The vessel can be miniaturized.

[0029] FIG. 8 is a circuit configuration diagram of still another embodiment of the transmission / reception switching device of the present invention. In this figure, members or parts having the same functions as those in FIGS. 1 to 7 above are designated by the same reference numerals.

[0030] In the present embodiment, in the transmission band filter 110, the node 117 and the first port (transmission port) 102 are connected by an inductor 120 which is an additional passive element, that is, the inductor 120 is connected to the series resonance elements 113 and 115. They are connected in parallel. Equivalent capacitor C of each series resonant element₀ An additional resonant circuit is formed between the and the inductor 120, which creates a new attenuation pole within the desired attenuation band (particularly near and above the passband), with fewer stages being better. Transmission filter characteristics can be obtained.

Further, in the present embodiment, the node 137 and the second port 104 are connected by a capacitor 140 which is an additional passive element, that is, the capacitor 140 is connected in parallel with the series resonant elements 133 and 135. .. An additional resonant circuit is formed between each series resonant element and the capacitor 140, which creates new attenuation poles within the desired attenuation band (particularly near and below the passband), resulting in less. Better reception filter characteristics can be obtained with the number of stages.

Although one adjusting thin film piezoelectric resonator 150 is used in the above embodiment, it is also possible to use two or more adjusting thin film piezoelectric resonators in the present invention.

[Effects of the Invention] As described above, according to the present invention, since the element made of the thin film piezoelectric resonator is used, the reliability or the stability of the filter characteristics can be improved even at a power level exceeding 1 watt. It is possible to provide a transmission / reception switching device having a sufficiently steep damping characteristic that is not impaired. In addition, it is possible to provide a transmission / reception switch that is considerably smaller and lower in height than a ceramic filter, and a thin-film piezoelectric resonator for adjustment is also used to connect the transmission band filter and reception band filter, making monolithicization easy. Therefore, the manufacturing cost of the transmission / reception switch can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS [Fig. 1] Fig. 1 is a block diagram showing a configuration of a transmission / reception switching device of the present invention.

FIG. 2 is a circuit configuration diagram of a transmission / reception switch of the present invention.

FIG. 3 is a schematic plan view of a thin film piezoelectric resonator.

4 is a cross-sectional view taken along the line XX of FIG.

FIG. 5 is a schematic cross-sectional view of a thin film piezoelectric resonator.

FIG. 6 is an element equivalent circuit diagram of a thin film piezoelectric resonator.

FIG. 7 is a graph showing an example of transmission / passage characteristics and reception / passage characteristics of the transmission / reception switching device of the present invention.

FIG. 8 is a circuit configuration diagram of a transmission / reception switch of the present invention.

[Code description] 10 Thin-film piezoelectric resonator 12 piezoelectric layer 14 through hole 16 substrate 18,20 electrode layer 22 piezoelectric resonator stack 26,28 electrode terminal 30 acoustic impedance converter 100 transmission / reception switch 102 transmission port 104 reception port 106 antenna Port 110 Transmission band filter 111,113,115 Transmission band filter series resonance element 112,114 Transmission band filter shunt resonance element 117,118 Node 130 Reception band filter series resonance element 132,134,136 Reception band filter shunt resonance element 137,138 Node 150 For adjustment Thin film piezoelectric resonator