CN100502239C - A surface acoustic wave duplexer - Google Patents

Abstract

The invention relates to a surface acoustic wave duplexer used for a handheld terminal of a trunking communication system, which includes a first surface acoustic wave filter at a transmitting end and a surface acoustic wave filter at a receiving end, and also includes a first surface acoustic wave filter arranged in front of a power amplifier The second surface acoustic wave filter of the transmitting end of the stage; the output terminal of the second surface acoustic wave filter of the transmitting end is connected to the input end of the final stage power amplifier of the transmitting circuit and then connected to the input end of the first surface acoustic wave filter of the transmitting end, and in addition One end is connected to the part of the front stage of the final power amplifier in the transmitting circuit through the electrode; the second surface acoustic wave filter at the transmitting end is composed of a trapezoidal surface acoustic wave filter and a surface acoustic wave band-stop filter in series, wherein the surface acoustic wave The wave band rejection filter is formed by connecting a single-ended surface acoustic wave resonator and an external inductor in a ∏ shape. The invention has the advantages of high transceiver isolation, low insertion loss, small volume and the like.

Description

A surface acoustic wave duplexer

technical field

The invention relates to a surface acoustic wave duplexer, in particular to a surface acoustic wave duplexer used for a handheld terminal of a trunking communication system.

Background technique

Duplexers are commonly used in frequency division duplex wireless communication systems. It is a three-terminal network, one port is connected to the antenna, one port is connected to the transmitting circuit, and the other port is connected to the receiving circuit; the function of the duplexer is to ensure that the signal from the transmitting circuit is radiated out through the antenna instead of flowing into the receiving circuit; the antenna receives The received signal is sent to the receiving circuit after passing through the duplexer, and does not flow into the transmitting circuit. Therefore, the basic requirements of the duplexer are: low insertion loss, high transceiver isolation.

In the prior art, there is a cavity-type duplexer, which has a good transceiver isolation, but its volume is too large, generally hundreds of cm ³ to several thousand cm ³ . It cannot be used in a trunking communication system handheld terminal. Therefore, it is expected to develop a duplexer with high transceiver isolation and small size.

Using a surface acoustic wave filter (SAW filter) in a duplexer can greatly reduce its volume. The surface acoustic wave (SAW) filter can achieve high stop-band rejection, and it can be used as a duplexer to achieve high transceiver isolation. But the disadvantage of the traditional surface acoustic wave filter is the large insertion loss. Therefore, the duplexer made by using the traditional SAW filter also has the problem of large insertion loss.

Yoshio Satoh et al. proposed a trapezoidal surface acoustic wave filter that can achieve very low insertion loss (see International Journal of High Speed Electronics and Systems, Vol.10, No.3(2000) PP825-865), its The basic structure is shown in Figure 2. The trapezoidal surface acoustic wave filter 8 is composed of a first piezoelectric substrate 7 and a series single-ended pair SAW resonator 15 and a parallel single-ended pair SAW resonator 14 fabricated on the first piezoelectric substrate 7 . The single-ended pair SAW resonator structure is shown in Figure 3, and it has an interdigital transducer 22, is placed on the upper surface of the first piezoelectric substrate 7 along the acoustic wave propagation direction, and reflective grating array 20 and 21 are placed on the interdigital both ends of the transducer 22. In the trapezoidal surface acoustic wave filter 8, as shown in Figure 2, since the two ends of the interdigital transducers in the SAW resonators 14 and 15 are placed with reflective gratings to form a resonant cavity, the sound wave is limited in the resonant cavity, so The trapezoidal surface acoustic wave filter 8 can obtain very low insertion loss. Its proximal stop-band suppression is better, but its distal stop-band suppression is poor. Using multi-stage filter cascading can improve the stop-band suppression, but the insertion loss increases accordingly, and the chip size increases accordingly, and the cost is higher.

The longitudinally coupled resonant filter proposed by Morita et al. can achieve very low insertion loss (see IEEE 1992 Ultrasonics Symposium Proceedings PP95-104), and its basic structure is shown in Figure 4. The longitudinally coupled resonant filter 13 has two interdigital transducers 16 and 17, which are placed on the upper surface of the second piezoelectric substrate 24 along the sound wave propagation direction, and the reflective grid arrays 18 and 19 are placed between the interdigital transducers 16 and 17. 17 ends. In the longitudinally coupled resonant SAW filter 13, since the reflective grating array is placed at both ends of the transducer to form a resonant cavity, the sound wave is confined in the resonant cavity, so a very low insertion loss can be obtained. However, in the longitudinally coupled resonant SAW filter 13, the stop-band rejection is poor, and the stop-band rejection can be improved by cascading multi-stage filters, but the insertion loss increases accordingly, so it cannot be used as a transmitter.

Contents of the invention

The purpose of the present invention is to overcome the defect of prior art, reduce the insertion loss of duplexer and improve the transceiver isolation of duplexer, and reduce the volume and cost of duplexer, thereby provide a SAW duplexer with stop-band suppression without increasing insertion loss.

The purpose of the present invention is achieved like this:

The surface acoustic wave duplexer provided by the present invention, as shown in Figure 1 and Figure 5, comprises a transmitting end surface acoustic wave filter 4, a receiving end surface acoustic wave filter 5 and an external phase shifter 6, the The input end of the surface acoustic wave filter 5 at the receiving end is connected in series with the phase shifter 6 and the output end of the surface acoustic wave filter 4 at the transmitting end is connected in parallel to the antenna through electrode 1, and the other end of the surface acoustic wave filter 5 at the receiving end passes through electrode 3 Electrically connected with the receiving circuit, the other end of the transmitting end surface acoustic wave filter 4 is connected to the output end of the transmitting circuit final stage power amplifier 25; it is characterized in that the described surface acoustic wave duplexer also includes a terminal arranged on the final stage power amplifier 25 The second surface acoustic wave filter 4' at the transmitting end of the front stage, the output terminal of the second surface acoustic wave filter 4' at the transmitting end is connected to the input end of the final stage power amplifier 25, and the other end is connected to the terminal in the transmitting circuit through the electrode 2 The front-stage part of the stage power amplifier 25 is electrically connected; the second surface acoustic wave filter 4 ' of the transmitting end is composed of a trapezoidal surface acoustic wave filter and a surface acoustic wave band-stop filter in series, wherein the trapezoidal acoustic wave The surface wave filter is composed of a series single-ended pair of surface acoustic wave resonators and a parallel connected single-ended pair of surface acoustic wave resonators, and the anti-resonant frequency of the parallel connected single-ended pair of surface acoustic wave resonators is the The resonant frequency of the surface acoustic wave resonator is 0.95-1.05 times, and the surface acoustic wave band stop filter is formed by connecting the surface acoustic wave resonator and the external inductor in a Π shape;

The transmitting end surface acoustic wave filter 4 is composed of a trapezoidal surface acoustic wave filter, and the trapezoidal surface acoustic wave filter is composed of a series single-ended pair of surface acoustic wave resonators and a parallel single-ended pair of surface acoustic wave resonators , the anti-resonant frequency of the parallel single-ended surface acoustic wave resonator is 0.95-1.05 times the resonance frequency of the serial single-ended surface acoustic wave resonator;

The receiving end surface acoustic wave filter 5 is composed of two or more cascaded longitudinally coupled resonant filters, or is composed of a trapezoidal surface acoustic wave filter and two or more cascaded longitudinally coupled resonant filters Composed in series; the trapezoidal surface acoustic wave filter is composed of the series single-ended pair of surface acoustic wave resonators and the described parallel single-ended pair of surface acoustic wave resonators, and the described parallel single-ended pair of surface acoustic wave The anti-resonant frequency of the resonator is 0.95-1.05 times of the resonant frequency of the described series single-ended surface acoustic wave resonator; the described longitudinally coupled resonant filter consists of the first IDT 16, the second fork finger transducer 17 and the first reflective grating array 18 and the second reflective grating array 19 at its two ends, the first interdigital transducer 16 and the second interdigital transducer 17 are not weighted, the first reflective grating The array 18 and the second reflection grid array 19 both use short-circuit grids, and the synchronization frequency of the interdigital transducer is 1-1.05 times of the synchronization frequency of the reflection grid array.

The phase shifter is composed of LC low-pass network or LC high-pass network.

The transmitting end surface acoustic wave filter 4, the receiving end surface acoustic wave filter 5 and the transmitting end second surface acoustic wave filter 4' are all made on the piezoelectric substrate; the piezoelectric substrate is rotated by 128 °Y cut X spread LiNbO, or Y cut Z spread LiNbO, or rotate 36°Y cut X spread LiTalate, or rotate 64°Y cut X spread LiNbO, or rotate 41°Y cut X spread lithium niobate.

The single-ended surface acoustic wave resonator is composed of an interdigital transducer and a reflective grating at both ends; the interdigital transducer is not weighted, and the reflective grating adopts a metal short-circuit reflective grating , or a metal open-circuit reflective grating, or a reflective groove, or a metal positive and negative reflective grating; the synchronous frequency of the interdigital transducer is 1-1.05 times the synchronous frequency of the reflective grating.

Advantages of the present invention:

In order to meet the requirements of low insertion loss and high transceiver isolation of the duplexer, the present invention divides the transmitting end into two stages, the second SAW filter of the transmitting end is placed before the final stage power amplifier of the transmitting circuit, and the first The surface acoustic wave filter is placed at the forefront and connected to the antenna. The first surface acoustic wave filter at the transmitting end adopts a surface acoustic wave trapezoidal structure, so that the front end transmitting end can achieve extremely low insertion loss (0.6dB); the second surface acoustic wave filter at the transmitting end adopts a trapezoidal surface acoustic wave filter Combined with the band-stop surface acoustic wave filter, it can achieve low insertion loss in the passband and high suppression of specific frequency bands (the suppression of the receiving frequency band 382MHz-386MHz is above 60dB), and because it is placed in the final power amplifier of the transmitting circuit Therefore, it does not increase the insertion loss of the transmitting end. Compared with the present embodiment and the common prior art, the surface acoustic wave duplexer of the present invention can realize the high transceiver isolation of transmission and reception, and can realize extremely low insertion loss (transmission filter insertion loss is 0.6dB, The insertion loss of the acceptance filter is 3.3dB), and the size and cost can also be reduced. Its volume is generally several hundred mm ³ , and compared with existing cavity-type duplexers, the volume is greatly reduced (generally a few hundredths of the cavity-type duplexer).

Description of drawings

Fig. 1 is a block diagram of the present invention;

Fig. 2 is a schematic plan view of a trapezoidal surface acoustic wave filter in an embodiment of the present invention;

Fig. 3 is a schematic plan view of a single-ended SAW resonator in an embodiment of the present invention;

Fig. 4 is a schematic plan view of a conventional SAW longitudinally coupled resonator filter in an embodiment of the present invention;

5 is a structural diagram of a surface acoustic wave duplexer according to an embodiment of the present invention;

6 is a frequency response curve of a surface acoustic wave filter at a transmitting end of a duplexer according to an embodiment of the present invention;

7 is a frequency response curve of the second surface acoustic wave filter at the transmitting end of the surface acoustic wave duplexer according to an embodiment of the present invention;

FIG. 8 is a frequency response curve of a surface acoustic wave filter at a receiving end of a surface acoustic wave duplexer according to an embodiment of the present invention.

Detailed ways

Taking the mobile phone as an example now, the operating principle of the present invention is described in detail as follows in conjunction with the accompanying drawings and embodiments:

Make a surface acoustic wave filter, with reference to Fig. 1 and Fig. 5, in the present embodiment, the piezoelectric substrate 7, 23 and 24 of duplexer adopts rectangular 42 ° YX-LiTaO piezoelectric substrate, in piezoelectric The upper surfaces of the substrates 7, 23 and 24 are respectively plated with metal aluminum, and then the transmitting end surface acoustic wave filter 4, the transmitting end second surface acoustic wave filter 4' and the receiving end surface acoustic wave filter 4' as shown in Figure 5 are respectively photoetched. The surface acoustic wave filter 5, the input terminal of the surface acoustic wave filter 5 at the receiving end is connected in parallel with the phase shifter 6 at the input end of the surface acoustic wave filter 5 at the transmitting end through the electrode 1, and the output terminal of the surface acoustic wave filter 5 at the receiving end is connected to The electrode 3, the surface acoustic wave filter 4 at the transmitting end are connected in series with the second surface acoustic wave filter 4' at the transmitting end through the final power amplifier 25 in the transmitting circuit, and finally connected to the electrode 2. In application, electrode 1 is used for electrical connection with mobile phone antenna, electrode 2 is used for electrical connection with mobile phone transmitting circuit (the transmitting circuit refers to the part of the front stage of final power amplifier in general transmitting circuit), and electrode 3 is used for connecting with Mobile phone receiving circuit electrically connected.

In the embodiment of the present invention, the transmitter surface acoustic wave filter 4 adopts the structure of a trapezoidal surface acoustic wave filter, and the structure of the trapezoidal surface acoustic wave filter 8 is shown in Figure 2. It is composed of a series single-ended pair SAW resonator 15 and a parallel single-ended pair SAW resonator 14 fabricated on the first piezoelectric substrate 7. The single-ended pair of SAW resonators wherein is as shown in Figure 3, the single-ended pair of SAW resonators 15 consists of the first piezoelectric substrate 7 and the interdigital transducer 22 made on the first piezoelectric substrate 7 and on it Metal reflective grating arrays 20 and 21 at both ends. The IDT 22 is unweighted, and the width and spacing of the interdigital electrodes are both 0.25 wavelength. The metal reflective grid arrays 20 and 21 adopt short-circuit grid bars, and the width and interval of the grid bars are both 0.25 wavelength. According to needs, the synchronous frequency of the IDT 22 and the reflective gratings 20, 21 is slightly different, and the synchronous frequency of the IDT 22 is 1-1.05 times of the synchronous frequency of the reflective grating arrays 20, 21. In the embodiment of the present invention, the synchronous frequency of the interdigital transducer 22 for the SAW resonator 15 in series is 1.01 times that of the synchronous frequency of the reflective grid arrays 20 and 21; the interdigital transducer 14 for the parallel single-ended The synchronization frequency of the transducer is twice that of the reflection grid array. The center frequency of the surface acoustic wave filter 4 at the transmitting end is 374MHz. Because the trapezoidal surface acoustic wave filter 8 is composed of a SAW resonator, it can achieve low insertion loss and meet the requirements of low insertion loss (less than 2dB) at the transmitting end of the duplexer .

Transmitting the second surface acoustic wave filter 4 ' is to adopt the structure of the trapezoidal surface acoustic wave filter in series with the surface acoustic wave bandstop filter, as shown in Figure 5, its center frequency is 374MHz, because the trapezoidal surface acoustic wave filter and the acoustic Surface wave band rejection filters are all composed of SAW resonators, so low insertion loss can be realized. The surface acoustic wave band-stop filter 12 can realize high suppression of the receiving frequency band, and meet the requirements of low insertion loss at the transmitting end of the duplexer and high suppression (greater than 60dB) of the receiving frequency band, wherein the surface acoustic wave band-stop filter 12 It is formed by connecting two parallel single-ended surface acoustic wave resonators through electrodes 10, 11 and an external series inductor 9 in a Π shape. In this embodiment, a structure of 4-stage trapezoidal SAW filter and 1-stage SAW band-stop filter is adopted in order to improve the suppression of the 382MHz-386MHz frequency band, that is, the transmit-receive isolation of the duplexer.

In the embodiment of the present invention, the surface acoustic wave filter 5 at the receiving end is composed of two cascaded longitudinally coupled resonant filters with a center frequency of 384 MHz. The structure of longitudinal coupling resonant filter 13 is shown in Figure 4, and it is made on the second piezoelectric substrate 24 and two interdigital transducers 16,17 on the second piezoelectric substrate 24 and at its two ends Metal reflective grating array 18,19 is formed. The interdigital transducers 16, 17 are not weighted, and the width and spacing of the interdigital electrodes are both 0.25 wavelength. The metal reflective grating arrays 18 and 19 adopt short-circuited gratings, and the width and interval of the gratings are both 0.25 wavelength. In the present embodiment, the synchronous frequency of the interdigital transducers 16, 17 is 1.01 times of the synchronous frequency of the reflective grating arrays 18, 19, and a two-level cascade connection is adopted to improve the out-of-band suppression, that is, the duplexer's transceiver isolation.

In the embodiment of the present invention, the phase shifter 6 is formed by connecting two series capacitors and one parallel inductor in a T shape (LC high-pass network).

As shown in Fig. 6, Fig. 7 and Fig. 8, Fig. 6 shows the amplitude-frequency response when the chip structure of the transmitting surface acoustic wave filter 4 shown in Fig. 5 is adopted, and the substrate material is 36 ° YX-LiTaO As can be seen from Figure 6, the center frequency is 372.45MHz, the 1dB bandwidth is 8.5MHz (covering the transmitting frequency range of 372MHz to 376MHz), and the insertion loss is 0.6dB, which meets the requirements of low insertion loss at the transmitting end; The chip structure of the second surface acoustic wave filter 4' shown in 5 and the amplitude-frequency response curve when the substrate material is 42°YX-LiTaO3 can be seen from Figure 7, the center frequency is 372.53MHz, and the bandwidth is 6.6MHz (basically covering the transmitting frequency range of 372MHz~376MHz), the insertion loss is 2.1dB, and the suppression of the receiving frequency band (382MHz~386MHz) is greater than 60dB, which meets the requirements of low insertion loss of the transmitting end in the transmitting frequency band and high suppression of the receiving frequency band; Fig. 8 is the amplitude-frequency corresponding curve when adopting the chip structure of the surface wave filter 5 at the receiving end shown in Fig. 5 and the substrate material using 42 ° YX-LiTaO3, as can be seen from Fig. 8, the center frequency is 384.7MHz, The bandwidth is 5.4MHz (covering the receiving frequency range of 382MHz~386MHz), the insertion loss is 3.3dB, and the suppression of the transmitting frequency band (372MHz~376MHz) is greater than 50dB, which meets the requirements of low insertion loss at the receiving end and high suppression of the transmitting frequency band.

The working principle of the surface acoustic wave duplexer in the embodiment of the present invention is described as follows. In the transmitting working state, the transmitting signal is input by the mobile phone transmitting circuit through the electrode 2, and passes through the second surface acoustic wave filter 4' at the transmitting end. ~386MHz) suppression is greater than 60dB, and after being amplified by the power amplifier, it passes through the surface acoustic wave filter 4 at the transmitting end. Enters the cell phone antenna and radiates outward. At this time, the signal in the receiving frequency band (382MHz～386MHz) in the signal from the transmitting end has been suppressed very weakly. In the receiving end, the transmitting signal enters the surface acoustic wave filter 5 at the receiving end through the phase shifter 6, as shown in FIG. 8, it can be seen that the suppression of the transmitting frequency band (372MHz-376MHz) by the SAW filter 5 at the receiving end is greater than 50dB, so the transmitting signal cannot enter the receiving circuit of the mobile phone through the SAW filter 5 at the receiving end.

In the receiving working state, the received signal is received by the antenna of the mobile phone and input to the phase shifter 6 through the electrode 1, and then input to the receiving circuit of the mobile phone through the electrode 3 through the surface acoustic wave filter 5 at the receiving end. At this time, although the received signal will enter the transmitting end through electrode 1, the signal entering the transmitting circuit generally does not have much impact on the quality of the call, so it is not necessary to consider it.

Compared with the present embodiment and the common prior art, the surface acoustic wave duplexer of the present invention can realize the high transceiver isolation of transmission and reception, and can realize extremely low insertion loss (transmission filter insertion loss is 0.6dB, The acceptance filter insertion loss is 3.3dB), and a small size can also be achieved. In this embodiment, when the duplexer is made into a finished product, the first SAW filter 4 at the transmitting end and the SAW filter 5 at the receiving end are packaged together, and the second SAW filter 4 at the transmitting end 'separately packaged, and the phase shifter is provided by an external system. The volumes of the two packages are 336mm ³ and 85.5mm ³ respectively. Compared with the existing cavity-type duplexer, the volume is greatly reduced (usually cavity-type duplexer a few hundredths of a tool).

Claims (4)

1. A surface acoustic wave duplexer comprising a transmitting end surface acoustic wave filter (4), a receiving end surface acoustic wave filter (5) and an external phase shifter (6), the receiving end acoustic wave After the input end of the surface wave filter (5) is connected in series with the phase shifter (6) and the output end of the transmitting end surface acoustic wave filter (4) is connected in parallel to the antenna through the electrode (1), the receiving end surface acoustic wave filter (5 ) is electrically connected to the receiving circuit through the electrode (3), and the other end of the transmitting end surface acoustic wave filter (4) is connected to the output end of the transmitting circuit final stage power amplifier (25); it is characterized in that the surface acoustic wave The wave duplexer also includes a second surface acoustic wave filter (4') at the transmitting end that is arranged on the front stage of the final stage power amplifier (25) of the transmitting circuit, and the second surface acoustic wave filter (4') at the transmitting end outputs The terminal is connected to the input end of the final stage power amplifier (25) of the transmitting circuit, and the other end is electrically connected with the front stage part of the final stage power amplifier (25) of the transmitting circuit by the electrode (2); the final stage power amplifier (25) of the transmitting circuit is electrically connected ) refers to the part of the front stage of the final power amplifier in the general transmitting circuit; the second surface acoustic wave filter (4 ') of the transmitting end is composed of a trapezoidal surface acoustic wave filter and a surface acoustic wave band The trapezoidal surface acoustic wave filter is formed in series, wherein the trapezoidal surface acoustic wave filter adopts 4-stage cascade connection, and its operating frequency is the transmission frequency. End-to-surface acoustic wave resonators, the anti-resonant frequency of the parallel single-ended surface acoustic wave resonator is 0.95-1.05 times the resonance frequency of the series single-ended surface acoustic wave resonator, the surface acoustic wave The band-stop filter is formed by connecting a single-ended surface acoustic wave resonator and an external inductor in a П shape; The transmitting end SAW filter (4) is composed of a trapezoidal SAW filter, and the trapezoidal SAW filter adopts a one-stage structure, and its operating frequency is the transmitting frequency, and the trapezoidal SAW filter The device is composed of a series single-ended pair of surface acoustic wave resonators and a parallel connected single-ended pair of surface acoustic wave resonators, and the anti-resonant frequency of the parallel connected single-ended pair of surface acoustic wave resonators is the series single-ended pair of surface acoustic wave resonant 0.95-1.05 times the resonant frequency of the device; The receiving end surface acoustic wave filter (5) is composed of two or more cascaded longitudinally coupled resonant filters, or is composed of a ladder-shaped surface acoustic wave filter and two or more cascaded longitudinally coupled resonant filters Filters are connected in series; the operating frequency of the ladder-shaped surface acoustic wave filter is the receiving frequency, and the ladder-shaped surface acoustic wave filter is composed of the described series single-ended pair of surface acoustic wave oscillators and the described parallel single-ended pair of acoustic Composed of surface wave resonators, the anti-resonance frequency of the parallel single-ended surface acoustic wave resonator is 0.95-1.05 times the resonance frequency of the series single-ended surface acoustic wave resonator; the longitudinal coupling resonance Filter, by the first IDT (16), the second IDT (17) and the two ends of the first IDT (16) and the second IDT (17) The first reflective grating array (18) and the second reflective grating array (19) are composed, and the first interdigital transducer (16) and the second interdigital transducer (17) are not weighted, and the first reflective grating array ( 18), the second reflective grating (19) all adopt short-circuit gratings, and the synchronous frequency of the interdigital transducer is 1-1.05 times of the synchronous frequency of the reflective grating. 2. The surface acoustic wave duplexer according to claim 1, characterized in that: said phase shifter is composed of an LC low-pass network or an LC high-pass network. 3. The surface acoustic wave duplexer according to claim 1, characterized in that: the transmitter surface acoustic wave filter (4), the receiver surface acoustic wave filter (5) and the second transmitter surface acoustic wave The wave filters (4') are all made on the piezoelectric substrate; the piezoelectric substrate adopts the method of rotating 128° Y-cutting X to propagate lithium niobate, or Y-cutting Z to propagate lithium niobate, or rotating 36° Y-cutting X Spread lithium tantalate, or rotate 64°Y to cut X to spread lithium niobate, or rotate 41°Y to cut X to spread lithium niobate. 4. The surface acoustic wave duplexer according to claim 1, characterized in that: the single-ended pair surface acoustic wave resonator is composed of an interdigital transducer and a reflection grating array at both ends of the interdigital transducer ; The interdigital transducer is not weighted, and the reflective grating adopts a metal short-circuit reflective grating, or a metal open-circuit reflective grating, or a reflective groove, or a metal positive and negative reflective grating; The synchronous frequency of the interdigital transducer of the end-to-surface acoustic wave resonator is 1-1.05 times that of the reflection grid array of the single-end to surface acoustic wave resonator.

Images