Abstract
A filter with reduced plate modes is specified. Thereto, the filter has a transducer system (WS) with two or more electroacoustic split transducers (TW) connected in parallel that replace a conventional transducer (W). The static capacity of the transducer system corresponds to the sum of the static capacities of the split transducers. Each split transducer has a lower electroacoustic coupling of a desired mode than the transducer system. The transducer system has an electroacoustic coupling of a plate mode corresponding to the electroacoustic coupling of the plate mode of a split transducer.
Claims
1. An electroacoustic filter (F), comprising: a plurality of transducers (W); and an inductive element (IE) connected to a single transducer (W) of the plurality of transducers that does not have a highest electroacoustic coupling of a plate mode among the plurality of transducers.
2. The electroacoustic filter (F) according to claim 1, wherein the inductive element (IE) is connected in series to the single transducer (W).
3. The electroacoustic filter (F) according to claim 1, wherein the inductive element (IE) is connected in parallel to the single transducer (W).
4-9. (canceled)
10. A duplexer with an electroacoustic filter according to any of claims 1-3.
11. A method for creating an electroacoustic filter (F), comprising: analyzing an electroacoustic coupling strength of a plate mode in each of a plurality of transducers (W); and replacing a single transducer (W) of the plurality of transducers having a highest electroacoustic coupling strength of the plate mode with a transducer system (WS) comprising a plurality of split transducers (TW) connected in parallel, such that the electroacoustic coupling strength of the plate mode of the transducer system (WS) is limited to the electroacoustic coupling strength of the plate mode of one of the split transducers (TW).
12. A method for creating an electroacoustic filter (F), comprising: analyzing an electroacoustic coupling strength of a plate mode in each of a plurality of transducers (W); and adding a serial or parallel inductive element (IE) to one of the plurality of transducers that does not have a highest electroacoustic coupling strength of the plate mode.
Description
[0045] The electroacoustic filter and its operation mode and electrical chat as well as execution examples of the invention are further explained based on the schematic figures.
[0046] Shown are:
[0047] FIG. 1: a separation of a transducer into a transducer system with split transducers,
[0048] FIG. 2: the separation of a transducer into a multigate resonator,
[0049] FIG. 3: the parallel circuit of an inductive element with a serial resonator,
[0050] FIG. 4: the parallel circuit of an inductive element with a parallel resonator,
[0051] FIG. 5: the parallel circuit of an inductive element with a serial resonator at concomitant serial circuit of a parallel resonator with an inductive element in a parallel path,
[0052] FIG. 6: comparison of an improved electroacoustic filter having a reduced stimulation strength of the plate modes to a conventional filter,
[0053] FIG. 7: comparison of a conventional resonator to a resonator interconnected in parallel or in series, respectively, to a inductive element,
[0054] FIG. 8: comparison of an improved electroacoustic filter having one or two inductive elements to a conventional electroacoustic filter.
[0055] FIG. 1 shows a layout where a transducer with is split in a transducer system WS with split transducers TW. The transducer with itself is part of a filter where three transducers with are adjoining. Correspondingly, the filter has three transducer systems WS each with nine split transducers. The separation degree of the transducer into split transducers is thus n=9. Thus, the stimulation strength of a plate mode is reduced basically to one ninth of the stimulation strength of the original transducerwith other electroacoustic chat remaining equal.
[0056] FIG. 2 shows an example of a split transducer as multiport-resonator. The original transducer was split into four split transducers.
[0057] A conventional acoustic element consists of two reflectors and the transducer itself. The reflectors are limiting the acoustic wave to the transducer area. Two conventional transducers have thus four transducers in total.
[0058] In case a transducer is split as per above, n split transducers result and 2n reflectors. Thus, one can replace two adjoining reflectors by a single one, saving thus place on the expensive piezoelectric monocrystal. Between two split transducers only one reflector is thus placed. In order to reduce the number of reflectors and thus save place, all split transducers can be placed in a row. In case of split transducers, there are thus necessary only n+1 reflectors, instead of 2n.
[0059] FIG. 3 shows an element of a ladder-type filter circuit of a HF filter F, to which a serial resonator SR is interconnected in the signal path. A parallel resonator PR is placed in a parallel path, which interconnects the signal path to ground. Depending on how the resonance frequency or the anti-resonance frequency, respectively, of the serial resonator SR and parallel resonator PR are matched one to another, this forms the element of a band-pass filter or of a notch filter. An inductive element IE, an inductance, e.g. a coil made as metallization in a multilayer substrate or a SMD coil is interconnected in parallel to the serial resonator SR and creates an additional null point of the admittance.
[0060] FIG. 4 shows the possibility of interconnecting an inductive element IE in series to the parallel resonator between the signal path and ground in order to achieve an additional pole point of the admittance.
[0061] FIG. 5 shows the possibility to interconnect both an inductive element IE parallel to an serial resonator SR and an inductive element IE in series to a parallel resonator PR, in order to achieve both an additional pole point and an additional null point of admittance.
[0062] FIG. 6 shows the frequency-dependent transmission (matrix element S.sub.21) in a logarithmic representation. Significantly above the pass-band PB of the filter, curve 1 of a conventional band-pass filter has a range of increased transmission, caused by a plate mode PM. In contrast to it, curve 2 presents the transmission of an analogue electroacoustic filter with a transducer system replacing a critical transducer. In the plate mode range, the transmission is significantly reduced, so that the specifications for frequency ranges are significantly easier to maintain outside the pass-band.
[0063] The admittance course in the pass-band range is virtually not changed when replacing a transducer by the transducer system.
[0064] FIG. 7 shows the frequency-dependent admittance of a conventional resonator 1. Curve 2 shows the admittance of the same transducer to which an inductance is connected in series. Curve 3 shows the admittance of a parallel circuit of the resonator of the curve 1 and an inductance. The admittance of the series circuit of resonator and inductivity has an additional pole point. The admittance of the parallel circuit of resonator and inductance has an additional pole point.
[0065] FIG. 8 shows the effect of additional inductance elements in band-pass filters. While the die admittances of various filter configurations in the pass-band PB range are quasi-unchanged and curve 1 shows the admittance of a filter without additional inductances, curve 2 shows the admittance of a filter where an inductance is interconnected in parallel to the first serial transducer looking to the signal direction. The additional null point was placed by selection of the inductance value so that it has about 2150 MHz in the plate mode range of the parallel resonators. Curve 3 shows the admittance of a filter where an inductance is connected in series to a parallel transducer. The additional pole is located in the region of the plate modes of the serial transducer at about 2250 MHz. Curve 4 shows the admittance of a filter where an inductance is connected in series to a parallel transducer and also an inductance is connected in parallel to a serial transducer. Correspondingly, undesired plate modes can be suppressed in parallel and serial transducers.
[0066] The electroacoustic filter, the duplexer and the procedure for creating of filters are not limited by the described chat and execution examples. Filters with additional circuit elements such as additional resonators or additional inductive and capacitive elements are also included.
LIST OF REFERENCE SIGNS
[0067] 1, 1, 1: frequency-depending admittance [0068] 2, 2, 2: frequency-depending admittance [0069] 3, 3: frequency-depending admittance [0070] 4: frequency-depending admittance [0071] AS: acoustic trace [0072] F: HF filter [0073] IE: inductive element [0074] MTW: Multi-gate transducer, multiport-resonator [0075] PB: Pass-band [0076] PM: Plate mode [0077] PR: Parallel resonator [0078] R: Reflector [0079] S21: Matrix element [0080] SR: Series resonator [0081] TW: split transducer [0082] W: Transducer [0083] WS: Transducer sys
