Abstract
A reconfigurable microacoustic filter is specified which comprises a ladder-type-like filter topology and a suitably placed adjustable capacitive element.
Claims
1. A microacoustic filter comprising: a characteristic frequency range; a signal path with an adjustable phase shifter and a series resonator; a plurality of parallel paths which connects the signal path to ground, each of the parallel paths having a parallel resonator; and at least one of the parallel paths further comprising an adjustable capacitive element connected in series to the parallel resonator of the at least one parallel path, wherein the filter can be reconfigured by varying the adjustable capacitive element and wherein the adjustable phase shifter can be switched between an adjustability in the inductive range and an adjustability in the capacitive range.
2. The microacoustic filter according to claim 1, wherein the adjustable phase shifter is connected to a duplexer.
3. A microacoustic filter comprising: a characteristic frequency range; a signal path with an adjustable phase shifter and at least one series resonator; a plurality of paths connecting the signal path to ground, each of the paths having a parallel resonator; and at least one of the plurality of paths further comprising a first adjustable capacitive element coupled to a shunted resonator, wherein the microacoustic filter is reconfigurable by varying the first adjustable capacitive element, and wherein the adjustable phase shifter is configured to be switched between an adjustability in an inductive range and an adjustability in a capacitive range.
4. The microacoustic filter according to claim 3, wherein a second adjustable capacitive element is connected in parallel to the at least one series resonator, and wherein the microacoustic filter is further reconfigurable by varying the second adjustable capacitive element.
5. The microacoustic filter according to claim 3, wherein a second adjustable capacitive element is connected in parallel to the parallel resonator of one of the plurality of paths, and wherein the microacoustic filter is further reconfigurable by varying the second adjustable capacitive element.
6. The microacoustic filter according to claim 3, wherein one of the plurality of paths comprises an inductive element coupled between the parallel resonator and a ground node, wherein a second adjustable capacitive element is connected in parallel to the inductive element, and wherein the microacoustic filter is further reconfigurable by varying the second adjustable capacitive element.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Principles and functionalities underlying the reconfigurable microacoustic filter, as well as some exemplary embodiments, are explained in more detail in schematic Figures.
(2) They show:
(3) FIG. 1a a possible basic structure of a reconfigurable filter with an adjustable capacity element in the first parallel path,
(4) FIG. 1b a possible basic structure of a reconfigurable filter with an adjustable capacity element connected parallel to an inductive element, in the first parallel path,
(5) FIG. 2 a logarithmic application of the transfer functions of the circuit topology of FIG. 1 for different values of the capacity of the adjustable capacity element,
(6) FIG. 3 an enlargement of the frequency range of the passband of FIG. 2,
(7) FIG. 4 the basic structure of a possible configuration with an adjustable capacity element in the second parallel path,
(8) FIG. 5 transfer functions for different values of the capacity of the adjustable capacity element of the topology of FIG. 4,
(9) FIG. 6 the basic structure of a topology with an adjustable capacity element connected parallel to the third series resonator,
(10) FIG. 7 transfer functions for different values of the adjustable capacity element of a bandpass filter based on the topology of FIG. 6,
(11) FIG. 8 an enlargement of the passband of FIG. 7,
(12) FIG. 9 the basic structure of a filter circuit, in which the adjustable capacitive element is connected parallel to the parallel resonator of the first parallel path,
(13) FIG. 10 transfer functions associated with the circuit of FIG. 9 for different values of the adjustable capacitive element,
(14) FIG. 11 an enlargement of the passband of FIG. 10,
(15) FIG. 12 a basic structure of a filter circuit in which the adjustable capacitive element is connected parallel to an inductive element in the first parallel path,
(16) FIG. 13 transfer functions associated with the circuit of FIG. 12 for different values of the capacity,
(17) FIG. 14 an enlargement of the passband of FIG. 13,
(18) FIG. 15a the basic structure of a filter circuit, in which an adjustable capacitive element is connected to ground between the parallel paths and a common inductive element,
(19) FIG. 15b the basic structure of another filter circuit, in which an adjustable capacitive element is connected to ground between the parallel paths and a common inductive element,
(20) FIG. 15c the basic structure of another filter circuit, in which an adjustable capacitive element is connected to ground between the parallel paths and a common inductive element,
(21) FIG. 16 a basic structure of a filter circuit with adjustable phase shifter,
(22) FIG. 17 a basic structure of a filter circuit, in which an adjustable capacitive element can be controlled in a parallel path and a phase shifter can be controlled by a control circuit,
(23) FIG. 18 a basic structure of a filter circuit, in which a controlled adjustable capacitive element is connected parallel to an inductive element,
(24) FIG. 19 a possible design of an adjustable phase shifter with an adjusting region and a switching region,
(25) FIG. 20 a possible design of a phase shifter which is connected to a TX filter input of a duplexer,
(26) FIG. 21 possible tuning ranges of the adjustable phase shifter in the inductive range and in the capacitive range.
DETAILED DESCRIPTION OF THE INVENTION
(27) FIG. 1a shows a basic structure of a possible HF filter circuit of a microacoustic filter MAF. A signal path SP is arranged between an input IN and an output OUT. A line of series resonators, in this case a quantity of three, are connected in the signal path SP. The filter MAF furthermore comprises three parallel paths PP which connect the respective nodes of the signal path SP to ground. A parallel resonator PR is arranged in each of the parallel paths PP. An inductive element IE is optionally connected between the respective parallel resonator PR and ground. In the first parallel path as viewed in the signal direction, an adjustable capacitive element AKE with adjustable capacity is connected between the parallel resonator and the inductive element.
(28) FIG. 1b shows a basic structure of another possible HF filter circuit of a microacoustic filter MAF. A signal path SP is arranged between an input IN and an output OUT. A line of series resonators, in this case a quantity of three, are connected in the signal path SP. The filter MAF furthermore comprises three parallel paths PP which connect the respective nodes of the signal path SP to ground. A parallel resonator PR is arranged in each of the parallel paths PP. An inductive element IE is connected between the respective parallel resonator PR and ground. A parallel circuit consisting of an inductive element and an adjustable capacitive element AKE with adjustable capacity is connected between the parallel resonator and ground in the first parallel path, as viewed in the signal direction.
(29) FIGS. 2 and 3 show the transfer functions of the filter of FIG. 1, designed as a bandpass filter, wherein different curves illustrate different values of the capacity of the adjustable capacitive element AKE. Despite varied capacities, the edges in the passband and the passband practically do not change. The frequency range above the passband is also almost not affected. Below the passband, a zero point of the transfer function exists, the position of which can be shifted by varying the capacity value.
(30) FIG. 4 shows an alternative embodiment of a circuit topology in which the adjustable capacitive element AKE is connected between the parallel resonator and an impedance element in the second parallel path. FIG. 5 shows the transfer functions associated with the different values of the capacity of the adjustable capacitive element. A zero point above the passband can be shifted. The positions of the passband itself and of a zero point below the passband remain almost unchanged.
(31) FIG. 6 shows an alternative possible topology in which the adjustable capacitive element AKE is connected parallel to the third series resonator SR.
(32) As can be seen in FIG. 7, the position of the zero point below the passband and the qualitative curve of the transfer function above the passband remain almost unchanged. The same applies to the bottom passband edge. The top passband edge, which can be seen more clearly in FIG. 8, is shifted by a variation of the capacity of the capacitive element. As a result, the bandwidth and the position of the center frequency are reconfigurable.
(33) FIG. 9 shows a possible filter topology in which the adjustable capacitive element AKE is connected parallel to the parallel resonator of the first parallel path, as viewed in the signal direction. FIG. 10 shows the associated transfer functions of different values of the capacity. The position of a zero point of the transfer function as well as the position of the top passband edge are adjustable, while the bottom passband edge and the qualitative curve of the transfer function above the passband remain almost unchanged.
(34) FIG. 11 shows the changeable top passband edge of FIG. 10 in an enlarged view.
(35) FIG. 12 shows a possible topology in which the adjustable capacitive element is connected in the first parallel path. An inductive element IE is connected between the parallel resonator PR and ground. The adjustable capacitive element AKE is connected parallel to the inductive element IE. FIG. 13 and the enlarged view of FIG. 14 show the transfer functions associated with different values of the capacity. The position of the pole below the passband and, to a lesser extent, the position of the top passband edge are configurable.
(36) FIG. 15a shows a possible topology in which a common inductive element IE connects the three parallel paths to ground. An adjustable capacitive element AKE is connected between the three parallel resonators and the inductive element IE.
(37) FIG. 15b again shows a possible topology in which a common inductive element IE connects the three parallel paths to ground. An adjustable capacitive element AKE is connected between the three parallel resonators and the inductive element IE. The output port OUT can at the same time be the port to an antenna connector of a multiplexer. The parallel resonator located closest to the antenna connector is additionally connected to ground via an inductive element with very little inductance.
(38) FIG. 15c shows a possible topology in which a common inductive element IE connects the three parallel paths to ground. An adjustable capacitive element AKE is connected between the three parallel resonators and the inductive element IE. The output port OUT can again at the same time be the port to an antenna connector of a multiplexer. The parallel resonator located closest to the antenna connector is connected to ground via an inductive element with very little inductance without any additional coupling to the adjustable capacitive element.
(39) FIG. 16 shows the use of an adjustable phase shifter AP in the signal path of a microacoustic filter, drawn in this case without any additional circuit elements for the sake of simplicity.
(40) FIG. 17 shows the use of a control circuit CS which can control the capacity of the adjustable capacitive element and/or the effect of the adjustable phase shifter AP on the phasing of an HF signal for improved interaction with other filters for carrier aggregation. The control circuit CS can in this case be part of the microacoustic filter MAF, or part of the logic circuits of the associated communication device.
(41) FIG. 18 shows a regulation of the capacity of the adjustable capacitive element AKE and/or of the phase shift of the adjustable phase shifter AP, wherein the adjustable capacitive element AKE is connected parallel to an inductive element.
(42) FIG. 19 shows a possible embodiment of the adjustable phase shifter AP which comprises an adjustable region AB and a switching region SB. The adjustable region contains a Pi circuit with two inductive elements to ground and an adjustable capacitive element between the inductive elements. How far the adjustable phase shifter AP rotates the phase of an HF signal received at the input IN is determined by varying the capacity of the adjustable capacitive element.
(43) Arranged in the switching region SB is a switch which connects the signal path to a switching state in the idle state (left), to a capacitive element (center), or to an inductive element (right). A connection to ground is achieved via the capacitive element or the inductive element. As a result of the right two possible switch positions, switching between a capacitive and an inductive operating mode of the adjustable phase shifter AP is possible.
(44) FIG. 20 shows a possible embodiment of an adjustable phase shifter with a capacitive element of constant capacitance in the signal path. An inductive element of constant inductance is connected in a parallel path. A first adjustable capacitive element is connected parallel to the capacitive element of constant capacitance. A second adjustable capacitive element is connected parallel to the inductive element.
(45) The adjustable phase shifter AP can be connected to a duplexer. As shown in FIG. 20, in this way the adjustable phase shifter can be connected between a port IN, at which HF signals are provided, and the input of a reception filter of the duplexer.
(46) FIG. 21 shows frequency-dependent possible starting points of the adjustable duplexer in the capacitive range and in the inductive range. Switching between the inductive and the capacitive range is possible by operating a switch. The phasing can be adjusted in small steps by varying the capacitance of the adjustable capacitive element of the adjustable phase shifter.
(47) The advantage of switching between an inductance and a capacitance in FIG. 19 exists in that the phase makes a distinct jump so that the range in which a duplexer can be shifted with respect to its phase is significantly extended. The range defined by the topology (which actually includes unreachable ranges, “blind spots”) can furthermore be switched so that the magnitude of the blind spots is reduced in the Smith chart or so that the blind spots are possibly eliminated.
(48) The reconfigurable microacoustic filter is not limited to the exemplary embodiments described and the Figures shown. Filters with additional resonators, such as series resonators in the signal path or parallel resonators in parallel paths; and additional circuit elements, such as impedance adjustment circuits; and additional filters of higher order multiplexers are also a component of the filter.
LIST OF REFERENCE SYMBOLS
(49) AB: Adjustment region AKE: Adjustable capacitive element AP: Adjustable phase shifter CS: Control circuit DU: Duplexer IE: Impedance element IN: Signal input MAF: Microacoustic filter OUT: Signal output PP: Parallel path PR: Parallel resonator SB: Switching region SP: Signal path SR: Series resonator
