Split-type, half-lattice micro-acoustic filter using a phase shifter and having broad bandwidth
A micro-acoustic RF filter comprises first and second ports ( 101, 102 ). First and a second signal paths ( 120, 110 ) are coupled between the first and second ports and include a corresponding resonator ( 111, 121 ). The resonator of at least one of the signal paths is a micro-acoustic resonator. One of the signal paths includes also a phase shifter ( 232 ) serially connected with the resonator ( 111 ). The micro-acoustic RF filter achieves a broad passband determined by the resonance frequencies of the micro-acoustic resonators. The filter allows flexible adaption of the passband and stopband performance.
1. A micro-acoustic RF filter, comprising:
a first port and a second port;
a first node coupled to the first port;
a second node coupled to the second port;
a first signal path coupled between the first node and the second node, the first signal path including a first resonator;
a second signal path coupled between the first node and the second node, the second signal path including a second resonator and a phase shifter connected in series to the second resonator, wherein at least one of the first resonator or the second resonator comprises a micro-acoustic resonator;
a third resonator, wherein the third resonator comprises an additional micro-acoustic resonator having a first end coupled directly to the second node and a second end coupled to a reference node; and
a fourth resonator having a first end coupled to the first port and a second end coupled directly to the first node,
wherein the third resonator and the fourth resonator are configured to provide a finite transmission zero (FTZ) function outside of a passband, and
wherein the first resonator, the second resonator, and the phase shifter configure a frequency response within the passband, and
wherein each of the first resonator, the second resonator, and the fourth resonator comprise a pair of resonators connected in anti-series having opposite polarities.
2. The micro-acoustic RF filter of claim 1 , further comprising a series connected parallel resonant circuit coupled in series between the second node and the second port.
3. The micro-acoustic RF filter of claim 2 , further comprising a shunt connected series resonant circuit having a first end and a second end;
wherein the series connected parallel resonant circuit comprises a first end coupled to the second node and a second end coupled to the first end of the shunt connected series resonant circuit; and
wherein the second end of the shunt connected series resonant circuit is coupled to the reference node.
4. The micro-acoustic RF filter of claim 3 , further comprising an inductor having a first end coupled to the second end of the series connected parallel resonant circuit and a second end coupled to the second port.
5. The micro-acoustic RF filter of claim 1 , further comprising a series connected parallel resonant circuit in series between the first port and the fourth resonator, wherein the series connected parallel resonant circuit has a second end coupled to the fourth resonator.
6. The micro-acoustic RF filter of claim 5 , further comprising a shunt connected series resonant circuit coupled between the second end of the series connected parallel resonant circuit and the reference node.
7. The micro-acoustic RF filter of claim 6 , further comprising an inductor coupled between the first port and the series connected parallel resonant circuit.
8. The micro-acoustic RF filter of claim 1 , wherein the first resonator and the second resonator of the first signal path and the second signal path each exhibit a resonance frequency, wherein the resonance frequency of the second resonator of the second signal path is lower than the resonance frequency of the first resonator of the first signal path wherein the phase shifter is connected to the second resonator of the second signal path.
9. The micro-acoustic RF filter of claim 8 , wherein the second resonator of the second signal path is realized by a micro-acoustic resonator technology providing losses and/or spurious modes below the resonance frequency of said second resonator and wherein the first resonator of the second signal path is realized by a micro-acoustic resonator technology providing losses and/or spurious modes above the resonance frequency of said first resonator.
10. The micro-acoustic RF filter of claim 1 , wherein the micro-acoustic RF filter is configured to exhibit a passband having a lower passband corner and an upper passband corner, wherein the second resonator is configured to form the lower passband corner and the first resonator is configured to form the upper passband corner, and wherein the phase shifter is connected to the second resonator configured to form the lower passband corner.
11. The micro-acoustic RF filter of claim 10 , wherein the second resonator is configured to form the lower passband corner comprises a bulk acoustic wave resonator exhibiting dispersion type II and the first resonator is configured to form the upper passband corner comprises a bulk acoustic wave resonator exhibiting dispersion type I.
12. The micro-acoustic RF filter of claim 1 , wherein the phase shifter is configured to perform a phase shift of 180° at least once within a passband of the micro-acoustic RF filter.
13. The micro-acoustic RF filter of claim 1 , wherein the phase shifter comprises at least one of: a highpass Pi circuit, a lowpass Pi circuit, an allpass circuit, or combinations thereof to realize phase-shifters consisting of at least three elements disposed in the second signal path.
14. The micro-acoustic RF filter of claim 1 , further comprising a matching circuit connected between at least one of the first port and the second port or the first signal path and the second signal path to provide passband matching.
15. The micro-acoustic RF filter of claim 1 , further comprising at least one or more of a micro-acoustic resonator and a parallel resonance circuit connected in series between the first signal path and the second signal path and one of the first port or the second port to perform a finite transmission zero function.
16. The micro-acoustic RF filter of claim 1 , further comprising at least one or more of a micro-acoustic resonator and a series resonance circuit connected in shunt to a node coupled between the first signal path and the second signal path and a terminal for ground potential to perform a finite transmission zero function.
17. The micro-acoustic RF filter of claim 1 , wherein at least one additional resonator is cascaded in each one of the first signal path and the second signal path.
18. The micro-acoustic RF filter of claim 1 , wherein the micro-acoustic RF filter is configured to exhibit a passband portion and an out-of-band portion, wherein the passband portion is in an n79 band or between 4.4 GHz and 5.0 GHz and the out-of-band portion is out of the n79 band or in a frequency range of less than 4.4 GHz and more than 5.0 GHz, wherein the first resonator and the second resonator are surface acoustic wave or bulk acoustic wave resonators comprising a piezoelectric substrate of at least one of lithium tantalate, lithium niobate, or aluminum scandium nitride.
19. The micro-acoustic RF filter of claim 1 , wherein the third resonator is a FTZ resonator.
20. The micro-acoustic RF filter of claim 1 , further comprising a FTZ filter coupled to the first port and the second port, wherein the FTZ filter comprises the third resonator.