ACOUSTIC TRANSFORMER IN TRANSMISSION CHAIN

Abstract

An acoustic transformer in a transmitter chain is disclosed. In one aspect, a differential power amplifier may produce a differential signal that is provided to a first transformer. A differential output of this first transformer is provided to an acoustic transformer that provides a single-ended output signal for use by an acoustic filter. By making the second transformer an acoustic transformer, the second transformer may be integrated into the same circuitry that forms the acoustic filter, thereby simplifying the die. Further, the acoustic transformer may be tuned if ferroelectric resonators are used, which provides strong out-of-band signal cancelation.

Claims

1. An acoustic filter comprising: a plurality of resonant elements configured to act as inductors or capacitors; and a tunable ferroelectric network element positioned in parallel with a first one of the plurality of resonant elements.

2. The acoustic filter of claim 1, wherein the plurality of resonant elements are arranged in a reduced order ladder configuration.

3. The acoustic filter of claim 1, further comprising a voltage generation source selectively coupled to the tunable ferroelectric network element.

4. The acoustic filter of claim 1, wherein the tunable ferroelectric network element comprises a negative capacitance for the acoustic filter.

5. The acoustic filter of claim 1, wherein the tunable ferroelectric network element comprises a first acoustic resonator.

6. The acoustic filter of claim 5, wherein the tunable ferroelectric network element further comprises a second acoustic resonator and a third acoustic resonator coupled to the second acoustic resonator with opposite polarity, the second and third acoustic resonators electrically parallel to the first acoustic resonator.

7. The acoustic filter of claim 6, further comprising a capacitor coupling the second and third acoustic resonators to ground.

8. The acoustic filter of claim 6, further comprising a switch configured to couple the second acoustic resonator to ground selectively.

9. The acoustic filter of claim 6, further comprising a switch configured to couple the third acoustic resonator to ground selectively.

10. A method of operating an acoustic filter, comprising: adjusting a voltage applied to a tunable ferroelectric network element positioned in parallel with a first one of a plurality of resonant elements to act as a negative capacitance; and using the plurality of resonant elements as inductors or capacitors.

11. An acoustic transformer comprising: a first inductor pair sharing a common node; and a shunt path comprising: a plurality of tunable ferroelectric network elements coupling the common node to ground.

12. The acoustic transformer of claim 11, wherein the plurality of tunable ferroelectric network elements comprises a first pair of acoustic resonators.

13. The acoustic transformer of claim 12, further comprising an intermediate node between the first pair of acoustic resonators, the intermediate node configured to be coupled to a voltage source.

14. The acoustic transformer of claim 12, further comprising a second pair of acoustic resonators positioned in parallel to the first pair of acoustic resonators.

15. The acoustic transformer of claim 11, further comprising an acoustic resonator positioned in parallel with the first inductor pair.

16. The acoustic transformer of claim 11, wherein the first inductor pair is negatively coupled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a block diagram of an exemplary transmitter that has a power amplifier and filter, which may benefit from aspects of the present disclosure;

[0012] FIG. 2 is a block diagram of a first aspect of the present disclosure, where a broadband differential transformer is cascaded with a narrowband acoustic transformer to assist in out-of-band rejection for an acoustic filter;

[0013] FIG. 3 is a block diagram of the acoustic transformer of FIG. 2 that uses current summing to provide a single-ended output;

[0014] FIG. 4 is a block diagram of the acoustic transformer of FIG. 3 with ferroelectric tuning used to improve cancelation of out-of-band signals;

[0015] FIG. 5 is a more detailed diagram of the acoustic transformer of FIG. 3, showing differential-to-single-ended current output;

[0016] FIG. 6 is a block diagram of the acoustic transformer of FIG. 2 that uses voltage summing to provide a single-ended output;

[0017] FIG. 7 is a block diagram of the acoustic transformer of FIG. 6 with ferroelectric tuning used to improve cancelation of out-of-band signals;

[0018] FIG. 8 is a block diagram of an acoustic filter that uses ferroelectric tuning with negative capacitance to assist in filter formation according to an exemplary aspect of the present disclosure;

[0019] FIG. 9 is a more detailed circuit diagram of the ferroelectric tuning of the acoustic filter of FIG. 8;

[0020] FIG. 10 is a block diagram of a voltage source being used to tune the ferroelectric elements of the acoustic filter of FIG. 8;

[0021] FIG. 11 is a circuit diagram of an alternate aspect of an acoustic filter according to an exemplary aspect of the present disclosure; and

[0022] FIG. 12 is a circuit diagram of a transmitter chain with an alternate aspect of the secondary transformer.

DETAILED DESCRIPTION

[0023] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0024] It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element without departing from the scope of the present disclosure. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

[0025] It will be understood that when an element such as a layer, region, or substrate is referred to as being on or extending onto another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being directly on or extending directly onto another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being over or extending over another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being directly over or extending directly over another element, there are no intervening elements present. It will also be understood that when an element is referred to as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being directly connected or directly coupled to another element, there are no intervening elements present.

[0026] Relative terms such as below or above or upper or lower or horizontal or vertical may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms a, an, and the are intended to include the plural forms as well unless the context clearly indicates otherwise. It will be further understood that the terms comprises, comprising, includes, and/or including, when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0028] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0029] Aspects disclosed in the detailed description include an acoustic transformer in a transmission chain. In particular, a differential power amplifier may produce a differential signal that is provided to a first transformer. A differential output of this first transformer is provided to a second acoustic transformer that provides a single-ended output signal for use by an acoustic filter. By making the second transformer an acoustic transformer, the second transformer may be integrated into the same circuitry or die that forms the acoustic filter, thereby simplifying the overall structure. Further, the acoustic transformer may be tuned if ferroelectric resonators are used, which provides strong out-of-band signal cancelation.

[0030] In this regard, FIG. 1 is a block diagram of a transmitter chain 100 that may be used in a mobile computing device. Signals to be transmitted are processed in a baseband processor (BBP) 102 and passed to an optional intermediate frequency (IF) processor 104 for upconversion and/or filtering. A radio frequency (RF) signal is created either by the BBP 102 or the IF processor 104 and provided to an amplifier chain 106, which amplifies the signal to a desired level before filtering in an RF filter 108 and transmission from an antenna 110. A power management integrated circuit (PMIC) 112 may receive information from the BBP 102 to assist in controlling the amplifier chain 106.

[0031] As the cellular and other wireless standards evolve, there has been increased pressure to provide proper amplification and proper filtering of the RF signals to be transmitted. The RF filtering is used to help achieve coexistence with other radios and with other RF frequencies as well as general compliance with applicable wireless protocol standards. In particular, the RF filtering is designed to provide strong out-of-band rejection. Typical implementations trade out-of-band rejection (i.e., the desired filtering) with in-band insertion losses and may consume extra current. Further, in many instances the amplifier chain 106 has a low impedance, but the antenna/air interface may have a comparatively high impedance. This impedance mismatch may create reflections at the antenna, and accordingly, there are circuits in the transmitter chain 100 to assist in impedance matching. Thus, providing desired RF filtering has proven challenging to implement.

[0032] Exemplary aspects of the present disclosure provide two ways to improve implementation of the impedance matching and filtering. In a first aspect, an acoustic transformer is added in front of an acoustic filter. Having both structures made from similar acoustic technologies simplifies construction of the overall device. Further, the use of an acoustic transformer may assist in impedance matching and changing from a differential signal to a single-ended signal. The use of such an acoustic transformer also assists in out-of-band cancellation, which allows greater flexibility in construction of the filter. In a second aspect, ferroelectric materials in the acoustic filter may be used to assist in tuning the acoustic filter with a negative capacitance element to allow greater flexibility in the design of the filter. A discussion of the first aspect is presented below with reference to FIGS. 2-7, and a discussion of the second aspect begins below with reference to FIG. 8.

[0033] In this regard, FIG. 2 illustrates a portion 200 of a transmitter chain that may be part of the transmitter chain 100 of FIG. 1. The portion 200 includes a differential power amplifier 202 (e.g., a final amplifier in the amplifier chain 106 of FIG. 1) having output lines 204(P) and 204(M). The signals on these output lines 204(P) and 204(M) may be considered broadband differential outputs. The output lines 204(P) and 204(M) are coupled to a first transformer 206 having primary coils 208(P) and 208(M) and secondary coils 210(P) and 210(M). The first transformer 206 is coupled to a second or acoustic transformer 212. As such, the acoustic transformer 212 may include a first resonator that compresses when a positive voltage is applied (CP) and a second resonator that compresses when a negative voltage is applied (CN). The acoustic transformer 212 is then coupled to an acoustic ladder filter 214. In exemplary aspect, the acoustic ladder filter 214 is a reduced order ladder filter. Because the acoustic transformer 212 and the acoustic ladder filter 214 may be formed from the same technologies, they may be implemented in a single acoustic die.

[0034] In a first aspect, the acoustic transformer 212 may sum currents at the output with one branch using opposite polarity of coupled resonators as better illustrated as acoustic transformer 212C in FIG. 3. To do this, the CP resonator of the acoustic transformer 212C may have the same polarity and the CN resonator of the acoustic transformer 212C may have opposite polarity.

[0035] Note further that the acoustic differential may be tuned through the use of ferroelectric resonators whose polarity may be adjusted via applying an external direct current (DC) supply, as better illustrated in FIG. 4. A separate voltage 400P and 400M may be applied to the different branches of the acoustic transformer 212 (regardless of whether the transformer is a current-summing transformer 212C or a voltage-summing transformer 212V discussed with reference to FIG. 6 below). The tuning may be done by selecting the voltage 400P and 400M by reference to a look-up table (LUT) 402 and a generation circuit 404. The LUT 402 may use a target frequency as an input to determine desired voltage levels. After tuning, the voltages 400P and 400M may be removed.

[0036] An example structure showing how the differential input signal is converted to a single-ended output signal is provided with reference to FIG. 5. Specifically, inputs 500M and 500P are provided to the acoustic transformer 212C, which sums the current on each branch to provide a single-ended output signal at output 502. A coupling layer 504 may be provided.

[0037] It should be appreciated that the acoustic transformer 212 is relatively narrow band. When cascaded with the broadband first transformer 206, the in-band desired signal will see two inversions in sign and thus will add up, while out-of-band signals will see a single inversion in sign. This results in cancelation of the out-of-band signals, which in turn enhances out-of-band rejection of the acoustic ladder filter 214.

[0038] Instead of summing current, it is also possible to make an acoustic transformer that sums voltage as better seen in FIG. 6. Here, an output 600 of the negative branch is added to a coupling layer 602 of the positive branch to provide a unified (summed voltage) output 604. The same sort of ferroelectric tuning may be done, as better illustrated in FIG. 7, where voltages 700P and 700M may be used to tune ferroelectric elements within the acoustic transformer 212V.

[0039] In addition to providing cancelation in the acoustic transformer 212 to improve out-of-band rejection, exemplary aspects of the present disclosure also add a tunable negative capacitance element to the acoustic ladder filter 214. In this regard, FIG. 8 illustrates a high-level diagram of this concept. In particular, the acoustic ladder filter 214 may include ladder elements 800(1)-800(i). Each ladder element 800 includes resonant sub-elements 802(1)-802(N) that may be or act as reactive elements such as inductors or capacitors, as is well understood. Exemplary aspects of the present disclosure add tunable ferroelectric network elements 804(1)-804(i) to one or more of the sub-elements 802(1)-802(N) (as shown, applied in parallel to the sub-element 802(1)). The ferroelectric network elements 804(1)-804(i) are independently tunable by application of a voltage level determined by a LUT 806 and voltage generation circuit 808. Information about the signal being transmitted (e.g., from the BBP 102 or other source) may be used to select values from the LUT 806.

[0040] The ferroelectric network elements 804(1)-804(i) may be a negative capacitance. With reference to FIG. 9, the math for the negative capacitance is provided Specifically:

[00001]$\mathrm{Vab}=\mathrm{Vac}+\mathrm{Vcb}$$\mathrm{Vac}=\mathrm{Vcb}=\mathrm{Vx}\mathrm{due}\mathrm{to}\mathrm{the}\mathrm{transformer}\mathrm{coupling}$$2\mathrm{Vx}=\mathrm{Vab}\mathrm{or}\mathrm{Vx}=\frac{\mathrm{Vab}}{2}$$\mathrm{Ic}=\frac{\mathrm{Vc}}{\mathrm{Zc}}$$\mathrm{Vb}=\mathrm{Zout}*\mathrm{Iout}=\mathrm{Zout}*(\mathrm{Iab}-\frac{\mathrm{Ic}}{2}$$\mathrm{Iab}=\frac{\mathrm{Va}-\mathrm{Vb}}{Z}$$\mathrm{Vb}=\mathrm{Zout}*\left\{\frac{\mathrm{Va}-\mathrm{Vb}}{Z}-\frac{\mathrm{Vc}}{2\mathrm{Zc}}\right\}=\mathrm{Zout}*\left\{\frac{\mathrm{Va}-\mathrm{Vb}}{Z}-\frac{\mathrm{Va}+\mathrm{Vb}}{4\mathrm{Zc}}\right\}$$\mathrm{Vb}=\mathrm{Va}*\mathrm{Zout}*\frac{\frac{1}{Z}-\frac{1}{4\mathrm{Zc}}}{1+\frac{\mathrm{Zout}}{Z}+\frac{\mathrm{Zout}}{4\mathrm{Zc}}}$

[0041] Vb can be zero when Zc=Z/4, since Z1/Co at out-of-band frequencies, so Zc will be Co and the middle capacitance is 4Co to get an ideal negative Co cancelation at out-of-band frequencies. This shows that it is possible to cancel RF current and make Vb=0 if 4Zc=Z in the frequencies of interest. Thus, if Zc=Z/4 with Zc, the impedance of the capacitance to ground network and Z is the impedance of the series acoustic resonator.

[0042] Implementing this math may look like the circuit illustrated in FIG. 10 where a voltage generation source 1000 (e.g., analogous to the voltage generation circuit 808 of FIG. 8) applies a tuning voltage to control each resonator and capacitor 1002. Switches 1004(1), 1004(2) may be used to apply tuning voltages from the voltage generation source 1000 as needed.

[0043] Where it is not possible to use two negatively-coupled acoustic resonators, two negatively-coupled inductors could be used as illustrated in FIG. 11. Specifically, a sub-element 802 may have two inductors 1102(1), 1102(2) that are negatively coupled. A shunt path 1104 may be formed that couples the midpoint to ground through two parallel acoustic branches 1106(1), 1106(2) each with a dedicated tuning voltage DCa, DCb.

[0044] This structure in FIG. 11 allows deactivation of one branch 1106(1), 1106(2) at a time (or both), or tune one branch 1106(1), 1106(2) series resonance or equivalent capacitance or tune such that both have similar series resonances with a constant sum capacitance. This topology offers great flexibility to tune the impedance Zc such that ZcZ/4 for the frequency of desired cancelation.

[0045] It may also be possible to use this structure as part of the second transformer 212 where the shunt path is coupled to a common node between the inductors as illustrated in FIG. 12.

[0046] It is also noted that the operational steps described in any of the exemplary aspects herein are described to provide examples and discussion. The operations described may be performed in numerous different sequences other than the illustrated sequences. Furthermore, operations described in a single operational step may actually be performed in a number of different steps. Additionally, one or more operational steps discussed in the exemplary aspects may be combined. It is to be understood that the operational steps illustrated in the flowchart diagrams may be subject to numerous different modifications, as will be readily apparent to one of skill in the art. Those of skill in the art will also understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0047] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.