Tunable match for shared filter with multiple lnas

Abstract

Methods and devices to improve impedance matching of RF receivers with multiple LNAs operating in different CA modes are disclosed. The described devices use a shared filter to accommodate a frequency band among the LNAs. Switching schemes to switch in and out an additional impedance matching element for improved LNA input matching are also described.

Description

TUNABLE MATCH FOR SHARED FILTER WITH MULTIPLE LNASCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application No. 63 / 605,731 filed on December 4, 2023, for “Tunable Match For Shared Filter With Multiple LNAs”, the contents of which is incorporated herein by reference in their entirety.TECHNICAL FIELD

[0002] The present disclosure is related to radio frequency (RF) receivers implementing multiple low noise amplifiers (LNAs). More particularly, the disclosed methods and devices address the problem of impedance matching of a shared filter with the implemented LNAs.BACKGROUND

[0003] Through this document the term “carrier aggregation (CA) mode” in radio frequency (RF) refers to a feature in cellular and other networks that allows combining multiple carrier frequencies or component carriers to provide wider bandwidth and higher data rates.

[0004] Modem mobile phones are often required to support various multiple input, multiple output (MIMO) and carrier aggregation (CA) modes of operation to achieve increased data throughput. The required hardware for accommodating such operational modes results in larger device size and greater cost.

[0005] Throughout this document, standard downlink receive frequency bands (Bl, B2, B3) representing 2210-2170 MHz, 1805-1880 MHz, and 2620-2690 MHz, respectively, have been used to illustrate the disclosed methods and devices. These essentially represent 3GPP 5G NR bands ‘nl’, ‘n3’, and ‘n7’. However, the teachings of the present disclosure are equally applicable to any number of frequency bands covering frequency ranges other than the ones above.

[0006] Fig. 1A shows a prior art RF receiver (100 A) of a mobile phone designed to accommodate three different operational frequency bands (Bl, B2, B3). As an example, the requirement could be to accommodate CA modes B1+B2, B1+B3, and B2+B3. The RFreceiver shown comprises input filters (Fl, F2, F3) corresponding to frequency bands (Bl, B2, B3). The outputs of the filters are coupled to respective low noise amplifiers (LNA1, LNA2, LNA3) through impedance matching inductors (LI, L2, L3). Such inductors have the function of input impedance matching of the corresponding LNA. Given that the receiver is configured to aggregate two frequency bands simultaneously, only two of the three low noise amplifiers are active concurrently under operational conditions. Consequently, this design is ineffective regarding cost and area optimization.

[0007] Continuing with the same exemplary requirement of three CA modes, reference is made to Fig. IB showing a prior art RF receiver (100B). In contrast with the receiver described above, RF receiver (100B) implements two LNAs (LNA1, LNA2) instead of three. This comes at the expense of including one additional filter (F2’), impedance matchings elements (Zl, Z2) and switches (SI 1, ..., S14). Filter (Fl) corresponds to frequency band (Bl) and connects to the respective low noise amplifier (LNA1) via switch (Si l). This switch is in an ON state (closed) when conveying the band (Bl) signal to LNA (LNA1) subsequent to filtering through filter (Fl). Similarly, filter (F3) corresponds to frequency band (B3) and connects to the respective low noise amplifier (LNA2) via switch (SI 4). When this switch is closed, the band (B3) signal is received by LNA (LNA2) subsequent to filtering through filter (F3).

[0008] With continued reference to Fig. IB, filters (F2, F2’) both correspond to frequency band (B2) and their role is to direct, through respective switches (S12, S13), the signal of this band to LNAs (LNA1, LNA2) respectively. Since the LNAs needs to support a wider bandwidth, the filters (F2, F2’) may need extra impedance matching elements (Zl, Z2) to match the filters to the LNAs. This will result in increased cost and spatial requirements for the design. An additional issue with this receiver is that a more complex design is required for the antenna switch (not shown).

[0009] Fig. 1C shows another prior art RF receiver (100C) illustrating a solution to support the CA mode as described above, with only two LNAs and a single filter (F2) (instead of the two filters (F2, F2’) of Fig. IB) supporting frequency band (B2). In this case, the issue is that the single matching element (Z) cannot match the filter (F2) to both LNAs (LNA1, LNA1). This leads to degraded performance in at least one of the two LNAs or both.

[0010] In view of the above, for the applications imposing stringent CA modes requirements, RF receivers offering an improved cost / space / performance tradeoff are needed.SUMMARY

[0011] The described methods and circuits address the above-mentioned issues and challenges.

[0012] According to a first aspect of the present disclosure, a radio frequency (RF) receiver is provided, comprising: a first low noise amplifier (LNA) and a second LNA; a first filter in correspondence with a first frequency band, the first filter having an output matched to an input impedance of the first LNA; a second filter in correspondence with a second frequency band; a third filter in correspondence with a third frequency band, the third filter having an output matched to an input impedance of the second LNA; a first impedance matching element coupled to an output of the second filter; and a selectively switchable second impedance matching element coupled to the output of the second filter, wherein: the first impedance matching element is configured to match the output of the second filter to an input impedance of the first LNA, and a combination of the first impedance matching element and the second impedance matching elements is configured to match the output of the second filter to an input impedance of the second LNA.

[0013] According to a second aspect of the present disclosure, a method of tunable impedance matching in a radio frequency (RF) receiver is disclosed, the RF receiver comprising: a first low noise amplifier (LNA) and a second LNA; a first filter in correspondence with a first frequency band; a second filter in correspondence with a second frequency band; a third filter in correspondence with a third frequency band; and a first impedance matching element and a second impedance matching element, the method comprising: A) in a first carrier aggregation (CA) mode where the first frequency band and the second frequency band are aggregated: al) filtering a signal corresponding to the first frequency band through the first filter to generate a first filtered signal; a2) directing the first filtered signal to the first LNA; a3) filtering a signal corresponding to the second frequency band to generate a second filtered signal; a4) directing the second filtered signal to the second LNA; and a5) matching an output of the second filter to an input of the second LNA through a combination of the first impedance matching element and the second impedance matching element; B) in a second carrier aggregation (CA) mode where the first frequency band and the third frequency band are aggregated: bl) filtering the signal corresponding to the first frequency band through the first filter to generate a first filtered signal; b2) directing the first filtered signal to the first LNA; b3) filtering a signal corresponding to the third frequency bandto generate a third filtered signal; and b4) directing the third filtered signal to the second LNA; C) in a third carrier aggregation (CA) mode where the second frequency band and the third frequency band are aggregated: cl) filtering the signal corresponding to the second frequency band through the second filter to generate the second filtered signal; c2) directing the second filtered signal to the first LNA; c3) matching an output of the first filter to an input impedance of the first LNA through the first impedance matching element without the second impedance matching element; c4) filtering a signal corresponding to the third band to generate the third filtered signal; and c5) directing the third filtered signal to the second LNA.

[0014] Further aspects of the disclosure are provided in the description, drawings and claims of the present application.DESCRIPTION OF THE DRAWINGS

[0015] Figs. 1A-1C show prior art RF receivers with multiple LNAs.

[0016] Fig. 2 A shows an exemplary RF receiver according to an embodiment of the present disclosure.

[0017] Fig. 2B shows an exemplary table illustrating example switching states of the switches in the embodiment of Fig. 2 A.

[0018] Figs. 2C-2F show exemplary signal paths for the embodiment of Fig. 2A when operating in different CA modes.

[0019] Fig. 2G shows an exemplary RF receiver according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0020] Fig. 2A shows an exemplary RF receiver (200A) according to an embodiment of the present disclosure. The structure and functionality of RF receiver (200A) is similar to what was described previously with regards to RF receiver (100C) of Fig. 1C except for the addition of impedance matching element (Z22) and corresponding switch (S25). The structure shown implements three filters (Fl, F2, F3) to accommodate exemplary frequency bands (Bl, B2, B3). This exemplary structure serves merely to illustrate the disclosed teachings. However, other embodiments comprising any number of filters corresponding to frequency bands other than those described herein may also be envisaged. The input impedance (Zinl) of LNA (LNA1) is defined as the impedance seen at node (Nl) into LNA (LNA1). Similarly, the input impedance (Zin2) of LNA (LNA2) is defined as the impedance seen at node (N2) into LNA (LNA2).

[0021] As noted previously with respect to RF receiver (100C) of Fig. 1C, depending upon the selected CA mode in which the receiver is operating, the signal corresponding to band frequency (B2), subsequent to filtering via filter (F2), may be routed to either of (LNA1, LNA2). As such LNAs are designed for distinct bands, and given that in both instances, the same impedance matching element, i.e. impedance matching (Z) of Fig. 1C, resides within the signal path, the impedance matching will be less than optimal for at least one of the bands, resulting in an overall performance degradation of the receiver. As will be elaborated upon in further detail below, the addition of impedance matching element (Z22) will help overcome this issue.

[0022] With continued reference to Fig. 2A, RF receiver (200A) further comprises a switching network including switches (S21, ..., S25). Such switches may be configured to accommodate concurrently a desired pair of frequency bands from amongst bands (Bl, B2, B3).

[0023] In this respect, Fig. 2B shows an exemplary table (200B) summarizing the states of switches for each carrier aggregate mode and respective LNA / frequency band correspondence. As a first example, when the CA mode B1+B2 is selected, switches (S21, S23, S25) are in the ON state (closed) and all other switches are in the OFF state (open). Accordingly, subsequent to being filtered via filter (Fl), the signal corresponding to frequency band (Bl) is directed to LNA (LNA1). This is shown by signal path (PC) in Fig. 2C. Moreover, the signalcorresponding to frequency band (B2), after being filtered by filter (F2), is routed to LNA (LNA2). Signal paths (PF1, PF2, PF3) of Fig. 2F indicate the signal paths of the signal of frequency band (B2) when such signal is routed to LNA (LNA2) while operating in CA mode B1+B2. As can be noticed, in this CA mode, impedance matching element (Z22) is switched in. Therefore, a combination of impedance matching elements (Z21, Z22) has the functionality of matching the output of filter (F2) to the input impedance (Zin2) of LNA (LNA2).

[0024] With reference to Fig. 2B, as a second example, when the CA mode B1+B3 is selected, switches (S21, S24) are in the ON state (closed) and all other switches are in the OFF state (open). Accordingly, subsequent to being filtered via filter (Fl), the signal corresponding to frequency band (Bl) is directed to LNA (LNA1). This is shown by signal path (PC) in Fig. 2C. Similarly, after being filtered by filter (F3), the signal corresponding to frequency band (B3) is routed to LNA (LNA2). This is shown by signal path (PD) in Fig. 2D.

[0025] With further reference to Fig. 2B, as a third example, when the CA mode B2+B3 is selected, switches (S22, S24) are in the ON state (closed) and all other switches are in the OFF state (open). Signal paths (PEI, PE2) of Fig. 2E indicate the signal paths of the signal of frequency band (B2) when such signal is routed to LNA (LNA1) while operating in CA mode B2+B3. In this case, impedance element (Z22) is switched out and the impedance matching element (Z21) serves to impedance match the output of filter (F2) to the input impedance (Zinl) of LNA (LNA1).

[0026] In view of what was described above, the following is noted:• Filter (F2) is shared between the CA modes B1+B2, and B2+B3 to convey the signal of frequency band (B2) to (LNA2, LNA1) respectively.• In operative CA conditions, both (LNA1, LNA2) are active regardless of the selected CA mode the receiver is operating in.• When operating in CA mode B1+B2, the signal of frequency band (B2) is directed to LNA (LNA2) and a combination of the impedance matching elements (Z21, Z22) are used to match the input impedance of LNA (LNA2). On the other hand, when operating in CA mode B2+B3, the signal of frequency band (B2) is routed to LNA (LNA1) and only the impedance matching element (Z21) is used to impedance match to the input of LNA (LNA1). In other words, RF receiver (200A) of Fig. 2A provides tunableimpedance matching to overcome the less effective impedance matching issue as described previously with regards to the RF receiver (100C) of Fig. IC.• In view of what was described above, depending on which CA mode the RF receiver is operating in, the switches are configured to selectively switch in two or more of the elements (Fl, F2, F3, Z22).• In various embodiments, depending on matching requirements, impedance matching elements (Z21, Z22) comprise reactive and / or resistive elements.

[0027] Fig. 2G shows an exemplary RF receiver (200G) according to an embodiment of the present disclosure. The principle of operation of this RF receiver is similar to what was described with regards to RF receiver (200A) of Fig. 2A except for the addition of switch (S26) which has the function of making impedance matching element (Z21) switchable. In other words, in this embodiment, both impedance matching elements (Z21, Z22) are switchable to give the design further flexibility at the expense of an additional switch. As an example, impedance matching element (Z21) may be switched out when operating in the B1+B3 CA mode, and switch in when operating in the B1+B2 or B2+B3 modes. When switched out, corresponding switch (S26) is in OFF state (open), thus providing further isolation.

[0028] With respect to the figures referenced in this disclosure, the dimensions for the various elements are not to scale; some dimensions have been greatly exaggerated vertically and / or horizontally for clarity or emphasis. In addition, references to orientations and directions (e.g., “top”, “bottom”, “above”, “below”, “lateral”, “vertical”, “horizontal”, etc.) are relative to the example drawings, and not necessarily absolute orientations or directions.

[0029] Various embodiments of the invention can be implemented to meet a wide variety of specifications. Unless otherwise noted above, selection of suitable component values is a matter of design choice. Various embodiments of the invention may be implemented in any suitable integrated circuit (IC) technology (including but not limited to MOSFET structures), or in hybrid or discrete circuit forms. Integrated circuit embodiments may be fabricated using any suitable substrates and processes, including but not limited to standard bulk silicon, high- resistivity bulk CMOS, silicon-on-insulator (SOI), and silicon-on-sapphire (SOS). Unless otherwise noted above, embodiments of the invention may be implemented in other transistor technologies such as bipolar, BiCMOS, LDMOS, BCD, GaAs HBT, GaN HEMT, GaAs pHEMT, and MESFET technologies. However, embodiments of the invention are particularlyuseful when fabricated using an SOI or SOS based process, or when fabricated with processes having similar characteristics. Fabrication in CMOS using SOI or SOS processes enables circuits with low power consumption, the ability to withstand high power signals during operation due to FET stacking, good linearity, and high frequency operation (z.e., radio frequencies up to and exceeding 300 GHz). Monolithic IC implementation is particularly useful since parasitic capacitances generally can be kept low (or at a minimum, kept uniform across all units, permitting them to be compensated) by careful design.

[0030] Voltage levels may be adjusted, and / or voltage and / or logic signal polarities reversed, depending on a particular specification and / or implementing technology (e.g., NMOS, PMOS, or CMOS, and enhancement mode or depletion mode transistor devices). Component voltage, current, and power handling capabilities may be adapted as needed, for example, by adjusting device sizes, serially “stacking” components (particularly FETs) to withstand greater voltages, and / or using multiple components in parallel to handle greater currents. Additional circuit components may be added to enhance the capabilities of the disclosed circuits and / or to provide additional functionality without significantly altering the functionality of the disclosed circuits.

[0031] Circuits and devices in accordance with the present invention may be used alone or in combination with other components, circuits, and devices. Embodiments of the present invention may be fabricated as integrated circuits (ICs), which may be encased in IC packages and / or in modules for ease of handling, manufacture, and / or improved performance. In particular, IC embodiments of this invention are often used in modules in which one or more of such ICs are combined with other circuit blocks (e.g. , filters, amplifiers, passive components, and possibly additional ICs) into one package. The ICs and / or modules are then typically combined with other components, often on a printed circuit board, to form part of an end product such as a cellular telephone, laptop computer, or electronic tablet, or to form a higher- level module which may be used in a wide variety of products, such as vehicles, test equipment, medical devices, etc. Through various configurations of modules and assemblies, such ICs typically enable a mode of communication, often wireless communication.

[0032] A number of embodiments of the invention have been described. It is to be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, some of the steps described above may be order independent, and thus can be performed in an order different from that described. Further, some of the stepsdescribed above may be optional. Various activities described with respect to the methods identified above can be executed in repetitive, serial, and / or parallel fashion.

[0033] It is to be understood that the foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the following claims, and that other embodiments are within the scope of the claims. In particular, the scope of the invention includes any and all feasible combinations of one or more of the processes, machines, manufactures, or compositions of matter set forth in the claims below. (Note that the parenthetical labels for claim elements are for ease of referring to such elements, and do not in themselves indicate a particular required ordering or enumeration of elements; further, such labels may be reused in dependent claims as references to additional elements without being regarded as starting a conflicting labeling sequence).

Claims

CLAIMS1. A radio frequency (RF) receiver comprising: a first low noise amplifier (LNA) and a second LNA; a first filter in correspondence with a first frequency band, the first filter having an output matched to an input impedance of the first LNA; a second filter in correspondence with a second frequency band; a third filter in correspondence with a third frequency band, the third filter having an output matched to an input impedance of the second LNA; a first impedance matching element coupled to an output of the second filter; and a selectively switchable second impedance matching element coupled to the output of the second filter, wherein: the first impedance matching element is configured to match the output of the second filter to an input impedance of the first LNA, and a combination of the first impedance matching element and the second impedance matching elements is configured to match the output of the second filter to an input impedance of the second LNA.

2. The RF receiver of claim 1, configured to aggregate any pair of frequency bands selected from the first, the second, and the third frequency bands.

3. The RF receiver claim 1 or 2, configured such that: in a first carrier aggregation (CA) mode, the first and the second frequency bands are aggregated; in a second CA mode, the first and the third frequency bands are aggregated, and in a third CA mode, the second the third frequency bands are aggregated.

4. The RF receiver of claim 3, further comprising a switching network being configured to selectively switch in, simultaneously, two or more of the first filter, the second filter, the third filter, and the second impedance matching element.

5. The RF receiver of claim 4, configured such that: in the first CA mode:after being filtered by the first filter, a signal corresponding to the first frequency band is received and amplified by the first LNA; and after being filtered by the second filter, a signal corresponding to the second frequency band is received and amplified by the second LNA.

6. The RF receiver of claim 4 or 5, wherein in the first CA mode: the first and the second filter are switched in; the third filter is switched out; and the second impedance matching element is switched in.

7. The RF receiver of claim 6, configured such that: in the second CA mode: after being filtered by the first filter, the signal corresponding to the first frequency band is received and amplified by the first LNA; and after being filtered by the third filter, the signal corresponding to the third frequency band is received and amplified by the second LNA.

8. The receiver of claim 7, wherein in the second CA mode: the first and the third filter are switched in; the second filter is switched out; and the second impedance matching element is switched out.

9. The RF receiver of claim 8 configured such that: in the third CA mode: after being filtered by the second filter, the signal corresponding to the second frequency band is received and amplified by the first LNA; and after being filtered by the third filter, the signal corresponding to the third frequency band is received and amplified by the second LNA.

10. The receiver of claim 9, wherein in the third CA mode: the second and the third filter are switched in; the first filter is switched out; and the second impedance matching element is switched out.

11. The RF receiver of claim 4, wherein the switching network comprises: a first switch, configured to switch the first filter in or out; a second and a third switch, configured to: switch the second filter in or out, and route a signal corresponding to the second frequency band towards either the first LNA or the second LNA; a fourth switch configured to switch the third filter in or out; and a fifth switch configured to switch the second impedance matching element in or out.

12. The receiver of claim 4, wherein the switching network is coupled to the first LNA via a first inductor matching the output of the first filter to the input impedance of the first LNA and to the second LNA via a second inductor matching the output of the third filter to the input impedance of the second LNA.

13. The receiver of any of claims 1 to 3, wherein the first impedance matching element is switchable.

14. The receiver of any of claims 1 to 3, wherein the first, second and the third frequency bands are in correspondence with the frequency ranges 2210-2170 MHz, 1805-1880 MHz, and 2620- 2690 MHz.

15. A radio frequency (RF) receiver including: a first low noise amplifier (LNA) selectively couplable to at least one of a first signal source or a second signal source; a second LNA selectively couplable to at least one of the second signal source or a third signal source; a first impedance matching element coupled to an output of the second signal source; and a selectively switchable second impedance matching element coupled to the output of the second signal source; wherein the selectively switchable second impedance is switched out when the first LNA is coupled to the first signal source and the second LNA is coupled to the third signal source, or when the second LNA is coupled to the first signal source and the second LNA is coupled to the third signal source; andwherein the selectively switchable second impedance is switched in when the first LNA is coupled to the first signal source and the second LNA is coupled to the second signal source.

16. The RF receiver of claim 15, wherein the first impedance matching element is selectively switchable.

17. A radio frequency (RF) receiver including: a first low noise amplifier (LNA) configured to selectively receive a first impedance matched signal from at least one of a first signal source or a second signal source; a second LNA configured to selectively receive a second impedance matched signal from at least one of the second signal source or a third signal source; a first impedance matching element coupled to an output of the second signal source; and a selectively switchable second impedance matching element coupled to the output of the second signal source; wherein the selectively switchable second impedance is switched in when the first LNA receives the first impedance matched signal from first signal source and the second LNA receives the second impedance matched signal from the second signal source, and otherwise the selectively switchable second impedance is switched out.

18. The RF receiver of claim 17, wherein the first impedance matching element is selectively switchable.

19. A method of tunable impedance matching in a radio frequency (RF) receiver, the RF receiver comprising: a first low noise amplifier (LNA) and a second LNA; a first filter in correspondence with a first frequency band; a second filter in correspondence with a second frequency band; a third filter in correspondence with a third frequency band; and a first impedance matching element and a second impedance matching element, the method comprising:A) in a first carrier aggregation (CA) mode where the first frequency band and the second frequency band are aggregated: al) filtering a signal corresponding to the first frequency band through the first filter to generate a first filtered signal; a2) directing the first filtered signal to the first LNA; a3) filtering a signal corresponding to the second frequency band to generate a second filtered signal; a4) directing the second filtered signal to the second LNA; and a5) matching an output of the second filter to an input of the second LNA through a combination of the first impedance matching element and the second impedance matching element;B) in a second carrier aggregation (CA) mode where the first frequency band and the third frequency band are aggregated: bl) filtering the signal corresponding to the first frequency band through the first filter to generate a first filtered signal; b2) directing the first filtered signal to the first LNA; b3) filtering a signal corresponding to the third frequency band to generate a third filtered signal; and b4) directing the third filtered signal to the second LNA;C) in a third carrier aggregation (CA) mode where the second frequency band and the third frequency band are aggregated: cl) filtering the signal corresponding to the second frequency band through the second filter to generate the second filtered signal; c2) directing the second filtered signal to the first LNA; c3) matching an output of the first filter to an input impedance of the first LNA through the first impedance matching element without the second impedance matching element; c4) filtering a signal corresponding to the third band to generate the third filtered signal; and c5) directing the third filtered signal to the second LNA.

20. A method of tunable impedance matching in a radio frequency (RF) receiver, including: selectively coupling a first low noise amplifier (LNA) selectively to at least one of a first signal source or a second signal source; selectively coupling a second LNA selectively to at least one of the second signal source or a third signal source; coupling a first impedance matching element to an output of the second signal source; and coupling a selectively switchable second impedance matching element to the output of the second signal source; switching out the selectively switchable second impedance when the first LNA is coupled to the first signal source and the second LNA is coupled to the third signal source, or when the second LNA is coupled to the first signal source and the second LNA is coupled to the third signal source; and switching in the selectively switchable second impedance when the first LNA is coupled to the first signal source and the second LNA is coupled to the second signal source.

21. The method of claim 20, wherein the first impedance matching element is selectively switchable.

22. A method of tunable impedance matching in a radio frequency (RF) receiver, including: selectively coupling a first low noise amplifier (LNA) to a first impedance matched signal from at least one of a first signal source or a second signal source; selectively coupling a second LNA configured to a second impedance matched signal from at least one of the second signal source or a third signal source; coupling a first impedance matching element to an output of the second signal source; coupling a selectively switchable second impedance matching element coupled to the output of the second signal source; and switching in the selectively switchable second impedance when the first LNA is coupled to the first impedance matched signal from first signal source and the second LNA is coupled to the second impedance matched signal from the second signal source, and otherwise switching out the selectively switchable second impedance.

23. The method of claim 22, wherein the first impedance matching element is selectively switchable.

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