# Patent

## Title
Tunable transmit cancellation in acoustic receiver filters

## Abstract

RF filtering circuitry includes a first input/output node, a second input/output node, a common node, first filtering circuitry, second filtering circuitry, and transmit signal cancellation circuitry. The first filtering circuitry is coupled between the first input/output node and the common node, and is configured to pass RF transmit signals within one or more transmit signal frequency bands while attenuating signals outside the one or more transmit signal frequency bands. The second filtering circuitry is coupled between the second input/output node and the common node, and is configured to pass RF receive signals within one or more receive signal frequency bands while attenuating signals outside the one or more receive signal frequency bands. The transmit signal cancellation circuitry is coupled between the common node and the second input/output node and is configured to generate a transmit cancellation signal from the RF transmit signals.

## Background
RELATED APPLICATIONS
This application claims the benefit of U.S. provisional patent application No. 62/205,818, filed Aug. 17, 2015, the disclosure of which is incorporated herein by reference in its entirety.


FIELD OF THE DISCLOSURE
The present disclosure relates to radio frequency (RF) filtering circuitry, and in particular to RF filtering circuitry including signal cancellation circuitry.
BACKGROUND
Radio frequency (RF) filtering circuitry is critical to the operation of modern wireless communications devices. RF filtering circuitry is often used to isolate RF signals within different frequency bands from one another, allowing wireless communications devices to communicate in a number of different frequency bands (i.e., operating bands), either separately or simultaneously. FIG. 1 illustrates conventional RF filtering circuitry 10. The conventional RF filtering circuitry 10 is a diplexer including a first input/output node 12A, a second input/output node 12B, and a common node 12C. A power amplifier 14, a low noise amplifier 16, and an antenna 18 are shown for context. The power amplifier 14 is coupled between a transmit signal node 20 and the first input/output node 12A. The low noise amplifier 16 is coupled between a receive signal node 22 and the second input/output node 12B. The antenna 18 is coupled to the common node 12C.
The conventional RF filtering circuitry 10 is configured to pass RF transmit signals TX within a transmit signal frequency band from the power amplifier 14 to the antenna 18 while attenuating signals outside the transmit signal frequency band. Further, the conventional RF filtering circuitry 10 is configured to pass RF receive signals RX within a receive frequency band from the antenna 18 to the low noise amplifier 16 while attenuating signals outside the receive frequency band. In general, the RF transmit signal provided by the power amplifier 14 is a high power signal when compared to the RF receive signals RX from the antenna 18. Accordingly, it is crucial for the conventional RF filtering circuitry 10 to adequately attenuate the RF transmit signal and harmonics thereof before it reaches the low noise amplifier 16. When the conventional RF filtering circuitry 10 supports only a small number of bands such as the diplexer shown in FIG. 1, providing adequate attenuation may be routine. However, as the number of bands supported by the conventional RF filtering circuitry 10 increases, the ability of the circuitry to provide adequate attenuation often decreases significantly.
FIG. 2 shows conventional RF filtering circuitry 24 configured to support a larger number of bands than that shown in FIG. 1. The conventional RF filtering circuitry 24 is a hexaplexer including a first input/output node 26A, a second input/output node 26B, a third input/output node 26C, a fourth input/output node 26D, a fifth input/output node 26E, a sixth input/output node 26F, and a common node 26G. A first power amplifier 28A, a second power amplifier 28B, a third power amplifier 28C, a first low noise amplifier 30A, a second low noise amplifier 30B, a third low noise amplifier 30C, and an antenna 32 are shown for context. The first power amplifier 28A is coupled between a first first input/output node 34A and the first input/output node 26A. The first low noise amplifier 30A is coupled between a first second input/output node 36A and the second input/output node 26B. The second power amplifier 28B is coupled between a second input/output node 34B and the third input/output node 26C. The second low noise amplifier 30B is coupled between a second second input/output node 36B and the fourth input/output node 26D. The third power amplifier 28C is coupled between a third first input/output node 34C and the fifth input/output node 26E. The third low noise amplifier 30C is coupled between a third second input/output node 36C and the sixth input/output node 26F. The antenna 32 is coupled to the common node 26G.
In operation, the conventional RF filtering circuitry 24 is configured to pass first RF transmit signals TX1 within a first transmit signal frequency band from the first power amplifier 28A to the antenna 32 while attenuating signals outside the first transmit signal frequency band, pass second RF transmit signals TX2 within a second transmit signal frequency band from the second power amplifier 28B to the antenna 32 while attenuating signals outside the second transmit signal frequency band, and pass third RF transmit signals TX3 within a third transmit signal frequency band from the third power amplifier 28C to the antenna 32 while attenuating signals outside the third transmit signal frequency band. Further, the conventional RF filtering circuitry 24 is configured to pass first
RF receive signals RX1 within a first receive signal frequency band from the antenna 32 to the first low noise amplifier 30A while attenuating signals outside the first receive signal frequency band, pass second RF receive signals RX2 within a second receive signal frequency band between the antenna 32 and the second low noise amplifier 30B while attenuating signals outside the second receive signal frequency band, and pass third RF receive signals RX3 within a third receive signal frequency band between the antenna 32 and the third low noise amplifier 30C while attenuating signals outside the third receive signal frequency band.
In general, the RF transmit signals provided by the first power amplifier 28A, the second power amplifier 28B, and the third power amplifier 28C may be high power signals when compared to the RF receive signals from the antenna 32. Accordingly, it is crucial for the conventional RF filtering circuitry 24 to adequately attenuate the RF transmit signals and harmonics thereof before they reach the first low noise amplifier 30A, the second low noise amplifier 30B, and/or the third low noise amplifier 30C. Failing to do so may result in desensitization and/or damage to these low noise amplifiers, especially when one or more harmonics of the RF transmit signals fall at or near the receive signal frequency band of the particular signal path.
When the conventional RF filtering circuitry 24 supports a large number of bands such as the hexaplexer shown in FIG. 2, it may be difficult to achieve the necessary isolation in each receive signal path to prevent desensitization of the first low noise amplifier 30A, the second low noise amplifier 30B, and/or the third low noise amplifier 30C. This problem may be exacerbated in carrier aggregation schemes in which multiple RF transmit signals and/or multiple RF receive signals are simultaneously processed by the conventional RF filtering circuitry 24, as intermodulation distortion products may form due to the interaction of the various signals at the common node 26G that may be particularly difficult to attenuate. Accordingly, there is a need for improved RF filtering circuitry able to adequately attenuate undesired signals.
SUMMARY
The present disclosure relates to radio frequency (RF) filtering circuitry, and in particular to RF filtering circuitry including signal cancellation circuitry. In one embodiment, RF filtering circuitry includes a first input/output node, a second input/output node, a common node, first filtering circuitry, second filtering circuitry, and transmit signal cancellation circuitry. The first filtering circuitry is coupled between the first input/output node and the common node, and is configured to pass RF transmit signals within one or more transmit signal frequency bands while attenuating signals outside the one or more transmit signal frequency bands. The second filtering circuitry is coupled between the second input/output node and the common node, and is configured to pass RF receive signals within one or more receive signal frequency bands while attenuating signals outside the one or more receive signal frequency bands. The transmit signal cancellation circuitry is coupled between the common node and the second input/output node and is configured to generate a transmit cancellation signal from the RF transmit signals and provide the transmit cancellation signal to the second input/output node in order to cancel one or more components of the RF transmit signals at the second input/output node. By using the transmit signal cancellation circuitry to cancel RF transmit signals at the second input/output node, isolation of the RF transmit signals from the RF receive signals may be improved. Further, the attenuation requirements of the second filtering circuitry at the one or more transmit signal frequency bands may be reduced, thereby improving the flexibility in the design of the RF filtering circuitry.
In one embodiment, the transmit cancellation signal is based on a transmit frequency of the RF transmit signals. By basing the transmit cancellation signal on the transmit frequency of the RF transmit signals, additional attenuation specifically targeted at the RF transmit signals may be provided, thereby improving the isolation of the RF transmit signals from the RF receive signals.
In one embodiment, the transmit cancellation circuitry comprises an adjustable attenuator configured to adjust an amplitude of the RF transmit signals and an adjustable phase shifter configured to adjust a phase of the RF transmit signals. Further, the RF filtering circuitry includes common node coupling circuitry and input/output node coupling circuitry. The common node coupling circuitry is coupled between the signal processing circuitry and the common node. The input/output node coupling circuitry is coupled between the signal processing circuitry and the second input/output node.
In one embodiment, the adjustable attenuator and the adjustable phase shifter may be adjusted based on a transmit frequency of the RF transmit signals.
Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
FIGS. 1 and 2 show conventional radio frequency (RF) filtering circuitry.
FIGS. 3 through 15 show RF filtering circuitry according to various embodiments of the present disclosure.



DETAILED DESCRIPTION
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the disclosure and illustrate the best mode of practicing the disclosure. Upon reading the following description in light of the accompanying drawings, 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.
FIG. 3 illustrates radio frequency (RF) filtering circuitry 36 according to one embodiment of the present disclosure. The RF filtering circuitry 36 includes a first input/output node 38A, a second input/output node 38B, and a common node 38C. First filtering circuitry 40A is coupled between the first input/output node 38A and the common node 38C. Second filtering circuitry 40B is coupled between the second input/output node 38B and the common node 38C. The first filtering circuitry 40A and the second filtering circuitry 40B may form a diplexer, duplexer, or any n-plexer, as shown in FIG. 3. Signal cancellation circuitry 42 is coupled between the common node 38C and the second input/output node 38B. Control circuitry 44 may be coupled to the signal processing circuitry 42.
In operation, the first filtering circuitry 40A may be configured to pass RF signals within a first frequency band between the first input/output node 38A and the common node 38C while attenuating signals outside of the first frequency band. The second filtering circuitry 40B may be configured to pass RF signals within a second frequency band between the second input/output node 38B and the common node 38C while attenuating signals outside of the second frequency band. Notably, as discussed above, if a transmit signal within the first frequency band is passed from the first input/output node 38A to the common node 38C, the second filtering circuitry 40B must significantly attenuate this signal to avoid desensitizing downstream receiver circuitry coupled to the second input/output node 38B. This may be difficult due to the strength of the transmit signal and the constraints on the design of the first filtering circuitry 40A and/or the second filtering circuitry 40B. Accordingly, the signal cancellation circuitry 42 is configured to generate a cancellation signal S_CAN from the RF signals within the first frequency band at the common node 38C and provide the cancellation signal to the second input/output node 38B in order to cancel one or more components of the RF signals within the first frequency band at the second input/output node.
By cancelling RF signals within the first frequency band at the second input/output node 38B, the isolation of the RF signals within the first frequency band from the RF signals within the second frequency band may be significantly improved when compared to using the first filtering circuitry 40A and the second filtering circuitry 40B alone. Further, providing additional attenuation within the first frequency band may significantly increase the flexibility afforded in the design of the first filtering circuitry 40A and/or the second filtering circuitry 40B, as the attenuation of this primary blocker signal (i.e., the RF signals within the first frequency band) generally dictate many of the design constraints thereof.
In some embodiments, the cancellation signal S_CAN generated by the signal cancellation circuitry 42 is based on a frequency of the RF signals within the first frequency band. As will be appreciated by those of ordinary skill in the art, the first frequency band may encompass a range of frequencies, while the RF signals within the first frequency band may be provided at a particular frequency or a sub-range of frequencies. For example, the first frequency band may be a Long Term Evolution (LTE) operating band, and the RF signals within the first frequency band may be provided at one or more resource blocks within the operating band. The ability of the signal cancellation circuitry 42 to provide the cancellation signal S_CAN may be limited to a relatively narrow bandwidth (e.g., one or two resource blocks). That is, the signal cancellation circuitry 42 may only be capable of generating the cancellation signal S_CAN in order to cancel signals within a narrow range of frequencies, rather than over the entirety of the first frequency band. By providing the cancellation signal S_CAN based on the specific frequency of the RF signals within the first frequency band, the cancellation may be provided at the precise frequency required to cancel the RF signals within the first frequency band, which may forego the need for wide bandwidth signal cancellation circuitry 42 and thereby reduce the necessary complexity and size of the signal cancellation circuitry 42.
The control circuitry 44 may provide one or more control signals to the signal cancellation circuitry 42 in order to control the amplitude, phase, or any other aspect of the transmit cancellation signal S_CAN. While the control circuitry 44 is shown integrated with the RF filtering circuitry 36, the control circuitry 44 may also be provided centrally along with other control mechanisms for a wireless communications device external to the RF filtering circuitry 36. For example, control signals may be provided to the signal cancellation circuitry 42 via a central controller that is part of RF front end circuitry including the RF filtering circuitry 36 without departing from the principles of the present disclosure.
As discussed above, the signal cancellation circuitry 42 may be used to cancel RF transmit signals in an RF receive path. However, the signal cancellation circuitry 42 may also be used to cancel RF transmit signals in a separate RF transmit path, or may be used to cancel any number of different undesired signals at the common node 38C, such as intermodulation distortion products, harmonics, or the like.
FIG. 4 shows the RF filtering circuitry 36 shown in FIG. 3 and additionally shows a power amplifier 46, a low noise amplifier 48, and an antenna 50 for context. The power amplifier 46 is coupled between a transmit signal node 52 and the first input/output node 38A. The low noise amplifier 48 is coupled between a receive signal node 54 and the second input/output node 38B. The antenna 50 is coupled to the third input/output node 38C. Similar to the above, the first filtering circuitry 40A is configured to pass RF transmit signals within a transmit signal frequency band between the first input/output node 38A and the common node 38B while attenuating signals outside the transmit signal frequency band. The second filtering circuitry 40B is configured to pass RF receive signals RX within a receive signal frequency band between the common node 38C and the second input/output node 38B while attenuating signals outside the receive signal frequency band. The power amplifier 46 is configured to receive RF transmit signals TX within the transmit signal frequency band from the transmit signal node 52, amplify the RF transmit signals TX, and provide the amplified RF transmit signals TX to the first filtering circuitry 40A, where they are then passed from the first input/output node 38A to the common node 38C by the first filtering circuitry 40A and radiated from the antenna 50. The low noise amplifier 48 is configured to receive RF receive signals RX within the receive signal frequency band received at the antenna 50 and passed from the common node 38C to the second input/output node 38B by the second filtering circuitry 40B, amplify the RF receive signals RX, and provide the amplified RF receive signals RX to the receive signal node, where they may then be further processed by downstream circuitry.
The signal cancellation circuitry 42 receives the signals at the common node 38C including the RF transmit signals TX within the transmit signal frequency band from the power amplifier 46. As discussed above, these RF transmit signals TX have a much higher amplitude than the RF receive signals RX received at the antenna 50. It is thus very important to attenuate the RF transmit signals TX before they reach the low noise amplifier 48 in order to avoid desensitization and/or damage thereto. Accordingly, the signal cancellation circuitry 42 generates a transmit cancellation signal S_CAN based on the RF transmit signals TX within the transmit signal frequency band at the common node 38C, and provides this transmit cancellation signal S_CAN to the second input/output node 38B in order to cancel one or more components of the RF transmit signals TX in the transmit signal frequency band before they reach the low noise amplifier 48. In some embodiments, the transmit cancellation signal S_CAN is based on the particular transmit frequency of the RF transmit signals TX within the transmit signal frequency band. For example, the transmit cancellation signal S_CAN may be based on a particular resource block or resource blocks used for the RF transmit signals TX within the transmit signal frequency band.
FIG. 5 shows the RF filtering circuitry 36 according to an additional embodiment of the present disclosure. The RF filtering circuitry 36 shown in FIG. 5 is substantially similar to that shown in FIG. 4, but further includes common node coupling circuitry 56 coupled between the signal cancellation circuitry 42 and the common node 38C and input/output node coupling circuitry 58 coupled between the signal cancellation circuitry 42 and the second input/output node 38B. The common node coupling circuitry 56 couples the RF transmit signals TX within the transmit signal frequency band from the common node 38C while providing minimal loading at the common node 38C and the antenna 50. Similarly, the input/output node coupling circuitry 58 couples the transmit cancellation signal S_CAN from the signal cancellation circuitry 42 to the second input/output node 38B while providing minimal loading to the second input/output node 38B and the low noise amplifier 48. As discussed below, the common node coupling circuitry 56 and the input/output node coupling circuitry 58 may provide resistive coupling, capacitive coupling, inductive coupling, or the like, and may comprise a directional coupler and/or a transformer in various embodiments. There are many different coupling circuitries known in the art that may be used for the common node coupling circuitry 56 and the input/output node coupling circuitry 58, all of which are contemplated herein.
FIG. 6 shows the RF filtering circuitry 36 according to an additional embodiment of the present disclosure. The RF filtering circuitry 36 shown in FIG. 6 is substantially similar to that shown in FIG. 5, but shows further details of the signal cancellation circuitry 42, the common node coupling circuitry 56, and the input/output node coupling circuitry 58. As shown, the common node coupling circuitry 56 and the input/output node coupling circuitry 58 are directional couplers. Further, the signal cancellation circuitry 42 includes an adjustable attenuator 60 and adjustable phase shifter 62 coupled in series. The adjustable attenuator 60 is configured to adjust an amplitude of the RF transmit signals TX within the first transmit signal band at the common node 38C. The adjustable phase shifter is configured to adjust a phase of the RF transmit signals TX within the first transmit signal band at the common node 38C. Adjusting the amplitude and phase of the RF transmit signals TX within the transmit signal frequency band provides the transmit cancellation signal S_CAN. In one embodiment, the amplitude and phase of the RF transmit signals TX within the transmit signal frequency band is adjusted such that the transmit cancellation signal S_CAN provides a signal that is equal but opposite the RF transmit signals TX that are not filtered by the second filtering circuitry 40B and thus provided at the second input/output node 38B.
The control circuitry 44 may be coupled to the adjustable attenuator 60 and the adjustable phase shifter 62 to control the amount of attenuation and phase shift provided, respectively. In one embodiment, the amount of attenuation provided by the adjustable attenuator 60 and the amount of phase shift provided by the adjustable phase shifter 62 is adjusted based on the transmit frequency of the RF transmit signals TX within the transmit signal frequency band as discussed above.
While the signal cancellation circuitry 42 is shown including the adjustable attenuator 60 and the adjustable phase shifter 62 in FIG. 6, any number of different signal processing components may be provided in the signal cancellation circuitry 42 without departing from the principles of the present disclosure. Those of ordinary skill in the art will recognize that any number of different signal processing components and/or techniques may be utilized to generate the transmit cancellation signal from the RF transmit signals TX within the transmit signal frequency band, all of which are contemplated herein.
FIG. 7 shows the RF filtering circuitry 36 according to an additional embodiment of the present disclosure. The RF filtering circuitry 36 shown in FIG. 7 is substantially similar to that shown in FIG. 6, but shows further details of the first filtering circuitry 40A and the second filtering circuitry 40B. Further, the common node coupling circuitry 56 is resistive coupling circuitry including a coupling resistor R_C in place of the directional coupler shown in FIG. 6. Finally, the components of each one of the first filtering circuitry 40A, the second filtering circuitry 40B, and the low noise amplifier 48 are shown enclosed in dashed boxes representing the organization of the components into discrete semiconductor and/or acoustic die. Specifically, a first semiconductor die 64 includes the low noise amplifier 48, and may further include the signal cancellation circuitry 42 and the input/output node coupling circuitry 58. A first acoustic die 66 includes a number of acoustic filtering components AF that make up the first filtering circuitry 40A. A number of filter inductors L_F are also included in the first filtering circuitry 40A, but may be located external to the first acoustic die 66. A second acoustic die 68 includes a number of acoustic filtering elements AF that make up the second filtering circuitry 40B. A number of filter inductors L_F are also included in the second filtering circuitry 40B, but are located external to the second acoustic die 68. Those of ordinary skill in the art will readily appreciate that the first filtering circuitry 40A and the second filtering circuitry 40B may be designed and provided in any number of different topologies using any number of different acoustic and or lumped element components, all of which are contemplated herein. The coupling resistor R_C may be provided on the second acoustic die 68 in some embodiments.
Replacing the directional coupler with the coupling resistor R_C may reduce the dependence of the RF signals coupled from the common node 38C to the signal cancellation circuitry 42 on the voltage standing wave ratio (VSWR) of the antenna 50. This may increase the consistence of RF transmit signal cancellation at the second input/output node 38B such that the cancellation is substantially independent of the VSWR of the antenna 50.
While the various parts of the RF filtering circuitry 36 are shown separated into specific semiconductor and/or acoustic die in FIG. 7, the present disclosure is not so limited. The various parts of the RF filtering circuitry 36 may be further separated into additional discrete die and/or combined onto a single die without departing from the principles of the present disclosure. Certain design constraints (e.g., the maximum bandwidth that can be accomplished via a single acoustic die) may dictate the particular separation between components in the RF filtering circuitry 36.
As discussed above, providing the signal cancellation circuitry 42 may relax certain design requirements on the first RF filtering circuitry 40A and/or the second RF filtering circuitry 40B. Generally, the largest blocker signal experienced by the second RF filtering circuitry 40B is the RF transmit signals TX within the transmit signal frequency band. Accordingly, the first filtering circuitry 40A and/or the second filtering circuitry 40B must be designed to provide a very high amount of attenuation for the RF transmit signals TX within the transmit signal frequency band in the path of the second filtering circuitry 40B. This may result in high order filters, increased complexity, real estate, and cost of the RF filtering circuitry 36. By using the signal cancellation circuitry 42 to reduce the largest blocker signal, the attenuation requirements of the first filtering circuitry 40A and the second filtering circuitry 40B for this signal may be significantly reduced, thereby allowing for the use of less complex filters, low order filters, and increased design flexibility for the filters.
FIG. 8 shows the RF filtering circuitry 36 according to an additional embodiment of the present disclosure. The RF filtering circuitry 36 shown in FIG. 8 is substantially similar to that shown in FIG. 7, except that the common node coupling circuitry 56 is capacitive coupling circuitry including a series coupling capacitor C_SE and a shunt coupling capacitor C_SH. The series coupling capacitor C_SE and the shunt coupling capacitor C_SH may be provided on the second acoustic die 68 in some embodiments.
Similar to the resistive coupling discussed above, replacing the directional coupler with the series coupling capacitor C_CSE and the shunt coupling capacitor C_SH may reduce the dependence of the RF signals coupled from the common node 38C to the signal cancellation circuitry 42 on the voltage standing wave ratio (VSWR) of the antenna 50. This may increase the consistence of RF transmit signal cancellation at the second input/output node 38B such that the cancellation is substantially independent of the VSWR of the antenna 50.
FIG. 9 shows the RF filtering circuitry 36 according to an additional embodiment of the present disclosure. The RF filtering circuitry 36 shown in FIG. 9 is substantially similar to that shown in FIG. 8, but further includes a cancellation filtering element AF_C coupled in a shunt configuration between the common node coupling circuitry 56 and the signal cancellation circuitry 42. The cancellation filtering element AF_C may be designed to pass the RF transmit signals TX within the transmit signal frequency band while attenuating signals outside the transmit signal frequency band. This may focus the transmit cancellation signal such that it cancels only the components of the RF transmit signals TX within the transmit signal frequency band at the second input/output node 38B, and does not degrade the RF receive signals RX within the receive signal frequency band. Alternatively, the cancellation filtering element AF_C may be designed to shunt the RF receive signals RX within the receive signal frequency band to ground while passing signals outside the receive signal frequency band. Again, this may prevent the transmit cancellation signal from degrading the RF receive signals RX within the receive signal frequency band.
While the cancellation filtering element AF_C is shown as an acoustic filtering element in FIG. 9, the present disclosure is not so limited. The cancellation filtering element AF_C may be a lumped element filter such as an LC filter, an active filter, or any other filtering element known in the art without departing from the principles of the present disclosure.
FIG. 10 shows the RF filtering circuitry 36 according to an additional embodiment of the present disclosure. The RF filtering circuitry 36 shown in FIG. 10 is substantially similar to that shown in FIG. 9, except that the cancellation acoustic filtering element AF_C is coupled in parallel with the common node coupling circuitry 56. The cancellation acoustic filtering element AF_C may be configured to pass the RF transmit signals TX within the transmit signal frequency band while attenuating signals outside the transmit signal frequency band. This may reduce the amount of attenuation on the RF transmit signals TX within the transmit signal frequency band that would normally be provided by the series coupling capacitor C_CSE and the shunt coupling capacitor C_CSH. The RF receive signals RX within the receive signal frequency band will be significantly attenuated by the series coupling capacitor C_CSE and the shunt coupling capacitor C_CSH, which reduces the impact of the transmit cancellation signal S_CAN on the RF receive signals RX at the second input/output node 38B.
Where the cancellation acoustic filtering element AF_C is tuned at or near the transmit signal frequency band, it may make more sense to provide the cancellation acoustic filtering element AF_C and the common node coupling circuitry 56 on the first acoustic die 66. Such an embodiment is shown in FIG. 11. The details of the RF filtering circuitry 36 and the operation thereof is substantially similar to that discussed above in FIG. 9. The acoustic filtering element AF_C shown in the parallel configuration in FIG. 10 may similarly be provided on the first acoustic die 66.
FIG. 12 shows RF filtering circuitry 70 according to an additional embodiment of the present disclosure. As discussed above, it is often the case in modern RF filtering circuitry 70 that several different transmit and/or receive frequency bands are supported. Accordingly, the RF filtering circuitry 70 shown in FIG. 12 includes a first input/output node 72A, a second input/output node 72B, a third input/output node 72C, a fourth input/output node 72D, and a common node 72E. First filtering circuitry 74A is coupled between the first input/output node 72A and the common node 72E. Second filtering circuitry 74B is coupled between the second input/output node 72B and the common node 72E. Third filtering circuitry 74C is coupled between the third input/output node 72C and the common node 72E. Fourth filtering circuitry 74D is coupled between the fourth input/output node 72D and the common node 72E. Common node coupling circuitry 76 is coupled to the common node 72E. First input/output node coupling circuitry 78A is coupled to the second input/output node 72B.
Second input/output node coupling circuitry 78B is coupled to the third input/output node 72C. Third input/output node coupling circuitry 78C is coupled to the fourth input/output node 72D. Signal cancellation circuitry 80 is coupled between the common node coupling circuitry 76, the first input/output node coupling circuitry 78A, the second input/output node coupling circuitry 78B, and the third input/output node coupling circuitry 78C. Control circuitry 82 is coupled to the signal cancellation circuitry 80.
For context, a power amplifier 84, a first low noise amplifier 86A, a second low noise amplifier 86B, a third low noise amplifier 86C, and an antenna 88 are shown. The power amplifier 84 is coupled between a transmit signal node 90 and the first input/output node 72A. The first low noise amplifier 86A is coupled between a first receive signal node 92A and the second input/output node 72B. The second low noise amplifier 86B is coupled between a second receive signal node 92B and the third input/output node 72C. The third low noise amplifier 86C is coupled between a third receive signal node 92C and the fourth input/output node 72D. The antenna 88 is coupled to the common node 72E.
In operation, the first filtering circuitry 74A is configured to pass RF transmit signals TX within a transmit signal frequency band between the first input/output node 72A and the common node 72E while attenuating signals outside the transmit signal frequency band. The second filtering circuitry 74B is configured to pass RF receive signals RX within a first receive signal frequency band between the common node 72E and the second input/output node 72B while attenuating signals outside the first receive signal frequency band. The third filtering circuitry 74C is configured to pass RF receive signals within a second receive signal frequency band between the common node 72E and the third input/output node 72C while attenuating signals outside the second receive signal frequency band. The fourth filtering circuitry 74D is configured to pass RF receive signals within a third receive signal frequency band between the common node 72E and the fourth input/output node 72D while attenuating signals outside the third receive signal frequency band.
The power amplifier 84 is configured to receive RF transmit signals TX within the transmit signal frequency band, amplify the RF transmit signals TX, and provide the amplified RF transmit signals TX to the first input/output node 72A, where they are then passed by the first filtering circuitry 74A to the common node 72E. The first low noise amplifier 86A is configured to receive first RF receive signals RX1 within the first receive signal frequency band received at the antenna 88 and passed from the common node 72E to the second input/output node 72B by the second filtering circuitry 74B, amplify the first RF receive signals RX1, and pass the first amplified RF receive signals RX1 to the first receive signal node, where they may be further processed by downstream circuitry. The second low noise amplifier 86B is configured to receive second RF receive signals RX2 within the second receive signal frequency band, amplify the second RF receive signals RX2, and pass the second amplified RF receive signals RX2 to the second receive signal node, where they may be further processed by downstream circuitry. The third low noise amplifier 86C may be configured to receive third RF receive signals RX3 within the third receive signal frequency band, amplify the third RF receive signals RX3, and pass the third RF receive signals RX3 to the third receive signal node, where they may be further processed by downstream circuitry.
The signal cancellation circuitry 80 receives the signals at the common node 72E including the RF transmit signals TX within the transmit signal frequency band from the power amplifier 84. As discussed above, these RF transmit signals TX have a much higher amplitude than the RF receive signals RX received at the antenna 88. It is thus very important to attenuate the RF transmit signals TX before they reach the first low noise amplifier 86A, the second low noise amplifier 86B, and/or the third low noise amplifier 86C. Accordingly, the signal cancellation circuitry 80 generates a transmit cancellation signal S_CAN based on the RF transmit signals TX within the transmit signal frequency band at the common node 72E, and provides this transmit cancellation signal S_CAN to one or more of the second input/output node 72B, the third input/output node 72C, and the fourth input/output node 72D in order to cancel one or more components of the RF transmit signals TX in the transmit signal frequency band before they reach the respective low noise amplifiers. In some embodiments, the transmit cancellation signal S_CAN is based on the particular transmit frequency of the RF transmit signals TX within the transmit signal frequency band. For example, the transmit cancellation signal S_CAN may be based on the particular resource block or resource blocks within the transmit signal frequency band that are utilized for transmission.
Notably, the details of the common node coupling circuitry 76, the first input/output node coupling circuitry 78A, the second input/output node coupling circuitry 78B, and the third input/output node coupling circuitry 78C may be similar to that shown above. In short, the common node coupling circuitry 76, the first input/output node coupling circuitry 78A, the second input/output node coupling circuitry 78B, and the third input/output node coupling circuitry 78C may be any one of resistive coupling circuitry, capacitive coupling circuitry, inductive coupling circuitry, a directional coupler, a transformer, or the like.
FIG. 13 shows the RF filtering circuitry 70 according to an additional embodiment of the present disclosure. The RF filtering circuitry 70 shown in FIG. 13 is substantially similar to that shown FIG. 12 but further includes switching circuitry 94 between the first input/output node coupling circuitry 78A, the second input/output node coupling circuitry 78B, the third input/output node coupling circuitry 78C, and the signal cancellation circuitry 80. The switching circuitry 94 may be coupled to the control circuitry 82 and configured to selectively provide the transmit cancellation signal S_CAN to one or more of the first input/output node coupling circuitry 78A, the second input/output node coupling circuitry 78B, and the third input/output node coupling circuitry 78C. In some cases, it may be desirable not to provide the transmit cancellation signal S_CAN to any one of the second input/output node 72B, the third input/output node 72C, and the third input/output node 72D, or to selectively provide the transmit cancellation signal S_CAN to one or more of these input/output nodes. The switching circuitry 94 may thus allow for the selective delivery of the transmit cancellation signal S_CAN.
While the foregoing embodiments have focused on cancelling RF transmit signals in a receive path of RF filtering circuitry, there may be situations in which it is desirable to cancel RF transmit signals in a separate transmit path of RF filtering circuitry. This may be necessary, for example, to reduce intermodulation distortion products formed by the combination of different harmonics of separate transmit signals in the RF filtering circuitry. Accordingly, FIG. 14 shows the RF filtering circuitry 70 according to an additional embodiment of the present disclosure, wherein the RF filtering circuitry 70 is coupled to a first power amplifier 84A, a second power amplifier 84B, a first low noise amplifier 86A, and a second low noise amplifier 86B.
Specifically, the first power amplifier 84A is coupled between a first transmit signal node 90A and the first input/output node 72A, the first low noise amplifier 86A is coupled between a first receive signal node 92A and the second input/output node 72B, the second power amplifier 84B is coupled between a second transmit signal node 90B and the third input/output node 72C, and the second low noise amplifier 86B is coupled between a second receive signal node 92B and the fourth input/output node 72D. The first filtering circuitry 74A is configured to pass RF transmit signals TX within a first transmit signal frequency band between the first input/output node 72A and the common node 72E while attenuating signals outside the first transmit signal frequency band. The second filtering circuitry 74B is configured to pass RF receive signals RX within a first receive signal frequency band between the common node 72E and the second input/output node 72B while attenuating signals outside the first receive signal frequency band. The third filtering circuitry 74C is configured to pass RF transmit signals TX within a second transmit signal frequency band between the third input/output node 72C and the common node 72E while attenuating signals outside the second transmit signal frequency band. The fourth filtering circuitry 74D is configured to pass RF receive signals RX within a second receive signal frequency band between the common node 72E and the fourth input/output node 72D while attenuating signals outside the second receive signal frequency band.
The first power amplifier 84A is configured to receive first RF transmit signals TX1 within the first transmit signal frequency band from the first transmit signal node 90A, amplify the first RF transmit signals TX1, and provide the first RF transmit signals TX1 to the first input/output node 72A, where they are then passed by the first filtering circuitry 74A to the common node 72E and radiated from the antenna 88. The first low noise amplifier 86A is configured to receive first RF receive signals RX1 within the first receive signal frequency band received at the antenna 88 and passed from the common node 72E to the second input/output node 72B by the second filtering circuitry 74B, amplify the first RF receive signals RX1, and provide the amplified first RF receive signals RX1 to the first receive signal node 92A, where they may be further processed by downstream circuitry. The second power amplifier 84B is configured to receive second RF transmit signals TX2 within the second transmit signal frequency band from the second transmit signal node 90B, amplify the second RF transmit signals TX2, and provide the second RF transmit signals TX2 to the third input/output node 72C, where they are then passed by the third filtering circuitry 74C to the common node 72E and radiated from the antenna 88. The second low noise amplifier 86B is configured to receive second RF receive signals RX2 within the second receive signal frequency band received at the antenna 88 and passed from the common node 72E to the fourth input/output node 72D by the fourth filtering circuitry 74D, amplify the second RF receive signals RX2, and provide the amplified second RF receive signals RX2 to the second receive signal node 92B, where they may be further processed by downstream circuitry.
The signal cancellation circuitry 80 receives the signals at the common node 72E including the RF transmit signals within the first transmit signal frequency band from the first power amplifier 84A, and generates the transmit cancellation signal S_CAN based on these RF transmit signals. The transmit cancellation signal S_CAN is then provided to the third input/output node 72C via the input/output node coupling circuitry 78, which is coupled to the third input/output node 72C in the present embodiment. Accordingly, one or more components of the RF transmit signals TX within the first transmit signal frequency band may be cancelled from the RF transmit signals TX within the second transmit signal frequency band. Such cancellation may prevent the amplification of intermodulation distortion products that may occur due to the combination of the RF transmit signals TX within the first transmit signal frequency band and the RF transmit signals TX within the second transmit signal frequency band. As discussed above, the transmit cancellation signal S_CAN may be based on the particular frequency of the RF transmit signals TX within the first transmit signal frequency band. For example, the transmit cancellation signal S_CAN may be based on the particular resource block or resource blocks that are utilized for transmission.
FIG. 15 shows the RF filtering circuitry 70 according to an additional embodiment in which the transmit cancellation signal S_CAN can be selectively provided to both transmit signal paths and receive signal paths. Specifically, first input/output node coupling circuitry 78A may allow the transmit cancellation signal S_CAN to be provided to the second input/output node 72B, second input/output node coupling circuitry 78B may allow the transmit cancellation signal S_CAN to be provided to the third input/output node 72C, and third input/output node coupling circuitry 78C may allow the transmit cancellation signal S_CAN to be provided to the fourth input/output node 72D. The switching circuitry 94 may allow the transmit cancellation signal S_CAN to be provide to each one of the first input/output node coupling circuitry 78A, the second input/output node coupling circuitry 78B, and the third input/output node coupling circuitry 78C or any subset thereof.
Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

## Claims

1. A radio frequency (RF) filtering circuitry comprising:
a first node;
a second node;
a common node;
first filtering circuitry comprising at least one first acoustic filtering component coupled between the first node and the common node and configured to pass RF transmit signals within one or more transmit signal frequency bands between the first node and the common node while attenuating signals outside the one or more transmit frequency bands;
second filtering circuitry comprising at least one second acoustic filtering component coupled between the second node and the common node and configured to pass RF receive signals within one or more receive signal frequency bands between the common node and the second node while attenuating signals outside the one or more receive frequency bands; and
transmit signal cancellation circuitry provided in a cancellation path extending between the common node and the second node, the transmit signal cancellation circuitry configured to generate a transmit cancellation signal from the RF transmit signals and provide the transmit cancellation signal to the second node in order to cancel one or more components of the RF transmit signals at the second node, the transmit signal cancellation circuitry comprising a capacitive divider attenuator comprising a series capacitor coupled in series in the cancellation path and a shunt capacitor coupled between the cancellation path and ground.

2. The RF filtering circuitry of claim 1 wherein the transmit cancellation signal is based on a transmit frequency of the RF transmit signals.

3. The RF filtering circuitry of claim 1 wherein:
the transmit signal cancellation circuitry comprises an adjustable attenuator configured to adjust an amplitude of the RF transmit signals and an adjustable phase shifter coupled in series with the adjustable attenuator and configured to adjust a phase of the RF transmit signals; and
the RF filtering circuitry further comprises:
common node coupling circuitry coupled between the transmit signal cancellation circuitry and the common node; and
node coupling circuitry coupled between the transmit signal cancellation circuitry and the second node.

4. The RF filtering circuitry of claim 3 wherein the adjustable attenuator and the adjustable phase shifter are adjusted based on a transmit frequency of the RF transmit signals.

5. The RF filtering circuitry of claim 3 wherein the common node coupling circuitry provides capacitive coupling between the common node and the transmit signal cancellation circuitry.

6. The RF filtering circuitry of claim 5 wherein the node coupling circuitry provides capacitive coupling between the second node and the transmit signal cancellation circuitry.

7. The RF filtering circuitry of claim 5 wherein the node coupling circuitry provides resistive coupling between the second node and the transmit signal cancellation circuitry.

8. The RF filtering circuitry of claim 5 wherein the node coupling circuitry is a directional coupler configured to couple the transmit cancellation signal from the transmit signal cancellation circuitry to the second node.

9. The RF filtering circuitry of claim 3 wherein the common node coupling circuitry provides resistive coupling between the common node and the transmit signal cancellation circuitry.

10. The RF filtering circuitry of claim 9 wherein the node coupling circuitry provides capacitive coupling between the second node and the transmit signal cancellation circuitry.

11. The RF filtering circuitry of claim 9 wherein the node coupling circuitry provides resistive coupling between the second node and the transmit signal cancellation circuitry.

12. The RF filtering circuitry of claim 9 wherein the node coupling circuitry is a directional coupler configured to couple the transmit cancellation signal from the transmit signal cancellation circuitry to the second node.

13. The RF filtering circuitry of claim 3 wherein the common node coupling circuitry is a directional coupler configured to couple signals at the common node to the transmit signal cancellation circuitry.

14. The RF filtering circuitry of claim 13 wherein the node coupling circuitry provides capacitive coupling between the second node and the transmit signal cancellation circuitry.

15. The RF filtering circuitry of claim 13 wherein the node coupling circuitry provides resistive coupling between the second node and the transmit signal cancellation circuitry.

16. The RF filtering circuitry of claim 13 wherein the node coupling circuitry is a directional coupler configured to couple the transmit cancellation signal from the transmit signal cancellation circuitry to the second node.

17. The RF filtering circuitry of claim 3 further comprising cancellation filtering circuitry coupled between the transmit signal cancellation circuitry and the common node coupling circuitry and configured to pass RF signals within the one or more transmit signal frequency bands while attenuating signals outside the one or more transmit signal frequency bands.

18. The RF filtering circuitry of claim 3 further comprising cancellation filtering circuitry coupled between the transmit signal cancellation circuitry and the common node coupling circuitry and configured to attenuate RF signals within the one or more receive signal frequency bands while passing signals outside the one or more receive signal frequency bands.

19. The RF filtering circuitry of claim 1 wherein the transmit signal cancellation circuitry comprises
an acoustic filtering element coupled between the second node and ground and configured to pass the RF transmit signals from the common node to the second node while attenuating signals outside the one or more transmit signal frequency bands.

20. The RF filtering circuitry of claim 19 wherein:
the first filtering circuitry is located on a first acoustic die;
the second filtering circuitry is located on a second acoustic die that is separate from the first acoustic die; and
the transmit signal cancellation circuitry is located on the first acoustic die.

21. The RF filtering circuitry of claim 1 wherein the transmit signal cancellation circuitry comprises
an acoustic filtering element coupled in series with the series capacitor such that the acoustic filtering element is coupled between the second node and the series capacitor, the acoustic filtering element configured to pass the RF transmit signals from the common node to the second node while attenuating signals outside the one or more transmit signal frequency bands.

22. A radio frequency (RF) filtering circuitry comprising:
a first node;
a second node;
a common node;
first filtering circuitry coupled between the first node and the common node and configured to pass RF signals within a first frequency band between the first node and the common node while attenuating signals outside of the first frequency band;
second filtering circuitry coupled between the second node and the common node and configured to pass RF signals within a second frequency band between the second node and the common node while attenuating signals outside of the second frequency band; and
signal cancellation circuitry provided in a cancellation path extending between the common node and the second node, the signal cancellation circuitry configured to generate a cancellation signal from the RF signals within the first frequency band and provide the cancellation signal to the second node in order to cancel one or more components of the RF signals within the first frequency band at the second node, the signal cancellation circuitry comprising a capacitive divider attenuator comprising a series capacitor coupled in series in the cancellation path and a shunt capacitor coupled between the cancellation path and ground.

23. The RF filtering circuitry of claim 22 wherein the cancellation signal is based on a frequency of the RF signals within the first frequency band.

24. The RF filtering circuitry of claim 1 wherein the transmit signal cancellation circuitry comprises an acoustic filtering element coupled to the cancellation path between the cancellation path and ground.

25. The RF filtering circuitry of claim 1 wherein the transmit signal cancellation circuitry comprises an acoustic filtering element coupled to and in series in the cancellation path.

26. The RF filtering circuitry of claim 1 wherein at least a portion of the transmit signal cancellation circuitry is located on an acoustic die of the first or second filtering circuitry.

27. A radio frequency (RF) filtering circuitry comprising:
a first node;
a second node;
a common node;
first filtering circuitry coupled between the first node and the common node and configured to pass RF transmit signals within one or more transmit signal frequency bands between the first node and the common node while attenuating signals outside the one or more transmit frequency bands;
second filtering circuitry coupled between the second node and the common node and configured to pass RF receive signals within one or more receive signal frequency bands between the common node and the second node while attenuating signals outside the one or more receive frequency bands; and
transmit signal cancellation circuitry provided in a cancellation path extending between the common node and the second node, the transmit signal cancellation circuitry configured to generate a transmit cancellation signal from the RF transmit signals and provide the transmit cancellation signal to the second node in order to cancel one or more components of the RF transmit signals at the second node, the transmit signal cancellation circuitry comprising an acoustic filtering element coupled to the cancellation path.

28. The RF filtering circuitry of claim 27, wherein the acoustic filtering element is coupled between the cancellation path and ground.

29. The RF filtering circuitry of claim 27, wherein the acoustic filtering element is coupled in series in the cancellation path.

30. The RF filtering circuitry of claim 27, wherein the acoustic filtering element is located on an acoustic die of the first or second filtering circuitry.

31. The RF filtering circuitry of claim 27, wherein the transmit signal cancellation circuitry comprises a capacitive divider attenuator comprising a series capacitor coupled in series in the cancellation path and a shunt capacitor coupled between the cancellation path and ground.

32. A radio frequency (RF) filtering circuitry comprising:
a first node;
a second node;
a common node;
first filtering circuitry coupled between the first node and the common node and configured to pass RF transmit signals within one or more transmit signal frequency bands between the first node and the common node while attenuating signals outside the one or more transmit frequency bands, the first filtering circuitry located on a first acoustic die;
second filtering circuitry coupled between the second node and the common node and configured to pass RF receive signals within one or more receive signal frequency bands between the common node and the second node while attenuating signals outside the one or more receive frequency bands, the second filtering circuitry located on a second acoustic die; and
transmit signal cancellation circuitry provided in a cancellation path extending between the common node and the second node, the transmit signal cancellation circuitry configured to generate a transmit cancellation signal from the RF transmit signals and provide the transmit cancellation signal to the second node in order to cancel one or more components of the RF transmit signals at the second node, the transmit signal cancellation circuitry located on the first or second acoustic die, wherein the transmit signal cancellation circuitry comprises:
a capacitive divider attenuator comprising a series capacitor coupled in series in a cancellation path and a shunt capacitor coupled between the cancellation path and ground; and
an acoustic filtering element coupled to the cancellation path between the cancellation path and ground.

33. A radio frequency (RF) filtering circuitry comprising:
a first node;
a second node;
a common node;
first filtering circuitry coupled between the first node and the common node and configured to pass RF transmit signals within one or more transmit signal frequency bands between the first node and the common node while attenuating signals outside the one or more transmit frequency bands, the first filtering circuitry located on a first acoustic die;
second filtering circuitry coupled between the second node and the common node and configured to pass RF receive signals within one or more receive signal frequency bands between the common node and the second node while attenuating signals outside the one or more receive frequency bands, the second filtering circuitry located on a second acoustic die; and
transmit signal cancellation circuitry provided in a cancellation path extending between the common node and the second node, the transmit signal cancellation circuitry configured to generate a transmit cancellation signal from the RF transmit signals and provide the transmit cancellation signal to the second node in order to cancel one or more components of the RF transmit signals at the second node, the transmit signal cancellation circuitry located on the first or second acoustic die, wherein the transmit signal cancellation circuitry comprises:
a capacitive divider attenuator comprising a series capacitor coupled in series in a cancellation path and a shunt capacitor coupled between the cancellation path and ground; and
an acoustic filtering element coupled to and in series in the cancellation path.