Customizable tunable filter

Abstract

This document provides a customizable tunable filter. In some embodiments, the tunable filter includes: a first filter bank including a plurality of high-pass filters, each high-pass filter having a different cutoff frequency; and a second filter bank including a plurality of low-pass filters, each low-pass filter having a different cutoff frequency. The tunable filter further includes: a first pair of switches configured to select a first filter selected from the first filter bank; and a second pair of switches configured to select a second filter selected from the second filter bank. The tunable filter operates at a first cutoff frequency of the first filter and a second cutoff frequency of the second filter.

Description

Technical Field

[0001] Embodiments of the present invention relate to electronic systems, and more specifically, to customizable tunable filters that can be used, for example, in software-defined radios. Background Technology

[0002] Electronic systems can use tunable filters to adjust the frequencies filtered within the signal chain. Tunable filters can be used in many different applications, including but not limited to software-defined radio and mixed-signal front-ends. To provide additional flexibility for a given application, greater customization of tunable filters is desired, allowing for more precise selection of the specific frequencies filtered by the tunable filter. Summary of the Invention

[0003] This document provides customizable tunable filters. In one aspect, a tunable filter with a controllable cutoff frequency is provided, wherein the tunable filter comprises: a first filter bank including a plurality of high-pass filters, each high-pass filter having a different cutoff frequency; a second filter bank including a plurality of low-pass filters, each low-pass filter having a different cutoff frequency; a first pair of switches configured to select a first filter selected from the first filter bank; and a second pair of switches configured to select a second filter selected from the second filter bank, wherein the tunable filter operates at a first cutoff frequency of the first filter and a second cutoff frequency of the second filter.

[0004] In another aspect, a method for tunable filtering includes: selecting a first filter from a first filter bank of the tunable filter using a first pair of switches, the first filter bank including a plurality of high-pass filters; selecting a second filter from a second filter bank of the tunable filter using a second pair of switches, the second filter bank including a plurality of low-pass filters; and filtering a radio frequency signal using the tunable filter, wherein the filtering is based on a first cutoff frequency of the first filter and a cutoff frequency of the second filter.

[0005] In another aspect, a radio frequency (RF) module includes: a module substrate; and a semiconductor die attached to the module substrate, wherein the semiconductor die includes: a first filter bank including a plurality of high-pass filters, each high-pass filter having a different cutoff frequency; a second filter bank including a plurality of low-pass filters, each low-pass filter having a different cutoff frequency; a first pair of switches configured to select a first filter selected from the first filter bank, wherein the first filter has a first cutoff frequency; and a second pair of switches configured to select a second filter selected from the second filter bank, wherein the second filter has a second cutoff frequency. Attached Figure Description

[0006] Figure 1 This is a schematic diagram of an example of an RF communication system that may include one or more tunable filters, based on the teachings of this document.

[0007] Figure 2 This is a diagram of an example of a tunable filter.

[0008] Figure 3 It is shown Figure 2 The frequency response curve of the tunable filter.

[0009] Figure 4 This is a diagram of an embodiment of a tunable filter according to aspects of this disclosure.

[0010] Figure 5 An example tunable filter configured to provide a bandpass filter response according to aspects of this disclosure is shown.

[0011] Figure 6 It shows that it can be tuned individually. Figure 5 The cutoff frequencies of the high-pass and low-pass filters of the tunable filter are used to provide multiple different bandpass responses.

[0012] Figure 7 It can be used Figure 4 An exemplary embodiment of the control circuit in a tunable filter.

[0013] Figure 8A This is an embodiment of a semiconductor die including a tunable filter.

[0014] Figure 8B This is another embodiment of a semiconductor die that includes a tunable filter.

[0015] Figure 8C It includes Figure 8B An example of a module for a semiconductor die.

[0016] Figure 9A This is an example of a controllable low-pass filter.

[0017] Figure 9B This is an example of a controllable high-pass filter. Detailed Implementation

[0018] The following detailed description of embodiments presents various descriptions of specific embodiments of the invention. In this specification, reference is made to the accompanying drawings, wherein similar reference numerals may denote the same or functionally similar elements. It should be understood that the elements shown in the drawings are not necessarily drawn to scale. Furthermore, it should be understood that some embodiments may include more elements than shown in the drawings and / or a subset of the elements illustrated in the drawings. Additionally, some embodiments may combine any suitable combination of features from two or more drawings.

[0019] Introduction to RF Communication Systems

[0020] Radio frequency (RF) communication systems communicate by wirelessly transmitting and receiving RF signals. Such RF communication systems may include one or more filters to filter out (e.g., attenuate) a fixed set of frequencies from the signal while allowing the remaining frequencies to pass through. Examples of filters include, but are not limited to, low-pass filters, high-pass filters, and band-pass filters.

[0021] While filters used in RF communication systems can be implemented to filter a fixed group of frequencies, some applications require tunable filters where the group of frequencies to be filtered can be selected. For example, this configurability allows for channel or band selection and / or provides adjustment of the filter's corner frequency.

[0022] It is also desirable to integrate filters for RF communication systems with other system components (such as switches, attenuators, and / or amplifiers) on a single chip. For example, integrated filters can reduce the overall system area and cost, and / or result in shorter connections between components, leading to lower insertion loss. Furthermore, integrating filters on a chip facilitates filter configuration because filter control circuitry can be easily fabricated on the chip along with the filter, and / or the data used to configure the filter can be provided via the chip's pins (e.g., using a serial interface or bus).

[0023] Conversely, some filters, such as acoustic filters and passive filters implemented with surface mount devices (SMD), are limited or lack configurability and / or cannot be integrated on-chip with other components of the RF communication system.

[0024] The tunable filter described in this article can filter signals over a wide frequency range, including not only RF signals between 100MHz and 7GHz, but also higher frequencies such as the X-band (approximately 7GHz to 12GHz) and K-band. u K-band (approximately 12GHz to 18GHz), K-band (approximately 18GHz to 27GHz), K aThe RF bands are approximately 27 GHz to 40 GHz, V-band (approximately 40 GHz to 75 GHz), and / or W-band (approximately 75 GHz to 110 GHz). Therefore, the teachings of this paper can be applied to a wide range of RF communication systems, including microwave communication systems.

[0025] RF signals filtered by tunable filters can be associated with a variety of communication standards, including but not limited to Global System for Mobile Communications (GSM), GSM Evolution Enhanced Data Rate (EDGE), Code Division Multiple Access (CDMA), Wideband CDMA (W-CDMA), 3G, Long Term Evolution (LTE), 4G and / or 5G, and other proprietary and non-proprietary communication standards.

[0026] Figure 1 This is a schematic diagram of an example of an RF communication system 10, which may include one or more tunable filters 5A-5C implemented in accordance with the teachings of this document.

[0027] Although the RF communication system 10 illustrates an example of an electronic system that may include one or more tunable filters 5A-5C as described herein, the tunable filters 5A-5C may also be used in other configurations of the electronic system.

[0028] Furthermore, despite Figure 1 The specific configuration of the components is shown, but the RF communication system 10 can be adapted and modified in a variety of ways. For example, the RF communication system 10 may include more or fewer receive paths and / or transmit paths. In addition, the RF communication system 10 can be modified to include more or fewer components and / or different component arrangements, including, for example, different RF switching circuits, amplifiers, and / or filter arrangements.

[0029] In the illustrated configuration, the RF communication system 10 includes a baseband processor 1, an I / Q modulator 2, an I / Q demodulator 3, a first tunable filter 5A, a power amplifier 6, a transmit / receive (T / R) switch 7, a low-noise amplifier (LNA) 8, an antenna 9, a second tunable filter 5B, and a third tunable filter 5C. Although the first to third tunable filters 5A-5C are each described as tunable filters, in some embodiments, one or more of the first to third tunable filters 5A-5C may be implemented as non-tunable filters and / or omitted in some embodiments. Furthermore, other locations of the tunable filters in the transmit and / or receive paths of the RF communication system 10 are also possible.

[0030] like Figure 1As shown, baseband processor 1 generates in-phase (I) and quadrature-phase (Q) transmit signals and provides them to I / Q modulator 2. Furthermore, baseband processor 1 receives I and Q receive signals from I / Q demodulator 3. The I and Q transmit signals correspond to signal components of the transmit signal with specific amplitude, frequency, and phase. For example, the I and Q transmit signals represent in-phase and quadrature-phase sinusoidal components, respectively, and can be equivalent representations of the transmit signals. Similarly, the I and Q receive signals correspond to signal components of the receive signal with specific amplitude, frequency, and phase.

[0031] In some implementations, the I transmit signal, Q transmit signal, I receive signal, and Q receive signal are digital signals. Furthermore, the baseband processor 1 may include a digital signal processor, a microprocessor, or a combination thereof for processing digital signals.

[0032] The I / Q modulator 2 receives I and Q transmit signals from the baseband processor 1 and processes them to generate a modulated RF signal. In some configurations, the I / Q modulator 2 may include a DAC configured to convert the I and Q transmit signals into an analog format, a mixer for up-converting the I and Q transmit signals to radio frequency, and a signal combiner for combining the up-converted I and Q signals into a modulated RF signal.

[0033] The first tunable filter 5A receives a modulated RF signal from the I / Q modulator 2 and provides the filtered RF signal to the input of the power amplifier 6. In some configurations, the first tunable filter 5A can implement a bandpass filter configured to provide bandpass filtering, wherein the lower and upper cutoff frequencies of the bandpass are tunable based on the input signal received by the first tunable filter 5A. In some embodiments, the first tunable filter 5A can also be configured to implement a low-pass filter, a bandpass filter, a notch filter, a high-pass filter, or a combination thereof based on the input signal, wherein each may include a tunable cutoff frequency. Therefore, a specific group of frequencies filtered by the first tunable filter 5A can be adjusted using the input signal applied to the first tunable filter 5A.

[0034] Power amplifier 6 amplifies the filtered RF signal to produce an amplified RF signal, which is provided to transmit / receive switch 7. Transmit / receive switch 7 is further electrically connected to the inputs of a second tunable filter 5B and a low-noise amplifier 8. The second tunable filter 5B is connected to antenna 9. Therefore, in this example, power amplifier 6 provides the amplified RF signal to antenna 9 via transmit / receive switch 7 and the second tunable filter 5B. However, other implementations are possible, such as omitting the configuration of the second tunable filter 5B.

[0035] In some configurations, the second tunable filter 5B can be configured to operate similarly to the first tunable filter 5A, for example, by selectively implementing a bandpass filter, low-pass filter, notch filter, high-pass filter, or a combination thereof based on the input signal received at the second tunable filter 5B, each of which may include a tunable cutoff frequency. Therefore, a specific group of frequencies filtered by the second tunable filter 5B can be adjusted using the input signal applied to the first tunable filter 5A.

[0036] The transmit / receive switch 7 can be used to selectively connect the antenna 9 (via the second tunable filter 5B) to the output of the power amplifier 6 or the input of the low-noise amplifier 8. In some embodiments, the transmit / receive switch 7 can provide many other functions, including but not limited to band switching and / or switching between different power modes.

[0037] LNA8 receives the antenna received signal from transmit / receive switch 7, generates an amplified antenna received signal, and provides it to the third tunable filter 5C. The third tunable filter 5C is configured to filter the received signal and provide the filtered received signal to I / Q demodulator 3.

[0038] In some configurations, the third tunable filter 5C can be configured to operate similarly to the first tunable filter 5A, for example, by selectively implementing a bandpass filter, low-pass filter, notch filter, high-pass filter, or a combination thereof based on the input signal received at the third tunable filter 5C, each of which may include a tunable cutoff frequency. Therefore, a specific group of frequencies filtered by the third tunable filter 5C can be adjusted using the input signal applied to the first tunable filter 5A.

[0039] As described above, the I / Q demodulator 3 can be used to generate I and Q received signals. In some configurations, the I / Q demodulator 3 may include a pair of mixers for mixing the attenuated received signal with a pair of clock signals that are out of phase by approximately 90 degrees. Furthermore, the mixers can generate a down-converted signal, which can be provided to the ADC used to generate the I and Q received signals.

[0040] Tunable filter

[0041] As mentioned above, filters can be used in many different electronic systems and are traditionally configured to filter out (e.g., attenuate) a fixed set of frequencies from a signal while allowing the remaining frequencies to pass through the filter. A tunable filter can be a filter with certain parameters that can be adjusted, for example, based on an input control signal.

[0042] For example, a tunable filter can be adjusted by selecting the filter type (e.g., whether the tunable filter is used as a low-pass, high-pass, band-pass, full-pass, no-pass, etc. filter) and / or the cutoff frequency associated with the selected filter. In another example, the attenuation of out-of-band signals by the tunable filter and / or the insertion loss of the tunable filter are adjustable.

[0043] Tunable filters can be used as components in building electronics systems. For example, tunable filters can be used within the RF signal chain, such as... Figure 1 The tunable filters shown are 5A-5C. Another example of an electronic system that can be enabled using tunable filters is a software-defined radio. Software-defined radios can include one or more components that are traditionally implemented in hardware rather than software. Tunable filters can also be used as part of a mixed-signal front-end (MxFE), which can be used in applications such as broadband networks.

[0044] This disclosure relates to tunable filters that can be tuned to filter a selected set of frequencies based on an input control signal, which can be analog, digital, or a combination thereof. In one example, one or more tunable filters are fabricated on a semiconductor die and programmed using filter control data provided to the die via a serial interface or bus.

[0045] In some embodiments, the tunable filter includes an RF input terminal, an RF output terminal, an optional high-pass filter bank, and an optional low-pass filter bank, with the optional low-pass filter bank connected in series between the optional high-pass filter bank and the RF output terminal. The optional high-pass filter bank includes an arrangement of high-pass filters connected in parallel and individually selectable, while the optional low-pass filter bank includes an arrangement of low-pass filters connected in parallel and individually selectable. Furthermore, desired high-pass and low-pass filters can be selected from the groups based on input control signals to achieve desired filter functionality. In some embodiments, at least some of the optional high-pass and / or at least some of the optional low-pass filters are individually configurable (e.g., tunable and / or programmable) to provide an additional layer of flexibility in achieving desired filter characteristics.

[0046] Each optional high-pass filter can have different filtering characteristics (e.g., cutoff frequency, out-of-band attenuation, and / or insertion loss) to provide a wide range of available high-pass filtering characteristics. Similarly, each optional low-pass filter can have different filtering characteristics to provide a wide range of available low-pass filtering characteristics.

[0047] In some implementations, optional high-pass filter banks and / or optional low-pass filter banks include bypass paths to help provide options for a full-pass filter response (bypassing both filter banks), a low-pass filter response (bypassing all high-pass filters), or a high-pass filter response (bypassing all low-pass filters). Furthermore, the tunable filter can be implemented by not selecting the option of high-pass and low-pass filters, thereby providing a no-pass response when needed. This can also be achieved by setting the corner frequencies of the high-pass and low-pass filters so that their passbands do not intersect, thus achieving a no-pass (full rejection) response.

[0048] The optional high-pass filter bank and optional low-pass filter bank can be in any order. For example, the optional high-pass filter bank can be closest to the RF input terminal, or the optional low-pass filter bank can be closest to the RF input terminal.

[0049] In some implementations, the tunable filter includes a pair of single-pole multithrow (SPnT) switches, and an optional high-pass filter bank includes multiple high-pass filters, each connected between a corresponding pair of throws of the switches. Furthermore, some implementations include bypass paths between pairs of throws. One or more high-pass filters may be configurable to further enhance flexibility. For example, in one example, one or more high-pass filters include an inductor and / or a capacitor connected as resonators, wherein the inductance of the inductor and / or the capacitance of the capacitor are controllable.

[0050] This control over a single high-pass filter can be used not only to tune a selected high-pass filter chosen by a switch, but also to tune one or more unselected filters. For example, a single-pole multi-throw switch suffers from limited isolation, and therefore a portion of the RF signal can leak into the path of an unselected filter. By tuning one or more unselected filters (e.g., at angular frequencies away from the selected high-pass filter), isolation problems such as reentry can be mitigated.

[0051] In some implementations, the tuned filter includes another pair of single-pole multi-throw switches, and the optional low-pass filter bank includes multiple low-pass filters, each connected between a corresponding pair of throws of the additional switch pair. Furthermore, a bypass path is included between the pairs of throws in some implementations. One or more low-pass filters can be configured to further enhance flexibility. This individual configurability of the low-pass filters can be applied to selected and / or unselected filters.

[0052] Figure 2This is an example diagram of a tunable filter 200. The tunable filter 200 includes a radio frequency (RF) input (RFIN) 202, an RF output (RFOUT) 204, a first switch 206, a second switch 208, a filter bank 210, and logic circuitry 212. Logic circuitry 212 can be configured to receive input signals from one or more input pins 214 and power supply / ground voltages from one or more power supply pins 216 to power the logic circuitry 212.

[0053] Filter bank 210 includes multiple filters 210A, 210B, 210C, 210D, 210E, ... 210N. Although the illustrated filter bank 210 includes six filters 210A-210N, the filter bank 210 may include two or more filters 210A-210N depending on the configuration. Each of the filters 210A-210N is implemented as a bandpass filter having a lower cutoff frequency and an upper cutoff frequency.

[0054] Logic circuit 212 can be configured to select one of filters 210A-210N based on an input signal received via one or more input pins 214. The first switch 206 and the second switch 208 can be implemented as single-pole multiple-throw (SPnT) switches, allowing RF input 202 and RF output 204 to be connected to one of filters 210A-210N at a time. Specifically, logic circuit 212 can be configured to connect one of filters 210A-210N to RF input 202 and RF output 204 by connecting the first switch 206 and the second switch 208 to one of the filters 210A-210N indicated by the input signal.

[0055] In one example, filter bank 210 may include filters with the following characteristics: Figure 2 The six bandpass filters are shown with corresponding cutoff frequencies. For example, the first filter 210A may have a lower cutoff frequency of 2.0 GHz and an upper cutoff frequency of 3.2 GHz, the second filter 210B may have a lower cutoff frequency of 2.5 GHz and an upper cutoff frequency of 4.5 GHz, the third filter 210C may have a lower cutoff frequency of 3.5 GHz and an upper cutoff frequency of 6.5 GHz, the fourth filter 210D may have a lower cutoff frequency of 5.5 GHz and an upper cutoff frequency of 9.0 GHz, the fifth filter 210E may have a lower cutoff frequency of 8.0 GHz and an upper cutoff frequency of 13.5 GHz, and the sixth filter 210N may have a lower cutoff frequency of 12.0 GHz and an upper cutoff frequency of 19.0 GHz.

[0056] Each of filters 210A-210N can also be connected to a lower cutoff frequency tuning input 218 and an upper cutoff frequency tuning output 220. The tuning signals applied to filters 210A-210N can collectively tune the lower and upper cutoff frequencies of filters 210A and 210N within a certain range, thereby allowing additional tuning of the entire tunable filter 200 beyond the corresponding cutoff frequencies marked on filters 210A-210N by filter bank 210. However, since the tuning signals are common across filters 210A-210N, there may be limitations on the amount of tuning when using the tuning signals applied to the lower cutoff frequency tuning input 218 and the upper cutoff frequency tuning output 220.

[0057] For example, in combination Figure 2 In the example described, a bandpass filter with a lower cutoff frequency of 2.0 GHz and an upper cutoff frequency of 19.0 GHz may not be available because each individual cutoff frequency can only be tuned within a specific range (e.g., ±1.0 GHz).

[0058] Furthermore, the depicted tunable filter 200 cannot provide low-pass, high-pass, or full-pass responses. Therefore, Figure 2 The amount of customization of the tunable filter 200 shown can be limited.

[0059] Figure 3 It is shown Figure 2 The frequency response curve of the tunable filter 200 is shown in Figure 300. Specifically, Figure 3 The curve 300 shows Figure 2 The frequency responses of each filter 210A-210N of the tunable filter 200 shown are 310A, 310B, 310C, 310D, 310E and 310N.

[0060] Figure 4 This is a diagram of an embodiment of a tunable filter 400 according to aspects of the present disclosure. The tunable filter 400 includes an RF input (RFIN) 402, an RF output (RFOUT) 404, a first pair of switches 406 and 408, a second pair of switches 410 and 412, a first filter bank 414, a second filter bank 416, and a control circuit 420.

[0061] The control circuit 420 can be configured to receive input signals from one or more input pins 422 and generate one or more switch control signals for setting the state of the switches. Therefore, the control circuit 420 can output switch control signals from one or more switch control output pins 424 to control the selected path chosen by the first and second pairs of switches 406-412.

[0062] Continue to refer to Figure 4The control circuit 420 can also be configured to generate one or more filter tuning control signals and output filter tuning control signals 418 via one or more filter tuning output pins to control filter banks 414 and 416. According to an embodiment, the control signals can be implemented as analog signals (e.g., for tuning varactor diodes) and / or digital signals (e.g., for setting the capacitance value of capacitor banks and / or the inductance value of inductor banks).

[0063] although Figure 4 The tunable filter is shown to include control circuitry 420, but in some embodiments, the tunable filter 400 may not include control circuitry 420, but instead receive control signals (e.g., via pins of a chip on which the tunable filter 400 is manufactured) for controlling first and second pairs of switches 406-412 and for tuning each filter in the first and second filter groups 414 and 416 from an external source.

[0064] The first filter bank 414 includes multiple filters, including a full-pass filter 414A (e.g., implemented as a bypass path for a conductor) and multiple high-pass filters 414B, 414C, ..., 414N-1 and 414N. Each of the high-pass filters 414B-414N may have a cutoff frequency at a different frequency. Similarly, the second filter bank 416 includes multiple filters, including a full-pass filter 416A and multiple low-pass filters 416B, 416C, ..., 416N-1 and 416N. Each of the low-pass filters 416B-416N may have a cutoff frequency at a different frequency.

[0065] The control circuit 420 can be configured to select one of filters 414A-414N from a first filter bank 414 and one of filters 416A-416N from a second filter bank 416 based on input signals received via one or more input pins 422. For example, the control circuit 420 can output a first switch control signal to a first pair of switches 406 and 408 via one or more switch control output pins 424 to select a filter from the first filter bank 414, and output a second switch control signal to a second pair of switches 410 and 412 via one or more switch output pins 424 to select a filter from the second filter bank 416.

[0066] Each of switches 406-412 can be implemented as a single-pole multiple-throw (SPnT) switch, such that the first pair of switches 406 and 408 can select a filter from the first filter bank 414, while the second pair of switches 410 and 412 can select a filter from the second filter bank 416. Thus, any combination of the first filter from the first filter bank 414 and the second filter from the second filter bank 416 can be connected between the RF input 402 and the RF output 404.

[0067] use Figure 4 The tunable filter 400 shown in the diagram can be configured to provide any of the following: a bandpass response with a tunable bandwidth, a low-pass response with a tunable frequency band, a full-pass response, or a full-rejection response. For example, the tunable filter 400 can provide a low-pass filter response by selecting one of a full-pass filter 414A and low-pass filters 416B-416N. The tunable filter 400 can provide a high-pass response by selecting one of a high-pass filter 414B-414N and a full-pass filter 416A. The tunable filter 400 can provide a full-pass response by selecting both full-pass filters 414A and 416A. The tunable filter 400 can provide a bandpass filter response by selecting one of a high-pass filter 414B-414N and one of a low-pass filter 416B-416N, wherein the lower cutoff frequency of the selected high-pass filter 414B-414N is lower than the upper cutoff frequency of the selected low-pass filter 416B-416N. The tunable filter 400 can also provide a full rejection response by selecting one of a high-pass filter 414B-414N and one of a low-pass filter 416B-416N, wherein the lower cutoff frequency of the selected high-pass filter 414B-414N is greater than the upper cutoff frequency of the selected low-pass filter 416B-416N.

[0068] The cutoff frequency of each selected filter response can also be selected by choosing an appropriate filter pair from filter banks 414 and 416. That is, each high-pass filter 414B-414N can have a different lower cutoff frequency, such that the desired lower cutoff frequency can be selected by choosing an appropriate one of the high-pass filters 414B-414N. Similarly, each of the low-pass filters 416B-416N can have a different upper cutoff frequency, such that the desired upper cutoff frequency can be selected by choosing an appropriate one of the low-pass filters 416B-416N.

[0069] Furthermore, each of the high-pass filters 414B-414N and low-pass filters 416B-416N can also be individually tuned using a filter tuning control signal 418 applied via one or more filter tuning output pins. For example, the filter tuning control signal 418 may include filter tuning control signals 418A1, 418A2, ..., 418AN-1 and 418AN applied to the high-pass filters 414B-414N, and filter tuning control signals 411b1, 418B2, ..., 418BN-1 and 418BN applied to the low-pass filters 416B-416N, respectively. Therefore, each of the high-pass and low-pass filters 414B-414N can receive individual filter tuning control signals 418A1-418AN, 418B1-418BN via one of the filter tuning output pins. Therefore, the control circuit 420 can individually tune the selected filters from the filter banks 414 and 416 to achieve the desired cutoff frequency.

[0070] In some embodiments, control circuitry 420 may also be configured to tune the unselected filters 414B-414N and 416B-416N from filter banks 414 and 416 to frequencies far removed from the cutoff frequencies of the selected filters 414B-414N and 416B-416N. For example, components of filters 414B-414N and 416B-416N may introduce reentry noise on the selected filters 414B-414N and 416B-416N. Reentry noise can refer to noise appearing at out-of-band frequencies, which can negatively impact the performance of the tunable filter. Figure 3 The reentry noise 320 that may appear in tunable filters 200 or 400 is shown.

[0071] The amount of reentry noise caused by the unselected filters 414B-414N and 416B-416N can depend on the cutoff frequencies of the unselected filters 414B-414N and 416B-416N. That is, the amount of reentry noise can increase when the cutoff frequencies of the unselected filters 414B-414N and 416B-416N are close to the cutoff frequencies of the selected filters 414B-414N and 416B-416N. Therefore, the control circuit 420 can be configured to tune the cutoff frequencies of the unselected filters 414B-414N and 416B-416N away from the cutoff frequencies of the selected filters 414B-414N and 416B-416N in order to reduce reentry noise in the frequency response of the tunable filter 400.

[0072] Figure 5 An example tunable filter 500 configured to provide a bandpass filter response according to aspects of this disclosure is shown. Figure 6This illustrates aspects according to this disclosure. Figure 5 The frequency response curve 600 of the tunable filter 500 in the configuration shown.

[0073] The tunable filter 500 includes an RF input (RFIN) 502, an RF output (RFOUT) 504, a first pair of switches 506 and 508, a second pair of switches 510 and 512, a first filter bank 514, and a second filter bank 516. Although not shown, the tunable filter 500 may also include control circuitry configured to provide control signals to the switches 506-412 and the filter banks 514 and 516, similar to... Figure 4 The control circuit 420.

[0074] The first filter bank 514 includes multiple filters, including a full-pass filter 514A and multiple high-pass filters 514B, 514C, 514D, and 514E, while the second filter bank 516 includes multiple filters, including a full-pass filter 516A and multiple low-pass filters 516B, 516C, 516D, and 516E. Each of the high-pass filters 514B-514E and the low-pass filters 516B-516E may have a different cutoff frequency, which may be tunable. Figure 5 In the configuration shown, the first pair of switches is connected to the high-pass filter 514B and the second pair of switches is connected to the low-pass filter 516C, so that the tunable filter 500 has a bandpass response.

[0075] Figure 6 It shows that it can be tuned individually. Figure 5 The cutoff frequencies of the high-pass filter 514B and low-pass filter 516C of the tunable filter 500 are used to provide multiple different bandpass responses. For example... Figure 6 As shown, the bandpass response of the tunable filter 500 can be adjusted to provide a wide range by tuning the cutoff frequencies of the high-pass filter 514B and the low-pass filter 516C. The cutoff frequencies of the selected filters can also be tuned when different filters are selected from the first filter bank 514 and the second filter bank 516, providing a wide range of customizability to the tunable filter 500.

[0076] Figure 7 It can be used Figure 4 An exemplary embodiment of the control circuit 420 in the tunable filter 400. As described above in conjunction with... Figure 4The control circuit 420 can be configured to receive input signals from one or more input pins 422 and generate one or more switch control signals. The control circuit 420 can output switch control signals from one or more switch control output pins 424 to control the first and second pairs of switches 406-412. The control circuit 420 can also be configured to generate one or more filter tuning control signals and output filter tuning control signals 418 via one or more filter tuning output pins to control filter banks 414 and 416.

[0077] like Figure 7 As shown, the control circuit 420 may include a memory 421, a state machine 423, and a single filter control circuit 525 for generating filter tuning control signals.

[0078] In some embodiments, the tunable filter 400 can be used as part of a frequency hopping spread spectrum (FHSS) system. In an FHSS system, the carrier frequency can be rapidly changed from different frequencies within a large frequency band. When included in an FHSS system, it may also be necessary for the tunable filter 400 to switch between various filters with different filter parameters (e.g., switching between filters with specific cutoff frequencies and passbands). If a filter bank required for a particular application is defined, the memory 421 can be programmed with the parameters required to implement each filter in that bank, and the state machine 423 can coordinate changes in filter tuning settings based on the programmed parameters in the memory 421.

[0079] For example, memory 421 can be programmed with multiple filter states, each filter state including parameters required to implement the corresponding filter. The parameters of a given filter state can define switching control signals required to select a pair of filters from the first and second filter groups 406-412, as well as filter tuning control signals for tuning one or more of the individual filters 414B-414N and 416B-416N.

[0080] By storing all the necessary parameters and / or control signals for implementing the filter states for a given application in memory 421, the tunable filter 400 can switch between different filter states more quickly. For example, without storing the parameters in memory 421, the control circuitry 420 may need to receive all the data required to define the parameters from an external source via input pin 422, which can be time-consuming and cause a delay in the tunable filter switching from one filter setting to another. In one embodiment, the control circuitry 420 may receive the filter state parameters via a Serial Peripheral Interface (SPI) word, which may be relatively long and require a relatively long time to receive the entire SPI word at the control circuitry 420.

[0081] Conversely, by storing the parameters of the filter state set in memory 421, control circuit 420 only needs to receive an indication of the next filter state to be implemented, which can significantly reduce the amount of data to be received compared to implementing the complete set of filter parameters. In this way, control circuit 420 can implement the filter state more quickly in response to the received filter state input signal.

[0082] Memory 421 can be implemented as random access memory (RAM), read-only memory (ROM), or other non-volatile memory. For example, when memory 421 is implemented as RAM, it can be reprogrammed to store filter states as needed for a particular implementation. Conversely, when implemented as ROM, memory 421 can implement the same set of filter states without needing to be reprogrammed after the control circuitry 420 is powered off. In some embodiments, memory 421 may include both RAM and ROM, allowing memory 421 to implement a set of filter states without programming the ROM portion, and also allowing reprogramming of a set of filter states using the RAM portion.

[0083] State machine 423 can be used to provide fast frequency up-and-down functionality without requiring reprogramming of memory 421. For example, state machine 423 can define multiple filter states of the tunable filter 400 and the allowed transitions between filter states. Thus, control circuitry 420 can receive input signals with instructions to adjust the filter frequency up or down, and state machine 423 can provide control signals (e.g., switch control signals and filter tuning control signals) based on the input signals to implement the next filter state. Utilizing this functionality, state machine 423 can be used to implement changes between filter states by sending only a single pulse to a dedicated pin in input pin 422, thereby reducing the amount of data required to implement filter state changes of the tunable filter 400.

[0084] Figure 8A This is an embodiment of a semiconductor die 810 that includes a tunable filter. The semiconductor die 810 includes an RF input pin (RFIN), an RF output pin (RFOUT), a selectable high-pass filter bank 801, a selectable low-pass filter bank 802, and control circuitry 803.

[0085] In the illustrated embodiment, a selectable high-pass filter bank 801 and a selectable low-pass filter bank 802 are cascaded between the RF input pin (RFIN) and the RF output pin (RFOUT). Control circuitry 803 is configured to output a control signal for selecting a single filter from the selectable high-pass filter bank 801 and the selectable low-pass filter bank 802.

[0086] Figure 8B This is another embodiment of a semiconductor die 820 including a tunable filter. The semiconductor die 820 includes an RF input pin (RFIN), an RF output pin (RFOUT), a first midpoint pin (MID1), a second midpoint pin (MID2), a selectable high-pass filter bank 801, a selectable low-pass filter bank 802, and control circuitry 803.

[0087] In the illustrated embodiment, an optional high-pass filter bank 801 is electrically connected between the RF input pin (RFIN) and the first midpoint pin (MID1), while an optional low-pass filter bank 802 is electrically connected between the second midpoint pin (MID2) and the RF output pin (RFOUT).

[0088] By implementing the semiconductor die 820 in this way, an optional high-pass filter bank 801 can be connected to an optional low-pass filter bank 802 using off-chip interconnects. For example, this connection can be direct (e.g., via a metal path) or via one or more RF components. This provides enhanced flexibility.

[0089] Figure 8C It includes Figure 8B An embodiment of module 820 with semiconductor die 830. Module 820 includes module substrate 821, semiconductor die 830, and one or more RF components 822 attached to module substrate 822. Figure 8C As shown, the optional high-pass filter bank 801 is electrically connected to the optional high-pass filter bank 802 via an external signal path 823 from a first midpoint pin (MID1), through one or more RF components 822, and a second midpoint pin (MID2).

[0090] Figure 9A This is an embodiment of a controllable low-pass filter 910. The controllable low-pass filter 910 includes series inductors 901A, 901B, ... 901N and parallel capacitors 902A, 902B, ... 902N, electrically connected between the input (IN) and the output (OUT) as shown. Any number of inductors and / or capacitors may be included.

[0091] A single filter control circuit 425 (which may be included in) Figure 4 In the control circuit 420, the component values ​​of any combination of the depicted components can be adjusted to achieve tuning. Furthermore, such tuning can be specific to a particular low-pass filter in a set of selectable low-pass filters. Control of component values ​​can be analog (e.g., when the parallel capacitor is implemented as a variable capacitor) and / or digital (e.g., when a set of selectable inductors or a set of selectable capacitors is used to implement a particular inductor or capacitor).

[0092] Figure 9B This is an embodiment of a controllable high-pass filter 920. The controllable high-pass filter 910 includes series capacitors 911A, 911B, ... 911N and parallel inductors 912A, 912B, ... 912N, electrically connected between the input (IN) and output (OUT) as shown. Any number of inductors and / or capacitors may be included.

[0093] A single filter control circuit 425 (which may be included in) Figure 4 The control circuit 420 can adjust the component values ​​of any combination of the depicted components to achieve tuning. Furthermore, this tuning can be specific to a particular high-pass filter from a set of selectable high-pass filters.

[0094] application

[0095] Devices employing the above-described solutions can be implemented as a variety of electronic devices. Examples of electronic devices include, but are not limited to, RF communication systems, consumer electronics, electronic test equipment, and communication infrastructure. For instance, power amplifiers can be used in a wide range of RF communication systems, including but not limited to base stations, mobile devices (e.g., smartphones or cell phones), laptops, tablets, and wearable electronic devices. The teachings herein apply to RF communication systems operating over a wide range of frequencies and bands, including those using Time Division Duplex (TDD) and / or Frequency Division Duplex (FDD).

[0096] in conclusion

[0097] The above description may refer to elements or features as “connected” or “coupled” together. As used herein, unless otherwise expressly stated, “connected” means that one element / feature is directly or indirectly connected to another element or feature, and not necessarily a mechanical connection. Similarly, unless otherwise expressly stated, “coupled” means that one element / feature is directly or indirectly coupled to another element or feature, and not necessarily a mechanical coupling. Therefore, although the various schematic diagrams shown in the figures depict exemplary arrangements of elements and components, additional intervening elements, devices, features, or components may be present in actual embodiments (assuming that the function of the depicted circuit is not adversely affected).

[0098] While the invention has been described with reference to certain embodiments, other embodiments, including those not providing all the features and advantages described herein, which will be apparent to those skilled in the art, are also within the scope of the invention. Furthermore, the various embodiments described above may be combined to provide further embodiments. Additionally, certain features shown in the context of one embodiment may be incorporated into other embodiments. Therefore, the scope of the invention is defined only by reference to the appended claims.

Claims

1. A tunable filter having a controllable cutoff frequency, wherein the tunable filter comprises: a first filter bank comprising a plurality of high-pass filters, each high-pass filter having a different cutoff frequency; a second filter bank comprising a plurality of low-pass filters, each low-pass filter having a different cutoff frequency; a first pair of switches configured to select a first filter selected from the first filter bank; a second pair of switches configured to select a second filter selected from the second filter bank; and a control circuit configured to generate a plurality of filter tuning control signals configured to individually tune at least a portion of the plurality of high-pass filters and individually tune at least a portion of the plurality of low-pass filters, wherein the tunable filter operates at a first cutoff frequency of the first filter and a second cutoff frequency of the second filter, and wherein the first filter bank further comprises an all-pass filter and the second filter bank further comprises an all-pass filter.

2. The tunable filter of claim 1, wherein the first filter bank comprises a first plurality of unselected filters that are not selected by the first pair of switches, wherein the control circuit is further configured to tune a cutoff frequency of at least a portion of the first plurality of unselected filters to reduce re-entry noise.

3. The tunable filter of claim 1, wherein the tunable filter operates as a selected filter type selected from a plurality of filter types comprising an all-pass filter type, a low-pass filter type, and a high-pass filter type.

4. The tunable filter of claim 1, wherein the control circuit is further configured to generate a plurality of switch control signals configured to control the first pair of switches and the second pair of switches.

5. The tunable filter of claim 4, wherein the control circuit comprises a memory configured to store a plurality of filter states, each filter state comprising a plurality of parameters for implementing a corresponding filter state, the control circuit further configured to generate the switch control signals and the plurality of filter tuning control signals based on the plurality of parameters.

6. The tunable filter of claim 5, wherein the control circuit is further configured to receive a serial peripheral interface (SPI) signal, the serial peripheral interface signal comprising an instruction for implementing one of the plurality of filter states.

7. The tunable filter of claim 4, wherein the control circuit comprises a state machine configured to store a plurality of filter states and allowed transitions between the filter states, each filter state comprising a plurality of parameters for implementing a corresponding filter state, the control circuit further configured to generate the switch control signals and the plurality of filter tuning control signals based on the parameters and the allowed transitions states.

8. A method of tunable filtering, the method comprising: selecting a first filter from a first filter bank of a tunable filter using a first pair of switches of the tunable filter, the first filter bank comprising a plurality of high-pass filters; and ​ selecting a second filter from a second filter bank of the tunable filter using a second pair of switches of the tunable filter, the second filter bank comprising a plurality of low pass filters; generating a plurality of filter tuning control signals using a control circuit to tune a plurality of cutoff frequencies of the high pass filter and the low pass filter; filtering a radio frequency signal using the tunable filter, wherein the filtering is based on a first cutoff frequency of the first filter and a cutoff frequency of the second filter; storing a plurality of filter states in a memory of the control circuit, each filter state comprising a plurality of parameters for implementing a corresponding filter state; and generating a plurality of switch control signals and a plurality of filter tuning control signals using the control circuit, the plurality of switch control signals for controlling the first pair of switches and the second pair of switches, the plurality of filter tuning control signals for tuning the plurality of cutoff frequencies of the high pass filter and the low pass filter based on parameters of the filter states stored in the memory.

9. The method of claim 8, further comprising tuning, using the control circuit, a cutoff frequency of one or more unselected high pass filters of the first filter bank and a cutoff frequency of one or more unselected low pass filters of the second filter bank to reduce re-entry noise.

10. The method of claim 8, wherein the first filter bank further comprises an all-pass filter and the second filter bank further comprises an all-pass filter.

11. The method of claim 8, wherein the first filter bank further comprises a first all-pass filter and the second filter bank further comprises a second all-pass filter, the method further comprising selecting at least one of the first all-pass filter or the second all-pass filter.

12. The method of claim 8, further comprising: storing a plurality of allowed transitions between the filter states in a state machine; and wherein generating the switch control signals and the plurality of filter tuning control signals is further based on the allowed transition states stored in the state machine.

13. A radio frequency (RF) module, comprising: a module substrate; and a semiconductor die attached to the module substrate, wherein the semiconductor die comprises: a first filter bank comprising a plurality of high pass filters, each high pass filter having a different cutoff frequency; a second filter bank comprising a plurality of low pass filters, each low pass filter having a different cutoff frequency; a first pair of switches configured to select a first filter selected from the first filter bank, wherein the first filter has a first cutoff frequency; a second pair of switches configured to select a second filter selected from the second filter bank, wherein the second filter has a second cutoff frequency; and a control circuit configured to generate a plurality of filter tuning control signals configured to individually tune at least a portion of the plurality of high pass filters and individually tune at least a portion of the plurality of low pass filters, wherein the first filter and the second filter are electrically connected in series through an off-chip path on the module substrate.

14. The RF module of claim 13, wherein the first filter and the second filter are electrically connected in series on the semiconductor die.

15. The RF module of claim 13, wherein the off-chip path includes at least one RF component attached to the module substrate.

16. The RF module of claim 13, wherein the first filter bank includes a first plurality of unselected filters that are not selected by the first pair of switches, wherein the control circuit is further configured to tune a cutoff frequency of at least a portion of the first plurality of unselected filters to reduce re-entry noise.

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