Apparatus and method for controlling and calibrating tunable filters

Abstract

Apparatuses and methods are provided for controlling and calibrating a tunable filter. In certain embodiments, the tunable filter includes at least one controllable component (e.g., a controllable inductor or a controllable capacitor) whose value changes or adjusts a center frequency of the tunable filter. For example, the controllable component can correspond to a controllable inductor or a controllable capacitor of an inductor-capacitor (LC) resonator of the tunable filter. The tunable filter also includes a control circuit that employs an approximation function to estimate a value of the controllable component for achieving a desired center frequency indicated by a frequency control signal.

Description

Technical Field

[0001] Embodiments of the present invention relate to electronic systems, and more specifically, to tunable filters for radio frequency electronic devices. 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 base stations, mobile devices, instrumentation, industrial electronics, military electronics, laptops, tablets, professional broadband digital radios, and compact and / or portable instruments. Compared to fixed filters, tunable filters offer additional flexibility for a given application by providing control over the specific frequencies being filtered. Summary of the Invention

[0003] Apparatus and methods are provided for controlling and calibrating tunable filters. In some embodiments, the tunable filter includes at least one controllable component (e.g., a controllable inductor or a controllable capacitor) whose value changes or adjusts the center frequency of the tunable filter. For example, the controllable component may correspond to a controllable inductor or a controllable capacitor in an inductor-capacitor (LC) resonator of the tunable filter. The tunable filter also includes control circuitry that employs an approximation function to estimate the value of the controllable component used to achieve a desired center frequency indicated by a frequency control signal. Therefore, instead of using a lookup table (LUT) to find the exact controllable component value corresponding to a given value of the desired center frequency, the control circuitry uses an approximation function to estimate the controllable component value to achieve the desired center frequency. Using an approximation function instead of a LUT can provide several advantages, including reduced chip layout area and faster calibration time. For example, although points or coefficients of the approximation function can be programmed to provide calibration, only a small range of calibration codes needs to be performed around a nominal point (e.g., obtained from simulation), rather than searching for all possible code values.

[0004] In one aspect, the tunable filter system includes a tunable filter configured to receive a radio frequency (RF) signal and output a filtered RF signal. The tunable filter includes an LC resonator having a first controllable component, wherein the center frequency of the tunable filter varies based on the value of the first controllable component. The tunable filter system also includes control circuitry configured to set the value of the first controllable component of the LC resonator based on an estimate obtained from an approximate function of the center frequency.

[0005] In another aspect, an adjustable filtering method is provided. The method includes: using an adjustable filter to filter an RF signal to generate a filtered RF signal; using a first controllable component of an LC resonator of the adjustable filter to control the center frequency of the adjustable filter; using an approximation function of the center frequency to estimate the value of the first controllable component; and using a control circuit to set the first controllable component of the LC resonator to the estimated value.

[0006] On the other hand, a tunable filter system is provided. The tunable filter system includes: a tunable filter configured to receive an RF signal and output a filtered RF signal, the tunable filter including an LC resonator having a first controllable component, wherein the center frequency of the tunable filter varies based on the value of the first controllable component. The tunable filter system further includes control circuitry configured to set the value of the first controllable component of the LC resonator, wherein the control circuitry includes components for estimating the value of the first controllable component as an approximation function of the center frequency. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of an adjustable filter system according to one embodiment.

[0008] Figure 2A This is a schematic diagram of an adjustable filter system according to another embodiment.

[0009] Figure 2B This is a schematic diagram of an adjustable filter system according to another embodiment.

[0010] Figure 3 This is a schematic diagram of an adjustable filter system according to another embodiment.

[0011] Figure 4A This is a schematic diagram of an adjustable filter system according to another embodiment.

[0012] Figure 4B This is a graph of an example of an approximate function of the resonator capacitor code and the center frequency code.

[0013] Figure 4C This is a graph of an example of an approximation function of the bandwidth capacitor code and the matched capacitor code versus the resonator capacitor code.

[0014] Figure 5A This is a schematic diagram of one embodiment of a control circuit used to determine the resonator capacitor code based on the center frequency code.

[0015] Figure 5B This is a graph of an example of an approximate function of the bandwidth or matched capacitor code versus the resonator capacitor code.

[0016] Figure 5C It is based on Figure 5B A schematic diagram of an embodiment of a control circuit for determining bandwidth or matching capacitor code based on resonator capacitor code.

[0017] Figure 6A This is a schematic diagram of one embodiment of a control circuit used to determine the resonator capacitor code based on the center frequency code.

[0018] Figure 6B This is another example of a graph showing an approximate function of the resonator capacitor code relative to the center frequency code.

[0019] Figure 6C This is another example of a graph showing the approximate function of the resonator capacitor code with respect to the center frequency code.

[0020] Figure 7 This is a flowchart of a method for calibrating an adjustable filter according to one embodiment.

[0021] Figure 8A This is a schematic diagram of an adjustable filter according to one embodiment.

[0022] Figure 8B This is a schematic diagram of an adjustable filter according to another embodiment.

[0023] Figure 9 This is a schematic diagram of an example of an RF communication system that may include one or more tunable filters in accordance with the teachings of this article.

[0024] Figure 10 This is a schematic diagram of a controllable capacitor according to one embodiment. Detailed Implementation

[0025] The following detailed description of embodiments presents various descriptions of specific embodiments of the invention. In this description, reference is made to the accompanying drawings, wherein similar reference numerals may indicate 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 a subset of those shown in the drawings and / or the accompanying drawings. Additionally, some embodiments may combine any suitable combination of features from two or more drawings.

[0026] Tunable filters can be used in a variety of applications to filter the frequency components of RF signals. For example, in wireless communication systems, a bandpass frequency response can be used to implement a tunable filter to limit the frequency content of an RF signal to a specific frequency range or band. Such tunable filters can be used in the transmit and / or receive paths of wireless communication systems. Compared to fixed filters, tunable filters offer additional flexibility.

[0027] This document provides apparatus and methods for controlling and calibrating tunable filters. In some embodiments, the tunable filter includes at least one controllable component (e.g., a controllable inductor or a controllable capacitor) whose value changes or adjusts the center frequency of the tunable filter. For example, the controllable component may correspond to a controllable inductor or a controllable capacitor in an inductor-capacitor (LC) resonator of the tunable filter. The tunable filter also includes control circuitry that uses an approximation function to estimate the value of the controllable component used to achieve a desired center frequency indicated by a frequency control signal. Therefore, instead of using a lookup table (LUT) to find an exact controllable component value corresponding to a given value of the desired center frequency, the control circuitry uses an approximation function to estimate the controllable component value to achieve the desired center frequency.

[0028] Using an approximation function instead of a LUT offers several advantages, including reduced chip layout area and faster calibration time. For example, while points or coefficients of the approximation function can be programmed to provide calibration, only a small range of calibration code needs to be performed around the nominal point (e.g., obtained from simulation), rather than searching for all possible code values.

[0029] The approximation function can be implemented in a variety of ways. In some implementations, the approximation function may correspond to a piecewise linear function or a polynomial function, used to estimate the controllable component values ​​required for the controllable component to achieve the desired center frequency indicated by the frequency control signal.

[0030] In some implementations, the tunable filter includes one or more additional controllable components for adjusting other frequency characteristics of the tunable filter, such as bandwidth, impedance matching, corner frequency, and / or notch frequency. Instead of using a LUT to set these additional controllable component values, another approximation function is used, where the input corresponds to the selected controllable component values ​​used to set the desired center frequency. Therefore, the component values ​​of these additional controllable components are selected based on the estimated component values ​​used to achieve the desired center frequency.

[0031] The tunable filter described in this paper can filter radio frequency signals of various frequencies, including not only those between 30 MHz and 7 GHz, but also higher frequency signals such as the X-band (approximately 7 GHz to 12 GHz) and K-band signals. u K-band (approximately 12 GHz to 18 GHz), K-band (approximately 18 GHz to 27 GHz), K a Signals in the V band (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 herein apply to a wide range of RF systems, including microwave systems.

[0032] Figure 1This is a schematic diagram of an adjustable filter system 10 according to one embodiment. The adjustable filter system 10 includes an adjustable filter 1 and a control circuit 2.

[0033] like Figure 1 As shown, the tunable filter 1 receives RF input from RF. IN Receive RF signals and provide the filtered RF signals to the RF output. OUT In some implementations, the tunable filter system 10 is fabricated on a semiconductor die (also referred to herein as a semiconductor chip), and the RF input RF... IN and RF output RF OUT Corresponding to the pins of a semiconductor die.

[0034] The tunable filter 1 includes at least one controllable LC resonator 3 having one or more component values ​​set by the control circuit 2. Although shown as control component values ​​for the controllable LC resonator 3, the control circuit 2 may also control the tunable filter 1 in other ways, such as by setting component values ​​for one or more bandwidth adjustment components, notch frequency components, corner frequency components, and / or matching components.

[0035] The tunable filter 1 may include a variety of controllable components. In one example, the tunable filter 1 includes a controllable capacitor, which can be implemented in various ways. For example, the controllable capacitor can be implemented using a set of optional capacitor cells, a varactor diode, a pin diode capacitor, a microelectromechanical system (MEMS) capacitor, and / or any other structure with controllable capacitance. In another example, the tunable filter 1 includes a controllable inductor, such as a set of optional inductor cells, an inductor with variable length using a switch, and / or any other structure with controllable inductance. Although various tuning examples are provided, the teachings herein apply to a variety of implementations of controllable components.

[0036] In the illustrated embodiment, the control circuit 2 receives a frequency control signal F that indicates the desired center frequency of the tunable filter 1. CTL In some implementations, the control signal F CTL Received via a bus on a semiconductor chip, such as a serial interface.

[0037] like Figure 1 As shown, control circuit 2 is implemented using approximation function 4 to estimate the values ​​of one or more controllable components of tunable filter 1 to achieve the desired center frequency. Therefore, instead of using a LUT to map the indicated center frequency to the corresponding component values ​​of tunable filter 1, control circuit 2 uses approximation function 4. In some implementations, the approximation function is implemented using digital logic gates and the memory of control circuit 2.

[0038] By implementing control circuit 2 with an approximate function 4, a reduced chip area and faster calibration time are achieved. For example, when mapping using a large LUT, the LUT size is typically approximately M*N*k if the filter is tunable to M center frequencies and contains N tunable elements, each controlled by k bits. Furthermore, the dimensionality of such a LUT expands further for each supported bandwidth. Additionally, without knowing the correlation between tunable elements, it is necessary to search all possible tunable codes (N*2). k To determine the calibration code for each of the M center frequencies.

[0039] In contrast, using approximation function 4 offers area efficiency and fast calibration time. The points of approximation function 4 are programmable during calibration, but only require searching a small range of codes around the nominal point (as opposed to the full range of all codes) to achieve reduced calibration time. The points of approximation function 4 are also referred to as coefficients or parameters in this paper.

[0040] Figure 2A This is a schematic diagram of an adjustable filter system 20 according to another embodiment. The adjustable filter system 20 includes an adjustable filter 1 and a control circuit 12.

[0041] Figure 2A The tunable filter system 20 is similar to Figure 1 The tunable filter system 10 is different. Figure 2A The tunable filter system 20 is implemented using a specific approximation function. Specifically, Figure 2A The control circuit 12 is implemented using a piecewise linear function 14, which is used to control the frequency based on the frequency control signal F. CTL The desired center frequency is indicated to set the values ​​of one or more controllable components of the tunable filter 1. The piecewise linear function 14 can have any suitable number of linear segments, such as two or more.

[0042] Figure 2B This is a schematic diagram of an adjustable filter system 30 according to another embodiment. The adjustable filter system 30 includes an adjustable filter 1 and a control circuit 22.

[0043] Figure 2B The tunable filter system 30 is similar to Figure 1 The tunable filter system 10 differs in that Figure 2B The tunable filter system 30 is implemented using a specific approximation function. Specifically, Figure 2B The control circuit 22 is implemented using a polynomial function 24, which is used to control the frequency signal F. CTL The desired center frequency is indicated to set the values ​​of one or more controllable components of the tunable filter 1. The polynomial function 24 can have any suitable order, such as second order or higher.

[0044] Figure 3 This is a schematic diagram of an adjustable filter system 50 according to another embodiment. The adjustable filter system 50 includes an adjustable filter 31, a control circuit 32, and a calibration circuit 33.

[0045] In the illustrated embodiment, the tunable filter 31 includes a series electrical connection to the RF input RF. IN and RF output RF OUT The adjustable filter 31 includes a controllable input matching capacitor 44a, a controllable bandwidth capacitor 43, and a controllable output matching capacitor 44b. Furthermore, the adjustable filter 31 also includes a first controllable resonant capacitor 41a and a first resonant inductor 42a, which are connected in parallel between the first terminal of the controllable bandwidth capacitor 43 and ground. Further, the adjustable filter 31 also includes a second controllable resonant capacitor 41b and a second resonant inductor 42b connected in parallel between the second terminal of the controllable bandwidth capacitor 43 and ground. In this embodiment, the first resonant inductor 42a and the second resonant inductor 42b are coupled with a coupling coefficient k, thereby providing a coupled resonant structure.

[0046] Although an example of a tunable filter has been described, the teachings of this paper apply to tunable filters implemented in a variety of ways. Therefore, other implementations are possible.

[0047] The control circuit 32 is implemented using an approximation function 34, which operates based on a set of programmable points stored in a memory 39, which can be volatile or non-volatile. The control circuit 32 is based on a frequency control signal F. CTL The system operates based on the desired center frequency indicated by the signal and the desired bandwidth indicated by the bandwidth control signal BW. In some embodiments, the memory 39 stores a different set of programmable points for each value of the bandwidth control signal BW.

[0048] Continue to refer to Figure 3 The approximation function 34 is used to set the code values ​​in the resonator register 35, bandwidth register 36, and match register 37. For example... Figure 3 As shown, the code value in the resonator register 35 controls the capacitance values ​​of the first controllable resonant capacitor 41a and the second controllable resonant capacitor 41b. Additionally, the code value in the bandwidth register 36 controls the capacitance value of the controllable bandwidth capacitor 43, while the code value in the matching register 37 controls the capacitance values ​​of the controllable input matching capacitor 44a and the controllable output matching capacitor 44b.

[0049] like Figure 3As shown, calibration circuit 33 is used to adjust the values ​​of programmable points stored in memory 34. Therefore, calibration circuit 33 does not need to search all possible codes to control every controllable component; calibration circuit 33 can adjust the programmable points stored in memory 34 to provide calibration for variations caused by manufacturing and / or other sources.

[0050] In some implementations, the calibration circuit 33 is coupled to the RF input RF. IN and RF output RF OUT This helps to detect the performance of the tunable filter 31 for a specific value of the programmable point of the approximation function 34. In other embodiments, an external performance measurement device is used to detect the performance of the tunable filter 31 for a specific value of the programmable point. Such an external performance measurement device can be used in conjunction with a calibration circuit 33 (e.g., via bus communication) for calibration.

[0051] Figure 4A This is a schematic diagram of an adjustable filter system 60 according to another embodiment. The adjustable filter system 60 includes an adjustable filter 31, a control circuit 52, and a calibration circuit 33.

[0052] Figure 4A The tunable filter system 60 is similar to Figure 3 The tunable filter system 50 differs in that Figure 4A The tunable filter system 50 is implemented using a specific approximation function. Specifically, Figure 4A The control circuit 52 is implemented using a piecewise linear function 54, which operates on points Y0, Y1, ... Y2 stored in memory 59. L The functions V0, V1, V2, V0′, V1′, and V2′ operate as discussed below. In some implementations, for each possible bandwidth setting indicated by the bandwidth control signal BW, a different value or a portion of the storage point is stored.

[0053] Figure 4B This is a graph illustrating an example of an approximate function of the resonator capacitor code versus the center frequency code. The approximate function depicted is used for the desired center frequency (e.g., as shown in the image). Figure 4A F in CTL Instructions) generate a controllable resonant capacitor (e.g., Figure 4A The code values ​​for capacitors 41a and 41b.

[0054] For resonator-based bandpass filters, the resonator's impedance primarily determines the center frequency of the bandpass. Therefore, for Figure 4A In the embodiment, the resonant capacitance C of the first controllable resonant capacitor 41a and the second controllable resonant capacitor 41b RESO Set the center frequency. For example, the center frequency (F) of the adjustable filter 4A. 中心It can be roughly represented by the following equation 1.

[0055] Equation 1

[0056]

[0057] Continue to refer to Figure 4B function C RESO =f(F 中心 The curve is approximated as a piecewise linear function, dividing the entire curve into L sub-ranges with (L+1) points. The number of points can be chosen to achieve the desired precision. In this example, the points on the curve correspond to (0, Y0), (2... N *1 / L、Y1), (2 N *2 / L、Y2), (2 N [L-1] / L、Y L-1 ), and (2 N Y L In this example, the value of the Y point is programmable during the calibration process to accommodate variations.

[0058] In the illustrated embodiment, the step size of the x-axis (corresponding to the input code indicating the desired center frequency) is chosen as a power of 2 to allow efficient implementation of division (e.g., right shift) in hardware. However, other implementations are also possible. In one example, a power of 2 is used, and for the portion of the curve (subrange) with lower linearity (e.g., between 0 and 2 in the depicted graph). N Additional points were added between 1 / L. In another example, the points were evenly distributed across the input range. Any suitable x-axis step size can be used.

[0059] Figure 4C This is a graph of an example of an approximation function of the bandwidth capacitor code and the matched capacitor code versus the resonator capacitor code.

[0060] refer to Figures 4A-4C The code value C of the controllable bandwidth capacitor 43 BW The code value C of the controllable resonant capacitors 41a and 41b RESO Highly relevant. Furthermore, the code values ​​C for the controllable matching capacitors 44a and 44b are... 匹配 The code value C of the controllable resonant capacitors 41a and 41b RESO Highly relevant.

[0061] Therefore, the code value C BW and C 匹配 It can be based on from Figure 4A C obtained by approximating the function RESO The values ​​are used to generate it. For example, a linear relationship (offset and slope) can be used.

[0062] At the endpoints, deviations from the relation will occur due to circuit parasitics. This can be approximated well by varying the slope of the linear function within a subrange of the code. Figure 4C The example illustrates the double-slope linear approximation. In this example, points (U0, V0), (U1, V1), and (U2, V2) are used for C... RESO To approximate C BW Furthermore, points (U0, V0′), (U1, V1′), and (U2, V2′) are used based on C. RESO To approximate C 匹配 However, in general, this approximation can be made using as many different points as needed.

[0063] In some implementations, the slope of each bandwidth setting is different, and the points on the function can be reprogrammed or stored separately for each bandwidth setting (as shown by the bandwidth control signal BW).

[0064] Figure 5A This is a schematic diagram of one embodiment of a control circuit 330 for determining the resonator capacitor code based on the center frequency code.

[0065] In the illustrated embodiment, the control circuit 330 includes a detection circuit 301 for detecting a subrange of the input code X indicating the desired center frequency. The control circuit 330 also includes a first register 302 storing the x-values ​​of points of the approximation function, a second register 303 storing the y-values ​​of points of the approximation function, and a third register 304 storing the shifted y-values ​​(right-shifted by 1 bit) of the approximation function points. For clarity, these are also represented as two distinct registers; a shared register can be used to store all y-values.

[0066] The control circuit 330 also includes a first subtractor 321 for generating an XVAL signal based on the difference between the x value stored in the first register 302 and the input code X. The control circuit 330 also includes a second subtractor 322 for generating a slope (SLOPE) based on the difference between the shifted y value stored in the third register 304 and the y value stored in the second register 303. The control circuit 330 also includes a multiplier 325 for multiplying XVAL and the slope, a divider 326 for dividing the multiplication result by 2, and an adder 327 for adding the division result to the offset (OFFSET) represented by the y value stored in the third register 304.

[0067] By effectively using the information calculated for each subrange, C can be calculated using only one multiplier. RESO Therefore, efficient hardware implementation can be achieved. In some implementations, the digital circuit 330 is implemented using digital logic circuits and memory.

[0068] Figure 5B This is a graph of an example of an approximation function of the bandwidth or matched capacitor code versus the resonator capacitor code. In some implementations, the approximation function given by Equation 2 below is used to reduce hardware complexity.

[0069] Equation 2

[0070]

[0071] Therefore, calculate C BW and C 匹配 When dealing with code values, division of any numerator and any denominator can be replaced by multiplication and shifting, which improves hardware efficiency.

[0072] Figure 5C It is based on Figure 5B This is a schematic diagram of one embodiment of a control circuit 430 for determining bandwidth or a matching capacitor code based on a resonator capacitor code. Two instances of the control circuit 430 may be included for determining bandwidth and a matching capacitor code. The control circuit 430 employs Equation 2 above to reduce hardware complexity.

[0073] In the illustrated embodiment, the control circuit 430 includes a range detection circuit 401 for the input code U, a first register 402 for the u value, a second register 403 for the v value, a third register 404 for shifting the v value, a first multiplexer 411, a second multiplexer 412, a third multiplexer 413, a first subtractor 415, a second subtractor 416, a fourth register 417, a fourth multiplexer 418, a fifth register 419, a fifth multiplexer 420, a first multiplier 421, a second multiplier 422, a divider 423, and an adder 424.

[0074] Figure 6A This is a schematic diagram of one embodiment of a control circuit 440 for determining the resonator capacitor code based on the center frequency code.

[0075] In some embodiments of this paper, polynomial approximation functions are used to estimate the frequency characteristics of a tunable filter. For example, a polynomial approximation function of the resonator capacitor code relative to the center frequency code can be used to estimate a specific resonator capacitor code required to approximately realize a specific center frequency of the tunable filter. For example, Equation 3 corresponds to an expression for a polynomial approximation function, where f(x) is a function for obtaining the resonator capacitor code, x is the center frequency code, N is the order of the polynomial, and a i It is a polynomial approximation function. Any suitable number of coefficients can be used.

[0076] Equation 3

[0077]

[0078] Figure 6A The control circuit 440 depicts an example of a hardware-efficient implementation of the polynomial approximation function of Equation 3. The control circuit 440 includes a multiplier 431, an adder 432, a memory element 433 (e.g., a latch or flip-flop), a first multiplexer 435, a second multiplexer 436, a first multiplexer control circuit 437, and a second multiplexer control circuit 438. The control circuit 440 receives a signal X indicating the desired center frequency and generates a resonator capacitor (FREQ) code to approximately achieve the desired center frequency.

[0079] Figure 6B This is another example of a graph showing an approximate function of the resonator capacitor code relative to the center frequency code. In this example, it uses... Figure 6A The fourth-order polynomial approximation function (5 coefficients). In this example, a full-precision approximation (without rounding or saturation) is used.

[0080] Figure 6C This is another example of a graph showing an approximation of the resonator capacitor code as a function of the center frequency code. The graph is similar to... Figure 6A The difference lies in the use of rounding and saturation at the output of multiplier 431 to control bit growth. In this example, the total number of bits for the fourth-order polynomial approximation function is limited to 25.

[0081] like Figure 6B and 6C As shown, the polynomial approximation function closely tracks (overlaps) the golden model (lookup table) of the resonator capacitor code and the center frequency code. Furthermore, the implementation with rounding and saturation provides a similar root mean square (RMS) error compared to the implementation without rounding and saturation.

[0082] Figure 7 This is a flowchart of a method 510 for calibrating a tunable filter according to one embodiment. Method 510 can be performed by the tunable filter system described herein, for example, using... Figure 3 The calibration circuit 33 is combined with other components of the adjustable filter system 50.

[0083] Method 510 begins at step 501, where multiple initial values ​​for multiple programmable points of the approximation function of the tunable filter are selected. These initial values ​​can be obtained in various ways, such as through simulation.

[0084] Continue to refer to Figure 7 Method 510 continues to step 502, where the tunable filter is calibrated by searching a range of codes around multiple initial values. In step 502, characteristics of the tunable filter (e.g., one or more frequency characteristics, such as the center frequency) can be observed to determine whether the current value being searched performs better than any previous value. Thus, the calibration value of the programmable coefficients can be detected.

[0085] The number of search steps in calibration can be relatively small. For example, for Figures 4A-4C In this embodiment, the number of search steps can be less than (L1+L2+L3+3)*Δ, where L1 is C RESO The number of subranges, L2 is C BW The number of subranges, L3 is C 匹配 The number of subranges, Δ, is a programmable parameter representing the range of code to search from the initial starting value. In another implementation, separate programmable parameters Δ1, Δ2, and Δ3 are used for C... RESO C BW C 匹配 The number of search steps can be less than (L1+1)*Δ1+(L2+1)*Δ2+(L3+1)*Δ3.

[0086] Method 510 continues to step 503, where the tunable filter is programmed to operate using calibration values ​​of a plurality of programmable coefficients identified through the search in step 502. The calibration values ​​can be stored in memory, for example... Figure 3 Memory 39.

[0087] Figure 8A This is a schematic diagram of an adjustable filter 910 according to one embodiment. As shown, the adjustable filter 910 includes series inductors 901A, 901B, ... 901N and parallel capacitors 902A, 902B, ... 902N, which are electrically connected between the input terminal (IN) and the output terminal (OUT). Any number of inductors and / or capacitors can be included, and any combination of components can be controllable.

[0088] Control circuit ( Figure 8A (Not shown in the image) The component values ​​of the controllable element can be adjusted to achieve tuning.

[0089] Figure 8A The tunable filter 910 illustrates yet another example of a tunable filter that can be controlled and calibrated according to the teachings of this article.

[0090] Figure 8B This is a schematic diagram of an adjustable filter 920 according to another embodiment. As shown, the adjustable filter 920 includes series capacitors 911A, 911B, ... 911N and parallel inductors 912A, 912B, ... 912N, which are electrically connected between the input (IN) and the output (OUT). Any number of inductors and / or capacitors can be included, and any combination of components can be controllable.

[0091] Control circuit ( Figure 8B (Not shown in the image) The component values ​​of the controllable components can be adjusted to achieve tuning.

[0092] In one embodiment, Figure 8B tunable filter 920 and Figure 8A The 910 cascaded adjustable filters (in any order or sequence) provide an adjustable bandpass filter.

[0093] Figure 8B The tunable filter 920 illustrates yet another example of a tunable filter that can be controlled and calibrated according to the teachings of this article.

[0094] Figure 9 This is a schematic diagram of an example of an RF communication system 1010 that may include one or more tunable filters in accordance with the teachings of this document.

[0095] Although the RF communication system 1010 illustrates one example of an electronic system that may include one or more tunable filters as described herein, tunable filters may also be used in other configurations of the electronic system.

[0096] In addition, although Figure 9 The specific configuration of the components is shown, but the RF communication system 1010 can be adapted and modified in a variety of ways. For example, the RF communication system 1010 may include more or fewer receive paths and / or transmit paths. Furthermore, the RF communication system 1010 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.

[0097] In the illustrated configuration, the RF communication system 1010 includes a baseband processor 1001, an I / Q modulator 1002, an I / Q demodulator 1003, a first tunable filter 1005A, a power amplifier 1006, a transmit / receive (T / R) switch 1007, a low-noise amplifier (LNA) 1008, an antenna 1009, a second tunable filter 1005B, and a third tunable filter 1005C. Although the first to third tunable filters 1005A-1005C are example uses of tunable filters, other arrangements of tunable filters are possible in the transmit and / or receive paths of the RF communication system 1010.

[0098] like Figure 9As shown, the baseband processor 1001 generates an in-phase (I) transmit signal and a quadrature-phase (Q) transmit signal, which are provided to the I / Q modulator 1002. Furthermore, the baseband processor 1001 receives an I receive signal and a Q receive signal from the I / Q demodulator 1003. The I and Q transmit signals correspond to signal components of the transmit signal with specific amplitude, frequency, and phase. For example, the I transmit signal and the Q transmit signal represent the in-phase sine component and the quadrature-phase sine component, respectively, and can be equivalent representations of the transmit signal. Similarly, the I and Q receive signals correspond to signal components of the receive signal with specific amplitude, frequency, and phase.

[0099] In some embodiments, the I transmit signal, Q transmit signal, I receive signal, and Q receive signal are digital signals. Additionally, the baseband processor 1001 may include a digital signal processor, a microprocessor, or a combination thereof for processing digital signals.

[0100] The I / Q modulator 1002 receives I and Q transmit signals from the baseband processor 1001 and processes them to generate a modulated RF signal. In some configurations, the I / Q modulator 1002 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.

[0101] The first tunable filter 1005A receives the modulated RF signal from the I / Q modulator 1002 and provides the filtered RF signal to the input of the power amplifier 1006. In some configurations, the first tunable filter 1005A may implement a bandpass filter, configured to provide band filtering. In other embodiments, the first tunable filter 1005A implements a low-pass filter, a bandpass filter, a notch filter, a high-pass filter, or a combination thereof based on an input control signal. Therefore, a specific group of frequencies filtered by the first tunable filter 1005A can be adjusted using the input control signal applied to the first tunable filter 1005A.

[0102] Power amplifier 1006 amplifies the filtered RF signal to generate an amplified RF signal, which is provided to transmit / receive switch 1007. Transmit / receive switch 1007 is further electrically connected to the inputs of second tunable filter 1005B and low-noise amplifier 1008. Second tunable filter 1005B is connected to antenna 1009. Therefore, in this example, power amplifier 1006 provides the amplified RF signal to antenna 1009 via transmit / receive switch 1007 and second tunable filter 1005B. However, other implementations are possible, such as omitting the configuration of second tunable filter 1005B.

[0103] In some configurations, the second tunable filter 1005B can be configured to operate similarly to the first tunable filter 1005A, for example, by selectively implementing a bandpass filter, low-pass filter, notch filter, high-pass filter, or a combination thereof, based on a control input signal received at the second tunable filter 1005B. Therefore, a specific group of frequencies filtered by the second tunable filter 1005B can be adjusted using the input control signal applied to the second tunable filter 1005B.

[0104] The transmit / receive switch 1007 can be used to selectively connect the antenna 1009 (via the second tunable filter 1005B) to the output of the power amplifier 1006 or the input of the low-noise amplifier 1008. In some embodiments, the transmit / receive switch 1007 can provide many other functions, including but not limited to band switching and / or switching between different power modes.

[0105] LNA1008 receives the antenna signal from transmit / receive switch 1007 and generates an amplified antenna signal, which is provided to a third adjustable filter 1005C. This filter is configured to filter the received signal and provide the filtered received signal to I / Q demodulator 1003.

[0106] In some configurations, the third tunable filter 1005C can be configured to operate similarly to the first tunable filter 1005A, for example, by selectively implementing a bandpass filter, a low-pass filter, a notch filter, a high-pass filter, or a combination thereof, based on the input signal received at the third tunable filter 1005C.

[0107] The I / Q demodulator 1003 can be used to generate I and Q received signals, as described above. In some configurations, the I / Q demodulator 1003 may include a pair of mixers for mixing the attenuated received signals with a pair of clock signals that are out of phase by approximately ninety degrees. Furthermore, the mixers can generate down-converted signals that can be provided to the ADC used to generate the I and Q received signals.

[0108] Figure 10This is a schematic diagram of a controllable capacitor 1140 according to one embodiment. The controllable capacitor 1140 includes a first group of field-effect transistors (FETs) 1101a, 1101b, ... 1101n; a second group of field-effect transistors 1102a, 1102b, ... 1102n; a first group of capacitors 1103a, 1103b, ...; a second group of capacitors 1104a, 1104b, ... 1104n; a first group of gate resistors 1111a, 1111b, ... 1111n; and a second group of gate resistors 1112a, 1112b, ... 1112n. The controllable capacitor 1140 is controlled by control bits Sa, Sb, ... Sn, where the control bits Sa, Sb, ... Sn represent signals from the control circuit (now...). Figure 10 The capacitor control code is shown in the image.

[0109] The controllable capacitor 1140 illustrates one embodiment of a controllable capacitor that may be included in an adjustable filter. However, the teachings herein apply to other embodiments of the controllable capacitor.

[0110] In the illustrated embodiment, the controllable circuit 1140 is implemented using multiple circuit branches connected in parallel between the first RF terminal RF1 and the second RF terminal RF2. Furthermore, in this embodiment, each circuit branch includes a series combination of a pair of FETs and a pair of capacitors. For example, Figure 10 The leftmost branch includes a series combination of FET1101a, capacitor 1103a, capacitor 1104a and FET1102a.

[0111] Continue to refer to Figure 10 Control circuit (e.g., Figure 1 The control circuit 2) selectively activates any desired number of branches based on the values ​​of control bits Sa, Sb, ... Sn, which can be generated using an approximate function according to the teachings here. By activating the desired number of branches, the capacitance between the first RF terminal RF1 and the second RF terminal RF2 is controlled.

[0112] Therefore, control bits Sa, Sb, ... Sn select a specific branch by turning the FET in that branch on or off. For example... Figure 10 As shown, control bits are provided to each branch via gate resistors, providing isolation. Although an example with two FETs per branch is shown, more or fewer FETs can be included to achieve the desired power handling capability. FETs can be implemented in a variety of ways, including but not limited to metal-oxide-semiconductor FETs (MOSFETs), such as those fabricated using silicon-on-insulator (SOI) processes.

[0113] In the illustrated embodiment, each branch includes a pair of capacitors. Enhanced linearity and / or smaller capacitance steps can be achieved by including multiple capacitors in series, compared to an implementation with a single capacitor in each branch. Although an example of two capacitors per branch is shown, more or fewer capacitors can be included. Furthermore, while a specific order of components in the series is described, the order of components can be changed or interchanged. Capacitors can be implemented in a variety of ways, including but not limited to metal-insulator-metal (MIM) capacitors.

[0114] The FETs and capacitors in each branch can have any desired size. In some implementations, the capacitors in each branch are weighted according to a desired weighting scheme. By weighting the capacitors, a wider capacitance tuning range can be achieved relative to a fixed weighting for each branch. The transistor size may or may not be weighted depending on the implementation.

[0115] application

[0116] 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, radio frequency (RF) communication systems, consumer electronics, electronic test equipment, and communication infrastructure. For instance, tunable filters can be used in a wide range of RF communication systems, including but not limited to base stations, mobile devices, instrumentation, industrial electronics, military electronics, laptops, tablets, professional broadband digital radios, and compact and / or portable instruments. 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).

[0117] in conclusion

[0118] The foregoing description may refer to elements or features as “connected” or “coupled” together. As used herein, unless otherwise expressly stated, “connected” means one element / feature is directly or indirectly connected to another element / feature, and not necessarily a mechanical connection. Similarly, unless otherwise expressly stated, “coupled” means one element / feature is directly or indirectly coupled to another element / feature, and not necessarily a mechanical coupling. Therefore, although the various schematic diagrams shown in the figures depict exemplary arrangements of elements and assemblies, additional intermediate elements, devices, features, or assemblies may exist in actual embodiments (assuming that the functionality of the depicted circuit is not adversely affected).

[0119] Although the invention has been described with reference to certain embodiments, other embodiments that are obvious to those skilled in the art, including embodiments that do not provide all the features and advantages set forth herein, are also within the scope of the invention. Furthermore, the various embodiments described above can 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 system, comprising: a tunable filter configured to receive a radio frequency (RF) signal and output a filtered RF signal, the tunable filter including an inductor-capacitor (LC) resonator having a first controllable component, wherein a center frequency of the tunable filter varies based on a value of the first controllable component; and a control circuit configured to set the value of the first controllable component of the LC resonator based on an estimate obtained from an approximation function of the center frequency, wherein the tunable filter has a frequency characteristic that varies based on a value of a second controllable component, wherein the control circuit is further configured to set the value of the second controllable component based on the selected value of the first controllable component.

2. The tunable filter system of claim 1, wherein the approximation function is a piecewise linear function.

3. The tunable filter system of claim 2, wherein an input step size of at least a portion of the approximation function is a power of two.

4. The tunable filter system of claim 1, wherein the approximation function is a polynomial function.

5. The tunable filter system of claim 1, wherein the value of the second controllable component is selected based on a piecewise linear function that takes the value of the first controllable component as input.

6. The tunable filter system of claim 1, wherein the frequency characteristic is impedance matching.

7. The tunable filter system of claim 1, wherein the frequency characteristic is bandwidth.

8. The tunable filter system of claim 1, further comprising a calibration circuit configured to calibrate a plurality of points of the approximation function to account for variations.

9. The tunable filter system of claim 8, wherein the calibration circuit is further configured to calibrate the plurality of points by searching a code range around a plurality of starting values of a plurality of coefficients.

10. The tunable filter system of claim 1, wherein the controllable component is a controllable capacitor.

11. The tunable filter system of claim 1, wherein the tunable filter is a bandpass filter.

12. A tunable filtering method, the method comprising: filtering a radio frequency (RF) signal using a tunable filter to generate a filtered RF signal; controlling a center frequency of the tunable filter using a first controllable component of an inductor-capacitor (LC) resonator of the tunable filter; estimating a value of the first controllable component using an approximation function of the center frequency; setting the first controllable component of the LC resonator to the estimated value using a control circuit; and setting a value of a second controllable component based on the selected value of the first controllable component.

13. The method of claim 12, wherein the approximation function is a piecewise linear function.

14. The method of claim 13, wherein an input step size of at least a portion of the approximation function is a power of two.

15. The method of claim 12, wherein the approximation function is a polynomial function.

16. The method of claim 12, further comprising obtaining the value of the second controllable component based on a piecewise linear function that takes the value of the first controllable component as input.

17. The method of claim 12, further comprising calibrating a plurality of points of the approximation function to account for variations. ​ 18. A tunable filter system, comprising: a tunable filter configured to receive a radio frequency (RF) signal and output a filtered RF signal, the tunable filter comprising an inductance-capacitance (LC) resonator having a first controllable component, wherein a center frequency of the tunable filter varies based on a value of the first controllable component; and a control circuit configured to set a value of the first controllable component of the LC resonator, wherein the control circuit comprises a means for estimating the value of the first controllable component by an approximation function of the center frequency, wherein the tunable filter has a frequency characteristic that varies based on a value of a second controllable component, wherein the control circuit is further configured to set the value of the second controllable component based on the selected value of the first controllable component.

19. The tunable filter system of claim 18, wherein the value of the second controllable component is selected based on a piecewise linear function that takes the value of the first controllable component as input.

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