Gain calibration device and method of CIC filter

Abstract

The invention relates to a gain calibration device for a CIC filter, and the device comprises a gain calibration coefficient calculation module which is configured to receive an input parameter set of the CIC filter and an initial value of a quantization word length of a gain calibration coefficient, and generates a final gain calibration coefficient set through the corresponding quantization word length; the gain calibration module is electrically connected with the gain calibration coefficient calculation module and is used for calibrating the output of the CIC filter by utilizing the final gain calibration coefficient set; and the bit interception module is electrically connected with the gain calibration module and is used for carrying out low bit interception processing on the output of the gain calibration module. A large number of corresponding gain calibration coefficients can be calculated and stored according to randomly configured input parameters, and a certain operation precision requirement is met. The invention also relates to a gain calibration method of the CIC filter.

Description

Technical Field

[0001] The present application relates to the field of signal processing technology, and in particular to a gain calibration device and method for a CIC filter. Background Art

[0002] CIC filters are widely used in digital down-conversion. Their main advantages are simple structure, high efficiency, and reduced aliasing effects of the spectrum. The function of the CIC filter is filtering, not amplifying the input signal, so the gain of the CIC filter needs to be eliminated or the gain of the CIC filter needs to be calibrated before output. However, in practical applications, when down-converting a variety of intermediate frequency bandwidth signals, the input parameters of the CIC filter, such as the decimation rate R or the order N, are usually required to be variable, and the user can set any input parameters for the CIC filter through programming. Changes in these input parameters will cause changes in the internal gain of the CIC filter, so the output of the filter needs to be re-gained accordingly.

[0003] According to the frequency response characteristics of the CIC filter, the gain generated by the data after passing through the CIC filter is shown in formula (1): CIC gain = R N / 2 Bout-Bin (1) Among them, Bin is the input bit width of the CIC filter, and Bout is the output bit width of the CIC filter.

[0004] There are two main existing methods for CIC filter gain calibration.

[0005] One is to calculate a series of gain calibration coefficients through a large number of simulations or test experiments, and then multiply the gain calibration coefficients by the filter output for linear calibration. The gain calibration coefficients are stored in a lookup table, and the appropriate compensation value is selected from the lookup table at runtime according to the current configuration (such as the decimation rate, etc.). However, the disadvantage of this method is that it requires additional memory space to store the lookup table, and the lookup table may not provide accurate compensation values ​​for unforeseen working conditions.

[0006] The second is to monitor the input and output signals in real time and dynamically adjust the gain calibration coefficient according to the current working conditions. However, this method increases the computational complexity and resource consumption, may affect the real-time performance and response speed of the system, and is relatively complex to implement. Summary of the invention

[0007] In view of the technical problems existing in the prior art, the present application proposes a gain calibration device for a CIC filter, comprising: a gain calibration coefficient calculation module, configured to receive an input parameter set of the CIC filter including a sampling rate and a filter order, and an initial value of a quantization word length of a gain calibration coefficient; generate a set of gains based on the input parameter set, and use the reciprocal thereof as a first gain calibration coefficient set; use the quantization word length to enlarge and round the first gain calibration coefficient set to generate a second gain calibration coefficient set; then use the quantization word length to reduce the second gain calibration coefficient set to generate a third gain calibration coefficient set; based on the first gain calibration coefficient set, The invention relates to a method for generating a set of precisions of gain calibration coefficients by using a number set and the third gain calibration coefficient set; comparing the set of precisions with a preset precision threshold, and when there are still cases in the precision set that do not meet the precision threshold, updating the quantization word length until the precision set completely meets the precision threshold, and generating a final gain calibration coefficient set using the corresponding quantization word length; a gain calibration module, electrically connected to the gain calibration coefficient calculation module, calibrating the CIC filter output using the final gain calibration coefficient set; and a truncation module, electrically connected to the gain calibration module, configured to perform low-bit truncation processing on the output of the gain calibration module.

[0008] In particular, in the gain calibration device for the CIC filter, the truncation module is further configured to perform saturation truncation processing on the result after low-bit truncation.

[0009] In particular, the gain calibration device of the CIC filter, wherein the step of amplifying and rounding the first gain calibration coefficient set by using the quantization word length to generate the second gain calibration coefficient set comprises: amplifying the first gain calibration coefficient set by 2 a And rounding is performed to generate a second gain calibration coefficient set, where a is the quantization word length and a is an integer greater than or equal to 1.

[0010] In particular, in the gain calibration device of the CIC filter, the step of reducing the second gain calibration coefficient set by using the quantization word length to generate a third gain calibration coefficient set comprises reducing the second gain calibration coefficient set by 2 a A third gain calibration coefficient set is generated, where a is a quantization word length and a is an integer greater than or equal to 1.

[0011] In particular, in the gain calibration device for the CIC filter, the set of precisions of the gain calibration coefficients is a ratio of a difference between the third gain calibration coefficient set and the first gain calibration coefficient set to the first gain calibration coefficient set.

[0012] In particular, in the gain calibration device of the CIC filter, when there are multiple quantization word lengths so that the accuracy set meets the accuracy threshold, the quantization word length with the smallest number of bits or the smallest value is selected to generate the final gain calibration coefficient set.

[0013] In particular, in the gain calibration device of the CIC filter, the gain calibration coefficient calculation module includes a divider, which is a pipeline divider with a configurable dividend bit width, and the number of pipeline delay cycles is consistent with the dividend bit width.

[0014] In particular, an electronic device comprises a CIC filter and any gain calibration device of the CIC filter.

[0015] In particular, the gain calibration method of a CIC filter comprises the following steps: receiving a set of input parameters of the CIC filter including a sampling rate and a filter order, and an initial value of a quantization word length of a gain calibration coefficient; generating a set of gains based on the input parameter set, and taking the inverse of the set of gains as a first set of gain calibration coefficients; amplifying and rounding the first set of gain calibration coefficients using the quantization word length to generate a second set of gain calibration coefficients; reducing the second set of gain calibration coefficients using the quantization word length to generate a third set of gain calibration coefficients; generating a set of precisions of the gain calibration coefficients based on the first set of gain calibration coefficients and the third set of gain calibration coefficients; comparing the set of precisions with a preset precision threshold, and when there is still a situation in the precision set that does not meet the precision threshold, updating the quantization word length until the precision set completely meets the precision threshold, and generating a final set of gain calibration coefficients using the corresponding quantization word length; calibrating the CIC filter output using the final set of gain calibration coefficients; and performing low-bit truncation processing on the output of the CIC filter after the above calibration.

[0016] In particular, the gain calibration method further includes performing a saturation truncation process after performing a low-bit truncation process.

[0017] The present application calculates the corresponding gain calibration coefficient according to any configured input parameters in a digital circuit, and adapts to different accuracy requirements according to the selection of quantization word length. It can store and calculate a large number of gain calibration coefficients while meeting certain calculation accuracy requirements, thereby improving resource utilization and the practicality of previous CIC filter gain calibration methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Below, the preferred embodiments of the present application will be further described in detail with reference to the accompanying drawings, wherein: Figure 1 Schematic diagram of the structure of a CIC filter gain calibration device according to an embodiment of the present application; Figure 2 Schematic diagram of the working process of the CIC filter gain calibration device according to an embodiment of the present application; Figure 3 The present invention is a flow chart of a method for performing gain calibration on a CIC filter according to an embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] In the following detailed description, reference may be made to the various specification drawings that are part of the present application and are used to illustrate specific embodiments of the present application. In the accompanying drawings, similar reference numerals describe substantially similar components in different figures. The various specific embodiments of the present application are described below in sufficient detail so that a person of ordinary skill in the art with relevant knowledge and skills in the art can implement the technical solutions of the present application. It should be understood that other embodiments may also be used or structural, logical or electrical changes may be made to the embodiments of the present application.

[0021] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the following description is only for the convenience of understanding the technical solution of the present application and should not be used to limit the protection scope of the present application.

[0022] Figure 1 Schematic diagram of the structure of a CIC filter gain calibration device according to an embodiment of the present application.

[0023] Figure 2 Schematic diagram of the working process of the CIC filter gain calibration device according to an embodiment of the present application.

[0024] Reference below Figure 1 , Figure 2 The gain calibration device of the present application is described.

[0025] According to one embodiment, the device of the present application includes three modules: a gain calibration coefficient calculation module 110 , a gain calibration module 120 , and a truncation module 130 .

[0026] According to one embodiment, the gain calibration coefficient calculation module 110 may include at least a multiplier, a divider, and a register. When receiving the filter order N and the sampling rate R newly configured by the user, the module is started. After the module starts working, it solves the final gain calibration coefficient by calling the multiplier and the divider, and saves it to the register waiting for calling. According to one embodiment, after the final gain calibration coefficient is solved and saved in the register, the multiplier and divider in the gain calibration coefficient calculation module 110 and the unoccupied registers can be occupied by other functions of the system until new parameters are input and the final gain calibration coefficient needs to be recalculated. This can improve the utilization rate of system resources.

[0027] According to one embodiment, the divider in this embodiment can be a pipeline divider based on subtraction and shifting to realize configurable dividend bit width, and the number of pipeline delay cycles is consistent with the dividend bit width. Although this approach has a certain delay, it can save the hardware resources of the divider, and the parameterized design of the dividend bit width can adapt to different precision requirements. According to one embodiment, when the output rate of the CIC filter is faster than the divider pipeline delay, this situation can be avoided by two methods, such as allowing the pipeline to work in a faster clock domain, the pipeline delay will become shorter, or the divider is designed as a multi-bit parallel structure, which can effectively solve the problem. According to one embodiment, the design of the above-mentioned multiplier is similar to that of the divider, with both a pipeline design and a multi-bit parallel structure. The specific implementation method depends on the specific usage scenario and is not limited here.

[0028] According to one embodiment, the gain calibration module 120 may include at least a multiplier, which is electrically connected to the above-mentioned gain calibration coefficient calculation module 110 and the CIC filter. The gain calibration module 120 may use the multiplier to solve the filter output after gain calibration based on at least the CIC filter output result and the above-mentioned final gain calibration coefficient.

[0029] According to one embodiment, the truncation module 130 is electrically connected to the gain calibration module 120, and performs low-bit truncation processing on the output result of the gain calibration module 120. If the result obtained exceeds the range that can be represented by the output bit width Bout set by the user, the signal after low-bit truncation can be saturated and truncation processed to obtain the actual output signal of the CIC filter after gain calibration. After being processed by the truncation module 130, the value amplified by the quantization process of the gain calibration coefficient calculation module 110 can be reduced, and distortion caused by data overflow can be prevented, ensuring that the output value is always within the normal range.

[0030] Figure 3 The present invention is a flow chart of a method for obtaining a gain calibration coefficient of a CIC filter according to an embodiment of the present application.

[0031] Step 301, traverse all input parameters applicable to a CIC filter, such as the order N and the sampling rate R. The user can preset the signal input bit width Bin, the signal output bit width Bout, and the gain calibration accuracy threshold E. Based on these input parameters, the corresponding gain and its reciprocal are calculated by formula (1), and the set of the reciprocals of these gains is set as the first gain calibration coefficient set g0.

[0032] Step 302: amplify each value in the first gain calibration coefficient set g0 by 2 a times and rounded up as the second gain calibration coefficient set G, and each value in the second gain calibration coefficient set G is reduced by 2 a After multiple (e.g., right shift), the third gain calibration coefficient set g1 is obtained. Each value in the third gain calibration coefficient set g1 is compared with the corresponding value in the first gain calibration coefficient set g0, and the relationship between the change rate and the CIC filter gain calibration accuracy threshold E is determined, where a represents the quantization word length, which is an integer greater than or equal to 1.

[0033] According to one embodiment, in order to obtain a final gain calibration coefficient AG that satisfies the accuracy, it can be achieved by adjusting the gain calibration coefficient quantization word length a. Since the gain calibration coefficient may introduce errors during the quantization process, thereby reducing the calculation accuracy, it is necessary to ensure that all gain calibration coefficients, after being uniformly quantized, have a calculation accuracy that can meet the threshold representing the user's needs.

[0034] According to one embodiment, the user can assign an initial value to the quantization word length a, and amplify the first gain calibration coefficient set g0 by 2 a The second gain calibration coefficient set G is obtained by multiplying and rounding, as shown in formula (2): G=round(2 a *g0) (2) According to one embodiment, each value in the second gain calibration coefficient set G may be reduced by 2 a The third gain calibration coefficient set g1 is obtained by multiplying the gain calibration coefficient set g1, as shown in formula (3): g1=G / 2 a (3) According to one embodiment, the corresponding values ​​in the first gain calibration coefficient set g0 and the third gain calibration coefficient set g1 are compared to obtain the change rate or accuracy of the gain coefficient, as shown in formula (4): e=(g1-g0) / g0 (4) According to one embodiment, a user may preset a CIC filter gain coefficient accuracy threshold E.

[0035] According to an embodiment, when all e are less than or equal to the accuracy threshold E, a can be used as the final quantization word length; when some change rates e cannot meet the threshold E, a needs to be adjusted and reassigned.

[0036] Step 303: When all the change rates e meet the threshold E, the corresponding a value is used as the final quantization word length, and the final gain calibration coefficient AG of the quantization that finally meets the accuracy is calculated according to formula (2).

[0037] According to an embodiment, when it is required to ensure that a is minimized, the errors between all the first gain calibration coefficient sets g0 and the third gain calibration coefficient sets g1 meet the calculation accuracy requirements, and the quantization word length a at this time is the optimal solution, which can not only meet the accuracy requirements of the gain coefficients after quantization, but also meet the minimum hardware resource occupation.

[0038] Step 304, calibrate the gain of the CIC filter using the final gain calibration coefficient AG, as shown in formula (5): CIC_OUT1 = CIC_OUT*AG (5) Where CIC_OUT is the original output of the CIC filter, and CIC_OUT1 is the output of the CIC filter after calibration.

[0039] Step 305, perform low-order interception processing on the data CIC_OUT1 calibrated by the CIC filter, and convert the 2 a Gain removal: According to formula (3), the actual output signal of the CIC filter after gain calibration is obtained, and it is determined whether the actual output signal exceeds the range that can be expressed by the signal output bit width Bout preset by the user.

[0040] According to one embodiment, when the actual output signal exceeds the range expressed by the output bit width Bout, a saturation truncation process may be performed on it. For example, when the actual output signal is an unsigned number, the high bits exceeding the output bit width Bout may be discarded, and the remaining low bits may all be set to 1, that is, they may be limited to the maximum value allowed by the user. Performing a saturation truncation process may prevent distortion caused by data overflow, and ensure that the output value is always within a normal range.

[0041] According to one embodiment, the gain calibration of the CIC filter is implemented. The CIC filter order N is 3, the decimation rate R is 32*n, the gain calibration accuracy threshold E is 0.5 ten thousandths, the input bit width Bin is 1 bit, and the output bit width Bout is 24 bits, wherein the value of n can be arbitrarily configured from 1 to 2047.

[0042] First, substitute the known parameters into formula (1) to obtain the CIC filter gain (32*n) 3 / 2 23, take the inverse to get the first gain calibration coefficient set g0 of the filter as 2 23 / (32*n) 3 .

[0043] Then, the quantization word length a is set to an initial value of 40, and according to formula (3), all the third gain calibration coefficient sets g1 are obtained as round(g0*2 40 ) / 2 40 .

[0044] Finally, according to formula (4), the change rate between g1 and g0 is traversed and the quantization word length a is gradually adjusted until the gain change rate corresponding to all n values ​​is less than 0.5%, that is, the requirement for the accuracy threshold E is met. Finally, the quantization word length a of this embodiment is 45.

[0045] According to one embodiment, before the first gain calibration coefficient set g0 and the value a are substituted into formula (2), the calculation of the CIC gain is simplified to obtain the CIC gain as (32*n) 3 / 2 23 = n 3 / 2 8 According to this simplified formula, we can know that the calculation result may contain decimals or even irrational numbers. In this step, the CIC gain is amplified by logical left shift 2 8 times, making the CIC gain n 3 , becomes an integer. When performing calculations, it can be ensured that the calculation accuracy of different extraction rates R will not differ too much after the division.

[0046] Substituting g0 and a into formula (2) yields G as round (2 45 / n 3 ), the calculation of the final gain calibration coefficient set AG is completed through a divider and rounding operation.

[0047] According to one embodiment, after the final gain calibration coefficient of the CIC filter is obtained, it can be used to calibrate the CIC filter. For example, according to formula (5), the output of the CIC filter is multiplied by the final gain calibration coefficient AG through a multiplier to obtain a calibrated signal CIC_OUT*AG.

[0048] According to one embodiment, low-bit truncation and saturation truncation processing may be performed on the output of the calibrated CIC filter.

[0049] The low-order truncation is accomplished by logically shifting right 45 bits to remove the 2 introduced during the quantization process. 45The saturation truncation process ensures that the output signal width after calibration is 24 bits. The actual output value obtained after the CIC filter gain calibration meets the accuracy requirements and occupies the least resources is (CIC_OUT*AG) / 2 45 .

[0050] According to another embodiment, the gain calibration of the CIC filter is implemented, wherein the filter order N is 4, the decimation rate R is 32*n, the calculation accuracy E is 0.5 ten thousandths, the input bit width Bin is 1 bit, the output bit width Bout is 24 bits, and the value of n can be arbitrarily configured from 1 to 2047.

[0051] First, substitute the known parameters into formula (1) to obtain the theoretical gain of the CIC filter: (32*n) 4 / 2 23 , take the inverse to get the corresponding filter first gain calibration coefficient set g0 is 2 23 / (32*n) 4 .

[0052] Then, an initial value of 50 is set for the quantization word length a, and according to formula (3), all the second gain calibration coefficient sets g1 are obtained as round(g0*2 50 ) / 2 50 .

[0053] Finally, according to formula (4), the change rate between g1 and g0 is traversed and the quantization word length a is gradually adjusted until the change rate corresponding to all n values ​​is less than 0.5%, that is, the requirement for the accuracy threshold E is met. Finally, the quantization word length a of this embodiment is 63.

[0054] According to one embodiment, before the first gain calibration coefficient set g0 and the value a are substituted into formula (2), the calculation of the CIC gain is simplified to obtain the CIC gain as (32*n) 4 / 2 23 = n 4 / 2 3 According to this simplified formula, we can know that the calculation result may contain decimals or even irrational numbers. In this step, the CIC gain is amplified by logical left shift 2 3 times, making the CIC gain n 4 , becomes an integer. When performing calculations, it can be ensured that the calculation accuracy of different extraction rates R will not differ too much after the division.

[0055] Substituting the values ​​of g0 and a into formula (2), we get AG as round (2 63 / n 4 ), through the divider and rounding operation, the calculation of the final gain calibration coefficient set AG is completed.

[0056] According to one embodiment, after obtaining the final gain calibration coefficient of the CIC filter, the CIC filter can be calibrated using it. For example, according to formula (5), the output of the CIC filter is multiplied by the final gain calibration coefficient set AG that meets the accuracy through a multiplier to obtain a calibrated signal CIC_OUT*AG.

[0057] According to one embodiment, low-bit truncation and saturation truncation processing may be performed on the output of the calibrated CIC filter.

[0058] The low-order truncation is achieved by logically shifting right by 63 bits to remove the 2 introduced in the process of quantization coefficients. 63 The calibrated output signal width is 24 bits after saturation truncation. The actual output value after CIC filter gain calibration that meets the accuracy requirements and occupies the least resources is (CIC_OUT*AG) / 2. 63 .

[0059] The gain calibration device and method of the CIC filter of the present application calculates the corresponding gain calibration coefficient according to the input parameters of any configuration in the digital circuit, and adapts to different accuracy requirements according to the selection of the quantization word length. It can store and calculate a large number of gain calibration coefficients while meeting certain calculation accuracy requirements, thereby improving resource utilization and the practicality of the previous CIC filter gain calibration method.

[0060] The above embodiments are only used to illustrate the present application, and are not intended to limit the present application. Ordinary technicians in the relevant technical field may make various changes and modifications without departing from the scope of the present application. Therefore, all equivalent technical solutions should also fall within the scope disclosed in the present application.

Claims

1. A gain calibration device for a CIC filter, characterized in that: include, Gain calibration coefficient calculation module, configured as: A set of input parameters for receiving the CIC filter includes a decimation rate and a filter order, and an initial value of a quantization word length of a gain calibration coefficient; Generate a set of gains based on the input parameter set, and use the reciprocals of the gains as a first set of gain calibration coefficients; Using the quantization word length to amplify and round the first gain calibration coefficient set to generate a second gain calibration coefficient set; Using the quantization word length to reduce the second gain calibration coefficient set to generate a third gain calibration coefficient set; generating a set of precisions of gain calibration coefficients based on the first set of gain calibration coefficients and the third set of gain calibration coefficients; Compare the precision set with a preset precision threshold, and when there is still a situation in the precision set that does not meet the precision threshold, update the quantization word length until the precision set completely meets the precision threshold, and generate a final gain calibration coefficient set using the corresponding quantization word length; a gain calibration module, electrically connected to the gain calibration coefficient calculation module, and calibrating the CIC filter output using the final gain calibration coefficient set; as well as, The truncation module is electrically connected to the gain calibration module and is configured to perform low-bit truncation processing on the output of the gain calibration module.

2. The gain calibration device of the CIC filter according to claim 1, characterized in that: The truncation module is further configured to perform saturation truncation processing on the result after the low-bit truncation.

3. The gain calibration device of the CIC filter according to claim 1, characterized in that: Using the quantization word length to amplify and round the first gain calibration coefficient set to generate a second gain calibration coefficient set includes amplifying the first gain calibration coefficient set by 2 a And rounding is performed to generate a second gain calibration coefficient set, where a is the quantization word length and a is an integer greater than or equal to 1.

4. The gain calibration device of the CIC filter according to claim 3, characterized in that: Then using the quantization word length to reduce the second gain calibration coefficient set to generate a third gain calibration coefficient set includes reducing the second gain calibration coefficient set by 2 a A third gain calibration coefficient set is generated, where a is a quantization word length and a is an integer greater than or equal to 1.

5. The gain calibration device of the CIC filter according to claim 1, characterized in that: The set of precisions of the gain calibration coefficients is a ratio of a difference between the third gain calibration coefficient set and the first gain calibration coefficient set to the first gain calibration coefficient set.

6. The gain calibration device of the CIC filter according to claim 1, characterized in that: When there are multiple quantization word lengths so that the precision set meets the precision threshold, the quantization word length with the smallest number of bits or the smallest value is selected to generate the final gain calibration coefficient set.

7. The gain calibration device of the CIC filter according to claim 1, characterized in that: The gain calibration coefficient calculation module includes a divider, which is a pipeline divider with a configurable bit width of the dividend, and the number of pipeline delay cycles is consistent with the bit width of the dividend.

8. An electronic device, characterized in that: It comprises a CIC filter and a gain calibration device for the CIC filter as claimed in any one of claims 1 to 7.

9. A gain calibration method for a CIC filter, characterized in that: The steps include: receiving a set of input parameters of the CIC filter including a decimation rate and a filter order, and an initial value of a quantization word length of a gain calibration coefficient; generating a set of gains based on the input parameter set, and using the inverse of the set of gains as a first set of gain calibration coefficients; Using the quantization word length to amplify and round the first gain calibration coefficient set to generate a second gain calibration coefficient set; Then, reducing the second gain calibration coefficient set by using the quantization word length to generate a third gain calibration coefficient set; generating a set of precisions of gain calibration coefficients based on the first set of gain calibration coefficients and the third set of gain calibration coefficients; Compare the precision set with a preset precision threshold, and when there is still a situation in the precision set that does not meet the precision threshold, update the quantization word length until the precision set completely meets the precision threshold, and generate a final gain calibration coefficient set using the corresponding quantization word length; calibrating the CIC filter output using the final gain calibration coefficient set; and, The output of the CIC filter after the above calibration is subjected to low-bit interception processing.

10. The gain calibration method according to claim 9, characterized in that: It also includes performing saturation truncation processing after performing low-bit truncation processing.

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