A gain calibration device and method for a CIC filter

Abstract

The present application relates to a gain calibration device for a CIC filter, including a gain calibration coefficient calculation module configured to receive a set of input parameters of the CIC filter and an initial value of the quantization word length of the gain calibration coefficient, and generate a final set of gain calibration coefficients using the corresponding quantization word length; a gain calibration module electrically connected to the gain calibration coefficient calculation module, calibrating the output of the CIC filter using the final set of gain calibration coefficients; and a truncation module electrically connected to the gain calibration module, performing a low-bit truncation process on the output of the gain calibration module. It can calculate and store a large number of corresponding gain calibration coefficients according to arbitrarily configured input parameters, and meet certain operation accuracy requirements. The present application also relates to a gain calibration method for a CIC filter.

Description

Technical Field

[0001] This application relates to the technical field of signal processing, and particularly to a gain calibration device and method for a CIC filter. Background Art

[0002] CIC filters are widely used in digital down-conversion. The main advantages are simple structure, high efficiency, and the ability to reduce spectral aliasing effects. The function of a CIC filter is to filter, rather than amplify the input signal. Therefore, it is necessary to eliminate the gain of the CIC filter or perform gain calibration on the CIC filter before output. However, in practical applications when performing down-conversion processing on multiple intermediate frequency bandwidth signals, it is usually required that the input parameters of the CIC filter, such as the decimation rate R or the order N, are variable, and the user can set arbitrary input parameters for the CIC filter through programming. The change of these input parameters will cause the internal gain of the CIC filter to change, so it is necessary to re-perform gain calibration on the output of the filter accordingly.

[0003] According to the frequency response characteristics of the CIC filter, the gain generated by the data passing through the CIC filter is as shown in formula (1):

[0004] CIC gain = R N / 2 Bout-Bin (1)

[0005] Where, Bin is the input bit width of the CIC filter, and Bout is the output bit width of the CIC filter.

[0006] There are mainly two existing methods for CIC filter gain calibration.

[0007] 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 look-up table, and a suitable compensation value is selected from the look-up table according to the current configuration (such as the decimation rate, etc.) during operation. However, the disadvantage of this method is that it requires additional memory space to store the look-up table, and for unforeseen working conditions, the look-up table may not provide accurate compensation values.

[0008] The other is to monitor the input and output signals in real time and dynamically adjust the gain calibration coefficients 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

[0009] In view of the technical problems existing in the prior art, the present application proposes a gain calibration device for a CIC filter, including: a gain calibration coefficient calculation module configured to receive an input parameter set of the CIC filter including a decimation rate, a filter order, and an initial value of the quantization word length of the gain calibration coefficient; generating a set of gains based on the input parameter set and taking the reciprocal thereof as a first gain calibration coefficient set; multiplying and rounding up the first gain calibration coefficient set by the quantization word length to generate a second gain calibration coefficient set; then reducing the second gain calibration coefficient set by the quantization word length to generate a third gain calibration coefficient set; generating a set of precisions of the gain calibration coefficient based on the first gain calibration coefficient set and the third gain calibration coefficient set; 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 gain calibration coefficient set using the corresponding quantization word length; a gain calibration module electrically connected to the gain calibration coefficient calculation module for calibrating the output of the CIC filter using the final gain calibration coefficient set; and a truncation module electrically connected to the gain calibration module and configured to perform a low-bit truncation process on the output of the gain calibration module.

[0010] In particular, for the gain calibration device of the CIC filter, the truncation module further includes being configured to perform a saturation truncation process on the result after low-bit truncation.

[0011] In particular, for the gain calibration device of the CIC filter, where multiplying and rounding up the first gain calibration coefficient set by the quantization word length to generate a second gain calibration coefficient set includes multiplying the first gain calibration coefficient set by 2 a and rounding up 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.

[0012] In particular, for the gain calibration device of the CIC filter, where then reducing the second gain calibration coefficient set by the quantization word length to generate a third gain calibration coefficient set includes dividing the second gain calibration coefficient set by 2 a to generate a third gain calibration coefficient set, where a is the quantization word length and a is an integer greater than or equal to 1.

[0013] In particular, for the gain calibration device of the CIC filter, where the set of precisions of the gain calibration coefficient is the ratio of the difference between the third gain calibration coefficient set and the first gain calibration coefficient set to the first gain calibration coefficient set.

[0014] In particular, for the gain calibration device of the CIC filter, when there are multiple quantization word lengths such 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.

[0015] In particular, for the gain calibration device of the CIC filter, the gain calibration coefficient calculation module includes a divider, which is a pipelined divider with configurable dividend bit width, and the number of pipeline delay cycles is the same as the dividend bit width.

[0016] In particular, an electronic device includes a CIC filter and a gain calibration device for any of the CIC filters.

[0017] In particular, a gain calibration method for a CIC filter includes the following steps: receiving an input parameter set of the CIC filter including the decimation rate and the filter order, and an initial value of the quantization word length of the gain calibration coefficient; generating a set of gains based on the input parameter set, and taking the reciprocal of the set of gains as the first gain calibration coefficient set; using the quantization word length to magnify and round the first gain calibration coefficient set to generate a second gain calibration coefficient set; then using the quantization word length to shrink the second gain calibration coefficient set to generate a third gain calibration coefficient set; generating a set of accuracies of the gain calibration coefficient based on the first gain calibration coefficient set and the third gain calibration coefficient set; comparing the set of accuracies with a preset accuracy threshold, and when there is still a situation where the accuracy set does not meet the accuracy threshold, updating the quantization word length until the accuracy set completely meets the accuracy threshold, and generating a final gain calibration coefficient set using the corresponding quantization word length; calibrating the output of the CIC filter using the final gain calibration coefficient set; and performing a low-bit truncation process on the output of the CIC filter after the above calibration.

[0018] In particular, the gain calibration method further includes performing a saturation truncation process after the low-bit truncation process.

[0019] In this application, by calculating the corresponding gain calibration coefficient according to arbitrarily configured input parameters in a digital circuit and adapting to different accuracy requirements by selecting the quantization word length, a large number of gain calibration coefficients can be stored and calculated, while meeting certain operation accuracy requirements, improving resource utilization, and improving the practicality of the conventional gain calibration method for CIC filters. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Next, the preferred embodiments of the present application will be further described in detail with reference to the drawings, where:

[0021] Figure 1Schematic diagram of the structure of a CIC filter gain calibration device according to an embodiment of the present application;

[0022] Figure 2 Schematic diagram of the working process of a CIC filter gain calibration device according to an embodiment of the present application;

[0023] Figure 3 Flowchart of a method for performing gain calibration on a CIC filter according to an embodiment of the present application. Detailed implementation manners

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0025] In the following detailed description, reference may be made to the various schematic drawings that form a part hereof and that show, by way of illustration, specific embodiments in which the present application may be practiced. In the drawings, like reference numerals generally refer to like components in different diagrams. The specific embodiments of the present application have been described in sufficient detail below to enable those of ordinary skill in the art with relevant knowledge and technology to practice the technical solutions of the present application. It should be understood that other embodiments may be utilized or structural, logical, or electrical changes may be made to the embodiments of the present application.

[0026] The technical solutions of the present application will be further described below through specific implementation manners. Those skilled in the art should understand that the following description is only for the convenience of understanding the technical solutions of the present application and should not be used to limit the protection scope of the present application.

[0027] Figure 1 Schematic diagram of the structure of a CIC filter gain calibration device according to an embodiment of the present application.

[0028] Figure 2 Schematic diagram of the working process of a CIC filter gain calibration device according to an embodiment of the present application.

[0029] Next, reference is made to Figure 1 、 Figure 2 to describe the gain calibration device of the present application.

[0030] 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.

[0031] According to one embodiment, the gain calibration coefficient calculation module 110 may at least include a multiplier, a divider, and a register. When receiving the newly configured filter order N and sampling rate R from the user, this module is started. After this module starts to work, it solves for the final gain calibration coefficient by invoking the multiplier and the divider, and saves it to the register for waiting to be invoked. According to one embodiment, after solving for the final gain calibration coefficient and saving it in the register, the multiplier, the divider, and the unoccupied registers in the gain calibration coefficient calculation module 110 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.

[0032] According to one embodiment, in this embodiment, the divider may be a pipelined divider based on subtraction and shift that enables the dividend bit width to be configurable, and the number of pipeline delay cycles is the same as 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 pipeline delay of the divider, two methods can be used to avoid this situation. For example, making the pipeline work in a faster clock domain will shorten the pipeline delay, or designing the divider into a multi-bit parallel structure can effectively solve the problem. According to one embodiment, the design of the above-mentioned multiplier is similar to that of the divider, having both a pipelined design and a multi-bit parallel structure. The specific implementation method depends on the specific usage scenario and is not limited here.

[0033] According to one embodiment, the gain calibration module 120 may at least include a multiplier, and is electrically connected to the above-mentioned gain calibration coefficient calculation module 110 and the CIC filter. The gain calibration module 120 can solve for the filter output after gain calibration based at least on the output result of the CIC filter and the above-mentioned final gain calibration coefficient by using the multiplier.

[0034] According to one embodiment, the truncation module 130 is electrically connected to the gain calibration module 120, and performs a low-bit truncation process on the output result of the gain calibration module 120. If the obtained result exceeds the range that can be represented by the user-set output bit width Bout, saturation truncation processing can be performed on the signal after low-bit truncation to obtain the actual output signal of the CIC filter after gain calibration. After being processed by the truncation module 130, not only can the value amplified during the quantization process of the gain calibration coefficient calculation module 110 be reduced, but also data overflow leading to distortion can be prevented, ensuring that the output value is always within the normal range.

[0035] Figure 3 It is a flowchart of a method for obtaining the gain calibration coefficient of a CIC filter according to an embodiment of the present application.

[0036] Step 301: Traverse all input parameters applicable to a CIC filter, such as the order N and the decimation 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, calculate the corresponding gain and its reciprocal through formula (1), and set the set of reciprocals of these gains as the first gain calibration coefficient set g0.

[0037] Step 302: Multiply each value in the first gain calibration coefficient set g0 by 2 a times, round it to an integer as the second gain calibration coefficient set G, and divide each value in the second gain calibration coefficient set G by 2 a times (e.g., right shift) to obtain the third gain calibration coefficient set g1. Compare each value in the third gain calibration coefficient set g1 with the corresponding value in the first gain calibration coefficient set g0, and judge the relationship between the change rate and the CIC filter gain calibration accuracy threshold E, where a represents the quantization word length, which is an integer greater than or equal to 1.

[0038] According to one embodiment, in order to obtain the final gain calibration coefficient AG that meets the accuracy, it can be achieved by adjusting the gain calibration coefficient quantization word length a. Since errors will be introduced during the quantization of the gain calibration coefficient, resulting in a reduction in calculation accuracy, it is necessary to ensure that after all gain calibration coefficients are uniformly quantized, their calculation accuracies can meet the threshold representing the user's requirements.

[0039] According to one embodiment, the user can assign an initial value to the quantization word length a, multiply the first gain calibration coefficient set g0 by 2 a times and round it to obtain the second gain calibration coefficient set G, as shown in formula (2):

[0040] G = round(2 a *g0) (2)

[0041] According to one embodiment, each value in the second gain calibration coefficient set G can be divided by 2 a times to obtain the third gain calibration coefficient set g1, as shown in formula (3):

[0042] g1 = G / 2 a (3)

[0043] According to one embodiment, compare the corresponding values in the first gain calibration coefficient set g0 and the third gain calibration coefficient set g1 to obtain the change rate or accuracy of the gain coefficient, as shown in formula (4):

[0044] e = (g1 - g0) / g0 (4)

[0045] According to one embodiment, the user can preset the precision threshold E of the CIC filter gain coefficient.

[0046] According to one embodiment, when all e are less than or equal to the precision threshold E, a can be used as the final quantization word length; when some change rates e do not meet the threshold E, a needs to be adjusted and re-assigned.

[0047] Step 303, when all change rates e meet the threshold E, use the corresponding a value as the final quantization word length, and calculate the final gain calibration coefficient AG of the quantization that finally meets the precision according to formula (2).

[0048] According to one embodiment, it is required to ensure that under the condition of the smallest a, the error between all the first gain calibration coefficient sets g0 and the third gain calibration coefficient sets g1 meets the calculation precision requirements. At this time, the quantization word length a is the optimal solution. It can not only ensure the precision requirements for the gain coefficient after quantization, but also meet the least occupation of hardware resources.

[0049] Step 304, calibrate the gain of the CIC filter using the final gain calibration coefficient AG, as shown in formula (5):

[0050] CIC_OUT1 = CIC_OUT * AG (5)

[0051] Where CIC_OUT is the original output of the CIC filter, and CIC_OUT1 is the output of the CIC filter after calibration.

[0052] Step 305, perform low-bit truncation processing on the data CIC_OUT1 calibrated by the CIC filter, and remove the 2-fold gain amplified in step 303. a According to formula (3), obtain the actual output signal of the CIC filter after gain calibration, and determine whether the actual output signal exceeds the range that can be expressed by the user-preset signal output bit width Bout.

[0053] According to one embodiment, when the actual output signal exceeds the range expressed by the output bit width Bout, it can be subjected to saturation truncation processing. For example, when the above actual output signal is an unsigned number, the high bits exceeding the output bit width Bout can be discarded, and all the remaining low bits can be set to 1, that is, it is limited to the maximum value allowed by the user. Performing saturation truncation processing can prevent data overflow from causing distortion and ensure that the output value is always within the normal range.

[0054] According to one embodiment, the gain calibration of the CIC filter is realized. The order N of the CIC filter is 3, the decimation rate R is 32 * n, the gain calibration precision threshold E is five ten-thousandths, the input bit width Bin is 1 bit, and the output bit width Bout is 24 bits, where the n value can be arbitrarily configured from 1 to 2047.

[0055] First, substitute the known parameters into Equation (1) to obtain the CIC filter gain as (32 * n) 3 / 2 23 , take the reciprocal to obtain the first gain calibration coefficient set g0 of the filter as 2 23 / (32 * n) 3 .

[0056] Then, set an initial value of 40 for the quantization word length a, and obtain all the third gain calibration coefficient sets g1 as round(g0 * 2 40 ) / 2 40 according to Equation (3).

[0057] Finally, traverse the change rate between g1 and g0 according to Equation (4), and gradually adjust the quantization word length a until the gain change rate corresponding to all n values is less than five ten-thousandths, that is, the requirement for the precision threshold E is met. Finally, the quantization word length a of this embodiment can be obtained as 45.

[0058] According to one embodiment, before substituting the first gain calibration coefficient set g0 and the a value into Equation (2), simplify the calculation of the CIC gain to obtain the CIC gain as (32 * n) 3 / 2 23 = n 3 / 2 8 . According to this simplified formula, it can be known that the calculation result may have decimal or even irrational numbers. In this step, the CIC gain is amplified by 2 8 times through logical left shift, so that the CIC gain becomes n 3 , becoming an integer. When performing operations, it can ensure that the calculation precision does not vary too much after division for different decimation rates R.

[0059] Substitute the g0 and a values into Equation (2) to obtain G as round(2 45 / n 3 ), and complete the calculation of the final gain calibration coefficient set AG through a divider and rounding operation.

[0060] 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, multiply the output of the CIC filter by the final gain calibration coefficient AG through a multiplier according to Equation (5) to obtain the calibrated signal as CIC_OUT * AG.

[0061] According to one embodiment, low-bit truncation and saturation truncation processing can be performed on the output of the calibrated CIC filter.

[0062] Low-bit truncation is completed through logical right shift by 45 bits to remove the 2 introduced during the quantization coefficient process45 The double gain and saturation truncation processing ensure that the bit width of the calibrated output signal is 24 bits. Finally, the actual output value that meets the accuracy requirements and occupies the least resources after the CIC filter gain calibration is (CIC_OUT * AG) / 2 45 。

[0063] According to another embodiment, the gain calibration of the CIC filter is realized. Among them, the filter order N is 4, the decimation rate R is 32 * n, the calculation accuracy E is five ten-thousandths, the input bit width Bin is 1 bit, and the output bit width Bout is 24 bits, where the n value can be arbitrarily configured from 1 to 2047.

[0064] First, substitute the known parameters into formula (1) to obtain the theoretical gain of the CIC filter as (32 * n) 4 / 2 23 , take the reciprocal to obtain the corresponding first gain calibration coefficient set g0 of the filter as 2 23 / (32 * n) 4 。

[0065] Then, set an initial value of 50 for the quantization word length a, and obtain all the second gain calibration coefficient sets g1 as round(g0 * 2 50 ) / 2 50 。

[0066] Finally, traverse the change rate between g1 and g0 according to formula (4), and gradually adjust the quantization word length a until the change rate corresponding to all n values is less than five ten-thousandths, that is, the requirement for the accuracy threshold E is met. Finally, the quantization word length a of this embodiment can be obtained as 63.

[0067] According to an embodiment, before substituting the first gain calibration coefficient set g0 and the a value 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, it can be known that there will be cases of decimals or even irrational numbers in its calculation results. In this step, the CIC gain is amplified by 2 through logical left shift 3 times, so that the CIC gain is n 4 , becoming an integer. When doing operations, it can ensure that the calculation accuracies do not differ too much after division for different decimation rates R.

[0068] Substitute the g0 and a values into formula (2) to obtain AG as round(2 63 / n 4 ), and complete the calculation of the final gain calibration coefficient set AG through the divider and rounding operation.

[0069] 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 set of final gain calibration coefficients AG that meet the accuracy through a multiplier to obtain the calibrated signal as CIC_OUT * AG.

[0070] According to one embodiment, the output of the calibrated CIC filter can be subjected to low-bit truncation and saturation truncation processing.

[0071] The low-bit truncation is achieved by logically shifting 63 bits to remove the 2-fold gain introduced during the quantization coefficient process. 63 The saturation truncation processing results in a calibrated output signal width of 24 bits. The actual output value that meets the accuracy requirements and minimizes resource occupation after the CIC filter gain calibration is finally obtained as (CIC_OUT * AG) / 2. 63 .

[0072] The gain calibration device and method of the CIC filter in this application calculate the corresponding gain calibration coefficients according to arbitrarily configured input parameters in the digital circuit, and adapt to different accuracy requirements according to the selection of the quantization word length. It can not only store and calculate a large number of gain calibration coefficients, but also meet certain operation accuracy requirements, improve the resource utilization rate, and improve the practicality of the previous CIC filter gain calibration method.

[0073] The above embodiments are only for illustrating this application and are not intended to limit this application. Those of ordinary skill in the relevant technical field can make various changes and modifications without departing from the scope of this application. Therefore, all equivalent technical solutions should also fall within the scope of the disclosure of this 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; Comparing the set of precisions with a preset precision threshold, and when there is still a situation in the set of precisions that does not meet the precision threshold, updating the quantization word length until the set of precisions 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, 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 as claimed in 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 as claimed in 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; Comparing the set of precisions with a preset precision threshold, and when there is still a situation in the set of precisions that does not meet the precision threshold, updating the quantization word length until the set of precisions completely meets the precision threshold, and generating 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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