CN204290909U - The digital filter that a kind of bandwidth, center frequency point are adjustable - Google Patents

Abstract

The utility model discloses a digital filter with adjustable bandwidth and central frequency point, which includes clock frequency division, bandwidth channel configuration, CIC filter group and FIR filter; the CIC filter group consists of several groups of CIC filters and corresponding Composed of compensation filter and gain correction module, the CIC filter is used to reduce the sampling rate of the input signal, and through the compensation filter and gain correction module to make the passband flat and realize the input and output bit width matching, after processing, the data is input into the FIR filter Receive the band selection information in the SPI through the bandwidth channel configuration module, read the extraction factor of the CIC filter group and the coefficient of the FIR filter in the EEPROM, and complete the adjustment of the FIR filter at the bandwidth center frequency point; the utility model realizes 5kHz, 50kHz, 100kHz, 200kHz, 1MHz, 2MHz, bandpass filters with different bandwidths and center frequencies to complete the selection of different channel signals.

Description

A Digital Filter with Adjustable Bandwidth and Center Frequency

technical field

The utility model belongs to the digital signal processing part in the wireless communication system, adopts the design method of VLSI (Very Large Scale Integration) according to the requirements of the communication system, and proposes a bandwidth, center Frequency adjustable digital filter VLSI structure.

Background technique

Wireless communication technology has brought great convenience to people's life and promoted the development of society. With the wide application of wireless communication, all kinds of wireless communication chips have also been developed by leaps and bounds. At the same time, the competition for wireless communication chips is becoming increasingly fierce, especially chips for private networks in various industries. Due to their large application volume and involving industry and national information security, they are increasingly valued by the state. Therefore, the design and production of chips for industrial private networks has become an important research topic in the national high-tech field ^[1] .

In the wireless access system of various industry private networks, the RF front-end chip is often the most important chip in all kinds of communication equipment. Its main function is to amplify, convert, filter, and quantify the tiny signal received by the antenna end of the receiver. wait. There are more and more types of frequency points and bandwidths used by industry private networks, and the frequency points, radio frequency bandwidths and signal bandwidths used by each private network are different. The frequency points are mainly concentrated in the range of 100MHz to 1.2GHz, and the signal bandwidth is in the range of 5kHz to 2MHz. Internally, the standards are not uniform, resulting in different RF chips used in private network equipment in various industries. At the same time, the demand for RF front-end chips is difficult to form a scale effect, and the cost is high and matching is difficult. Therefore, designing a wireless broadband RF chip with adjustable bandwidth and center frequency can meet the needs of many private networks and form economies of scale.

The filter is an important module in the wireless broadband radio frequency chip with adjustable bandwidth and center frequency, which completes the elimination of input signal noise and the selection of target channel signals. Filter design methods are divided into two types: analog filters and digital filters. Compared with analog filters, digital filters are superior to analog filters in terms of speed, circuit scale, power consumption, and flexibility, and are more suitable for modern digital filters. The communication system is conducive to improving the integration level of the chip. Since the filter is an important module in the wireless broadband RF chip, the performance of the filter directly determines the performance quality of the RF front-end chip, so the research on filter design is crucial to improving the quality of the RF front-end chip and improving the overall communication System performance is of great significance ^[2][3] .

At present, research on digital filters at home and abroad mainly focuses on the following two aspects. On the one hand, for different application backgrounds, design corresponding digital filtering systems, such as digital up-down conversion systems applied to software radios, blurring or sharpening filters applied to image processing, etc., for ASIC (Application Specific Integrated Circuit, Application Specific Integrated Circuits) implementation or FPGA (Field Programmable Gate Array, Field Programmable Gate Array) experiments are involved ^[4][5] . On the other hand, according to the digital filter theory, the key parts of the filter are optimized, such as the optimization of the performance and area of the multiplier or adder, or the optimization method is used to adjust the filter calculated by the window function method. filter coefficients to achieve higher performance indicators.

Compared with the design method of ASIC, the main advantage of FPGA to realize digital filter is that the design is more flexible and configurable. The disadvantage is that it is not conducive to system integration. Today, with the continuous development of communication systems and integrated circuit manufacturing, communication systems 1. The integration requirements of communication chips are getting higher and higher, and communication chips are constantly developing in the direction of SoC (System-on-a-Chip), which requires more digital filters to be realized by ASIC methods. Therefore, in view of the current research status at home and abroad and the requirements of radio frequency chips in wireless communication systems, a utility model is designed with a circuit structure of a digital bandpass filter with configurable bandwidth and center frequency, and the modules in it are designed and simulated verify.

references:

[1] Tang Youxi, Yi Xinping, Shao Shihai. Features of the New Generation Mobile Communication System - IMT-Advanced [J]. Journal of University of Electronic Science and Technology of China, 2008, 02:161-167.

[2] Yu Haixia. A high-performance AGC amplifier design based on wireless radio frequency chip research and development [D]. Tianjin University, 2012

[3] Zhang Yongman, Liang Liping, Guan Wu, etc.; High-performance and low-complexity digital front-end filter for LTE-A [J], Microelectronics and Computers, 2014, 9:008.

[4]Wenjing H, Guoyun Z, Waiyun L. Self-Programmable Multipurpose Digital Filter DesignBased on FPGA[C]//Internet Technology and Applications(iTAP), 2011International Conference on. IEEE, 2011:1-5.

[5] Ye Yadong, Lin Zhiting, Fan Yuhong; Design and Simulation of FIR Digital Filter Based on FPGA [J], Electronic Science and Technology, 2014, 27(7):67-70.

Utility model content

Aiming at the prior art, the utility model provides a digital filter with adjustable bandwidth and center frequency and a design method thereof, including a CIC (Cascade Integrator Comb, Cascade Integrator Comb) filter and compensation filter bank, bandwidth center Frequency adjustable FIR filter, signed and unsigned conversion, bandwidth channel configuration, frequency division module, etc. According to different application requirements, by configuring the decimation factor of the CIC filter, the downsampling rate of different magnifications can be realized for the input 20MHz signal, and by configuring the coefficient of the FIR (Finite Impulse Response) bandpass filter, 5kHz can be realized , 50kHz, 100kHz, 200kHz, 1MHz, 2MHz, band-pass filters with different bandwidths and center frequencies to complete the selection of different channel signals. Digital Filter System and Circuit Structure Applied in Wireless Broadband RF Chip

In order to solve the above-mentioned technical problems, the utility model proposes a digital filter with adjustable bandwidth and center frequency, including a clock frequency division module, a bandwidth channel configuration module, a CIC filter bank and an FIR filter; the CIC filter bank The input end of the FIR filter and the output end of the FIR filter are respectively connected with an unsigned number conversion module; the CIC filter bank is composed of several groups of CIC filters and the same number of compensation filters and gain correction modules. The filter is used to reduce the sampling rate of the input signal, and through the compensation filter and the gain correction module to make the passband of the CIC filter bank flat while realizing the matching of the input and output bit width, and then input the processed or data into the FIR filter; the FIR filter realizes the adjustable bandwidth center frequency point after the received data operation and processing, and outputs through the signed number conversion module; the bandwidth channel configuration module is connected with the CIC filter bank and the FIR filter The bandwidth channel configuration module is also connected with SPI and EEPROM; the bandwidth channel configuration module reads the decimation factor of the CIC filter bank in the EEPROM and the coefficient of the FIR filter by receiving the band selection information in the SPI, and completes Adjustment to the CIC filter bank and the FIR filter; the clock frequency division module is connected to the CIC filter bank and the FIR filter; the clock frequency division module generates a bandwidth channel configuration module, a CIC filter , compensation filter, gain correction module and the clock required by the FIR filter.

Compared with the prior art, the beneficial effects of the utility model are:

Figure 5 shows the simulation results of the filter when the decimation factor is 4 and the passband is 100-200kHz. The input signal is a sine wave superposition signal of equal amplitude at 100kHz and 400kHz. Since 400kHz is in the stopband of the filter, the attenuation is 60dB, the waveform of the 400kHz component can no longer be seen in the simulated output waveform, and only the 100kHz sine wave can be observed.

Change the input signal into a 50kHz to 400kHz, equal-amplitude sine wave superposition signal with an interval of 25kHz, and use Matlab to perform spectrum analysis on the input and output signals, and the results are shown in Figure 6. It can be seen that in the passband (100-200kHz), the signal has almost no attenuation, but for the 50kHz and 250kHz in the transition zone, the calculated attenuation is about -3dB, and for the stopband (greater than 300kHz), the signal is very weak.

In the same way, the passbands are respectively 0-5kHz (input 1kHz, 2kHz...10kHz equal-amplitude superimposed sinusoidal signal), 0-50kHz (input 10kHz, 20kHz...100kHz equal-amplitude superposition sinusoidal signal), 0-200kHz (input 50kHz, 100kHz...500kHz equal-amplitude sine superposition signal), 0-1MHz (input 100kHz, 200kHz...2MHz equal-amplitude superposition sine signal), 0-2MHz (input 200kHz, 400kHz...4MHz equal-amplitude superposition sine signal) input and output spectrum The comparison is listed in Figure 7 to Figure 11.

Description of drawings

Fig. 1 is a system structure diagram of a digital filter;

Fig. 2 is a schematic diagram of a CIC filter circuit;

Figure 3 is a 5-stage CIC filter with a decimation factor of 4 and its compensation filter frequency response, where (a) is the frequency response of the CIC filter, and (b) is the frequency response of the compensation filter;

Fig. 4 is a structural diagram of a linear phase FIR filter;

Figure 5 is the simulation result when the decimation factor is 4 and the passband is 100-200kHz;

Fig. 6 is the frequency spectrum and output spectrum of filter input sinusoidal superposition signal, wherein (a) is the frequency spectrum of input sinusoidal superposition signal, (b) is the output spectrum of filter;

Fig. 7 is 0-5kHz filter input and output frequency response, wherein (a) is input spectrum, (b) is output spectrum;

Fig. 8 is 0-50kHz filter input and output frequency response, wherein (a) is input spectrum, (b) is output spectrum;

Fig. 9 is 0-200kHz filter input and output frequency response, wherein (a) is input spectrum, (b) is output spectrum;

Fig. 10 is 0-1MHz filter input and output frequency response, wherein (a) is input spectrum, (b) is output spectrum;

Figure 11 is the input and output frequency response of the 0-2MHz filter, where (a) is the input spectrum and (b) is the output spectrum.

Detailed ways

The technical scheme of the utility model will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

The core modules of the digital filter with adjustable bandwidth and center frequency of the utility model are a CIC filter and an FIR filter. Before the data is input to the FIR filter, it needs to pass through the CIC filter bank to reduce the sampling rate of the input signal, and pass through the compensation filter and the gain correction module to ensure the flatness in the passband and the matching of the input and output bit width. The data processed by the FIR filter is output through the conversion module. The bandwidth channel configuration module reads the CIC filter bank in EEPROM (Electrically Erasable Programmable Read-Only Memory) by receiving the band selection information in SPI (Serial Peripheral Interface, Serial Peripheral Interface) The decimation factor and the FIR filter coefficient are used to complete the adjustment of the CIC filter bank and the FIR filter. The clock frequency division module generates the clock required by each module. The specific structure of a digital filter with adjustable bandwidth and center frequency of the utility model is shown in Fig. 1 . The digital filter includes a clock frequency division module, a bandwidth channel configuration module, a CIC filter bank and an FIR filter.

The input end of the CIC filter bank and the output end of the FIR filter are respectively connected with an unsigned number conversion module; the CIC filter bank is composed of several groups of CIC filters and the same number of compensation filters and gain correction Composed of modules, the CIC filter bank is used to reduce the sampling rate of the input signal, and through the compensation filter and the gain correction module, the passband of the CIC filter bank is flat while realizing the matching of the input and output bit widths, and then The data of processing or is input into the FIR filter; the FIR filter realizes the adjustable center frequency point of the bandwidth after the received data operation processing, and outputs through the conversion module with or without symbols; the bandwidth channel configuration module and The CIC filter bank is connected with the FIR filter, and the bandwidth channel configuration module is also connected with SPI and EEPROM; the bandwidth channel configuration module reads the extraction of the CIC filter bank in the EEPROM by receiving the band selection information in the SPI Factor and the coefficient of FIR filter, finish the adjustment to described CIC filter bank and described FIR filter; Described clock frequency division module is connected with described CIC filter bank and FIR filter; Described clock frequency division module Generate the clocks required by the bandwidth channel configuration module, CIC filter, compensation filter, gain correction module and FIR filter.

The implementation method of the digital filter with adjustable bandwidth and center frequency in the utility model includes the following contents:

1. Since the bandwidth of the effective signal in the band communication system is often much lower than the sampling rate of the input signal, if the input signal is filtered at the original sampling rate, the order of the FIR filter will be very high and the number of multipliers will be large, which is difficult to realize , therefore, the digital filtering system needs to reduce the sampling rate of the input signal at the input end.

The operation of downsampling rate is done by CIC filter. The principle of the CIC filter is shown in Figure 2, where D is the decimation factor and M is the delay factor (usually 1 or 2). The CIC filter bank is composed of several groups of CIC filters, corresponding compensation filters and gain correction modules. Each group of CIC filters implements decimation of the input signal at different ratios to reduce the sampling rate of the input signal.

The main design parameters of the CIC filter are the decimation factor D and the number of series N. In the design, the delay factor M is designed to be 1. The design of the decimation factor and the number of series is mainly determined by the sideband suppression ratio. The higher the sideband suppression ratio, the better the anti-aliasing The better the stacking characteristics. The concept of bandwidth scaling factor b is introduced, and its calculation method is shown in formula (1):

$\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula (1), B is the signal bandwidth, D is the decimation factor of the CIC filter, and fs is the original sampling rate of the input signal. For CIC filters, the smaller the bandwidth scale factor, the higher the order, the higher the sideband suppression ratio, and the better the anti-aliasing effect, but the smaller the bandwidth scale factor, the higher the order of the FIR filter, and the multiplier As the number increases, it is more difficult to realize. Generally, the bandwidth scaling factor is greater than 1/100. The wireless broadband radio frequency chip requires that the sideband (stop band) attenuation of the filter is greater than 55dB. For 5KHz, 50KHz, 100KHz, and 200KHz bandwidth, the number of stages N is selected to be 5, the bandwidth scaling factor b is 1/50, and the corresponding extraction factor D is 80, 8, 4, 2, the sideband attenuation is greater than 55dB, and for 1MHz, 2MHz bandwidth, because the ratio of the signal bandwidth to the sampling rate is small, it is not extracted, and the signal is directly transmitted to the subsequent FIR filter , and meet the system design requirements by designing the frequency characteristics of the FIR filter.

Figure 3 is the frequency response of a 5-stage CIC filter with a decimation factor of 4 and a delay factor of 1. Since the passband of the CIC filter is not flat, the attenuation in the passband increases with the increase of the number of stages. Therefore, in order to obtain a good passband flatness when cascading multiple stages, after the CIC filter, compensation filtering is required. The amplifier compensates for its amplitude-frequency characteristics. The operating frequency of the compensation filter is the output frequency of the CIC, which is the frequency after deceleration, and the amplitude-frequency response of the compensation filter is approximately an inverse sinc function.

After the signal passes through the CIC filter and compensation filter, its gain is 60.2dB within the effective 2MHz bandwidth. For the input 12bit signed number, after passing through the decimation filter and compensation filter, the bit width will increase. The final output bit width is given by formula (2):

B _out =B _in +N log ₂ (DM) (2)

After calculation, the output bit width is 22bit. However, the broadband radio frequency chip requires 12 bits for the input and output of the filter, so gain correction is required in the digital filter system to keep the input and output bit width consistent.

2. Gain correction is performed at the output of the CIC filter. Since the gain of the FIR filter in the passband is 1, it will not increase the bit width, so the bit width increase of the digital filter is all brought by the CIC filter. Performing gain correction after the CIC filter can not only realize the matching of the input and output bit width, but also reduce the bit width of the subsequent FIR filter to reduce its area and power consumption, which is beneficial to the implementation of VLSI.

The expression of the gain G is G=(DM) ^N . If the product of DM in this formula is in the form of a power exponent of 2, that is, G=(DM) ^N =2 ^KN (KN is a power exponent), then directly cut off the low KN bits of the output data and retain the same bit width as the input The high part of the . If the product of IM is not in the form of a power of 2, it needs to be multiplied by the coefficient in the output part The gain calibration is completed. At this point, change the gain expression to the following form:

$\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; DM</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}^{\mathrm{<span\; class="notranslate">\; N</span>}}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; DM</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In formula (3), Y is the largest power of 2 smaller than DM, where the gain correction of the product of Y ^N can be directly completed by truncation (right shift), and the other part of the product then by multiplying by its reciprocal To achieve gain correction, this design method can reduce the bit width of the multiplier, thereby reducing the circuit area.

3. Input the output data of the CIC filter bank to the FIR filter to realize narrowband bandpass filtering:

Let h[n] represent the impulse response of the filter, 0≤n≤N-1, x[n] is the input sequence, y[n] is the output sequence, N is the number of stages of the filter, then N-stage FIR filtering The input and output relationship of the device is:

$\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

The FIR filter can be directly realized according to formula (4), that is, the FIR filter is completed with registers, adders and N multipliers. Usually, in design and application, the FIR filter is directly implemented according to formula (4), and the impulse response h[n] of the FIR filter has even symmetric characteristics, and its center of symmetry is the impulse corresponding to N/2 point The excitation response is h(N/2), where N is the number of stages of the FIR filter. This kind of filter with symmetrical impulse response is a linear phase filter, and its structure is shown in Figure 4. The linear phase filter only needs N/2 multipliers, which greatly reduces the number of circuit units and has a small area, which is suitable for VLSI implementation.

For a bandpass filter with a bandwidth of 100kHz, the chip requires the passband ripple to be less than 0.05dB, the stopband attenuation to be greater than 55dB, and the transition bandwidth to be less than 120kHz. For 100kHz bandwidth, the CIC filter decimation factor is 4, and the sampling rate after frequency reduction is 5MHz. According to these design requirements, use the FDA Tool box and use the equiripple method, the order is 160, and the center frequency is 150kHz. Use the same design method for all band-pass filters to obtain the coefficients of the filter and quantize it to a 16-bit signed number. Due to the use of linear phase filters, 80 coefficients are required, and all filter coefficients are stored in EEPROM. When the bandwidth channel configuration module receives the configuration information, it reads the 80 filter coefficients corresponding to this channel information in the EEPROM, and configures For the coefficient register in the FIR filter, the coefficient is multiplied by the input of the symmetrical addition after shifting, and finally the multiplication result is accumulated, and the result is output to complete the linear phase filtering operation.

4. Since other parts of the wireless broadband RF chip deal with unsigned numbers, and the filter deals with signed numbers, a signed and unsigned number conversion module is required at the input and output ends of the filter. For 12bit unsigned numbers, the quantization range is 0~4095, while for 12bit signed numbers, the quantization range is -2048~+2047. The unsigned numbers and signed numbers correspond to one by one, 0 corresponds to -2048, and 4095 corresponds to + 2047, in binary, 0000_0000_0000 corresponds to 1000_0000_0000, and 1111_1111_1111 corresponds to 0111_1111_1111.

5. The bandwidth channel configuration module reads the 8-bit band selection information given by the SPI interface and reads the corresponding CIC extraction factor from the EEPROM to select a corresponding group of filters in the CIC filter and turn off other filter groups. Then read the coefficients of the FIR filter in the EEPROM and assign them to the coefficient registers of the FIR filter.

Sixth, the clock frequency division module provides the input synchronous sampling clock and the frequency division clock after sampling. The fastest clock in this digital filter system is the input synchronous sampling clock, 20MHz. In addition, a frequency-divided clock after downsampling is also required. The extraction factors of this system design are 80, 8, 4, 2, correspondingly need 80 frequency division, 8 frequency division, 4 frequency division, 2 frequency division clocks, namely 250kHz, 2.5MHz, 5MHz and 10MHz four clocks, these clocks All are obtained by frequency division of the 20MHz main clock in the frequency division module.

Best practice:

Figure 1 is a digital filter system structure with adjustable bandwidth and center frequency. Carry out simulation through modelsim and VCS to verify whether the circuit structure of the digital filter meets the requirements of the design index, and optimize the parameters of the circuit design according to the simulation results and the relevant calculation formulas of the digital filter, and finally determine the 5-stage CIC filter with a delay factor of 1 For 5KHz, 50KHz, 100KHz, 200KHz bandwidth, the corresponding extraction factors D are 80, 8, 4, 2, and for 1MHz, 2MHz bandwidth, because the ratio of the signal bandwidth to the sampling rate is small, it is not extracted; The FIR adopts the equi-ripple method, the order is 160, and the coefficients are 80.

The design of this system adopts the Global Foundry 0.18μm process library for Design Compiler logic synthesis, and Encounter for digital back-end layout and wiring. The simulation verification structure is shown in Figure 5 to Figure 11. The results are good and meet the requirements of the design indicators. Among them, Fig. 5 is the simulation result when the decimation factor is 4 and the passband is 100-200kHz; Fig. 6 is the spectrum and output spectrum of the filter input sinusoidal superposition signal; Fig. 7 is the input and output frequency response of the 0-5kHz filter; Fig. 8 is the input and output frequency response of the 0-50kHz filter; Figure 9 is the input and output frequency response of the 0-200kHz filter; Figure 10 is the input and output frequency response of the 0-1MHz filter; Figure 11 is the input and output frequency response of the 0-2MHz filter .

Although the utility model has been described above in conjunction with the accompanying drawings, the utility model is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the enlightenment of the utility model, many deformations can be made without departing from the purpose of the utility model, and these all belong to the protection of the utility model.

Claims (1)

1. bandwidth, a digital filter that center frequency point is adjustable, comprise clock frequency division module, it is characterized in that, also comprise bandwidth channel configuration module, cic filter group and FIR filter;

The input of described cic filter group and the output of described FIR filter are connected with unsigned number conversion module respectively;

Described cic filter group is made up of the compensating filter of several groups of cic filters and equal number and gain calibration module, described cic filter is for reducing the sample rate of input signal, and by described compensating filter and gain calibration module make smooth in cic filter group passband while realize the coupling of input and output bit wide, then by process or data input described FIR filter;

Described FIR filter is adjustable by realizing bandwidth center frequency after the data operation process received, and by there being unsigned number conversion module to export;

Described bandwidth channel configuration module is connected with described cic filter group and FIR filter, and described bandwidth channel configuration module is also connected with SPI and EEPROM; Described bandwidth channel configuration module selects information by receiving in SPI, reads the extraction factor of cic filter group and the coefficient of FIR filter in EEPROM, completes the adjustment to described cic filter group and described FIR filter;

Described clock frequency division module is connected with FIR filter with described cic filter group; The clock that described clock frequency division module generating strap fat pipe configuration module, cic filter, compensating filter, gain calibration module and FIR filter need.