CN109905095A - The narrowband tunable filter of low-frequency range - Google Patents
The narrowband tunable filter of low-frequency range Download PDFInfo
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Abstract
The present invention is the narrowband tunable filter of low-frequency range, is solved in traditional filter circuit design, it is difficult to the problem of realizing low frequency signal filtering frequency range adjustment.The present invention is by using voltage controlled capacitor chip, and the method for substituting traditional capister, solving the problems, such as that capister control channel is superimposed with signal path leads to wave distortion.LRC filter circuit is improved and combined simultaneously, is solved the problems, such as under traditional RC filter circuit quality factor.The features such as present invention has frequency range narrow, and quality factor are high, and filtered signal deformation is small, while by capacitor Parallel Design, frequency band adjustable extent has further been widened, the noise filtering of low frequency harmony circuit and high precision collecting circuit can be widely used in.
Description
Technical field
The present invention relates to data collecting fields, and in particular to the analog signal filtering system in data acquisition.
Background technique
With the development of electron electric power technology and large-scale integrated technique, information processing system is to data collection system performance
Requirement it is higher and higher.To need system bandwidth as wide as possible on the basis of high-precision, however the main face of conventional filter
The problem of facing is that the signal-to-noise ratio of signal can reduce with the broadening of system bandwidth, and directly widening bandwidth will lead to whole system
Accuracy decline.In fact, precision has been able to meet demand, therefore how to realize under broadband condition under narrowband condition
Filter high precision collecting becomes and improves the problem of system performance must be taken into consideration.
Summary of the invention
The object of the present invention is to provide one kind in low-frequency range maximum band adjustable extent 110KHz, frequency range is narrow, quality because
Number is high, the narrowband tunable filter of the small low-frequency range of filtered signal deformation.
The present invention is implemented as follows:
1, the narrowband tunable filter of low-frequency range, which is characterized in that
(1) original input signal, i.e., the signal that need to be filtered by narrowband tunable filter, by analog circuit interface P2 into
Entering the input terminal that circuit connects low-pass filter, the output end J1 of low-pass filter connects the input terminal of the narrowband LRC tunable filter,
The output J2 for filtering that the narrowband LRC is adjustable connects the reverse phase proportional amplifier negative input of the 3rd operational amplifier OP3 composition, reverse phase
Proportional amplifier output terminates total output terminal P3,
(2) control signal is entered the input terminal of programmable gate array FPGA, programmable gate by user's input control interface P1
The input terminal of the output termination digital analog converter DAC of array, the output of digital analog converter DAC terminate the narrowband LRC tunable filter,
(3) original input signal enters circuit by the total interface P2 of analog circuit, by the 1st, 2 grade of RC filter circuit, connects
The positive input for the positive proportional amplifier that 1st operational amplifier OP1 is constituted,
The output of (4) the 1st operational amplifier OP1 connects the 2nd operational amplifier OP2 composition through narrowband tunable filter LRC
Phase inverter negative input,
The reverse phase proportional amplifier negative sense that the output of (5) the 2nd operational amplifier OP2 connects the 3rd operational amplifier OP3 composition is defeated
Enter end,
Total output end of the output of (6) the 3rd operational amplifier OP3 as circuit, meets output terminal P3,
(7) narrowband LRC tunable resonator is by the 5th, 6 resistance R5, R6, the 1st, 2 inductance L1, L2, the 1st, 2 tunable capacitors
CC1, CC2 composition, wherein the practical capacitance of CC1, CC2 is controlled by the output of digital analog converter DAC, and the 5th, 6 resistance R5, R6 are resonance
Resistance, the 1st, 2 inductance L1, L2 are resonant inductance, and R5, L1, CC1 are composed in series series resonant circuit, and R6, L2, CC2 are composed in parallel
Antiresonant circuit, resonance circuit need to guarantee that parameter matches, i.e. R5=R6, L1=L2, CC1=CC2, while use phase as far as possible
With the device of model,
(8) control access is made of programmable gate array FPGA, digital analog converter DAC, the output end of digital analog converter DAC
The control terminal of the 1st, 2 voltage controlled capacitor CC1, CC2 of the narrowband LRC tunable filter is connect, above-mentioned two resonance circuit needs having the same
Circuit parameter,
(9) program of programmable gate array FPGA is as follows: determining the bound of the narrowband LRC tunable filter centre frequency f
Parameter, upper limit fmax, lower limit fmin,
(10) control of the position m the signal Con1, m for defining control interface P1 are the bit wide of P1 control interface, correspond to 0~2m- 1 it
Between 2mA m bit coding, the coding can only use part, remainder reserved, adjust according to actual needs, control
The narrowband LRC tunable filter centre frequency f processed is from fminTo fmaxVariation, it is (f that single step, which adjusts stepping,max-fmin)/(2m- 1), then
The corresponding relationship of the narrowband LRC tunable filter centre frequency f and control signal Con1 are as follows: f=fmax-Con1×(fmax-fmin)/
(2m- 1),
(11) according to the corresponding relationship of control signal Con1 and filter centre frequency f, the number of definition is 0~2m- 1
2mGroup control signal Con1, for transmitting the narrowband LRC tunable filter center frequency information, i.e. Con1 encodes corresponding one group of LRC
The centre frequency f of narrowband tunable filter, from maximum frequency fmaxTo minimum frequency fminVariable quantity, single step step-length is
(fmax-fmin)/(2m- 1), i.e., Con1 is numerically represented sequentially as fmax, fmax-(fmax-fmin)/(2m- 1), fmax-2×(fmax-
fmin)/(2m- 1) ..., fmin,
(12) the 1st, the capacitance C of 2 voltage controlled capacitor CC1, CC2 is equal, and the calculation formula of real-time capacitance C isL is the 1st inductance L1 numerical value of the narrowband LRC tunable filter circuit in formula,
(13) the control voltage of the 1st, 2 voltage controlled capacitor CC1, CC2 is set as Vcon, capacitor's capacity C, according to CC1's or CC2
Voltage and capacitance relational graph are controlled, determines the two linear fit relationship Vcon=kC+b, k, b are that voltage controlled capacitor controls voltage in formula
With the slope and displacement constant of practical capacitance linear relationship expression formula, VconIt is DAC output voltage,
(14) Con2 is set as the control code of DAC, is expressed as sixteen bit, signed binary coded voltage can be by Con1
It is determined by following formula:
L is the 1st inductance L1 numerical value in formula, and k, b are respectively matched curve VconThe slope and displacement constant of=kC+b, formula
The middle expression of subscript 2 needs to be converted to binary system,
(15) after completing the self-test of device and the initialization of digital analog converter DAC after the power-up, the narrowband LRC tunable filter
Centre frequency is placed on fmaxAfter place, FPGA scans user's input control interface P1 with 100Hz frequency cycle, detects whether
There is control signal incoming,
(16) FPGA scan round user input control interface P1 judges whether there is signal input, if without input,
The filter circuit of the narrowband LRC tunable filter remains unchanged, and continues to scan on user input control interface P1,
(17) it detects control signal, the corresponding DAC control of control signal Con1 has been prestored with array form inside FPGA
The corresponding informance of code Con2 processed, Con1 is as subscript in array, and corresponding Con2 control code is as the corresponding target element down of array A, A
[Con1]=Con2 then can quickly be found FPGA according to control signal Con1 by subscript and need to export to the control of DAC
Code Con2,
(18) control code Con2 is sent to DAC by FPGA, i.e., changeable DAC output voltage, to change the 1st, 2 voltage-controlled electricity
Hold the practical capacitance of CC1, CC2, the centre frequency of the mobile narrowband LRC tunable filter, filtering is completed.
The narrowband tunable filter of low-frequency range, which is characterized in that
(1) according to the channel gain system of the amplitude confirmation RC low-pass filter by input end of analog signal mouth P2 input signal
Number K1,
(2) according to the frequency range by input end of analog signal mouth P2 input signal, confirm the adjustable filtering in the narrowband LRC
Device centre frequency f adjusts lower limit fmin,
(3) according to the frequency range by input end of analog signal mouth P2 input signal, confirm the adjustable filtering in the narrowband LRC
Device centre frequency f adjusts upper limit fmax,
(4) the 3rd resistance R3 of RC low-pass filter, the i.e. resistance value of proportion resistor are determined according to user's impedance requirements,
(5) according to channel gain COEFFICIENT K 1 and the 3rd resistance R3 resistance value, it may be determined that the 4th resistance R4 of RC low-pass filter compares
The resistance value of example resistance, the resistance value ratio of the 3rd, 4 resistance R3, R4 determine the channel gain of RC low-pass filter, by this way
RC low-pass filter channel gain can be set as K1,
R4=K1R3
(6) according to centre frequency upper limit fmax, low-pass filter resistance R, capacitor C parameter are determined, according to user's impedance requirements
Determine RC low-pass filter the 1st, 2 resistance R1, R2, i.e., the 1st, the resistance value R of 2 filter resistances,
(7) RC low-pass filter the 1st, 2 capacitor C1, C2, i.e., the 1st, the capacitance C of 2 filter capacitors can be acquired by following formula,
In formula R be RC low-pass filter the 1st, 2 resistance R1, R2 resistance values,
(8) the 1st, 2 voltage controlled capacitor CC1, CC2 capacitances are set as Cc, capacitance is adjustable, and lower limit is Cmin, as CC1, CC2 is adjustable
The minimum value of capacitor,
(9) the adjustable maximum capacitor value of CC1, CC2, by CminIt is determined by following formula
Wherein fminAnd fmaxThe respectively bound of the narrowband LRC tunable filter centre frequency,
(10) according to the adjusting lower limit C of selected voltage controlled capacitormin, can be found out by following formula the narrowband LRC tunable filter the 1st,
Resonant inductance value L needed for 2 resonant inductance L1, L2:
Wherein fmaxFor the upper limit of the narrowband LRC tunable filter centre frequency,
(11) selecting frequency characteristic of the narrowband LRC tunable filter is reflected by its quality factor q, determines product according to user demand
Prime factor Q, resonant inductance value L and C needed for the narrowband LRC tunable filter has been determined in above-mentioned stepsmaxAfterwards, it can find out pair
Resonant resistance R5, R6 resistance Rr needed for the narrowband the LRC tunable filter answered.
(12) 8-10 resistance R8-10 and the 3rd operational amplifier OP3 constitute reverse phase proportional amplifier, guarantee the 8th resistance R8
=the 9 the 8th resistance R8/2 of resistance R9, the 10th resistance R10=.
It realizes that narrowband-band logical is adjustable, inputs according to user under broadband condition of the present invention in low-frequency range, changes band logical filter
The centre frequency of wave device realizes frequency tracking in low-frequency range, to realize narrow-band filtering on broadband.Filter energy of the invention
Enough in fmax-fminUnder broadband condition in (maximum span 110KHz), parameter is inputted according to user, is changed in bandpass filter
Frequency of heart, while guaranteeing centre frequency in the moving process of entire frequency band ,-three dB bandwidth is basically unchanged.Any frequency in bandwidth
Under rate, real-time bandwidth is lower than 1KHz, can be realized 99% noise filtering, signal-to-noise ratio is substantially improved.Meanwhile the design have compared with
High flexibility, respective devices selection is not unique, can be adjusted flexibly according to user demand, need to only guarantee basic ratio
The convenience of relationship and acquisition, R3 and R4 as described in claim 1, CminWith CmaxDeng.Low-frequency range of the invention it is narrow
Band tunable filter according to the real-time frequency of input signal, can adjust bandpass filtering in low-frequency range (in 110KHz frequency band)
Device centre frequency reaches the filter effect of narrow band filter in broad frequency band (narrow band filter three dB bandwidth is lower than 1KHz).It is low
Frequency range frequency band adjustable narrow-band-bandpass filter is made of RC low-pass filter, the narrowband LRC tunable filter and control module: low
Bandpass filter is completed to filter the primary of input signal, and the signal other than 110KHz is decayed, signal noise is reduced；The narrowband LRC
The centre frequency of bandpass filter is adjusted to signal frequency then according to signal frequency by tunable filter, realizes real-time narrowband filter
Wave；Control module is then made of FPGA and DA, and corresponding filter parameter is determined according to the input parameter of the offer of control terminal,
Change D/A output voltage to change filter centre frequency, realizes that frequency band is adjustable.Amplitude-frequency with centre frequency in 100KHz is special
For linearity curve emulation (Fig. 9).99.42% noise can be filtered out under this condition.Figure 10, Figure 12 then show 30KHz,
Simulation waveform under 50KHz centre frequency.The superior function of the design narrow band filter, narrow band bandwidth remain at 635Hz
Left and right, very bandwidth is narrow, can effectively filter out 99% input noise, and signal-to-noise ratio promotes significant effect.The present invention uses voltage-controlled electricity
Hold chip and replace traditional varactor, solves the problems, such as varactor control voltage and signal superposition, and use can
Capacitor gating-parallel technology is adjusted, the adjustable range of equivalent capacity is improved, device is reduced and obtains difficulty.Simultaneously using humorous
Vibration technology completes tunable filter design, overcomes the low problem of RC filter circuit quality factor.
Detailed description of the invention
Fig. 1 is circuit block diagram of the invention.
Fig. 2 is principle of lowpass filter figure (J1 only indication circuit tie point, no practical devices in figure).
Fig. 3 be built using resonance circuit the narrowband LRC tunable filter schematic diagram (in figure J1, J2 only indication circuit connect
Contact, no practical devices).
Fig. 4 is voltage controlled capacitor device voltage-capacitance curve selected by the present invention.
Fig. 5 is the narrowband LRC tunable filter control code-centre frequency-capacitance-voltage relation table
Fig. 6 is the program flow diagram of programmable gate array FPGA.
Circuit diagram Fig. 7 of the invention.
Fig. 8 is spectral characteristic analogous diagram.
Frequency domain characteristic enlarged drawing when Fig. 9 is 100KHz.
Frequency domain characteristic enlarged drawing when Figure 10 is 30KHz.
Frequency domain characteristic enlarged drawing when Figure 11 is 50KHz.
Figure 12 is operation logic figure of the invention.
Specific embodiment:
Embodiment 1
In this example, the frequency of the narrowband LRC tunable filter adjusts upper limit fmaxIt is defined as 100KHz, frequency adjusts lower limit
fminIt is defined as 36.25KHz, the rate of FPGA scanning user's control port P1 is arranged to 100Hz, filter inductance L1, L2 number
Value is L=25mH, and it is 100pF~771pF that voltage controlled capacitor CC1, CC2, which correspond to adjustable range,
The program of programmable gate array FPGA is as follows: after the power-up complete device self-test and digital analog converter DAC just
Beginningization, the center the narrowband LRC tunable filter (including amplifier OP2, inductance L1, L2, voltage controlled capacitor CC1, CC2, resistance R5-R7) frequency
Rate is placed on fmaxAt=100KHz, later, FPGA scans user's control port P1 with the frequency cycle of 100Hz, has detected whether
It is incoming to control signal, control signal is defined by filter designer, as used in the design 8 bit length control codes (can indicate 0~
255 totally 256 kinds of situations), 256 groups of control signals that number is 0~255 are defined, corresponding from 100KHz to 36.25KHz, stepping
Length is linear corresponding relation f=100-Con1 × 0.25 of 0.25KHz, determines 256 narrowbands LRC tunable filter center frequency
Rate records point, for transmitting the narrowband LRC tunable filter center frequency information, since the two is set to linear correlation,
Storage of array user's control code Con1 and filter centre frequency f corresponding relationship need not be additionally used,
FPGA scan round control signal input mouth P1, judges whether there is input, if the narrowband LRC can without input
The filter circuit of tunable filter remains unchanged, and continues to scan on the port P1, if control input is received, with array shape inside FPGA
Formula has prestored DAC control routine corresponding with control signal, and array index is consistent with control routine numerical value, then is believed according to control
FPGA number can be quickly found by subscript to need to export to the control routine of DAC, control routine is sent to DAC by FPGA,
I.e. changeable DAC output voltage, to change the practical capacitance of voltage controlled capacitor CC1, CC2, thus the mobile narrowband LRC tunable filter
Centre frequency, filtering complete.
Prestore the determination method of array:
Before definition prestores array, user should determine the narrowband LRC tunable filter according to signal input range first
Frequency adjusts upper limit fmax, frequency adjust lower limit fminAnd FPGA is to the sweep speed of control signal mouth P1,
In this example, 256 groups of control signals that number is 0~255 are defined, corresponding from 100KHz to 36.25KHz, stepping
Length is the linear corresponding relation of 0.25KHz:
F=fmax-Con1×0.25
256 narrowband LRC tunable filter centre frequency record points are determined, for transmitting the narrowband LRC tunable filter
Center frequency information, then according to this linear corresponding relation, without using in additional storage of array control signal Con1 and filter
The one-to-one relationship of frequency of heart f corresponds to the narrowband LRC tunable filter centre frequency f, voltage controlled capacitor according to control signal Con1
CC1=CC2, capacitance C is by formula:
Determine voltage controlled capacitor capacitance C required for the corresponding narrowband LRC tunable filter centre frequency f, in formula, L is filtering
Inductance L1 numerical value, L=25mH in this example will control signal Con1 and the centre frequency f corresponding relationship generation of f=100-Con1 × 0.25
Entering above formula can obtain:
According to selected voltage controlled capacitor device characteristic (control voltage VconCapacitance C relational graph (Fig. 4)), pass through interpolation, minimum
The methods of square law obtains linear fit expression formula Vcon=kC+b, linear fitting expression in this example are as follows:
Vcon=-0.05C+10
In formula, C is voltage controlled capacitor CC1, CC2 capacitance, VconFor voltage value needed for voltage controlled capacitor is adjusted to capacitance C, according to
The formula determines the voltage value V exported needed for DACcon,
DAC control code Con2 is the sixteen bit signed binary coding of required output voltage values, need to only carry out numerical value
System conversion can obtain DAC control code, will control signal and DAC control code one-to-one correspondence establish array, can be completed pre-
Deposit the foundation of array, in this example, the final relationship of control signal Con1 and DAC control code Con2 is that (subscript 2 indicates to need to convert
For binary system):
L is the 1st inductance L1 numerical value in formula,
In this example, built by the array that prestores that user's input control signal Con1 to DAC control code Con2 can be completed in the formula
It is vertical, according to the array, the control signal Con1 that FPGA can be inputted according to user, control code needed for determining DAC, corresponding pin
The control code is exported, changes DAC output voltage, and then change the practical capacitance of voltage controlled capacitor, realizes in the narrowband LRC tunable filter
The movement of frequency of heart, filtering are completed.
Claims (2)
1. the narrowband tunable filter of low-frequency range, which is characterized in that
(1) original input signal, i.e., the signal that need to be filtered by narrowband tunable filter enter electricity by analog circuit interface P2
Road connects the input terminal of low-pass filter, and the output end J1 of low-pass filter connects the input terminal of the narrowband LRC tunable filter, and LRC is narrow
Output J2 with adjustable filtering connects the reverse phase proportional amplifier negative input of the 3rd operational amplifier OP3 composition, and reverse phase ratio is put
Big device output terminates total output terminal P3,
(2) control signal is entered the input terminal of programmable gate array FPGA, programmable gate array by user's input control interface P1
Output termination digital analog converter DAC input terminal, the output of digital analog converter DAC terminates the narrowband LRC tunable filter,
(3) original input signal enters circuit by the total interface P2 of analog circuit, by the 1st, 2 grade of RC filter circuit, connects the 1st fortune
The positive input for the positive proportional amplifier that amplifier OP1 is constituted is calculated,
The output of (4) the 1st operational amplifier OP1 connects the reverse phase of the 2nd operational amplifier OP2 composition through narrowband tunable filter LRC
Device negative input,
The output of (5) the 2nd operational amplifier OP2 connects the reverse phase proportional amplifier negative sense input of the 3rd operational amplifier OP3 composition
End,
Total output end of the output of (6) the 3rd operational amplifier OP3 as circuit, meets output terminal P3,
(7) narrowband LRC tunable resonator is by the 5th, 6 resistance R5, R6, the 1st, 2 inductance L1, L2, the 1st, 2 tunable capacitor CC1,
CC2 composition, wherein the practical capacitance of CC1, CC2 is controlled by the output of digital analog converter DAC, and the 5th, 6 resistance R5, R6 are resonance electricity
Resistance, the 1st, 2 inductance L1, L2 are resonant inductance, and R5, L1, CC1 are composed in series series resonant circuit, and R6, L2, CC2 are composed in parallel simultaneously
Joining resonance circuit, resonance circuit need to guarantee that parameter matches, i.e. R5=R6, L1=L2, CC1=CC2,
(8) control access is made of programmable gate array FPGA, digital analog converter DAC, the output termination of digital analog converter DAC
The control terminal of the 1st, 2 voltage controlled capacitor CC1, CC2 of the narrowband LRC tunable filter, above-mentioned two resonance circuit need electricity having the same
Road parameter,
(9) program of programmable gate array FPGA is as follows: determine the bound parameter of the narrowband LRC tunable filter centre frequency f,
The upper limit is fmax, lower limit fmin,
(10) control of the position m the signal Con1, m for defining control interface P1 are the bit wide of P1 control interface, correspond to 0~2mBetween -1
2mA m bit coding, the coding can only use part, remainder reserved, adjust according to actual needs, control
The narrowband LRC tunable filter centre frequency f is from fminTo fmaxVariation, it is (f that single step, which adjusts stepping,max-fmin)/(2m- 1), then LRC
The corresponding relationship of narrowband tunable filter centre frequency f and control signal Con1 are as follows: f=fmax-Con1×(fmax-fmin)/(2m-
1),
(11) according to the corresponding relationship of control signal Con1 and filter centre frequency f, the number of definition is 0~2mThe 2 of -1mGroup
Signal Con1 is controlled, for transmitting the narrowband LRC tunable filter center frequency information, i.e. Con1 encodes corresponding one group of narrowband LRC
The centre frequency f of tunable filter, from maximum frequency fmaxTo minimum frequency fminVariable quantity, single step step-length be (fmax-
fmin)/(2m- 1), i.e., Con1 is numerically represented sequentially as fmax, fmax-(fmax-fmin)/(2m- 1), fmax-2×(fmax-fmin)/
(2m- 1) ..., fmin,
(12) the 1st, the capacitance C of 2 voltage controlled capacitor CC1, CC2 is equal, and the calculation formula of real-time capacitance C isL is the 1st inductance L1 numerical value of the narrowband LRC tunable filter circuit in formula,
(13) the control voltage of the 1st, 2 voltage controlled capacitor CC1, CC2 is set as Vcon, capacitor's capacity C, according to the control of CC1 or CC2
Voltage and capacitance relational graph determine the two linear fit relationship Vcon=kC+b, k, b are that voltage controlled capacitor controls voltage and reality in formula
The slope and displacement constant of border capacitance linear relationship expression formula, VconIt is DAC output voltage,
(14) Con2 is set as the control code of DAC, is expressed as sixteen bit, and signed binary coded voltage can be passed through by Con1
Following formula determines:
L is the 1st inductance L1 numerical value in formula, and k, b are respectively matched curve VconThe slope and displacement constant of=kC+b, in formula under
Mark 2 indicates to need to be converted to binary system,
(15) after the power-up complete device self-test and digital analog converter DAC initialization after, the narrowband LRC tunable filter will in
Frequency of heart is placed on fmaxAfter place, FPGA scans user's input control interface P1 with 100Hz frequency cycle, has detected whether control
Signal processed is incoming,
(16) FPGA scan round user input control interface P1 judges whether there is signal input, if LRC is narrow without input
Filter circuit with tunable filter remains unchanged, and continues to scan on user input control interface P1,
(17) it detects control signal, the corresponding DAC control code of control signal Con1 has been prestored with array form inside FPGA
The corresponding informance of Con2, Con1 is as subscript in array, and corresponding Con2 control code is as the corresponding target element down of array A, A
[Con1]=Con2 then can quickly be found FPGA according to control signal Con1 by subscript and need to export to the control of DAC
Code Con2,
(18) control code Con2 is sent to DAC by FPGA, i.e., changeable DAC output voltage, to change the 1st, 2 voltage controlled capacitors
The practical capacitance of CC1, CC2, the centre frequency of the mobile narrowband LRC tunable filter, filtering are completed.
2. the narrowband tunable filter of low-frequency range according to claim 1, which is characterized in that
(1) according to the channel gain coefficient of the amplitude confirmation RC low-pass filter by input end of analog signal mouth P2 input signal
K1,
(2) according to the frequency range by input end of analog signal mouth P2 input signal, confirm in the narrowband LRC tunable filter
Frequency of heart f adjusts lower limit fmin,
(3) according to the frequency range by input end of analog signal mouth P2 input signal, confirm in the narrowband LRC tunable filter
Frequency of heart f adjusts upper limit fmax,
(4) the 3rd resistance R3 of RC low-pass filter, the i.e. resistance value of proportion resistor are determined according to user's impedance requirements,
(5) according to channel gain COEFFICIENT K 1 and the 3rd resistance R3 resistance value, it may be determined that the 4th resistance R4 of RC low-pass filter, i.e. ratio electricity
The resistance value ratio of the resistance value of resistance, the 3rd, 4 resistance R3, R4 determines the channel gain of RC low-pass filter, by this way
RC low-pass filter channel gain is set as K1,
R4=K1R3
(6) according to centre frequency upper limit fmax, determine low-pass filter resistance R, capacitor C parameter, determined according to user's impedance requirements
RC low-pass filter the 1st, 2 resistance R1, R2, i.e., the 1st, the resistance value R of 2 filter resistances,
(7) RC low-pass filter the 1st, 2 capacitor C1, C2, i.e., the 1st, the capacitance C of 2 filter capacitors can be acquired by following formula,
In formula R be RC low-pass filter the 1st, 2 resistance R1, R2 resistance values,
(8) the 1st, 2 voltage controlled capacitor CC1, CC2 capacitances are set as Cc, capacitance is adjustable, and lower limit is Cmin, as CC1, CC2 tunable capacitor
Minimum value,
(9) the adjustable maximum capacitor value of CC1, CC2, by CminIt is determined by following formula,
Wherein fminAnd fmaxThe respectively bound of the narrowband LRC tunable filter centre frequency,
(10) according to the adjusting lower limit C of selected voltage controlled capacitormin, it is humorous the narrowband LRC tunable filter the 1st, 2 can be found out by following formula
Shake resonant inductance value L needed for inductance L1, L2:
Wherein fmaxFor the upper limit of the narrowband LRC tunable filter centre frequency,
(11) selecting frequency characteristic of the narrowband LRC tunable filter is reflected by its quality factor q, according to user demand determine quality because
Number Q, resonant inductance value L and C needed for the narrowband LRC tunable filter has been determined in above-mentioned stepsmaxAfterwards, it can find out corresponding
Resonant resistance R5, R6 resistance Rr needed for the narrowband LRC tunable filter,
(12) 8-10 resistance R8-10 and the 3rd operational amplifier OP3 constitute reverse phase proportional amplifier, guarantee the 8th resistance R8=the
9 the 8th resistance R8/2 of resistance R9, the 10th resistance R10=.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111077815A (en) * | 2019-11-27 | 2020-04-28 | 成都芯通软件有限公司 | Compensation system and method for multi-band HFC (hybrid fiber coaxial) equipment with automatically tunable output level |
| CN111669148A (en) * | 2020-06-19 | 2020-09-15 | 中国电子科技集团公司第二十六研究所 | Tunable bandpass filter, apparatus and method |
| CN114167491A (en) * | 2021-12-07 | 2022-03-11 | 威海双丰物探设备股份有限公司 | Detector with source compensation circuit |
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| CN111077815A (en) * | 2019-11-27 | 2020-04-28 | 成都芯通软件有限公司 | Compensation system and method for multi-band HFC (hybrid fiber coaxial) equipment with automatically tunable output level |
| CN111669148A (en) * | 2020-06-19 | 2020-09-15 | 中国电子科技集团公司第二十六研究所 | Tunable bandpass filter, apparatus and method |
| CN114167491A (en) * | 2021-12-07 | 2022-03-11 | 威海双丰物探设备股份有限公司 | Detector with source compensation circuit |
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