CN115913171A - Low-frequency-domain active band-pass filter and test system thereof - Google Patents
Low-frequency-domain active band-pass filter and test system thereof Download PDFInfo
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- CN115913171A CN115913171A CN202211493264.6A CN202211493264A CN115913171A CN 115913171 A CN115913171 A CN 115913171A CN 202211493264 A CN202211493264 A CN 202211493264A CN 115913171 A CN115913171 A CN 115913171A
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Abstract
The utility model provides a low frequency domain active band-pass filter and test system thereof relates to electronic circuit technical field. The present disclosure provides a low frequency domain active band pass filter, comprising an active high pass filter and an active low pass filter connected in series; the active high-pass filter and the active low-pass filter respectively comprise a first-stage operational amplifier, a second-stage operational amplifier and a third-stage operational amplifier which are connected in series. The low-frequency-domain active band-pass filter can effectively extract a frequency band of 15K-250 KHz in a radar low-frequency signal, removes invalid clutter smaller than 15KHz and larger than 250KHz in the radar low-frequency signal, and meets the requirement of technical performance indexes within a controllable range through testing signal attenuation.
Description
Technical Field
The disclosure relates to the technical field of electronic circuits, in particular to a low-frequency-domain active band-pass filter and a test system thereof.
Background
For the processing of the low-frequency domain signal, a digital signal processing method is usually adopted to extract a useful signal, and for the low-frequency domain signal generated by the self-mixing system, because the signal is weak and the amplitude is small, the low-frequency domain signal cannot be directly processed digitally, the low-frequency domain signal needs to be amplified and filtered first, and a low-frequency domain active band-pass filter with a gain amplification function needs to be designed based on the circuit.
Compared with a passive filter, the active filter has the advantages of high efficiency, strong load carrying capacity, good frequency characteristic, filtering, amplification of a useful signal and the like, and is widely applied. The common active filter consists of an RC and an operational amplifier, the RC is small in size and low in cost, and the size of the active filter can be reduced in an integrated mode due to the fact that an inductor is not used, and the amplification factor of a signal can be adjusted easily. Another advantage of active filtering is that signals above the cut-off frequency can be attenuated more quickly, and the requirements on capacitance and resistance of the filtering characteristics are not high.
Disclosure of Invention
The purpose of the present disclosure is to overcome the disadvantages of the prior art, and to provide a low frequency active band pass filter, which can effectively extract the frequency band of 15K to 250KHz from the radar low frequency signal, so as to extract the effective low frequency signal.
According to a first aspect of embodiments of the present disclosure, there is provided a low frequency domain active band pass filter, the band pass filter comprising an active high pass filter and an active low pass filter connected in series;
the active high-pass filter and the active low-pass filter respectively comprise a first-stage operational amplifier, a second-stage operational amplifier and a third-stage operational amplifier which are connected in series.
In one embodiment, the first stage operational amplifier, the second stage operational amplifier and the third stage operational amplifier are all composed of two negative feedback circuits.
In one embodiment, the active high pass filter is a butterworth high pass filter and the active low pass filter is a butterworth active low pass filter.
In one embodiment, in the active high pass filter,
the passband gain of the first operational amplifier is 4.642 times, the cut-off frequency is 15KHz, the quality factor is 0.52, the circuit topology form is multiple feedback, and the minimum gain bandwidth product is 3.6208MHz;
the passband gain of the second operational amplifier is 4.642 times, the cut-off frequency is 15KHz, the quality factor is 0.71, the circuit topology form is multiple feedback, and the minimum gain-bandwidth product is 4.94378MHz;
the passband gain of the third operational amplifier is 4.642 times, the cutoff frequency is 15KHz, the quality factor is 1.93, the circuit topology form is multiple feedback, and the minimum gain bandwidth product is 13.4386MHz.
In one embodiment, in the active low pass filter,
the passband gain of the first operational amplifier is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 0.52, the circuit topology form is multiple feedback, and the minimum gain bandwidth product is 28.002MHz;
the passband gain of the second operational amplifier is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 0.71, the circuit topology form is multiple feedback, and the minimum gain bandwidth product is 38.2335MHz;
the passband gain of the third operational amplifier is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 1.93, the circuit topology form is multiple feedback, and the minimum gain bandwidth product is 103.9305MHz.
In one embodiment, in the active high pass filter,
the first operational amplifier, the second operational amplifier and the third operational amplifier comprise a first capacitor, a first inductor, a second capacitor, a third capacitor, a second inductor and a first operational amplifier.
In one embodiment, in the active low pass filter,
the first operational amplifier, the second operational amplifier and the third operational amplifier comprise a third inductor, a fourth capacitor, a fifth inductor, a fifth capacitor and a second operational amplifier.
In one embodiment, the model of the first operational amplifier is AD8048AR, the bandwidth is 150MHz, and the slew rate is 1000 mus/V; the model of the second operational amplifier is 0PA621KU, the bandwidth is 500MHz, and the slew rate is 500 mus/V.
According to a second aspect of the embodiments of the present disclosure, a system for testing a low-frequency active band-pass filter is provided, where the system includes a signal source, a first attenuator, a low-frequency active band-pass filter, a second attenuator, a spectrometer, and a power regulator connected to the low-frequency active band-pass filter; wherein the content of the first and second substances,
the input end of the low-frequency-domain active band-pass filter is connected with the output end of the first attenuator, the input end of the first attenuator is connected with the signal source, the output end of the low-frequency-domain active band-pass filter is connected with the input end of the second attenuator, and the output end of the second attenuator is connected with the frequency spectrograph;
the low-frequency-domain active band-pass filter is the low-frequency-domain active band-pass filter.
In one embodiment, the signal source outputs a continuous wave signal with a frequency of 3-650 KHz and a power level of 0-40dBm; the attenuation of the attenuator is 0dB to 40dB, and the attenuation step is 1dB; the lowest frequency of the frequency spectrograph test is 3Hz, and the minimum power of the frequency spectrograph test is-140 dBm.
The active band-pass filter in the low frequency domain in the embodiment of the disclosure comprises an active high-pass filter and an active low-pass filter which are connected in series, wherein a first-stage operational amplifier, a second-stage operational amplifier and a third-stage operational amplifier in the active high-pass filter form a three-stage cascade operational amplifier, and the first-stage operational amplifier, the second-stage operational amplifier and the third-stage operational amplifier in the active low-pass filter also form the three-stage cascade operational amplifier, so that a frequency band of 15K-250 KHz in radar low-frequency signals can be effectively extracted, invalid noise waves smaller than 15KHz and larger than 250KHz are removed from the radar low-frequency signals, and the attenuation of the tested signals is in a controllable range, thereby meeting the requirement of technical performance indexes.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure.
Fig. 1 is a circuit diagram of a low-frequency active band-pass filter according to an embodiment of the present disclosure.
Fig. 2 is a circuit diagram of the active high-pass filter in the present embodiment.
Fig. 3 is a circuit diagram of the active low-pass filter in the present embodiment.
Fig. 4 is a circuit diagram of a first operational amplifier in the active high-pass filter in the present embodiment.
Fig. 5 is a circuit diagram of a second operational amplifier in the active high-pass filter in the present embodiment.
Fig. 6 is a circuit diagram of a third operational amplifier in the active high-pass filter in the present embodiment.
Fig. 7 is a circuit diagram of the first operational amplifier in the active low-pass filter in the present embodiment.
Fig. 8 is a circuit diagram of a second operational amplifier in the active low-pass filter in the present embodiment.
Fig. 9 is a circuit diagram of a third operational amplifier in the active low-pass filter in the present embodiment.
Fig. 10 is a block diagram of a test system of a low-frequency active band-pass filter in this embodiment.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the exemplary embodiments below are not intended to represent all implementations consistent with the present disclosure. Rather, they are merely examples of systems and methods consistent with certain aspects of the present disclosure, as detailed in the appended claims.
Fig. 1 is a circuit diagram of a low-frequency active band-pass filter according to an embodiment of the present disclosure. As shown in fig. 1, the band pass filter includes an active high pass filter and an active low pass filter connected in series;
fig. 2 is a circuit diagram of the active high-pass filter in the present embodiment. As shown in fig. 2, the active high pass filter includes a first stage operational amplifier, a second stage operational amplifier, and a third stage operational amplifier connected in series.
Fig. 3 is a circuit diagram of the active low-pass filter in the present embodiment. As shown in fig. 3, the active low pass filter includes a first stage operational amplifier, a second stage operational amplifier, and a third stage operational amplifier connected in series.
In this embodiment, the active high-pass filter parameters are: the passband frequency is 15KHz (-3 dB), the attenuation at the stopband 3KHz is 80dBc, the in-band ripple is less than 1dB, and the gain is about 40dB; the design parameters of the active low-pass filter are as follows: the passband is 250KHz at-3 dB frequency, the attenuation at 600KHz of the stop band is 45dBc, the in-band ripple is less than 1dB, and the gain is 20dB.
As shown in fig. 1, the terminal of output 1 is connected to the terminal of input 2 in this embodiment, and each stage + VCC and-VDD is added with a capacitive filter.
The active band-pass filter in the low frequency domain in the embodiment of the disclosure comprises an active high-pass filter and an active low-pass filter which are connected in series, wherein a first-stage operational amplifier, a second-stage operational amplifier and a third-stage operational amplifier in the active high-pass filter form a three-stage cascade operational amplifier, and the first-stage operational amplifier, the second-stage operational amplifier and the third-stage operational amplifier in the active low-pass filter also form the three-stage cascade operational amplifier, so that a frequency band of 15K-250 KHz in radar low-frequency signals can be effectively extracted, invalid clutter smaller than 15KHz and larger than 250KHz in the radar low-frequency signals are removed, and the attenuation of the tested signals is in a controllable range, thereby meeting the requirement of technical performance indexes.
In one embodiment, the first stage operational amplifier, the second stage operational amplifier and the third stage operational amplifier are each formed by two sections of negative feedback circuits.
In this embodiment, the first-stage operational amplifier, the second-stage operational amplifier, and the third-stage operational amplifier of the active high-pass filter are all formed by two negative feedback circuits, so that six sections of high-pass filters in a multiple feedback form can be formed; the first-stage operational amplifier, the second-stage operational amplifier and the third-stage operational amplifier of the active low-pass filter are all composed of two sections of negative feedback circuits, so that a six-section low-pass filter in a multiple feedback mode can be formed.
In one embodiment, the active high pass filter is a butterworth high pass filter and the active low pass filter is a butterworth active low pass filter.
In this embodiment, theoretical analysis and simulation calculation are performed, a butterworth function is selected as a mathematical model of an active high-pass filter, three stages of operational amplifier cascades are designed, each stage adopts a form of two negative feedback circuits to form six high-pass filters in a multiple feedback form, so that the total voltage gain of the active high-pass filter in the implementation is 100 times (40 dB), the passband ripple is 0.5dB, the passband frequency is 15KHz, the voltage gain is attenuated to 37dB, the stopband frequency is 3KHz, and the stopband voltage gain is attenuated to 80dB.
Through theoretical analysis and simulation calculation, a Butterworth function is selected as a mathematical model of the active low-pass filter, three-stage operational amplifier cascade is designed, each stage adopts a two-stage negative feedback circuit form, six low-pass filters in a multiple feedback form are formed, and therefore the total voltage gain of the active low-pass filter in the embodiment is 10 times (20 dB), the passband ripple is 0.5dB, the voltage gain is attenuated to 17dB at a passband frequency of 250KHz, and the stopband voltage gain is attenuated to 45dB at a stopband frequency of 600 KHz.
Fig. 4 is a circuit diagram of a first operational amplifier in the active high-pass filter in the present embodiment. As shown in fig. 4, the passband gain of the first operational amplifier in the active high pass filter is 4.642 times, the cutoff frequency is 15KHz, the quality factor is 0.52, the circuit topology is a multiple feedback, and the minimum gain bandwidth product is 3.6208MHz;
fig. 5 is a circuit diagram of a second operational amplifier in the active high-pass filter in the present embodiment. As shown in fig. 5, the passband gain of the second operational amplifier in the active high pass filter is 4.642 times, the cutoff frequency is 15KHz, the quality factor is 0.71, the circuit topology is a multiple feedback, and the minimum gain-bandwidth product is 4.94378MHz;
fig. 6 is a circuit diagram of a third operational amplifier in the active high-pass filter in the present embodiment. As shown in fig. 5, the passband gain of the third operational amplifier in the active high pass filter is 4.642 times, the cutoff frequency is 15KHz, the quality factor is 1.93, the circuit topology is a multiple feedback, and the minimum gain-bandwidth product is 13.4386MHz.
Fig. 7 is a circuit diagram of the first operational amplifier in the active low-pass filter in the present embodiment. As shown in fig. 7, the pass band gain of the first operational amplifier in the active low pass filter is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 0.52, the circuit topology form is multiple feedback, and the minimum gain-bandwidth product is 28.002MHz;
fig. 8 is a circuit diagram of a second operational amplifier in the active low-pass filter in the present embodiment. As shown in fig. 8, the pass band gain of the second operational amplifier in the active low pass filter is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 0.71, the circuit topology form is multiple feedback, and the minimum gain-bandwidth product is 38.2335MHz;
fig. 9 is a circuit diagram of a third operational amplifier in the active low-pass filter of the present embodiment. As shown in fig. 9, the passband gain of the third operational amplifier in the active low pass filter is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 1.93, the circuit topology is in the form of multiple feedback, and the minimum gain-bandwidth product is 103.9305MHz.
As shown in fig. 3-5, in the active high pass filter,
the first operational amplifier, the second operational amplifier and the third operational amplifier comprise a first capacitor, a first inductor, a second capacitor, a third capacitor, a second inductor and a first operational amplifier.
As shown in fig. 6-8, in the active low pass filter,
the first operational amplifier, the second operational amplifier and the third operational amplifier comprise a third inductor, a fourth capacitor, a fifth inductor, a fifth capacitor and a second operational amplifier.
In one embodiment, the model of the first operational amplifier is AD8048AR, the bandwidth is 150MHz, and the slew rate is 1000 mus/V; the model of the second operational amplifier is 0PA621KU, the bandwidth is 500MHz, and the slew rate is 500 mus/V.
In this embodiment, the first operational amplifier is a high-performance low-noise operational amplifier AD8048AR, and the performance parameters are shown in table 1; the second operational amplifier is high-performance low-noise operational amplifier 0PA621KU, and the performance parameters are shown in Table 2.
TABLE 1
TABLE 2
It should be noted that, because there are errors in the actually used resistance values and capacitance values, the resistance error J is ± 5%, and the capacitance error J is ± 5%, a list of the actually used resistance values and capacitance values is shown in table 3, and table 3 is a list of components used in the active band-pass filter in this embodiment.
TABLE 3
Fig. 10 is a block diagram of a low-frequency active band-pass filter testing system in this embodiment, as shown in fig. 10, the system includes a signal source 101, a first attenuator 102, a low-frequency active band-pass filter 103, a second attenuator 104, a spectrometer 105, and a power regulator 106 connected to the low-frequency active band-pass filter 103; wherein, the first and the second end of the pipe are connected with each other,
the input end of the low-frequency active band-pass filter 103 is connected with the output end of the first attenuator 102, the input end of the first attenuator 102 is connected with the signal source 101, the output end of the low-frequency active band-pass filter 103 is connected with the input end of the second attenuator 104, and the output end of the second attenuator 104 is connected with the spectrometer 105;
the low-frequency active band-pass filter is the low-frequency active band-pass filter.
In one embodiment, the signal source outputs a continuous wave signal with a frequency of 3-650 KHz and a power level of 0-40dBm; the attenuation of the attenuator is 0dB to 40dB, and the attenuation step is 1dB; the lowest frequency tested by the frequency spectrograph is 3Hz, and the minimum power tested is-140 dBm.
In this embodiment, the active band-pass filter plate is tested and recorded by adjusting the frequency and output power level of the signal source, the attenuation of the attenuator, and the detection power level reference of the spectrometer, and the test result is shown in table 4.
TABLE 4
| Frequency (KHz) | Amplitude relative output value (dBc) | Remarks for note |
| 600 | -46.0 | |
| 400 | -33.0 | |
| 300 | -28.0 | |
| 250 | -3.0 | |
| 200 | 0.2 | |
| 150 | 0.7 | |
| 100 | 1.0 | |
| 50 | 1.0 | |
| 40 | 0.6 | |
| 30 | 0.8 | |
| 20 | 0.2 | |
| 15 | -3.0 | |
| 10 | -39.0 | |
| 8 | -52.0 | |
| 6 | -65.0 | |
| 4 | -70.0 | |
| 3 | -80.5 | |
| 2 | -85.0 |
According to the test data recorded in table 4, the simulation design of the low-frequency active band-pass filter and the test system thereof provided in this embodiment is consistent with the actual test result, and the performance index requirements are met.
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This disclosure is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true and spirit of the disclosure being indicated by the following claims.
It will be understood that the present disclosure is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The present disclosure is limited only by the following claims.
Claims (10)
1. A low frequency active band pass filter, characterized in that the band pass filter comprises an active high pass filter and an active low pass filter connected in series;
the active high-pass filter and the active low-pass filter respectively comprise a first-stage operational amplifier, a second-stage operational amplifier and a third-stage operational amplifier which are connected in series.
2. The low frequency active band pass filter of claim 1, wherein the first, second and third stage operational amplifiers are each formed by two negative feedback circuits.
3. A low frequency domain active band pass filter according to claim 2, characterized in that the active high pass filter is a butterworth high pass filter and the active low pass filter is a butterworth active low pass filter.
4. A low frequency active band pass filter according to claim 2, characterized in that in the active high pass filter,
the passband gain of the first operational amplifier is 4.642 times, the cut-off frequency is 15KHz, the quality factor is 0.52, the circuit topology form is multi-feedback, and the minimum gain bandwidth product is 3.6208MHz;
the passband gain of the second operational amplifier is 4.642 times, the cut-off frequency is 15KHz, the quality factor is 0.71, the circuit topology form is multiple feedback, and the minimum gain-bandwidth product is 4.94378MHz;
the passband gain of the third operational amplifier is 4.642 times, the cutoff frequency is 15KHz, the quality factor is 1.93, the circuit topology form is multi-feedback, and the minimum gain bandwidth product is 13.4386MHz.
5. A low frequency active band pass filter according to claim 2, characterized in that in the active low pass filter,
the passband gain of the first operational amplifier is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 0.52, the circuit topology form is multi-feedback, and the minimum gain bandwidth product is 28.002MHz;
the passband gain of the second operational amplifier is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 0.71, the circuit topology form is multiple feedback, and the minimum gain bandwidth product is 38.2335MHz;
the passband gain of the third operational amplifier is 2.154 times, the cut-off frequency is 250KHz, the quality factor is 1.93, the circuit topology form is multiple feedback, and the minimum gain bandwidth product is 103.9305MHz.
6. A low frequency active band pass filter according to any one of claims 1 to 5, characterized in that in the active high pass filter,
the first operational amplifier, the second operational amplifier and the third operational amplifier comprise a first capacitor, a first inductor, a second capacitor, a third capacitor, a second inductor and a first operational amplifier.
7. A low frequency active band pass filter according to claim 6, characterized in that in the active low pass filter,
the first operational amplifier, the second operational amplifier and the third operational amplifier respectively comprise a third inductor, a fourth capacitor, a fifth inductor, a fifth capacitor and a second operational amplifier.
8. The low-frequency-domain active band-pass filter according to claim 7, wherein the first operational amplifier has a model AD8048AR, a bandwidth of 150MHz, and a slew rate of 1000 μ s/V; the model of the second operational amplifier is 0PA621KU, the bandwidth is 500MHz, and the slew rate is 500 mus/V.
9. A low-frequency active band-pass filter test system is characterized by comprising a signal source, a first attenuator, a low-frequency active band-pass filter, a second attenuator, a frequency spectrograph and a power supply voltage stabilizer connected with the low-frequency active band-pass filter; wherein the content of the first and second substances,
the input end of the low-frequency-domain active band-pass filter is connected with the output end of the first attenuator, the input end of the first attenuator is connected with the signal source, the output end of the low-frequency-domain active band-pass filter is connected with the input end of the second attenuator, and the output end of the second attenuator is connected with the frequency spectrograph;
the low frequency active band pass filter is the low frequency active band pass filter of any one of claims 1-8.
10. The low frequency active band-pass filter according to claim 9, wherein the signal source outputs a continuous wave signal having a frequency of 3 to 650KHz and a power level of 0 to-40 dBm; the attenuation of the attenuator is 0dB to 40dB, and the attenuation step is 1dB; the lowest frequency of the frequency spectrograph test is 3Hz, and the minimum power of the frequency spectrograph test is-140 dBm.
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