CN213186061U

CN213186061U - Digital tuning band-pass filter circuit and filter

Info

Publication number: CN213186061U
Application number: CN202022013331.2U
Authority: CN
Inventors: 梁连生
Original assignee: Shenzhen Shunluo Xunda Electronic Co ltd
Current assignee: Shenzhen Shunluo Xunda Electronic Co ltd
Priority date: 2020-09-15
Filing date: 2020-09-15
Publication date: 2021-05-11
Anticipated expiration: 2030-09-15

Abstract

The utility model provides a digital tuning live-wire circuit and wave filter, its circuit includes: a first resonant circuit and a second resonant circuit, the first resonant circuit and the second resonant circuit being coupled via a third inductance; the first resonant circuit comprises a first inductor and a first capacitor, and the first inductor is connected with the first capacitor in parallel; the second resonant circuit comprises a second inductor and a second capacitor, and the second inductor is connected with the second capacitor in parallel; the inductance values of the first inductor, the second inductor and the third inductor are fixed and unchanged, and the capacitance values of the first capacitor and the second capacitor are adjustable. The inductance is set as a fixed value, the resonance frequency can be changed by changing the resonance capacitance, and the band-pass filtering function of a certain frequency band can be realized only by one narrow-band-pass filter; the number of the narrow-band-pass filters is reduced, a radio frequency switch is not needed, and the size and the cost of the whole band-pass filter are greatly reduced.

Description

Digital tuning band-pass filter circuit and filter

Technical Field

The utility model relates to a wave filter technical field especially relates to a digital tuning band-pass filter circuit and wave filter.

Background

Filters are important components of communication systems that can be used to separate or combine different frequencies. In a communication system, when transmitting signals, a filter can limit a high-power transmitter to radiate in a specified frequency band; conversely, when receiving signals, the filter can inhibit signal interference outside the frequency band. Filters can be classified into low-pass, high-pass, band-pass and band-stop filters according to different attenuation characteristics; a low-pass filter is an electronic filtering device that allows signals below a cutoff frequency to pass, but does not allow signals above the cutoff frequency to pass; a high-pass filter: the combined device is a combined device of devices such as a capacitor, an inductor, a resistor and the like which allows signal components above a certain frequency to pass through and greatly inhibits the signal components below the frequency; band-pass filter: a filter that passes frequency components in a certain frequency range, but attenuates frequency components in other ranges to an extremely low level; band elimination filter: refers to a filter that passes most of the frequency components, but attenuates some range of frequency components to a very low level.

For the band-pass filter, because of the requirements of bandwidth and out-of-band rejection, the conventional practice at present needs to divide the band-pass filter into a plurality of narrow-band-pass filters, and then combine the filters through a radio frequency switch, so as to realize the band-pass filtering function in a certain frequency range. At present, a common radio frequency switch group has a single-pole six-throw structure, a plurality of band-pass filters are controlled and selected, and a plurality of radio frequency switches are needed for an input end and an output end respectively; in addition, the wiring of the radio frequency switch in the filter and the narrow-band filter need to be blocked to avoid mutual interference, so that the size of the filter is large.

SUMMERY OF THE UTILITY MODEL

In order to solve the above problem, the utility model provides a digital tuning band-pass filter circuit and wave filter, its volume that can reduce the wave filter greatly.

The utility model provides a digital tuning band-pass filter circuit, include: a first resonant circuit and a second resonant circuit, the first resonant circuit and the second resonant circuit being coupled via a third inductance; the first resonant circuit comprises a first inductor and a first capacitor, and the first inductor is connected with the first capacitor in parallel; the second resonant circuit comprises a second inductor and a second capacitor, and the second inductor is connected with the second capacitor in parallel; the inductance values of the first inductor, the second inductor and the third inductor are fixed and unchanged, and the capacitance values of the first capacitor and the second capacitor are adjustable.

The utility model also provides a digital tuning band pass filter, include as above digital tuning band pass filter circuit.

The utility model also provides a 108 supple digital tuning band-pass filter circuit of 174MHz, include as above digital tuning band-pass filter circuit.

The utility model also provides a 108-.

The utility model has the advantages that: the inductance is set as a fixed value, the resonance frequency can be changed by changing the resonance capacitance, and the band-pass filtering function of a certain frequency band can be realized only by one narrow-band-pass filter; the number of the narrow-band-pass filters is reduced, a radio frequency switch is not needed, and the size and the cost of the whole band-pass filter are greatly reduced.

Drawings

Fig. 1 is a schematic block diagram of a filter for implementing 108-174MHz band-pass filtering in the prior art.

Fig. 2 is a circuit diagram of a narrow band-pass filter in a filter for implementing the 108-174MHz band-pass filtering function in the prior art.

Fig. 3 is a circuit diagram of a narrow band pass filter constructed in simulation software according to an embodiment of the present invention.

Fig. 4 is a simulation result of a narrow band pass filter circuit constructed in simulation software according to an embodiment of the present invention.

Fig. 5 is a circuit diagram of a band pass filter according to an embodiment of the present invention.

Fig. 6 is a circuit diagram of the resonant capacitor C of fig. 5 for performing equivalent transformation in the embodiment of the present invention.

Fig. 7 is a circuit diagram of the switch circuit in fig. 6 according to an embodiment of the present invention.

Fig. 8 is a diagram of simulation results showing the change of the center frequency of the circuit shown in fig. 5 with the change of the capacitance in the embodiment of the present invention.

Fig. 9 is a circuit diagram of a band-pass filter for implementing the 108-174MHz band-pass filtering function in the embodiment of the present invention.

Fig. 10 is a circuit diagram of a switching circuit of each resonant capacitor in fig. 9 according to an embodiment of the present invention.

Fig. 11 is a standing wave ratio and simulation result of the bandpass filter shown in fig. 9 operating at a center frequency of 174MHz according to the embodiment of the present invention.

Fig. 12 shows a standing wave ratio and a simulation result of the bandpass filter shown in fig. 9 when the operating center frequency is 108.2MHz in the embodiment of the present invention.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments and with reference to the attached drawings, it should be emphasized that the following description is merely exemplary and is not intended to limit the scope and application of the present invention.

Taking the band-pass filter with the frequency range of 108-174MHz as an example, the indexes include: frequency range 108-: 4.5dB or less, 3dB bandwidth: 3% -5%, Fo (1 ± 10%) out-of-band inhibition: not less than 24dBc, distal inhibition: 2Fo is more than or equal to 50dB, and the matching impedance is as follows: 50 Ω, standing-wave ratio: less than or equal to 1.6.

Because of the requirements of bandwidth and out-of-band rejection, the conventional method in the prior art, as shown in the schematic block diagram of fig. 1, needs to divide 108 + 174MHz into a plurality of narrow band pass filters, and then combine them through the rf switch, so as to implement the 108 + 174MHz band pass filtering function. According to the calculation of the bandwidth requirement of 3%, about 20 narrow-band filters are needed for frequency segmentation, and then the required working frequency is selected by switching to the required narrow-band-pass filters through the radio frequency switch. At present, a common radio frequency switch group has a single-pole six-throw structure, 20 band-pass filters are controlled and selected, and 4 radio frequency switches are needed at an input end and an output end respectively; in addition, the wiring of the radio frequency switch in the filter and the narrow-band filter need to be blocked to avoid mutual interference, so that the size of the filter is large. In the prior art, each narrow band pass filter adopts a two-order coupling type band pass filter design, and the circuit diagram of the narrow band pass filter is shown in fig. 2, wherein L and Lk represent inductors, and C represents a capacitor; the values of the inductor and the capacitor in each narrow-band-pass filter are fixed and unchanged; in the plurality of narrow-band-pass filters, according to the frequency requirement, the inductance and the capacitance in the whole circuit are changed by switching the radio frequency switch.

According to the frequency formula

It is known that to change the frequency, one can do this by: a. simultaneously changing the inductance and the capacitance; b. the capacitance is unchanged, and the inductance is changed; c. the inductance is unchanged and the capacitance is changed. In the prior art, the inductance and the capacitance of each narrow-band-pass filter are fixed values, so that the index requirements can be met only by combining a plurality of narrow-band-pass filters.

In the embodiment of the application, the inductor is set to be a fixed value, the resonant frequency can be changed by changing the resonant capacitor, and the band-pass filtering function of 108-174MHz can be realized only by one narrow-band-pass filter.

As shown in fig. 3, a narrow band pass filter circuit is built in the simulation software, wherein L1 is a resonant inductor, C1 is a resonant capacitor, and L2 is a coupling inductor; the resonant capacitance C1 was set as a variable, multipoint scan simulated. Fig. 4 is a simulation result of scanning 20 points. According to the simulation result, the inductance is unchanged, the resonance frequency can be changed by changing the resonance capacitor, the narrow band-pass filter with different frequencies can be obtained by changing the resonance capacitor once, if the value of the resonance capacitor changed each time is small enough, which is equivalent to a plurality of narrow band-pass filters, one band-pass filter with a changeable capacitance value can replace a plurality of band-pass filters with fixed inductance capacitance values, and the requirement of band-pass filtering of the whole band of 108-band 174MHz can be realized without using a radio-frequency switch.

According to the parallel connection principle of the capacitors, one capacitor can be divided into a plurality of capacitors which are connected in parallel; therefore, the total resonance capacitor is divided into a plurality of capacitors which are connected in parallel, and then a switch is added to each capacitor, so that the band-pass filter with a plurality of fixed inductance and capacitance values can be replaced.

Consider that inductance, electric capacity obtain higher Q value, produce more easily or lectotype, carry out impedance transformation and inductance T type equivalent conversion with the circuit simultaneously, the utility model discloses a product circuit schematic block diagram is shown in fig. 5, and wherein La, Lb, Lc, Lp, Lq are the inductance, and C is resonant capacitance. Wherein the resonant capacitance is tunable in capacitance value by the equivalent of fig. 6. K1, K2, K3... Kn in fig. 6 is a switching circuit that controls C1, C2, C3... Cn resonant capacitance.

The switching circuits K1, K2, K3... Kn are designed according to the forward and reverse functional characteristics of PIN diodes, and the circuit diagram thereof is shown in fig. 7. The switching function is realized by controlling the forward conduction and reverse cut-off characteristics of the PIN diode. When Vcc > V1, the PIN diode is conducting; when Vcc < V1, the PIN diode turns off. By controlling the voltage of V1, the resonant capacitor C1 can be controlled, as can the other parallel circuits in fig. 6. The total capacitance value of the resonant capacitor can be changed by controlling the on-off of the PIN tube of each switch group. The center frequency of the narrow-band-pass filter changes with each change of the total resonance capacitance. The difference of the center frequencies of the narrow-band-pass filters before and after the change of the total resonance capacitance is less than or equal to 0.8MHz, and the band-pass filtering of the whole frequency band of the product can be met (see figure 8).

For example, the product requirement frequency range is 108-174MHz, and total 66MHz, at least 85 band-pass filters are required according to a point calculation of 0.8MHz, namely, the total resonant capacitance C has 85 different values. According to the filter designed in FIG. 6, if there are n sets of capacitors connected in parallel, the total capacitance is 2ⁿA different value, i.e. 2ⁿA band pass filter. The product needs more than 85 band-pass filters, and n is more than or equal to 7. In this embodiment, n is 8 to obtain denser frequency coverage.

Summarizing the design concept, the product design circuit is shown in fig. 9, where Ca is a small capacitance, and when the product frequency is too high, the capacitance of Ca can be increased properly. The K-switch circuit for each resonant capacitor is shown in fig. 10. The PIN diode is selected from BAP65-02 of Enzhipu. Vn is a control voltage of each set of the switching circuits, and Vn is 20v or 0 v. The control voltages Vn of C1-C8 are independent.

And establishing a model in ADS simulation software according to a product circuit diagram for simulation, wherein the Q value of the inductor is set to be 120, and the Q value of the capacitor is set to be 1000. The capacitance and inductance values after simulation optimization are shown in table 1 and table 2. The capacitance value is determined according to the distance between two similar resonance points when the resonance capacitance changes, and if the bandwidth is large, the distance between the resonance points can be correspondingly set to be larger.

TABLE 1 capacitance value (pF)

C1	C2	C3	C4	C5	C6	C7	C8	Ca
									0.38	0.58	0.94	1.55	2.5	4.8	9.5	19	0.7

TABLE 2 inductance value (nH)

La	Lb	Lc	Lp	Lq
					83	63	31	142.6	10.1

FIG. 11 is a simulation result of the product with an operating center frequency of 174 MHz. The index meets the protocol requirements.

FIG. 12 is a simulation result of the product operating center frequency at 108.2 MHz. The index meets the protocol requirements.

The product has the lowest out-of-band suppression at 108MHz, and the indexes of each frequency point can meet the protocol requirements.

The filter of the embodiment changes the resonant capacitance by controlling V1-V8, and the control end Vn is in two states of 20V or 0V. The product has 8 groups of switch circuits, so that the product is equivalent to 2⁸Narrow band-pass filters of different center frequencies are used for selecting the required resonance frequency by controlling V1-V8.

The foregoing is a more detailed description of the present invention, taken in conjunction with the specific/preferred embodiments thereof, and it is not intended that the invention be limited to the specific embodiments shown and described. For those skilled in the art to which the invention pertains, a plurality of alternatives or modifications can be made to the described embodiments without departing from the concept of the invention, and these alternatives or modifications should be considered as belonging to the protection scope of the invention.

Claims

1. A digital tuned bandpass filter circuit, comprising:

a first resonant circuit and a second resonant circuit, the first resonant circuit and the second resonant circuit being coupled via a third inductance; the first resonant circuit comprises a first inductor and a first capacitor, and the first inductor is connected with the first capacitor in parallel; the second resonant circuit comprises a second inductor and a second capacitor, and the second inductor is connected with the second capacitor in parallel; the inductance values of the first inductor, the second inductor and the third inductor are fixed and unchanged, and the capacitance values of the first capacitor and the second capacitor are adjustable.

2. The digitally-tuned bandpass filter circuit of claim 1 wherein said first inductor, second inductor and third inductor are T-configured and said circuit performs impedance transformation.

3. The digitally-tuned bandpass filter circuit according to claim 2 wherein said first capacitor and said second capacitor are connected in parallel by n sub-capacitors, respectively, and each sub-capacitor is connected in series with a switching circuit.

4. The digitally tuned bandpass filter circuit according to claim 3 wherein said switching circuit is comprised of a PIN diode.

5. A digitally tuned bandpass filter, characterized in that it comprises a digitally tuned bandpass filter circuit according to any one of claims 1 to 4.

6. A 108-174MHz digitally tuned bandpass filter circuit comprising the digitally tuned bandpass filter circuit of claim 4.

7. The 108-174MHz digital tuned bandpass filter circuit of claim 6, wherein the number n of sub-capacitors is greater than or equal to 7.

8. The 108-band 174MHz digital tuned bandpass filter circuit of claim 6 wherein the number n of sub-capacitors is 8.

9. The 108-174MHz digitally tuned bandpass filter circuit of claim 8 wherein the first capacitor and the second capacitor comprise 8 sub-capacitors and a supplemental capacitor.

10. A 108-174MHz digitally tuned bandpass filter comprising the 108-174MHz digitally tuned bandpass filter circuit as claimed in any one of claims 6-9.