Adjustable N-path non-reflection filter and superheterodyne receiver

Abstract

The invention relates to the technical field of tunable N-path filters, in particular to an adjustable N-path non-reflection filter and a superheterodyne receiver, the adjustable N-path non-reflection filter comprises a signal source, an N-path band-pass filtering unit, an N-path band-stop filtering unit, an output resistor and a split-phase clock generation circuit; wherein the output end of the signal source is connected with one end of the N-path band-pass filtering unit and one end of the N-path band-stop filtering unit, the other end of the N-path band-stop filtering unit is connected with the output resistor, and the split-phase clock generation circuit is connected with grid electrodes of a plurality of MOS switches in the N-path band-pass filtering unit and the N-path band-stop filtering unit and outputs control signals. The adjustable N-path non-reflection filter provided by the invention has excellent frequency selectivity, can effectively suppress higher harmonics, and can adjust a pass band and a stop band by changing the switching frequency. Meanwhile, the filter can eliminate reflected signals and prevent the reflected signals from inducing a mixer and a high-gain amplifier in a system to generate intermodulation interference and gain fluctuation.

Description

Technical Field

[0001] The present invention relates to the technical field of tunable N-path filters, and in particular to an tunable N-path reflectionless filter and a superheterodyne receiver. Background Art

[0002] With the continuous development and progress of wireless communication technology, the requirements for the signal processing capabilities of RF front-end circuits are getting higher and higher. In the future, SDR will be combined with artificial intelligence to process signals. In SDR communications, programmability is not only required in the digital backend, but also in the analog front end. A major challenge of this type of radio technology is to realize RF filters whose operating characteristics (including operating frequency, etc.) are adjustable over a wide frequency range. To address this challenge, programmable N-path filters are a feasible technical solution.

[0003] However, filters that lack reflection absorption processing will reflect stopband signals to the source end, which can cause intermodulation interference and gain fluctuations in mixers and high-gain amplifiers. Therefore, reflectionless filters have attracted much attention in recent years to meet the interference suppression needs of advanced communication applications. Summary of the invention

[0004] The object of the present invention is to provide an adjustable N-path reflectionless filter for solving the problem that the existing filter lacks reflection absorption processing and thus causes intermodulation interference and gain fluctuation in mixers and high-gain amplifiers.

[0005] In one aspect, the present application provides an adjustable N-path reflectionless filter, comprising: a signal source, an N-path bandpass filter unit, an N-path bandstop filter unit, an output resistor, and a phase-splitting clock generation circuit;

[0006] Among them, the output end of the signal source is connected to one end of the N-path bandpass filter unit and the N-path bandstop filter unit respectively, the other end of the N-path bandpass filter unit outputs the filtered signal, the other end of the N-path bandstop filter unit is connected to the output resistor, and the phase-splitting clock generating circuit is connected to the gates of multiple MOS switches in the N-path bandpass filter unit and the N-path bandstop filter unit, and outputs a control signal.

[0007] Optionally, the N-path bandpass filter unit is composed of a plurality of switch-type inductor subunits connected in series, the output end of the signal source is connected to a series end of the plurality of switch-type inductor subunits connected in series, and another series end of the plurality of switch-type inductor subunits connected in series is a filter signal output end;

[0008] The switch-type inductor subunit is composed of a MOS switch and an inductor connected in parallel, the source of the MOS switch is connected to one end of the inductor, and the drain of the MOS switch is connected to the other end of the inductor;

[0009] Among them, the drain of the MOS switch in the first end switch-type inductor subunit connected to the output end of the signal source is connected to the output end of the signal source, and the source of the MOS switch in the first end switch-type inductor subunit is connected to the drain of the MOS switch in the next series-connected switch-type inductor subunit.

[0010] Optionally, the N-path band-stop filter unit is composed of a plurality of parallel switch-type capacitor subunits, wherein a parallel end of the plurality of parallel switch-type capacitor subunits is connected to an output end of a signal source, and another parallel end is connected to one end of an output resistor, and the other end of the output resistor is grounded;

[0011] The switch-type capacitor subunit includes a capacitor, a second MOS switch and a third MOS switch, the drain of the second MOS switch is connected to the output end of the signal source, the source of the second MOS switch is connected to one end of the capacitor, the other end of the capacitor is connected to the drain of the third MOS switch, and the source of the third MOS switch is connected to one end of the output resistor.

[0012] Optionally, the number of switch-type inductor sub-units in the N-path band-pass filter unit is the same as the number of switch-type capacitor sub-units in the N-path band-stop filter unit.

[0013] Optionally, the phase-splitting clock generating circuit is used to output a square wave signal with N phases that do not overlap and a duty cycle of 1 / N;

[0014] The square wave signals output by the phase-splitting clock generating circuit correspond one-to-one to the switch-type inductor subunit and the switch-type capacitor subunit, respectively, and the square wave signals are used as control signals for the gates of the MOS switch tubes in the corresponding switch-type inductor subunit and the switch-type capacitor subunit.

[0015] Optionally, in the N-phase square wave signal, the phase angle difference between the m-th phase and the m+N / 2-th phase square wave signal is 180°, and m is a positive integer less than N / 2.

[0016] In a second aspect, the present application provides a superheterodyne receiver, comprising an antenna, a preselection filter, a low noise amplifier, an adjustable N-path reflectionless filter and a variable gain amplifier connected in sequence.

[0017] The beneficial effects of the present invention are:

[0018] The adjustable N-path reflectionless filter provided by the present invention has excellent frequency selectivity, can effectively suppress high-order harmonics, and can adjust the passband and stopband by changing the switching frequency.

[0019] At the same time, the filter can eliminate reflected signals and prevent them from inducing intermodulation interference and gain fluctuations in the mixer and high-gain amplifier within the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of the circuit structure of a conventional N-path bandpass filter of prior art 1;

[0022] Figure 2 It is a schematic diagram of the architecture of a reflectionless bandpass filter according to the second prior art;

[0023] Figure 3 1 is the experimental data of the reflectionless bandpass filter of the prior art 2, wherein (a) is the |S11| parameter of the main channel, and (b) is the |S11| parameter of the secondary channel;

[0024] Figure 4 This is a schematic diagram of the architecture of the adjustable N-path reflectionless filter described in an embodiment of the present application;

[0025] Figure 5 is the |S21| parameter of the N-path bandpass filter and the N-path bandstop filter in the embodiment of the present application;

[0026] Figure 6 This is a schematic diagram of signal flow within the passband according to an embodiment of the present application;

[0027] Figure 7 A schematic diagram of the flow of out-of-band signals described in the application embodiment;

[0028] Figure 8 The impedance diagram of two channels in the adjustable N-path reflectionless filter architecture;

[0029] Fig. 9 Schematic diagram of an N-path reflectionless bandpass filter described in Example 2;

[0030] Fig.10It is a comparison diagram of simulation results of the N-path non-reflective bandpass filter in Example 2 and the traditional N-path bandpass filter;

[0031] Fig.11 A schematic diagram of the structure of a superheterodyne receiver described in an embodiment of the present application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0034] Embodiment 1:

[0035] Before describing the adjustable N-path reflectionless filter disclosed in the present application, it is necessary to briefly describe the existing conventional N-path bandpass filter, such as Figure 1 As shown in the figure, it is the existing technical solution 1, which is a traditional N-path bandpass filter. This structure realizes spectrum shifting by changing the switching frequency, and moves the low-pass filter waveform to the vicinity of the switching frequency to form a bandpass filter. This structure has a higher quality factor (Q value) and higher frequency selectivity. The |S11| parameter measured by this structure is between -5dB and -10dB in a wide frequency range, and the reflected signal is relatively large.

[0036] like Figure 2 As shown in FIG. 1 , it is the existing technical solution 2, which is a non-reflective bandpass filter. The filter consists of two parallel complementary channels, and its |S11| parameters are as follows: Figure 3 -(a) Figure 3 -(b). The main channel is composed of a bandpass filter, and the auxiliary channel is composed of a bandstop filter and a load resistor RL. The two channels are connected in parallel to achieve wideband reflection-free. This bandpass filter is not programmable, and the passband and stopband cannot be adjusted by software, which has limitations in SDR communication.

[0037] Based on the above solution, the traditional N-path filter has an adjustable passband / stopband, but has a reflected signal; while the reflectionless filter can eliminate the reflected signal, but the passband / stopband is not adjustable. This embodiment proposes a new architecture combining the above technology, and its structural diagram is as follows Figure 4 As shown, an adjustable N-path reflectionless filter includes: a signal source, an N-path bandpass filter unit, an N-path bandstop filter unit, an output resistor and a phase-splitting clock generating circuit, wherein the phase-splitting clock generating circuit is used to output a square wave signal with N phases that do not overlap and a duty cycle of 1 / N, such as Figure 4 S1-SN in;

[0038] Among them, the output end of the signal source is connected to one end of the N-path bandpass filter unit and the N-path bandstop filter unit respectively, the other end of the N-path bandpass filter unit outputs the filtered signal, the other end of the N-path bandstop filter unit is connected to the output resistor, the phase-splitting clock generation circuit is connected to the gates of multiple MOS switches in the N-path bandpass filter unit and the N-path bandstop filter unit, and outputs a control signal. This architecture can solve the problems of the prior art, realize adjustable passband / stopband and eliminate reflected signals, and the specific implementation method is as follows:

[0039] Figure 4 Where S1, S2...SN are a set of square wave signals with different phases and a frequency of f CLK By changing f CLK The center operating frequency and bandwidth of the N-path bandpass filter and the N-path bandstop filter can be adjusted by the value of f. CLK , their |S21| are as follows Figure 5 -(a) Figure 5 -(b) as shown.

[0040] To understand this architecture from the perspective of energy flow, all signals within the passband pass through the N-path bandpass filter and are output from port 2, as shown in Figure 2. Figure 6 As shown; all signals outside the passband pass through the N-path band-stop filter and are absorbed by RL, as shown Figure 7 shown.

[0041] Figure 8 Schematic diagram of input impedance. ZM is the input impedance of the total channel, ZM1 and ZM2 are the input impedances of the main channel and the sub-channel respectively, where ZM=ZM1 / / ZM2. Select appropriate ZM1 and ZM2 to make ZM conjugate matching with the source impedance in the full frequency band, and achieve full-band reflection-free characteristics.

[0042] Example 2

[0043] like Fig. 9 As shown, the present application is based on Example 1 and is used to disclose a specific N-path non-reflective bandpass filter structure, wherein the N-path bandpass filter unit is composed of a plurality of switch-type inductor subunits connected in series, the output end of the signal source is connected to the series end of the plurality of switch-type inductor subunits connected in series, and the other series end of the plurality of switch-type inductor subunits connected in series is a filter signal output end;

[0044] The switch-type inductor subunit is composed of a MOS switch and an inductor connected in parallel, the source of the MOS switch is connected to one end of the inductor, and the drain of the MOS switch is connected to the other end of the inductor;

[0045] The drain of the MOS switch in the first end switch-type inductor subunit connected to the output end of the signal source is connected to the output end of the signal source, and the source of the MOS switch in the first end switch-type inductor subunit is connected to the drain of the MOS switch in the next series-connected switch-type inductor subunit;

[0046] The N-path band-stop filter unit is composed of a plurality of parallel switch-type capacitor subunits, wherein a parallel end of the plurality of parallel switch-type capacitor subunits is connected to an output end of a signal source, and another parallel end is connected to one end of an output resistor, and the other end of the output resistor is grounded;

[0047] The switch-type capacitor subunit includes a capacitor, a second MOS switch and a third MOS switch, the drain of the second MOS switch is connected to the output end of the signal source, the source of the second MOS switch is connected to one end of the capacitor, the other end of the capacitor is connected to the drain of the third MOS switch, and the source of the third MOS switch is connected to one end of the output resistor; wherein the number of the switch-type inductor subunits in the N-path band-pass filter unit is the same as the number of the switch-type capacitor subunits in the N-path band-stop filter unit.

[0048] The square wave signals output by the phase-splitting clock generation circuit correspond to the switch-type inductor subunits and the switch-type capacitor subunits one by one, respectively, and the square wave signals are used as control signals for the gates of the MOS switch tubes in the corresponding switch-type inductor subunits and the switch-type capacitor subunits, such as Fig. 9 As shown in the figure, P1, P2...PN are a group of square wave signals with different phases, and Pm and Pm+N / 2 differ by 180° (m is a positive integer less than or equal to N / 2); Q1, Q2...QN are another group of square wave signals with different phases, and Qm and Qm+N / 2 differ by 180°. The simulation results are compared with those of the traditional N-path filter. Fig.10 As shown, it can be seen that the filter has adjustable passband and stopband, and can effectively reduce the reflected signal.

[0049] Example 3

[0050] like Fig.11 As shown, this embodiment is based on Embodiment 2 and is used to provide a superheterodyne receiver, including an antenna, a preselection filter, a low noise amplifier, an adjustable N-path reflectionless filter and a variable gain amplifier connected in sequence.

[0051] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An adjustable N-path reflectionless filter, characterized in that: include: Signal source, N-path bandpass filter unit, N-path bandstop filter unit, output resistor and phase split clock generation circuit; Among them, the output end of the signal source is connected to one end of the N-path bandpass filter unit and the N-path bandstop filter unit respectively, the other end of the N-path bandpass filter unit outputs the filtered signal, the other end of the N-path bandstop filter unit is connected to the output resistor, and the phase-splitting clock generating circuit is connected to the gates of multiple MOS switches in the N-path bandpass filter unit and the N-path bandstop filter unit, and outputs a control signal.

2. The adjustable N-path reflectionless filter according to claim 1, characterized in that: The N-path bandpass filter unit is composed of a plurality of switch-type inductor subunits connected in series, the output end of the signal source is connected to the series end of the plurality of switch-type inductor subunits connected in series, and the other series end of the plurality of switch-type inductor subunits connected in series is the filter signal output end; The switch-type inductor subunit is composed of a MOS switch and an inductor connected in parallel, the source of the MOS switch is connected to one end of the inductor, and the drain of the MOS switch is connected to the other end of the inductor; Among them, the drain of the MOS switch in the first end switch-type inductor subunit connected to the output end of the signal source is connected to the output end of the signal source, and the source of the MOS switch in the first end switch-type inductor subunit is connected to the drain of the MOS switch in the next series-connected switch-type inductor subunit.

3. The adjustable N-path reflectionless filter according to claim 2, characterized in that: The N-path band-stop filter unit is composed of a plurality of parallel switch-type capacitor subunits, wherein a parallel end of the plurality of parallel switch-type capacitor subunits is connected to an output end of a signal source, and another parallel end is connected to one end of an output resistor, and the other end of the output resistor is grounded; The switch-type capacitor subunit includes a capacitor, a second MOS switch and a third MOS switch, the drain of the second MOS switch is connected to the output end of the signal source, the source of the second MOS switch is connected to one end of the capacitor, the other end of the capacitor is connected to the drain of the third MOS switch, and the source of the third MOS switch is connected to one end of the output resistor.

4. The adjustable N-path reflectionless filter according to claim 1, characterized in that: The number of the switch-type inductor subunits in the N-path bandpass filter unit is the same as the number of the switch-type capacitor subunits in the N-path bandstop filter unit.

5. The adjustable N-path reflectionless filter according to claim 4, characterized in that: The phase-splitting clock generation circuit is used to output a square wave signal with N phases that do not overlap and a duty cycle of 1 / N; The square wave signals output by the phase-splitting clock generating circuit correspond one-to-one to the switch-type inductor subunit and the switch-type capacitor subunit, respectively, and the square wave signals are used as control signals for the gates of the MOS switch tubes in the corresponding switch-type inductor subunit and the switch-type capacitor subunit.

6. The adjustable N-path reflectionless filter according to claim 5, characterized in that: In the N-phase square wave signal, the phase angle difference between the m-th phase and the m+N / 2-th phase square wave signal is 180°, and m is a positive integer less than N / 2.

7. A superheterodyne receiver, characterized in that: It includes an antenna, a preselection filter, a low noise amplifier, an adjustable N-path reflectionless filter and a variable gain amplifier which are connected in sequence.

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