An adjustable n-path reflectionless filter and superheterodyne receiver

Abstract

The application relates to the technical field of tunable N-path filter, in particular to a tunable N-path reflection-free filter and a superheterodyne receiver. The tunable N-path reflection-free filter comprises a signal source, an N-path band-pass filter unit, an N-path band-stop filter unit, an output resistor and a phase-splitting clock generating circuit. The output end of the signal source is connected with one end of the N-path band-pass filter unit and the N-path band-stop filter unit respectively, the other end of the N-path band-stop filter unit is connected with the output resistor, the gate of a plurality of MOS switches in the N-path band-pass filter unit and the N-path band-stop filter unit is connected with the phase-splitting clock generating circuit, and the phase-splitting clock generating circuit outputs a control signal. The tunable N-path reflection-free filter provided by the application has excellent frequency selectivity, can effectively suppress high-order harmonics, and can adjust the passband and the stopband by changing the switching frequency. Meanwhile, the filter can eliminate the reflected signal, prevent the intermodulation interference and gain fluctuation of the mixer and the high-gain amplifier in the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunable N-path filter, in particular to a tunable N-path reflectionless filter and a superheterodyne receiver. BACKGROUND

[0002] With the continuous development and progress of wireless communication technology, the current requirement for the signal processing capability of the radio frequency front-end circuit is higher and higher. In the future, SDR will be combined with artificial intelligence to process signals. In SDR communication, programmability is not only required for the digital back end, but also for the analog front end. One of the main challenges of such radio technology is to realize a radio frequency filter whose operating characteristics (including operating frequency, etc.) are adjustable in a wide frequency range. To solve this challenge, programmable N-path filters are a feasible technical solution.

[0003] However, filters lacking reflection absorption processing will reflect the stopband signal to the source end, which will cause intermodulation interference and gain fluctuation in the mixer and high-gain amplifier. Therefore, reflectionless filters have attracted much attention in recent years to meet the interference suppression requirements of advanced communication applications. SUMMARY

[0004] The purpose of the present application is to provide a tunable N-path reflectionless filter to solve the problem that the existing filter lacks reflection absorption processing, thereby causing intermodulation interference and gain fluctuation in the mixer and high-gain amplifier.

[0005] In one aspect, the present application provides a tunable 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] 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 a 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 a plurality of 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 series-connected switch-type inductor sub-units. The output end of the signal source is connected to the series-connected end of the plurality of series-connected switch-type inductor sub-units. The other series-connected end of the plurality of series-connected switch-type inductor sub-units is the filtered signal output end.

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

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

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

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

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

[0013] Optionally, the phase-splitting clock generation circuit is used for outputting N-phase non-overlapping square wave signals with a duty cycle of 1 / N.

[0014] 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, and the square wave signals are used as control signals of the gates of the MOS switches in the corresponding switch-type inductor subunits and switch-type capacitor subunits.

[0015] Optionally, the phase angle between the mth phase and the m+N / 2th phase square wave signals in the N-phase square wave signals 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 pre-selection filter, a low-noise amplifier, an adjustable N-path reflectionless filter and a variable gain amplifier connected in sequence.

[0017] The present application has the following advantages:

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

[0019] Meanwhile, the filter can eliminate reflected signals, prevent intermodulation interference and gain fluctuation of mixers and high-gain amplifiers in the system. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

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

[0022] Figure 2 It is a schematic diagram of a non-reflection bandpass filter structure of prior art 2.

[0023] Figure 3 It is experimental data of the non-reflection bandpass filter of prior art 2, wherein (a) is the |S11| parameter of the main channel, and (b) is the |S11| parameter of the auxiliary channel.

[0024] Figure 4 It is a schematic diagram of an adjustable N-path non-reflection filter structure according to the embodiments of the present application.

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

[0026] Figure 6 It is a schematic diagram of signal flow in the passband according to the embodiments of the present application.

[0027] Figure 7 It is a schematic diagram of signal flow out of the passband according to the embodiments of the present application.

[0028] Figure 8 It is a schematic diagram of the impedance of two channels under the structure of the adjustable N-path non-reflection filter.

[0029] Figure 9 It is a schematic diagram of an N-path non-reflection bandpass filter according to embodiment 2.

[0030] Figure 10This is a comparison of simulation results between the N-path reflection-free bandpass filter in Example 2 and the traditional N-path bandpass filter;

[0031] Figure 11 This is a schematic diagram of the structure of a superheterodyne receiver according to an embodiment of this application. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0033] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] Example 1:

[0035] Before describing the tunable N-path reflectionless filter disclosed in this application, it is necessary to briefly explain the existing conventional N-path bandpass filters, such as... Figure 1 The image shows an existing technical solution, a traditional N-path bandpass filter. This structure achieves spectrum shifting by changing the switching frequency, moving the low-pass filter waveform to near the switching frequency to form a bandpass filter. This structure has a high quality factor (Q value) and high frequency selectivity. The measured |S11| parameter of this structure is between -5dB and -10dB over a wide frequency range, and the reflected signal is relatively large.

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

[0037] Based on the above scheme, the traditional N-path filter has an adjustable passband / rejection band, but has a reflected signal; while the non-reflection filter can eliminate the reflected signal, but the passband / rejection band is not adjustable. The embodiment proposes a new architecture combining the above technologies, the structural schematic diagram of which is shown in Figure 4 An adjustable N-path non-reflection 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 generating circuit, wherein the phase-splitting clock generating circuit is used to output N-phase non-overlapping square wave signals with a duty cycle of 1 / N, as shown in Figure 4 S1-SN in (a) and (b).

[0038] Wherein, the output end of the signal source is connected with 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 a filtered signal, the other end of the N-path bandstop filter unit is connected with the output resistor, and the phase-splitting clock generating circuit is connected with the gate of a plurality of 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 in the prior art, realize adjustable passband / rejection band and eliminate reflected signals. The specific implementation manner is as follows:

[0039] Figure 4 S1, S2…SN are a group of square wave signals with different phases, and the frequency is f CLK . By changing the value of f CLK , the center working frequency and the working bandwidth of the N-path bandpass filter and the N-path bandstop filter can be adjusted, wherein the center working frequencies of the N-path bandpass filter and the N-path bandstop filter are equal to f CLK , and the |S21| of the two is shown in (a) and (b). Figure 5 Figure 5

[0040] From the perspective of energy flow, the signals in the passband all pass through the N-path bandpass filter and are output from port 2, as shown in Figure 6 ; the signals outside the passband all pass through the N-path bandstop filter and are absorbed by RL, as shown in Figure 7 .

[0041] Figure 8 The input impedance schematic diagram is shown in (a). ZM is the input impedance of the total channel, ZM1 and ZM2 are the input impedances of the main channel and the auxiliary channel respectively, and ZM=ZM1 / / ZM2. By selecting appropriate ZM1 and ZM2, the ZM and the source end impedance are conjugate matched in the whole frequency band, so as to realize the non-reflection characteristic in the whole frequency band.

[0042] Embodiment 2 ​​

[0043] like Figure 9 As shown, this application, based on Embodiment 1, discloses a specific N-path reflection-free bandpass filter structure. The N-path bandpass filter unit is composed of multiple series-connected switching inductor subunits. The output terminal of the signal source is connected to the series terminal of the multiple series-connected switching inductor subunits, and the other series terminal of the multiple series-connected switching inductor subunits is the filter signal output terminal.

[0044] The switch-type inductor subunit consists 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] In this unit, the drain of the MOS switch in the first end-switch type inductor subunit connected to the output terminal of the signal source is connected to the output terminal 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 multiple parallel switched capacitor sub-units. The parallel terminals of the multiple parallel switched capacitor sub-units are connected to the output terminal of the signal source, and the other parallel terminal is connected to one end of the output resistor, and the other end of the output resistor is grounded.

[0047] The switched 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 terminal 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. The number of switched inductor subunits in the N-path bandpass filter unit is the same as the number of switched capacitor subunits in the N-path bandstop filter unit.

[0048] The square wave signals output by the phase-splitting clock generation circuit correspond one-to-one with the switching inductor subunit and the switching capacitor subunit, respectively. These square wave signals are used as control signals for the gates of the MOS switching transistors in the corresponding switching inductor subunit and switching capacitor subunit. Figure 9 As shown, P1, P2...PN are a group of square wave signals with different phases, and Pm and Pm+N / 2 are 180° out of phase (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 are 180° out of phase. The simulation results are compared with those of a traditional N-path filter as follows: Figure 10 As shown, the filter has an adjustable passband and stopband and can effectively reduce reflected signals.

[0049] Example 3

[0050] As shown in Figure 11 Figure 3, this example is based on Example 2 to provide a superheterodyne receiver comprising, in sequence, an antenna, a preselection filter, a low-noise amplifier, an adjustable N-path reflectionless filter, and a variable gain amplifier.

[0051] The above description is merely that of the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical range disclosed by the present application and the inventive concept thereof, can make equivalent replacements or changes within the technical range disclosed by the present application, and all of them should be encompassed within the protection scope of the present application.

Claims

1. An adjustable N-path reflectionless filter, characterized by, The adjustable N-path reflectionless filter comprises a signal source, an N-path band-pass filter unit, an N-path band-stop filter unit, an output resistor and a phase-splitting clock generating circuit. The output of the adjustable N-path reflectionless filter is the output of the N-path band-pass filter unit, and the output of the N-path band-stop filter unit is absorbed by a grounding resistor without participating in the output of the adjustable N-path reflectionless filter. The input impedance of the N-path band-pass filter unit and the N-path band-stop filter unit in parallel is conjugate matched with the source impedance in the whole frequency band. The output end of the signal source is connected with one end of the N-path band-pass filter unit and the N-path band-stop filter unit respectively, the other end of the N-path band-pass filter unit outputs a filtered signal, the other end of the N-path band-stop filter unit is connected with the output resistor, the gate of a plurality of MOS switches in the N-path band-pass filter unit and the N-path band-stop filter unit is connected with the phase-splitting clock generating circuit, and the phase-splitting clock generating circuit outputs a control signal, the phase-splitting clock generating circuit is used for outputting N-phase non-overlapping square wave signals with a duty cycle of 1 / N, and the square wave signals output by the phase-splitting clock generating circuit correspond to the MOS switch gate control signals of the inductance control subunit and the switch capacitor subunit respectively. The N-path band-pass filter unit is composed of a plurality of inductance control subunits connected in series, the output end of the signal source is connected with the series end of the plurality of inductance control subunits connected in series, and the other series end of the plurality of inductance control subunits connected in series is the filtered signal output end. The inductance control subunit is composed of a MOS switch and an inductor connected in parallel, the source of the MOS switch is connected with one end of the inductor, and the drain of the MOS switch is connected with the other end of the inductor. The drain of the MOS switch in the first end inductance control subunit connected with the output end of the signal source is connected with the output end of the signal source, and the source of the MOS switch in the first end inductance control subunit is connected with the drain of the MOS switch in the next inductance control subunit connected in series. The number of the inductance control subunits in the N-path band-pass filter unit is the same as the number of the switch capacitor subunits in the N-path band-stop filter unit. The N-path band-stop filter unit is composed of a plurality of switch capacitor subunits connected in parallel, the parallel end of the plurality of switch capacitor subunits connected in parallel is connected with the output end of the signal source, the other parallel end is connected with one end of the output resistor, and the other end of the output resistor is grounded.

2. The tunable N-path notch filter of claim 1, wherein, The switch capacitor subunit comprises a capacitor, a second MOS switch and a third MOS switch, the drain of the second MOS switch is connected with the output end of the signal source, the source of the second MOS switch is connected with one end of the capacitor, the other end of the capacitor is connected with the drain of the third MOS switch, and the source of the third MOS switch is connected with one end of the output resistor. ​ 3. The tunable N-path filter of claim 1, wherein, The phase angle between the mth phase and the m+N / 2th phase square wave signals in the N-phase square wave signal differs by 180°, and m is a positive integer less than N / 2.

4. A superheterodyne receiver characterized by The application relates to a receiver comprising an antenna, a pre-selection filter, a low-noise amplifier, an adjustable N-path reflectionless filter and a variable gain amplifier connected in sequence, wherein the adjustable N-path reflectionless filter is an adjustable N-path reflectionless filter according to any one of claims 1 to 3.

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