CN117579020A - N-path filter circuit based on LC resonant cavity - Google Patents
N-path filter circuit based on LC resonant cavity Download PDFInfo
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- CN117579020A CN117579020A CN202311438964.XA CN202311438964A CN117579020A CN 117579020 A CN117579020 A CN 117579020A CN 202311438964 A CN202311438964 A CN 202311438964A CN 117579020 A CN117579020 A CN 117579020A
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- 238000004377 microelectronic Methods 0.000 abstract description 2
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/01—Frequency selective two-port networks
- H03H7/06—Frequency selective two-port networks including resistors
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/01—Frequency selective two-port networks
- H03H7/17—Structural details of sub-circuits of frequency selective networks
- H03H7/1741—Comprising typical LC combinations, irrespective of presence and location of additional resistors
Abstract
The invention belongs to the technical field of microelectronics, and particularly relates to an N-path filter circuit based on an LC resonant cavity. The N-path filter circuit comprises a switch circuit and an LC resonant cavity; wherein, the control signals of the 4 switch circuits are four-phase signals, and the signal phase differences are sequentially as followsN-path filter based on LC resonant cavity and resonating at eigenfrequency f through LC resonant cavity LC The characteristics of the filter are that the N-path filter with high center frequency is realized by the switch circuit working at lower frequency, and the requirements of the N-path filter on the switch working frequency and the clock driving circuit are relaxed.
Description
Technical Field
The invention belongs to the technical field of microelectronics, and particularly relates to an N-path filter circuit based on an LC resonant cavity.
Background
The trend in reconfigurable radio transceiver architecture requires bandpass filters with good selectivity and flexibly tunable center frequencies, as shown in fig. 1. An off-chip solution that is available is to use a series of dedicated, bulky off-chip and non-tunable filters, such as SAW filters. Although BAW filters have been introduced as one system in packaging solutions, their center frequency is very sensitive to thickness variations of the piezoelectric material and the achievable tunability is very limited.
Due to the lack of reverse isolation, passive mixers perform impedance transformation. This characteristic of passive mixers has been used to synthesize high Q bandpass filters by converting low Q baseband impedance to radio frequency RF. The center frequency of these high Q bandpass impedances is precisely controlled by the clock frequency, which makes them very attractive for reconfigurable receivers where it is desirable to have a high Q bandpass filter that can be precisely tuned over a wide frequency range. Since these structures are implemented with only switches and capacitors, the resulting high Q filter is very linear and flicker noise is not a problem since the switches do not carry direct current.
The simplest implementation of such a filter is a 4-phase filter, which, as shown in fig. 2, consists of four baseband impedances and four switches driven by four non-overlapping 25% duty cycle clocks. The resulting on-chip 4-phase high Q bandpass filter can replace external Surface Acoustic Wave (SAW) filters in many narrowband RF applications, such as cellular. A fully integrated quad band receiver for global system for mobile communications (GSM) uses a 4 photo high Q band pass filter to handle strong out-of-band blocking. While 4-phase filters are useful in cellular receivers and other narrowband applications, they are not suitable for wideband applications such as television tuning because the blockage around all odd harmonics of the clock frequency will fold on top of the desired signal. For such applications, folding of the 3 rd and 5 th order harmonics is unacceptable and should be avoided. The M-phase high Q bandpass filter is a solution because it moves the closest folding frequency component to the (M-1) th harmonic. Such a high-Q band-pass filter was first introduced in 1960 and is called an N-path filter.
However, the clock driving circuit of the N-path filter generally operates at a frequency multiplication of the center frequency of the filter to generate a multi-phase signal through a frequency divider, which makes the high frequency application of the N-path filter limited. Therefore, it is still a great challenge to design an N-path filter with a high center frequency.
Disclosure of Invention
The invention aims to provide an N-path filter circuit based on an LC resonant cavity, which solves the problems that an N-path filter is limited by the working frequency of a switch circuit, a high-frequency clock generation circuit is difficult to realize and the N-path filter cannot be applied to the high-frequency circuit.
The N-path filter circuit based on the LC resonant cavity provided by the invention has the advantages that the center frequency is positioned at the eigenfrequency f LC Through the bidirectional characteristic of the switch, the impedance frequency presented at the input and output terminals is at f LC ±f LO Consider the frequency of interest to be f LC +f LO Thus, the circuit can realize a high-frequency filter with only a small clock signal input.
The N-path filter circuit based on the LC resonant cavity provided by the invention comprises a switch circuit 110 and an LC resonant cavity 120; wherein:
the switch circuit 110 is composed of 4 identical switches, each of which has a period of T and a frequency of f LO Is controlled by a periodic square wave signal. The duty ratio of each path of clock control signal isThe control signals of every two adjacent paths have delay +.>
The LC resonant cavity 120 is composed of a parallel resistor R, an inductance L and a capacitance C, and has an intrinsic resonant frequencyThe bandwidth is determined by the RC product.
Wherein the control signals of the 4 switches are four-phase square wave signals, and the signal phase differences are sequentially as followsThe signal is fed from the input end and is based on LC resonanceAnd the N-path filter of the vibration cavity outputs the filtered signals at the output end.
Further, the center frequency of the N-path filter is determined by the eigen-resonance frequency f of the LC cavity 120 LC And a switching input frequency f LO Is determined as f LC ±f LO 。
The switching input frequency f is different from the conventional N-path filter LO Not equal to the center frequency f of the N-path filter filter 。
The working principle of the N-path filter is described as follows:
for frequency f in For the input current signal of (a), one of the switches behaves as a mixer, whenIs opened and closed within the time period of (2)>Is turned off in the time of (2), thus by the clock frequency f LO The driven switch shifts the frequency spectrum of the input current signal, and the shifted frequency spectrum is at f in -f LO And f in +f LO . Let the resonant frequency f of the LC resonant cavity 120 LC Equal to f in -f LO The frequency converted current can thus be filtered by the LC resonator 120, and the current signal exhibits a voltage with bandpass characteristics after passing through the LC resonator impedance with bandpass characteristics. Because the switch has bidirectional characteristics, the voltage signal on the LC resonator 120 is also shifted by the switch spectrum, and the shifted spectrum is at f LC -f LO And f LO +f LO . Considering only signals at the desired frequency band, the center frequency of the filtered output signal is at f LC +f LO Where it is located. The center frequency of the final implementation of the entire N-path filter is affected by the eigenfrequency of LC cavity 120, i.e., a lower frequency switch controlled high frequency N-path filter is implemented.
Further, the switch circuit 110 may be implemented by a single-ended switch or a differential switch.
Further, the LC resonant cavity 120 may be implemented by a parallel circuit or a series circuit.
Further, LC cavity 120 may be implemented using an on-chip cavity or an off-chip cavity.
Further, the N-path filter based on the LC resonant cavity can be applied to a radio frequency front end as a pre-filter and can also be applied to a low-noise amplifier post-stage circuit.
Further, an N-path filter based on an LC resonator may be implemented by a 4-way switch and an LC resonator, or may be implemented by an 8-way switch and an LC resonator, and generally, the N-path filter is implemented by a 4-k-way switch and an LC resonator, where k is a natural number 1,2,3, ….
Further, an N-path filter based on an LC resonator may be applied to a radio frequency circuit, a millimeter wave circuit, a receiver, a transmitter, and other frequency conversion circuits, including but not limited to the listed applications, as well as other applications.
Further, an N-path filter based on an LC resonator may be implemented in a CMOS process, or may be implemented in a compound semiconductor process, such as GeSi, gaN, or the like, or may be implemented in a BiCMOS process, including but not limited to the listed processes, as well as other processes.
The invention realizes a high-frequency filter by using the LC resonant cavity and using only a clock circuit with lower frequency to control the switch, and finally realizes a high-frequency N-path filter controlled by the lower frequency switch.
Compared with the prior art, the invention has the remarkable advantages that:
the filtering module of the traditional N-path filter is only composed of a resistor R and a capacitor C which are connected in parallel, and the center frequency of the baseband module is in the vicinity of DC, so that the center frequency of the whole N-path filter is determined by the working frequency of a switch. However, the N-path filter is difficult to operate at high frequencies, limited by the difficulty of high frequency clock implementation. The N-path filter based on the LC resonant cavity is adopted by introducing the LC resonant cavity into the baseband moduleResonating the baseband module at a frequency f determined by LC L After the frequency conversion of the switch, the center frequency of the whole filter is f at the concerned frequency band LC +f LO Thus a lower frequency switching circuit controlled high frequency filter is realized.
Drawings
Fig. 1 is a radio frequency pre-selection filter in a receiver chain.
Fig. 2 is a diagram showing a conventional resistor-capacitor based N-path filter circuit structure.
Fig. 3 is a schematic diagram of an N-path filter circuit based on an LC resonator according to the present invention.
Fig. 4 is a schematic diagram of an implementation method of the present invention applied to a receiver front end.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
According to the N-path filter circuit based on the LC resonant cavity, the LC resonant cavity is introduced into the N-path filter circuit, the N-path band-pass filter with a central frequency band controlled by the LC resonant cavity and the switch circuit simultaneously is realized by utilizing the band-pass characteristic of the LC resonant cavity, the central frequency of the band-pass filter is higher than the frequency of the switch circuit, and finally the high-frequency N-path filter circuit is realized by the low-frequency switch circuit.
As shown in fig. 3, an N-path filter circuit based on an LC resonant cavity of the present invention includes a switching circuit 110 and an LC resonant cavity 120; wherein the control signals of the 4 switches are four-phase square wave signals, and the signal phase differences are sequentially as followsThe signal is fed in from the input end, filtered by the N-path filter based on the LC resonant cavity and then output from the output end. Frequency f in The signal of (2) is fed from the input terminal, the switch is equivalent to a mixer, and the frequency spectrum of the input signal is shifted. The circuit for driving the switch is composed of a clock, and the frequency spectrum shifting interval is subject to a clock frequency f LO Therefore, after the switching and mixing, the signal frequency at the end of the LC resonant cavity 120 is f in -f LO And f in +f LO . LC cavity 120 has an eigen-resonant frequency f affected by inductance L and capacitance C LC And a bandwidth affected by the resistor R and the capacitor C. The LC resonator 120 has a bandpass filter characteristic that filters signals. The filtered signal is further spectrally shifted to the input frequency by the bi-directional nature of the switch, thereby implementing a high frequency bandpass filter. The whole N-path filter circuit based on the LC resonant cavity has a center frequency f LC +f LO And f LC -f LO . The filter may implement a high frequency N-path filter using a switching circuit that operates below the center frequency of the filter, taking only the desired frequency band into account.
As can be seen from the above, the invention adopts the inductance-capacitance resonant baseband filter module to make the switching frequency of the N-path filter circuit be the difference between the center frequency of the required filter and the resonant frequency of the LC resonant cavity, so that the high-frequency N-path filter circuit can be realized by only driving the switch by a clock circuit with relatively smaller frequency. The technology relaxes the requirement of the N-path filter on the working frequency of the switching circuit and improves the center frequency of the N-path filter.
As shown in fig. 4, an embodiment of the LC resonator-based N-path filter circuit of the present invention for use as receiver front-end frequency pre-selection filtering is shown as applied in a radio frequency/millimeter wave wideband receiver. The LC-resonator-based N-path filter circuit has eight switches and resonators, the switch circuit 110 is the switch circuit 210 in fig. 4, and the circuit shifts signals in the frequency domain through the switching behavior, and has a bi-directional conduction characteristic to filter the shifted signalsAnd again shifted back to the high frequency. The LC resonant cavity 120 is the LC resonant cavity (220) in fig. 4, which is composed of an inductance L, a capacitance C and a resistance R, and has an intrinsic resonant frequency f LC And the bandwidth affected by resistor R and capacitor C, the bandpass characteristics of LC cavity 220 may filter the mixed signal to achieve channel selection. The signal input circuit 230 characterizes the antenna of the receiver front-end circuit and the receiver signal from the antenna, wherein the resistor Rs is equivalent to the characteristic impedance of the antenna and the voltage source Vin is equivalent to the received signal. The bi-directional nature of the switch shifts the impedance of the LC cavity 220, seen from the signal input, spectrally to a frequency f LC +f LO The bandwidth is determined by R, C and the number of paths of the filter. By impedance matching, the input signal is centered at f LC +f LO The band-pass impedance filtering at the position realizes the function of frequency pre-selection filtering, and the whole N-path filter can realize a filter with higher center frequency through a switching circuit with lower frequency.
According to the N-path filter circuit based on the LC resonant cavity, the resonant cavity with inductance and capacitance resonance is adopted, frequency mixing is realized through the switching circuit, the impedance spectrum of the LC resonant cavity with band-pass characteristics is moved to a high frequency, and then the N-path filter with band-pass filter characteristics is realized.
The whole N-path filter circuit based on the LC resonant cavity, which is applied to the pre-selection filtering of the frequency at the front end of the receiver, has the working flow as follows:
as shown in fig. 4, the antenna receives a signal from the space, which is equivalent to the power supply voltage Vin in the signal input circuit, and the antenna having equivalent characteristic impedance Rs is a resistor Rs. The signal is directly connected to an 8-route 8-phase clock driven switching circuit, and the working frequency of each switch is the same as f LO The period is T, the phase difference isThe 8-phase clock signal is 8 non-overlapped square waves, and the duty ratio is +.>Thus at each instant only one switch is open and the remaining switches are off. Firstly considering the working state of one path, the on-off signal is frequency spectrum shifted in frequency because the switch has the function of mixing, the switch firstly up-down converts the received radio frequency signal, and the frequency interval is the working frequency f of the switch circuit LO Only the high frequency band of interest is considered, where the input signal is down-converted onto the LC resonator. The LC resonant cavity has f LC The frequency is determined by the inductance L and the capacitance C, and the bandwidth is affected by the resistance R and the capacitance C. The LC resonant cavity filters the down-converted input signal, and an output signal is generated at the same end after the down-converted input signal is filtered by the LC resonant cavity, and the input down-converted signal is up-converted due to the bidirectional characteristic of the switch, so that the filtering of the input signal is finally realized. The center frequency of the whole filter implementation is f LC +f Lo The center frequency is determined by the working frequency of the switching circuit and the local oscillation resonant frequency of the LC resonant cavity, and after the frequency of the LC resonant cavity is fixed, the working frequency of the switching circuit can regulate the center frequency of the whole N-path filter, so that the configurable band-pass filtering function of an input signal is realized.
In summary, the invention provides an N-path filter circuit based on an LC resonant cavity, which changes the center frequency of baseband filtering by introducing the LC resonant cavity into the N-path filter, and uses a switching circuit working at a lower frequency to realize a high-frequency N-path filter, thereby relaxing the requirements on the switching frequency and clock driving circuit and expanding the frequency coverage range of the N-path filter.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered by the scope of the claims of the present invention.
Claims (3)
1. An N-path filter circuit based on an LC resonant cavity is characterized by comprising a switching circuit (110) and the LC resonant cavity (120); wherein:
the switching circuit (110) is composed of 4k identical switches, each of which has a period of T and a frequency of f LO Is controlled by a periodic square wave signal; the duty ratio of each path of clock control signal isThe control signals of every two adjacent paths have delay +.>
The LC resonant cavity (120) is composed of a parallel resistor R, an inductor L and a capacitor C, namely an inductance-capacitance parallel resonant cavity; the resonant cavity has an intrinsic resonant frequencyThe bandwidth is determined by the RC product;
wherein the control signals of the 4 switches are four-phase square wave signals, and the signal phase differences are sequentially as followsThe signal is fed in from an input end, is output at an output end after being filtered by an N-path filter based on an LC resonant cavity, and k is a natural number of 1, 2.
2. The N-path filter circuit according to claim 1, wherein the center frequency of the filter is defined by the eigen-resonance frequency f of the LC cavity (120) LC And a switching input frequency f LO Is determined as f LC ±f LO 。
3. An N-path filter circuit according to claim 1 or 2, characterized in that the operation is as follows:
for frequency f in One of the switches is represented as a mixer, in whichIs opened and closed within the time period of (2)>Is turned off by the clock frequency f LO The driven switch shifts the frequency spectrum of the input current signal, and the shifted frequency spectrum is at f in -f LO And f in +f LO The method comprises the steps of carrying out a first treatment on the surface of the Let the resonant frequency f of the LC resonant cavity (120) LC Equal to f in -f LO The frequency converted current can be filtered by an LC resonant cavity (120), and the current signal shows voltage with bandpass characteristic after passing through the impedance of the LC resonant cavity with bandpass characteristic; because the switch has bidirectional characteristics, the voltage signal on the LC resonant cavity (120) is also shifted by the switch frequency spectrum, and the shifted frequency spectrum is positioned at f LC -f LO And f LO +f LO The method comprises the steps of carrying out a first treatment on the surface of the Considering only signals at the desired frequency band, the center frequency of the filtered output signal is at f LC +f LO A place; the center frequency of the whole N-path filter is finally influenced by the eigenfrequency of the LC resonant cavity (120), namely a high-frequency N-path filter controlled by a lower-frequency switch is realized.
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| CN202311438964.XA CN117579020A (en) | 2023-10-31 | 2023-10-31 | N-path filter circuit based on LC resonant cavity |
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| CN202311438964.XA CN117579020A (en) | 2023-10-31 | 2023-10-31 | N-path filter circuit based on LC resonant cavity |
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