Bandwidth and frequency band can be adjusted simultaneously differential band-pass filter

Abstract

This invention addresses the problem of effectively filtering multi-band and multi-bandwidth spectral signals by proposing a differential bandpass filter with simultaneously adjustable bandwidth and frequency band, featuring reconfigurable center frequency and bandwidth. The differential bandpass filter structure has two main parts: a resonant inverter and a parallel resonator. The programmability and reconfigurability of the differential bandpass filter are achieved by adjusting the resonant characteristics of the even / odd mode sub-circuit network of the resonant inverter. The bandwidth can be adjusted when the relative relationship between these resonators and the transmission zeros of the parallel resonator changes; when all resonant points shift while maintaining their spectral bandwidth, the center frequency is tuned to a constant absolute bandwidth. Therefore, the center frequency and bandwidth of the differential bandpass filter can be arbitrarily reconfigured and programmed within their maximum range of variation.

Description

Technical Field

[0001] This invention belongs to the field of filter circuit design, specifically relating to a differential bandpass filter whose bandwidth and frequency band can be adjusted simultaneously. Background Technology

[0002] Reconfigurable bandpass filters have been studied for decades, resulting in numerous design techniques and circuits. Much of this work aims to achieve a tunable operating frequency with controllable coupling coefficients or to maintain a constant bandwidth. Another approach is to use switched filter banks as the preferred discrete-selectable filter response. However, both design methods face challenges and limitations in highly generalized RF front-end systems (software-defined radio systems). Traditional reconfigurable filters treat resonance and coupling as two separate tuning variables, tuning each separately to achieve reconfigurability. In practical multi-mode filtering implementations in software-defined radio systems, it is necessary to simultaneously implement and control both resonant tuning and coupling tuning modes. Traditional filter combination design methods encounter limitations in bandwidth selection flexibility and relatively large circuit dimensions.

[0003] Existing variable frequency filters can be implemented in the following ways: PIN diode switching filter bank, PIN diode controlling capacitor bank, YIG magnetic tuning filter, MEMS, varactor diode, etc. Filter banks consist of filters with fixed frequencies and variable frequency points. They offer excellent filtering performance but are complex in structure and large in size. The more variable frequency points a filter has, the larger its size and the higher its cost. Furthermore, the switching speed of the PIN diode determines the speed of the variable frequency filter. PIN diodes achieve frequency switching by controlling a fixed capacitor. They are smaller than filter banks, but like filter banks, the more variable frequency points a filter has, the larger its size and the higher its cost. The switching speed of the PIN diode also determines the speed of the variable frequency filter. YIG magnetically tuned filters have the advantage of variable frequency points in a frequency range exceeding octave bands, but their variable frequency rate is affected by hysteresis and is difficult to improve, significantly impacting the performance of the variable frequency filter. MEMS filters offer advantages such as simple structure, small size, and high precision, but the capacitance value of MEMS cannot be changed significantly, greatly affecting the variable frequency range of the filter. Varactor diode-based variable frequency filters have continuously adjustable center frequencies, are simple to design, low in cost, small in size, and have a fast variable frequency speed. Therefore, varactor diode-based variable frequency filters are widely used in variable frequency transceivers.

[0004] Coupled resonator filters are a common design for narrowband bandpass filters (i.e., filters with high Q values). Their circuitry includes series or parallel resonant circuits coupled together by capacitors or inductors. In this design, varactor diodes are typically used to change the capacitance value of the circuit, thereby altering the resonant frequency. Figure 1 This is a schematic diagram of this type of filter. The N-order resonator coupled bandpass filter consists of N resonators and N-1 coupling elements K.

[0005] like Figure 1 As shown, current technology still has the following major shortcomings: it cannot simultaneously achieve arbitrary reprogramming of bandwidth and frequency band within their maximum variation range. Existing filters can only perform sliding filtering for simple frequency selectivity, and cannot simultaneously achieve flexible bandwidth selection filtering for wide-band spectrum signals, nor can they effectively select filters for multi-band and multi-band spectrum signals. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention proposes a programmable differential bandpass filter with transmission zero characteristics, featuring reconfigurable center frequency and bandwidth. The differential bandpass filter structure has two main parts: a differential resonant inverter and a differential parallel resonator. The programmability or reconfigurability of the programmable differential bandpass filter is achieved by adaptively changing the resonant points of the even-odd mode sub-circuit network of the resonant inverter. The bandwidth can be adjusted when the relative resonant points across the transmission zeros of the resonator and one of the parallel resonators change; when all resonators change their resonant points while maintaining their spectral independence, the center frequency can be adjusted to a constant absolute bandwidth. Thus, the center frequency and bandwidth of the bandpass filter can be arbitrarily reconfigured within their maximum possible range of variation. Specifically:

[0007] The reconfigurable differential bandpass filter proposed in this invention allows for arbitrary reconfiguration and modification of both bandwidth and frequency band within their maximum range of variation. The differential bandpass filter structure consists of two main parts: a differential resonant inverter and a differential parallel resonator. The programmability and reconfigurability of the differential bandpass filter are achieved by adjusting the resonant characteristics of the even / odd mode sub-circuit network of the resonant inverter. When all resonant points are simultaneously shifted while maintaining their spectral bandwidth, the center frequency is tuned to a constant absolute bandwidth.

[0008] The differential bandpass filter of this invention specifically consists of two differential resonant inverters and one differential parallel resonator, with the differential parallel resonator located between the two differential resonant inverters. Each differential resonant inverter includes four inductors, two capacitors, and four adjustable capacitors. The differential signal has a dual-path transmission structure. The positive input stage of the signal is connected to one end of the first inductor, the other end of the first inductor is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the second inductor, and the other end of the second inductor is connected to the positive output stage. A first adjustable capacitor is connected in parallel between the first inductor and the first capacitor, and a third adjustable capacitor is connected in parallel between the first capacitor and the second inductor. The inverting input stage of the signal is connected to one end of the third inductor, the other end of the third inductor is connected to one end of the second capacitor, and the other end of the second capacitor is connected to the fourth adjustable capacitor. One end of the inductor is connected, and the other end of the fourth inductor is connected to the inverting output stage; a first adjustable capacitor is connected in parallel between the first inductor and the first capacitor, a third adjustable capacitor is connected in parallel between the first capacitor and the second inductor, a second adjustable capacitor is connected in parallel between the third inductor and the second capacitor, and a fourth adjustable capacitor is connected in parallel between the second capacitor and the fourth inductor; the first and second adjustable capacitors are connected in series, and the third and fourth adjustable capacitors are connected in series; the differential parallel resonator includes 4 inductors and 2 adjustable capacitors. The forward and inverting input stages are connected to the output stage, and two branches are connected in parallel between them. The first parallel branch is formed by connecting the fifth inductor and the fifth adjustable capacitor in series, and then connecting them in series with the sixth inductor; the second parallel branch is formed by connecting the seventh inductor and the sixth adjustable capacitor in series, and then connecting them in series with the eighth inductor.

[0009] Furthermore, when the relative relationship between the capacitor of the differential resonator inverter and the transmission zero of the differential parallel resonator changes, the bandwidth can be adjusted; the capacitor value is adjusted by changing the voltage applied to the capacitor, which in turn changes the capacitor value accordingly.

[0010] Furthermore, when the tuning current of the differential resonator inverter and the differential parallel resonator shifts while maintaining the spectral bandwidth, the center frequency is tuned to a constant absolute bandwidth during the resonant point adjustment. The capacitance value is adjusted by changing the voltage applied to the capacitor, which in turn changes the capacitance value accordingly.

[0011] The beneficial effects of this invention are as follows:

[0012] To address the problem of effectively filtering multi-band and multi-bandwidth spectral signals, a differential bandpass filter is proposed that allows for simultaneous reconstruction of the center frequency and bandwidth, thus expanding the adaptability and versatility of software-defined radio systems for various signals. This invention is highly versatile, has low implementation costs, and enjoys wide applicability. Attached Figure Description

[0013] Figure 1The diagram shows the structure of an existing third-order resonator-coupled variable bandpass filter and S21.

[0014] Figure 2 This is a schematic diagram illustrating the innovative principle of the present invention.

[0015] Figure 3(a) is a diagram of the bandpass filter of the present invention.

[0016] Figure 3(b) is the equivalent circuit diagram of the differential resonant inverter.

[0017] Figure 3(c) is the equivalent circuit diagram of the differential parallel resonator. Detailed Implementation

[0018] To better understand the above-mentioned objectives, features, and advantages of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this application can be combined with each other.

[0019] The programmable differential bandpass filter proposed in this invention includes two flexible programmable functions: a reconfigurable center frequency and a sharp suppression filtering response with bandwidth. For example... Figure 2 As shown, it can be applied in general-purpose RF front-end systems (software-defined radio) as a flexible RF signal preselection block.

[0020] I. Bandwidth Reconfiguration

[0021] The bandwidth reconfiguration depends on the relative positions of the different poles of the bandpass filter resonance. This needs to be discussed under different conditions, such as internal and external even / odd mode resonant inverter sub-circuit network resonances, and the same for parallel-branch resonances (i.e., overall transmission zeros). In all three cases, parallel-branch resonances produce two transmission zeros, define the passband of the inter-band poles, and improve the out-of-band rejection of the bandpass filter. The remaining bandpass filter poles are generated by the resonant inverter.

[0022] When the resonance of the even / odd-mode resonant inverter subcircuit network exceeds the bandwidth defined by the parallel branch, a total of three reflection zeros are generated across the entire bandwidth. Although the resonant inverter alone exhibits a second-order Chebyshev filter response, its resonance is partially suppressed on the real frequency axis. In this case, the resonant inverter contributes only one reflection zero to the entire bandwidth, while simultaneously providing coupling to the parallel resonant branch. This differs from traditional reconfigurable filter designs, which explicitly allocate separate resonances and couplings. The proposed resonant inverter integrates these two characteristics into a single circuit network, thus avoiding separate tuning of resonance and coupling to control the center frequency and bandwidth. It is also important to note that as the bandwidth of the even / odd-mode resonant inverter subcircuit network's resonant frequency increases, the bandwidth of the bandpass filter also increases.

[0023] For wider bandwidths, the resonance of the even / odd mode resonant inverter sub-circuit network and the resonance of the parallel branch (i.e., the transmission zero position) are equal. On the other hand, by appropriately allocating these two types of resonators, a variable intermediate bandwidth can be generated.

[0024] For wideband (or even ultra-wideband) applications, the resonance of the even / odd mode resonant inverter sub-circuit network can exceed the tuning boundary of the parallel branch resonance (i.e., the transmission zero of the bandpass filter). In this case, there can be multiple reflection zeros (up to 5) across the entire passband, with a relative tuning ratio as high as 12:1.

[0025] II. Center Frequency Reconstruction

[0026] The center frequency reconstruction with constant absolute bandwidth utilizes the synchronous movement of all resonators to different resonant points while maintaining their relative bandwidth spacing. The process is the same as above.

[0027] Figures 3(a)-(c) show the filter circuit structure and the circuit schematics of the two resonator components, respectively. The differential resonant inverter [JR] itself has a Chebyshev filter response, which can provide tunable coupling and adaptive reflection zeros or poles in reconfigurable bandpass filter designs. The differential parallel resonator consists of two branches, each of which generates a transmission zero tunable resonator to increase selectivity. In addition, an additional pole is generated between the two transmission zero branches. The programmable differential bandpass filter then controls the resonant poles in these two types of resonant modules, namely the resonant points of one of the even / odd mode resonant inverter sub-circuit structures [JR] and the two parallel branch circuit structures.

[0028] The differential bandpass filter of this invention simultaneously changes the reconfigurable center frequency and bandwidth between narrowband and ultra-wideband states. Therefore, it can be used for the filtering requirements of highly flexible RF front-end systems. Bandwidth control is achieved by reallocating the resonators and their relative pole positions; constant absolute bandwidth center frequency tuning is achieved by moving the variable resonant zero position and making relatively independent adjustments to the resonators.

[0029] This invention is not limited to the specific embodiments described above, and various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made to the above embodiments based on the technical essence of this invention should be included within the scope of protection of this invention.

Claims

1. A differential bandpass filter with simultaneously adjustable bandwidth and frequency band, characterized in that: It consists of two differential resonant inverters and one differential parallel resonator. The two differential resonant inverters are connected in series, and the differential parallel resonator is connected in parallel between them. The differential resonant inverter includes a first inductor, a second inductor, a third inductor, a fourth inductor, a first capacitor, a second capacitor, a first adjustable capacitor, a second adjustable capacitor, a third adjustable capacitor, and a fourth adjustable capacitor. The differential signal has a dual-path transmission structure. The positive input stage of the signal is connected to one end of the first inductor, the other end of the first inductor is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the second inductor, and the other end of the second inductor is connected to the positive output stage. The first adjustable capacitor is connected in parallel between the first inductor and the first capacitor, and the third adjustable capacitor is connected in parallel between the first capacitor and the second inductor. The inverting input stage of the signal is connected to one end of the third inductor. The third inductor's other end is connected to one end of the second capacitor, the second capacitor's other end is connected to one end of the fourth inductor, and the fourth inductor's other end is connected to the inverting output stage. A second adjustable capacitor is connected in parallel between the third inductor and the second capacitor, and a fourth adjustable capacitor is connected in parallel between the second capacitor and the fourth inductor. The first and second adjustable capacitors are connected in series, and the third and fourth adjustable capacitors are connected in series. The differential parallel resonator includes a fifth inductor, a sixth inductor, a seventh inductor, an eighth inductor, a fifth adjustable capacitor, and a sixth adjustable capacitor. The forward and inverting input stages are connected to the output stage, with two branches connected in parallel between them. The first parallel branch is formed by connecting the fifth inductor and the fifth adjustable capacitor in series, and then connecting them in series with the sixth inductor. The second parallel branch is formed by connecting the seventh inductor and the sixth adjustable capacitor in series, and then connecting them in series with the eighth inductor.

2. The differential bandpass filter with simultaneously adjustable bandwidth and frequency band as described in claim 1, characterized in that: When the relative relationship between the transmission zeros of the differential resonant inverter capacitor and the differential parallel resonator capacitor changes, the bandwidth can be adjusted; the capacitance value is tuned by changing the voltage applied to the capacitor, which in turn changes the capacitance value accordingly.

3. The differential bandpass filter with simultaneously adjustable bandwidth and frequency band as described in claim 1, characterized in that: When the tuning points of the differential resonant inverter and the differential parallel resonator shift while maintaining the spectral bandwidth, the center frequency is tuned to a constant absolute bandwidth during the resonant point adjustment. The capacitance value is tuned by changing the voltage applied to the capacitor, which in turn changes the capacitance value.

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