IPD high-selectivity band-pass filter based on weak coupling transformer technology

Abstract

An IPD high-selectivity band-pass filter based on a weak coupling transformer technology comprises an LC parallel resonance circuit, an LC series resonance circuit, an LC parallel resonance circuit and a fourth capacitor C4, and inductors in the LC parallel resonance circuit and inductors in the LC parallel resonance circuit have a weak transformer coupling relation; the coupling coefficient required by the weak coupling transformer provided by the invention is very small and can be realized in a mode of adjacently placing metals on the same layer, so that the structural complexity of the filter is effectively reduced; the band-pass filter is based on an IPD technology, an extra decoupling equivalent inductor is introduced through a weak transformer coupling technology, the extra decoupling equivalent inductor and a parallel capacitor which is connected between the input end and the output end of the filter in a bridging mode form a new resonance path, and a transmission zero point is introduced into an upper stop band and a lower stop band of the filter respectively to improve the selectivity of the filter. According to the invention, the selectivity of the filter can be effectively improved on the premise of not additionally introducing an inductance element and not increasing the order of the filter.

Description

Technical Field

[0001] This invention belongs to the field of filter circuit technology, specifically relating to an IPD high-selectivity bandpass filter based on weakly coupled transformer technology. Background Technology

[0002] With the development of fifth-generation communication technology (5G), radio frequency (RF) front-end systems are placing higher demands on filter performance. Currently commercially available 5G frequency bands in China, such as n77 (3.3GHz-4.2GHz) and n79 (4.2GHz-5.0GHz), are characterized by high frequency and large bandwidth. However, these bands also experience significant interference from adjacent frequency bands. Therefore, to ensure signal quality, filters must be able to achieve highly selective signal transmission across a wide bandwidth. Furthermore, 5G communication typically employs more transceiver components to guarantee communication quality and speed, placing extremely high demands on the integration of RF front-end modules in 5G base stations and terminal equipment.

[0003] Traditional filter technologies such as surface acoustic wave (SAW) and bulk acoustic wave (BAW) suffer from frequency limitations (typically below 3GHz) due to high-frequency performance degradation, making them unsuitable for 5G high-frequency applications. While low-temperature co-fired ceramic (LTCC) technology can achieve multi-layer structures, its complex manufacturing process and limitations in miniaturization hinder integration with RF chips. Against this backdrop, integrated passive device (IPD) technology, with its advantages of high precision, small size, and low cost, has become a popular solution for 5G filter design.

[0004] In traditional IPD filter design, the filter schematic, consisting of multiple LC elements, is typically obtained using filter synthesis based on the selected attenuation function type. However, to achieve highly selective filters within the wide bandwidth required for 5G communication, it is often necessary to increase the filter order and add more LC resonant circuits to improve the filter's bandwidth and selectivity. This results in filters with complex topologies and larger sizes, making miniaturization and low cost difficult.

[0005] The patent application with publication number CN104682910A uses a multi-stage inductor interleaved coupling structure to introduce a controllable transmission zero to improve the selectivity of the filter and reduce the filter area. However, this technology requires a large coupling coefficient to achieve the transmission zero. Therefore, a complex overlapping trace inductor coupling structure is required to improve the coupling coefficient between inductors. This places high demands on the process precision. At the same time, the trace method of multiple layer changes will introduce a large number of vias, which will increase a large number of parasitic capacitances and parasitic resistances, resulting in an increase in the passband insertion loss of the overall filter. Summary of the Invention

[0006] To overcome the problems of the prior art, the present invention aims to use weakly coupled transformer technology. The equivalent inductance and the introduced capacitance introduced by the weak transformer coupling between the primary and secondary coils form an additional LC resonant path. A transmission zero is introduced in the upper and lower stopbands of the filter, respectively. Thus, a miniaturized IPD high-selectivity bandpass filter can be achieved with lower manufacturing difficulty without increasing the filter order or adding additional inductors.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A high-selectivity bandpass filter based on weakly coupled transformer technology includes: an LC series resonant circuit 2, the first end of which is connected to the input terminal IN of the filter and the first end of an LC parallel resonant circuit 1, and the second end of the LC parallel resonant circuit 1 is grounded; the second end of the LC series resonant circuit 2 is connected to the output terminal OUT of the filter and the first end of an LC parallel resonant circuit 3, and the second end of the LC parallel resonant circuit 3 is grounded; a fourth capacitor C4 is also connected between the first end and the second end of the LC series resonant circuit 2.

[0009] The LC parallel resonant circuit 1 includes a first inductor L1 and a first capacitor C1, which are connected in parallel. The first terminals of the first inductor L1 and the first capacitor C1 are connected to the input terminal IN of the filter, and the second terminals of the first inductor L1 and the first capacitor C1 are grounded.

[0010] The LC series resonant circuit 2 includes a second capacitor C2 and a second inductor L2 connected in series. The first end of the second capacitor C2 is connected to the input terminal IN of the filter, the second end of the second capacitor C2 is connected to the first end of the second inductor L2, and the second end of the second inductor L2 is connected to the output terminal OUT of the filter.

[0011] The LC parallel resonant circuit 3 includes a third inductor L3 and a third capacitor C3, which are connected in parallel. The first end of the third inductor L3 and the third capacitor C3 is connected to the output terminal OUT of the filter, and the second end of the third inductor L3 and the third capacitor C3 is grounded.

[0012] The first inductor L1 in the LC parallel resonant circuit 1 and the third inductor L3 in the LC parallel resonant circuit 3 have a transformer coupling relationship with a coupling coefficient of k.

[0013] The transformer coupling relationship between the first inductor L1 and the third inductor L3 can be equivalent to a π-type decoupling equivalent circuit. The π-type decoupling equivalent circuit includes a fourth inductor L4, a fifth inductor L5, and a sixth inductor L6. The first terminal of the fourth inductor L4 is connected to the input terminal of the filter, and the second terminal of the fourth inductor L4 is grounded. The first terminal of the fifth inductor L5 is connected to the output terminal of the filter, and the second terminal of the fifth inductor L5 is grounded. The first terminal of the sixth inductor L6 is connected to the input terminal of the filter, and the second terminal of the sixth inductor L6 is connected to the output terminal of the filter.

[0014] The sixth inductor L6 and the fourth capacitor C4 in the π-type decoupling equivalent circuit are connected in parallel to form an LC parallel resonant circuit 4.

[0015] When the inductance values ​​of the first inductor L1 and the third inductor L3 are both l, the inductance value of the fourth inductor L4 is l×(1-k), the inductance value of the fifth inductor L5 is l×(1-k), and the inductance value of the sixth inductor L6 is l×k. By adjusting the inductance values ​​of the first inductor L1 and the third inductor L3, as well as the coupling coefficient k, the passband frequency of the filter is kept stable. At the same time, the position of the transmission zero point is adjusted so that the transmission zero point falls within the upper stopband and lower stopband of the filter, respectively.

[0016] The first inductor L1, the second inductor L2, and the third inductor L3 are planar spiral inductors made of single or multiple layers of metal, and their shapes can be circular, square, or octagonal.

[0017] The first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are MIM parallel plate capacitors or MOM dielectric capacitors.

[0018] Compared with existing technologies, the advantages of this invention are as follows:

[0019] 1. The IPD high-selectivity bandpass filter of the present invention, based on the third-order Chebyshev filter composed of LC parallel resonant circuit 1, LC series resonant circuit 2 and LC parallel resonant circuit 3, introduces an adjustable transmission zero in the upper stopband and lower stopband of the filter. Compared with the traditional third-order Chebyshev bandpass filter, the present invention significantly improves the transition band steepness and stopband attenuation performance of the filter without increasing the overall circuit area, and realizes a high-selectivity IPD high-selectivity bandpass filter circuit without increasing the filter order.

[0020] 2. The transformer coupling technology introduced in this invention does not require a high coupling coefficient. Compared with designs that require overlapping inductors to achieve a high coupling coefficient, the inductors in this invention can use the same layer of metal, and the required coupling coefficient can be achieved by narrow-edge coupling achieved by adjacent placement. Therefore, this invention has the characteristics of simple structure and low process complexity. At the same time, due to the significant reduction in the use of through holes, this invention has a lower insertion loss.

[0021] In summary, this invention utilizes the synergistic effect of the equivalent inductance introduced by weak transformer coupling and the added parallel capacitor to generate an adjustable transmission zero in both the upper and lower stopbands of a traditional third-order Chebyshev bandpass filter. This significantly improves the transition band steepness and out-of-band attenuation performance while maintaining the circuit area and order unchanged. By employing a same-layer adjacent metal coupling structure to replace the overlapping design used in traditional inductive coupling, the required weak coupling coefficient is achieved through a proximity layout. This significantly reduces structural complexity, decreases the number of vias, and significantly optimizes insertion loss. It combines high-frequency performance with process advantages, providing a compact, highly selective bandpass filter solution for highly integrated RF front-ends. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the lumped circuit of an IPD high-selectivity bandpass filter applied to the n77 frequency band, provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the decoupling π-type equivalent circuit of the weak transformer coupling part of the IPD high-selectivity bandpass filter applied to the n77 frequency band provided in the embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the overall decoupling equivalent circuit of the IPD high-selectivity bandpass filter applied to the n77 frequency band provided in the embodiment of the present invention.

[0025] Figure 4 This is a layout implementation of an IPD high-selectivity bandpass filter applied to the n77 frequency band provided in this embodiment of the invention.

[0026] Figure 5 These are simulation results of S11 and S21 of the IPD high-selectivity bandpass filter applied to the n77 frequency band provided in the embodiments of the present invention.

[0027] Figure 6 These are the S11 and S21 electromagnetic simulation results of the IPD high-selectivity bandpass filter layout applied to the n77 frequency band provided in the embodiments of the present invention.

[0028] Wherein, C1 is the first capacitor, C2 is the second capacitor, C3 is the third capacitor, C4 is the fourth capacitor, L1 is the first inductor, L2 is the second inductor, L3 is the third inductor, L4 is the fourth inductor obtained by transformer decoupling, L5 is the fifth inductor obtained by transformer decoupling, L6 is the sixth inductor obtained by transformer decoupling, k is the transformer coupling coefficient, IN is the input port of the filter, OUT is the output port of the filter, and GND is the ground port of the filter. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0030] See Figure 1 , Figure 1 This is a structural diagram of the IPD high-selectivity bandpass filter applied to the n77 frequency band provided by the present invention, including: an LC series resonant circuit 2, the first end of which is connected to the input terminal IN of the filter and the first end of an LC parallel resonant circuit 1, and the second end of the LC parallel resonant circuit 1 is grounded; the second end of the LC series resonant circuit 2 is connected to the output terminal OUT of the filter and the first end of an LC parallel resonant circuit 3, and the second end of the LC parallel resonant circuit 3 is grounded; a fourth capacitor C4 is also connected between the first end and the second end of the LC series resonant circuit 2.

[0031] The LC parallel resonant circuit 1 includes a first inductor L1 and a first capacitor C1, which are connected in parallel. The first terminals of the first inductor L1 and the first capacitor C1 are connected to the input terminal IN of the filter, and the second terminals of the first inductor L1 and the first capacitor C1 are grounded.

[0032] The LC series resonant circuit 2 includes a second capacitor C2 and a second inductor L2 connected in series. The first end of the second capacitor C2 is connected to the input terminal IN of the filter, the second end of the second capacitor C2 is connected to the first end of the second inductor L2, and the second end of the second inductor L2 is connected to the output terminal OUT of the filter.

[0033] The LC parallel resonant circuit 3 includes a third inductor L3 and a third capacitor C3, which are connected in parallel. The first end of the third inductor L3 and the third capacitor C3 is connected to the output terminal OUT of the filter, and the second end of the third inductor L3 and the third capacitor C3 is grounded.

[0034] There is a transformer coupling relationship between the first inductor L1 in the LC parallel resonant circuit 1 and the third inductor L3 in the LC parallel resonant circuit 3. The coupling coefficient of this transformer coupling relationship is low. Such a low coupling coefficient can be achieved by placing the metals of the same layer adjacent to each other.

[0035] The integrated passive device IPD bandpass filter uses a high-resistivity silicon substrate.

[0036] The first inductor L1, the second inductor L2, and the third inductor L3 are planar spiral inductors made of single or multiple layers of metal, and their shapes can be circular, square, or octagonal.

[0037] The first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are MIM parallel plate capacitors or MOM dielectric capacitors.

[0038] Specifically, the LC parallel resonant circuit 1, the LC series resonant circuit 2, and the LC parallel resonant circuit 3 together constitute a traditional third-order Chebyshev bandpass filter topology through the aforementioned connection relationship. The three resonators interact to generate three transmission poles in the passband. These three poles together determine the passband frequency (3.3GHz to 4.2GHz) of the IPD high-selectivity bandpass filter applied to the n77 frequency band described in this invention.

[0039] The first inductor L1 in the LC parallel resonant circuit 1 and the third inductor L3 in the LC parallel resonant circuit 3 are connected by adjacent placement of metal in the same layer to achieve a weak transformer coupling relationship. The first inductor L1 and the third inductor L3 have an adjustable coupling coefficient k.

[0040] Specifically, please see Figure 2 The weak transformer coupling structure formed by the first inductor L1 and the third inductor L3 can be equivalent to a π-type decoupling equivalent circuit.

[0041] Specifically, please see Figure 2 , Figure 3 The π-type decoupling equivalent circuit includes a fourth inductor L4, a fifth inductor L5, and a sixth inductor L6. One end of the fourth inductor L4 is connected to the input terminal of the filter, and the other end is connected to the ground terminal of the filter. One end of the fifth inductor L5 is connected to the output terminal, and the other end is connected to the ground terminal of the filter. One end of the sixth inductor L6 is connected to the input terminal of the filter, and the other end is connected to the output terminal of the filter.

[0042] It should be noted that in the IPD high-selectivity bandpass filter for the n77 frequency band provided by this invention, the inductance values ​​of the first inductor L1 and the third inductor L3 are both 1. Therefore, the relationship between the inductance values ​​of the fourth inductor L4, the fifth inductor L5, and the sixth inductor L6 in the π-type decoupling equivalent circuit and the first inductor L1, the third inductor L3, and the transformer coupling coefficient is as follows:

[0043] L1 = L2 = l

[0044] L4 = L5 = (1 + k)·l

[0045]

[0046] It should be noted that the first inductor L1 and the third inductor L3 in the IPD high-selectivity bandpass filter applied to the n77 frequency band have a weak transformer coupling relationship, therefore the coupling coefficient k is relatively small. The value of k used in this embodiment is:

[0047] k = 0.2

[0048] By appropriately optimizing the first inductor L1, the third inductor L3, the first capacitor C1, the second capacitor C2, and the coupling coefficient k between the first inductor L1 and the third inductor L3, the pole positions of the IPD high-selectivity bandpass filter applied to the n77 frequency band can be kept unchanged, thereby ensuring that the passband frequency of the IPD high-selectivity bandpass filter applied to the n77 frequency band remains unchanged, still between 3.3 GHz and 4.2 GHz.

[0049] Please continue reading Figure 3 In the π-type decoupling equivalent circuit, the sixth inductor L6 and the fourth capacitor C4 are connected in parallel to form an LC parallel resonant circuit 4. The formed LC parallel resonant circuit 4 is connected in parallel with the LC series resonant circuit 3, and together they are connected across the input and output terminals of the filter.

[0050] The series resonant frequency of the LC series resonant circuit 3 is:

[0051]

[0052] The parallel resonant frequency of the LC parallel resonant circuit 4 is:

[0053]

[0054] The passband center frequency of the IPD high-selectivity bandpass filter applied to the n77 frequency band is:

[0055] f0 = 3.75GHz

[0056] Specifically, when the frequency f < min(f3,f0,f4), the LC series resonant circuit 3 exhibits capacitive characteristics, and the LC parallel resonant circuit 4 exhibits inductive characteristics. This results in a parallel LC notch filter structure being formed when f < min(f3,f0,f4), creating a transmission zero at the low-frequency end. When f > max(f3,f0,f4), the LC series resonant circuit 3 exhibits inductive characteristics, and the LC parallel resonant circuit 4 exhibits capacitive characteristics. This again results in a parallel LC notch filter structure being formed when f > max(f3,f0,f4), creating a transmission zero at the high-frequency end.

[0057] It is important to note that the transmission zeros at the high and low frequencies are related to the inductance values ​​of the first inductor L1 and the third inductor L3, the capacitance value of the fourth capacitor C4, and the coupling coefficient k between the first inductor L1 and the third inductor L3. By appropriately adjusting these parameters, the transmission zeros at the high and low frequencies can be controlled to fall within the upper and lower stopbands of the filter, respectively.

[0058] In this example, based on the third-order Chebyshev filter composed of LC parallel resonant circuit 1, LC series resonant circuit 2, and LC parallel resonant circuit 3, an adjustable zero is introduced in both the upper and lower stopbands of the filter, which improves the transition band roll-off coefficient and out-of-band attenuation performance of the filter, and effectively enhances the selectivity of the filter.

[0059] Further, see Figure 4 This paper presents a layout implementation method according to an embodiment of the present invention. The layout is implemented based on an IPD process using a high-resistivity silicon substrate. The first inductor L1 and the third inductor L3 are both planar spiral inductors made of top-layer thick metal. The first capacitor C1, the second capacitor C2, the third capacitor C3 and the fourth capacitor C4 are all MIM planar capacitors composed of multilayer metal to achieve high Q value capacitors.

[0060] Furthermore, this embodiment fully utilizes the advantages of IPD technology. The second inductor L2 is implemented by using a top-layer metal and a second-to-top-layer metal stacked wiring method, which effectively improves the Q value of the second inductor L2 with a large inductance value and can effectively reduce the in-passband insertion loss of the bandpass filter in the embodiment.

[0061] Please continue reading Figure 4 In the layout of the embodiment described above, both the first inductor L1 and the third inductor L3 are implemented on the same metal layer. The weak transformer coupling structure is achieved by placing the first inductor L1 and the third inductor L3 adjacent to each other. This method can achieve the weak coupling coefficient between the first inductor L1 and the third inductor L3 as described in this invention, reducing the use of a large number of overlapping traces across layers, effectively reducing the complexity of layout implementation, and improving the practicality of this invention.

[0062] The following simulation experiment further illustrates this point.

[0063] Simulation conditions:

[0064] The set of values ​​used in the embodiment is: L1 = 0.925nH, C1 = 1.67pF, L2 = 7nH, C2 = 0.28pF, L3 = 0.925nH, C3 = 1.67pF, C4 = 0.37pF, k = 0.2.

[0065] Simulation content:

[0066] like Figure 5 As shown in the figure, the circuit schematic of the IPD high-selectivity bandpass filter proposed in this invention for the n77 frequency band is simulated under the above conditions. The horizontal axis represents frequency, and the vertical axis represents the scattering parameters of the two-port network in this example. As can be seen from the figure, the passband frequency of the embodiment provided by this invention covers the n77 frequency band (3.3GHz~4.2GHz), with three transmission poles within the passband, achieving an in-band return loss S11 <-27.8dB. There is a low-frequency out-of-band transmission zero at 1.99GHz and a high-frequency out-of-band transmission zero at 5.33GHz. Simulation results show that the lower stopband has S21 <-32dB@0GHz~2.15GHz, and the upper stopband has S21 <-20.5dB@5.15GHz~10GHz, achieving a wide stopband, high out-of-band attenuation, and a high transition band roll-off factor, thereby effectively improving the selectivity of the filter.

[0067] like Figure 6 The figure shows the electromagnetic simulation results of the layout of the embodiment described in this invention. The horizontal axis represents frequency, and the vertical axis represents the scattering parameters of the two-port network in this embodiment. As can be seen from the figure, the passband frequency of this embodiment fully covers the n77 band (3.3GHz to 4.2GHz), and the in-band insertion loss is less than 1.5dB. Similarly, it has three transmission poles in the passband, achieving an in-band return loss S11 < -28dB. There is a low-frequency out-of-band transmission zero at 1.95GHz and a high-frequency out-of-band transmission zero at 5.36GHz. The lower stopband has S21 < -32dB@0GHz to 2.1GHz, and the upper stopband has S21 < -20.5dB@5.2GHz to 10GHz. The simulation results show that the waveforms of the layout electromagnetic simulation results are basically consistent with the circuit schematic simulation results, which fully demonstrates the feasibility of this invention.

Claims

1. A high-selectivity bandpass filter based on weakly coupled transformer technology using IPD, characterized in that, include: The first end of the LC series resonant circuit (2) is connected to the input terminal IN of the filter and the first end of the LC parallel resonant circuit (1), and the second end of the LC parallel resonant circuit (1) is grounded. The second end of the LC series resonant circuit (2) is connected to the output terminal OUT of the filter and the first end of the LC parallel resonant circuit (3), and the second end of the LC parallel resonant circuit (3) is grounded. A fourth capacitor C4 is also connected between the first end and the second end of the LC series resonant circuit (2).

2. The IPD high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 1, characterized in that, The LC parallel resonant circuit (1) includes a first inductor L1 and a first capacitor C1, which are connected in parallel. The first end of the first inductor L1 and the first capacitor C1 is connected to the input terminal IN of the filter, and the second end of the first inductor L1 and the first capacitor C1 is grounded.

3. The IPD high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 1, characterized in that, The LC series resonant circuit (2) includes a second capacitor C2 and a second inductor L2 connected in series. The first end of the second capacitor C2 is connected to the input terminal IN of the filter, the second end of the second capacitor C2 is connected to the first end of the second inductor L2, and the second end of the second inductor L2 is connected to the output terminal OUT of the filter.

4. The IPD high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 1, characterized in that, The LC parallel resonant circuit (3) includes a third inductor L3 and a third capacitor C3, which are connected in parallel. The first end of the third inductor L3 and the third capacitor C3 is connected to the output terminal OUT of the filter, and the second end of the third inductor L3 and the third capacitor C3 is grounded.

5. A high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 2, characterized in that, The first inductor L1 in the LC parallel resonant circuit (1) and the third inductor L3 in the LC parallel resonant circuit (3) have a transformer coupling relationship with a coupling coefficient of k.

6. The IPD high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 5, characterized in that, The transformer coupling relationship between the first inductor L1 and the third inductor L3 can be equivalent to a π-type decoupling equivalent circuit. The π-type decoupling equivalent circuit includes a fourth inductor L4, a fifth inductor L5, and a sixth inductor L6. The first terminal of the fourth inductor L4 is connected to the input terminal of the filter, and the second terminal of the fourth inductor L4 is grounded. The first terminal of the fifth inductor L5 is connected to the output terminal of the filter, and the second terminal of the fifth inductor L5 is grounded. The first terminal of the sixth inductor L6 is connected to the input terminal of the filter, and the second terminal of the sixth inductor L6 is connected to the output terminal of the filter.

7. A high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 6, characterized in that, The sixth inductor L6 and the fourth capacitor C4 in the π-type decoupling equivalent circuit are connected in parallel to form an LC parallel resonant circuit (4).

8. A high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 6, characterized in that, When the inductance values ​​of the first inductor L1 and the third inductor L3 are both l, the inductance value of the fourth inductor L4 is l×(1-k), the inductance value of the fifth inductor L5 is l×(1-k), and the inductance value of the sixth inductor L6 is l×k. By adjusting the inductance values ​​of the first inductor L1 and the third inductor L3, as well as the coupling coefficient k, the passband frequency of the filter is kept stable. At the same time, the position of the transmission zero point is adjusted so that the transmission zero point falls within the upper stopband and lower stopband of the filter, respectively.

9. A high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 2, characterized in that, The first inductor L1, the second inductor L2, and the third inductor L3 are planar spiral inductors made of single or multiple layers of metal, and their shapes can be circular, square, or octagonal.

10. A high-selectivity bandpass filter based on weakly coupled transformer technology according to claim 2, characterized in that, The first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are MIM parallel plate capacitors or MOM dielectric capacitors.

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