A symmetric source-load coupled bandpass filter based on GaAs IPD process

Abstract

This invention belongs to the field of passive radio frequency microwave devices, and discloses a symmetrical source-load coupled bandpass filter based on GaAs IPD technology. The filter includes a MIM grounding capacitor, a coupling capacitor, a resonant capacitor, and a planar spiral inductor integrated on a GaAs substrate. Symmetrical Pi-type structures are arranged on both sides of the input and output terminals. A source-load coupled filter loop is formed in the middle by the coupling capacitor and two parallel grounded resonators. Transmission zeros are introduced on both sides outside the passband, and additional zeros are formed on the high-frequency side. With this structure, low insertion loss, high out-of-band rejection, and miniaturized integration can be achieved in the 1GHz-10GHz range.

Description

A Symmetrical Source-Load Coupled Bandpass Filter Based on GaAs IPD Technology Technical Field

[0001] This invention relates to the field of passive radio frequency microwave devices, specifically to a symmetrical source-load coupled bandpass filter based on GaAs IPD technology. Background Technology

[0002] With the rapid development of mobile communication, the Internet of Things, and automotive electronics, the requirements for wireless signal transmission quality in terminal devices and base station equipment are constantly increasing. Bandpass filters, as one of the key passive components in the RF front-end link, are mainly used to limit the frequency band of useful signals and suppress out-of-band noise and interference. Their insertion loss, out-of-band rejection ratio, and size directly affect the system's transmit efficiency, receive sensitivity, overall size, and cost, thus occupying an important position in RF front-end design.

[0003] Traditional LTCC (Low Temperature Co-fired Ceramic), discrete LC (Discrete Inductors and Capacitors), or microstrip filters are relatively large, which is not conducive to high-density integration. IPD (Integrated Passive Device) technology can integrate passive devices such as inductors, capacitors, and resistors on a substrate, offering advantages such as small size, high integration density, good process consistency, ease of packaging, and mass production. Therefore, it has become one of the important technical routes for realizing the bandpass filtering function of RF front-ends. Currently, with the increase in operating frequency, system bandwidth, and multi-mode applications, IPD bandpass filters must meet the requirements of miniaturization and low-cost packaging, while also taking into account performance requirements such as low insertion loss, high selectivity, and good stopband suppression. This has become an important technical issue of concern in this field. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, the purpose of this invention is to propose a symmetric source-load coupled bandpass filter based on GaAs IPD technology, achieving low insertion loss, high out-of-band rejection, and high integration of the filter.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A symmetrical source-load coupled bandpass filter based on GaAs IPD technology includes a passive circuit disposed on a GaAs substrate and an input terminal and an output terminal electrically connected to the passive circuit; the passive circuit includes a grounding capacitor C1, a grounding capacitor C2, a coupling capacitor C3, a coupling capacitor C4, a coupling capacitor C5, a resonant capacitor C6, a resonant capacitor C7, a grounding capacitor C8, a grounding capacitor C9, and inductors L1, L2, L3, L4, and L5;

[0007] One end of the grounding capacitor C1 is connected to one end of the inductor L1, and this connection node is connected to the input pad to form the input terminal; the other end of the inductor L1 is simultaneously connected to one end of the grounding capacitor C2, one end of the coupling capacitor C3, and one end of the coupling capacitor C4, and the other end of the grounding capacitor C1 and the other end of the grounding capacitor C2 are grounded together; the grounding capacitor C1, the inductor L1, and the grounding capacitor C2 constitute the first Pi structure.

[0008] The other end of the coupling capacitor C4 is electrically connected to one end of the inductor L2, one end of the resonant capacitor C6 and one end of the inductor L3. The other end of the resonant capacitor C6 is electrically connected to the other end of the inductor L3 and grounded, forming the first parallel grounded resonator.

[0009] The other end of inductor L2 is electrically connected to one end of coupling capacitor C5, one end of resonant capacitor C7 and one end of inductor L4. The other end of resonant capacitor C7 is electrically connected to the other end of inductor L4 and grounded, forming a second parallel grounded resonator.

[0010] The other end of coupling capacitor C5 is electrically connected to the other end of coupling capacitor C3, one end of grounding capacitor C8, and one end of inductor L5; the other end of inductor L5 is connected to one end of grounding capacitor C9, and this connection node is connected to output pad Port2 to form the output terminal. The other ends of grounding capacitor C8 and grounding capacitor C9 are grounded, thereby grounding capacitor C8, inductor L5, and grounding capacitor C9 form the second Pi structure.

[0011] The coupling capacitor C3, together with the coupling capacitor C4, inductor L2, coupling capacitor C5, the first parallel ground resonator and the second parallel ground resonator, constitute a source-load coupled filter circuit, thereby forming a symmetrical source-load coupled bandpass filter structure.

[0012] Furthermore, the first Pi structure is used to suppress high-frequency components in the input signal and improve the high-frequency out-of-band suppression of the filter, while the second Pi structure is used to perform low-pass filtering on the output signal and together with the first Pi structure, ensures the symmetry of the overall filter structure.

[0013] Furthermore, the grounding capacitor C1, grounding capacitor C2, coupling capacitor C3, coupling capacitor C4, coupling capacitor C5, resonant capacitor C6, resonant capacitor C7, grounding capacitor C8, and grounding capacitor C9 are all MIM capacitors.

[0014] Furthermore, the coupling capacitor C4 and the coupling capacitor C5 have the same capacitance value, the resonant capacitors C6 and C7 have the same capacitance value, the grounding capacitor C1 and the grounding capacitor C9 have the same capacitance value, and the grounding capacitor C2 and the grounding capacitor C8 have the same capacitance value.

[0015] Furthermore, the inductors L1, L2, and L5 are arranged in a circular planar double-layer spiral winding form in the metal layer of the GaAs substrate, and are connected to the upper and lower metal layers by vias to form a double-layer spiral structure. The inductors L3 and L4 are arranged in a square planar double-layer spiral winding form.

[0016] Furthermore, the inductors L1 and L5 have the same inductance value, and the inductors L3 and L4 have the same inductance value.

[0017] Furthermore, taking the straight line obtained by connecting coupling capacitor C3 and inductor L2 as the central axis, grounding capacitors C1 and C9, C2 and C8, coupling capacitors C4 and C5, resonant capacitors C6 and C7, inductors L1 and L5, and inductors L3 and L4 are arranged symmetrically with respect to this central axis. The input and output terminals are also arranged symmetrically with respect to this central axis.

[0018] Furthermore, both the input and output terminals adopt a ground-signal-ground structure for their RF pin wiring.

[0019] Furthermore, the bandpass filter is suitable for the 2GHz-10GHz operating frequency band, the inductance value of each inductor is selected in the range of 1nH-10nH, and the capacitance value of each capacitor element is selected in the range of 0.1pF-10pF.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The present invention adopts the design of IPD process. The inductor design uses a combination of circular spiral inductors and square spiral inductors to balance high Q value and small area. The capacitor adopts MIM (metal-insulator-metal) capacitor, which can achieve high integration and miniaturization, thereby effectively reducing the size of the filter.

[0022] (2) The symmetrical source-load coupled bandpass filter based on IPD proposed in this invention has two Pi structures that can suppress high-frequency out-of-band signals and improve stopband performance and operating frequency range; the source-load coupled filter circuit introduces two zeros, and the dual parallel ground resonator introduces additional high-frequency zeros. After combination, the stopband suppression of the bandpass filter is significantly improved. Attached Figure Description

[0023] Figure 1 is a circuit schematic diagram of a symmetrical source-load coupled bandpass filter chip according to an embodiment of the present invention.

[0024] Figure 2 is a circuit schematic diagram of a symmetrical source-load coupled bandpass filter chip according to an embodiment of the present invention.

[0025] Figure 3 is a graph showing the S-parameter simulation results of a symmetrical source-load coupled bandpass filter chip with a simulation frequency band of 1-10 GHz involved in the embodiments of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described are only for illustrating the present invention and are not intended to limit the scope of protection of the present invention.

[0027] As shown in Figures 1 and 2, this embodiment provides a symmetrical source-load coupled bandpass filter based on GaAs IPD technology. The bandpass filter includes a passive circuit disposed on a GaAs substrate, and an input terminal and an output terminal electrically connected to the passive circuit. The passive circuit includes grounding capacitor C1, grounding capacitor C2, coupling capacitor C3, coupling capacitor C4, coupling capacitor C5, resonant capacitor C6, resonant capacitor C7, grounding capacitor C8, and grounding capacitor C9, as well as inductors L1, L2, L3, L4, and L5. All capacitors and inductors are integrated on the GaAs substrate using IPD technology.

[0028] One end of the grounding capacitor C1 is connected to one end of the inductor L1, and this connection point is connected to the input pad to form the input terminal of the bandpass filter in this embodiment. The other end of the inductor L1 is simultaneously connected to one end of the grounding capacitor C2, one end of the coupling capacitor C3, and one end of the coupling capacitor C4. The other end of the grounding capacitor C1 and the other end of the grounding capacitor C2 are grounded together. Thus, the grounding capacitor C1, the inductor L1, and the grounding capacitor C2 constitute the first Pi structure. The first Pi structure is located after the input terminal and is used to suppress high-frequency components in the input signal, thereby improving the high-frequency out-of-band suppression of the filter.

[0029] The other end of the coupling capacitor C4 is electrically connected to one end of inductor L2, one end of resonant capacitor C6, and one end of inductor L3. The other end of resonant capacitor C6 is electrically connected to the other end of inductor L3 and grounded, forming a first parallel grounded resonator. The other end of inductor L2 is electrically connected to one end of coupling capacitor C5, one end of resonant capacitor C7, and one end of inductor L4. The other end of resonant capacitor C7 is electrically connected to the other end of inductor L4 and grounded, forming a second parallel grounded resonator. Through the above connections, the filter forms two parallel grounded resonant branches outside the main signal path.

[0030] The other end of the coupling capacitor C5 is electrically connected to the other end of the coupling capacitor C3, one end of the grounding capacitor C8, and one end of the inductor L5. The other end of the inductor L5 is connected to one end of the grounding capacitor C9. This connection node is connected to the output pad Port2 to form the output terminal of the bandpass filter in this embodiment. The other ends of the grounding capacitors C8 and C9 are grounded, thus the grounding capacitor C8, inductor L5, and grounding capacitor C9 constitute the second Pi structure. The second Pi structure is located before the output terminal and is used to perform low-pass filtering on the output signal. At the same time, it works with the first Pi structure to ensure the symmetry of the overall filter structure. The coupling capacitor C3, the coupling capacitor C4, the inductor L2, the coupling capacitor C5, and the first and second parallel ground resonators together constitute a source-load coupled filter circuit, thereby forming a symmetrical source-load coupled bandpass filter structure.

[0031] Therefore, after the input terminal passes through the first Pi structure, one signal is directly coupled to the node near the output terminal via coupling capacitor C3; the other signal passes sequentially through coupling capacitor C4, inductor L2, and coupling capacitor C5, and couples with the first and second parallel ground resonators along the way, forming a source-load coupling path. By rationally designing the capacitance values ​​of coupling capacitors C3, C4, and C5, as well as the parameters of inductors L2, C6, L3, C7, and L4, signals arriving at the node before the output terminal via different paths can have a specific phase difference. This creates two transmission zeros on both sides of the passband of the bandpass filter, effectively suppressing signals outside the passband. The dual parallel ground resonators also introduce additional high-frequency zeros on the high-frequency side, further improving stopband suppression.

[0032] In this embodiment, grounding capacitors C1, C2, C8, and C9 are all made using a MIM capacitor structure. Grounding capacitors C1 and C9 have the same capacitance value, and grounding capacitors C2 and C8 have the same capacitance value, ensuring structural and electrical parameter symmetry between the filter's input and output terminals. Coupling capacitors C3, C4, and C5 also use a MIM capacitor structure, with coupling capacitors C4 and C5 having the same capacitance value to achieve a symmetrical source-load coupling path. Resonant capacitors C6 and C7 also use a MIM capacitor structure and are designed with the same capacitance value, ensuring symmetry in capacitance parameters between the first parallel ground resonator and the second parallel ground resonator.

[0033] In this embodiment, inductors L1, L2, and L5 are arranged in a circular planar double-layer spiral winding form within the metal layer of the GaAs substrate. They are connected to vias through the upper and lower metal layers to form a double-layer spiral structure, achieving a large inductance value and a high quality factor Q within a small area. Inductors L1 and L5 are designed with the same inductance value. Inductors L3 and L4 are arranged in a square planar double-layer spiral winding form, both with the same inductance value, and together with resonant capacitors C6 and C7, they form a symmetrical parallel grounded resonator structure.

[0034] To further ensure the symmetry of the filter and the consistency of parasitic effects, the straight line connecting coupling capacitor C3 and inductor L2 is used as the central axis. The grounding capacitors C1 and C9, C2 and C8, coupling capacitors C4 and C5, resonant capacitors C6 and C7, inductors L1 and L5, and inductors L3 and L4 are arranged symmetrically with respect to this central axis. The input and output terminals are also symmetrically positioned with respect to this central axis. This symmetrical layout reduces the impact of manufacturing variations on filter performance and improves the stability of the bandpass filter.

[0035] In this embodiment, both the input and output terminals adopt a ground-signal-ground (GSG) structure for RF pin routing. That is, ground pins are arranged on both sides of the signal pins and connected to the ground metal layer under the chip through multiple ground vias. This reduces the parasitic inductance and capacitance of the leads and soldering areas, improves port impedance matching, and enhances the insertion loss and return loss performance in the passband.

[0036] In one design of this embodiment, the bandpass filter is suitable for the 2GHz-10GHz operating frequency band. The inductance values ​​of inductors L1-L5 are selected in the range of 1nH-10nH, and the capacitance values ​​of each capacitor are selected in the range of 0.1pF-10pF. Based on the target center frequency and bandwidth, the passband position and stopband width can be flexibly designed by adjusting the values ​​of coupling capacitors C3-C5 and components such as inductors L2, C6, L3, C7, and L4. Those skilled in the art can select appropriate parameter combinations within the above range to meet the application requirements of different frequency bands.

[0037] This invention utilizes GaAs IPD technology to realize the aforementioned capacitor, inductor, and metal interconnect structures. Specifically, a GaAs epitaxial wafer is used as a substrate, on which a lower metal layer, a dielectric layer, an upper metal layer, and a passivation layer are sequentially formed. The MIM capacitor is constructed by depositing upper and lower electrodes between the dielectric layers. The spiral inductor is formed by etching spiral traces in the upper metal layer and connecting them to the lower metal layer through vias to form a double-layer spiral structure. The GSG pads for the input and output terminals are located in the upper metal layer and grounded to the lower metal layer through vias. The entire filter circuit is integrated on a single chip, featuring small size and good process consistency.

[0038] Figure 3 shows the S-parameter simulation results obtained when the simulation frequency band of this embodiment is 1-10GHz. It can be seen that the bandpass filter of this embodiment has low insertion loss and good return loss within the target operating frequency band. Outside the passband, the multiple transmission zeros introduced by the source-load coupled filter circuit and the dual parallel grounded resonator significantly improve the stopband rejection, effectively suppressing high-frequency and low-frequency signals outside the passband, demonstrating the superior filtering performance of the circuit structure described in this invention.

[0039] It should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various equivalent substitutions or modifications made by those skilled in the art without departing from the spirit and substance of the present invention should fall within the protection scope of the present invention.

Claims

1. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology, characterized in that, The system includes a passive circuit disposed on a GaAs substrate and input and output terminals electrically connected to the passive circuit. The passive circuit includes a grounding capacitor C1, a grounding capacitor C2, a coupling capacitor C3, a coupling capacitor C4, a coupling capacitor C5, a resonant capacitor C6, a resonant capacitor C7, a grounding capacitor C8, a grounding capacitor C9, and inductors L1, L2, L3, L4, and L5. One end of the grounding capacitor C1 is connected to one end of the inductor L1, and this connection point is connected to the input pad to form an input terminal. The other end of the inductor L1 is simultaneously connected to one end of the grounding capacitor C2, one end of the coupling capacitor C3, and one end of the coupling capacitor C4. The other end of the grounding capacitor C1 and the other end of the grounding capacitor C2 are grounded together. The grounding capacitor C1, inductor L1, and grounding capacitor C2 form a first Pi structure. The other end of the coupling capacitor C4 is electrically connected to one end of the inductor L2, one end of the resonant capacitor C6, and one end of the inductor L3. The other end of the resonant capacitor C6 is connected to the other end of the inductor L3. One end of the inductor L2 is electrically connected to and grounded, forming a first parallel grounded resonator; the other end of the inductor L2 is electrically connected to one end of the coupling capacitor C5, one end of the resonant capacitor C7, and one end of the inductor L4, and the other end of the resonant capacitor C7 is electrically connected to and grounded, forming a second parallel grounded resonator; the other end of the coupling capacitor C5 is electrically connected to the other end of the coupling capacitor C3, one end of the grounding capacitor C8, and one end of the inductor L5; the other end of the inductor L5 is connected to one end of the grounding capacitor C9, and this connection node is connected to the output pad Port2 to form an output terminal; the other ends of the grounding capacitor C8 and the other ends of the grounding capacitor C9 are grounded, thus the grounding capacitor C8, inductor L5, and grounding capacitor C9 form a second Pi structure; the coupling capacitor C3, the coupling capacitor C4, the inductor L2, the coupling capacitor C5, and the first and second parallel grounded resonators together form a source-load coupled filter circuit, thereby forming a symmetrical source-load coupled bandpass filter structure.

2. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 1, characterized in that, The first Pi structure is used to suppress high-frequency components in the input signal and improve the high-frequency out-of-band suppression of the filter. The second Pi structure is used to implement low-pass filtering of the output signal, and together with the first Pi structure, it ensures the symmetry of the overall filter structure.

3. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 1, characterized in that, The grounding capacitor C1, grounding capacitor C2, coupling capacitor C3, coupling capacitor C4, coupling capacitor C5, resonant capacitor C6, resonant capacitor C7, grounding capacitor C8, and grounding capacitor C9 are all MIM capacitors.

4. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 3, characterized in that, The coupling capacitor C4 and coupling capacitor C5 have the same capacitance value, the resonant capacitors C6 and C7 have the same capacitance value, the grounding capacitor C1 and grounding capacitor C9 have the same capacitance value, and the grounding capacitor C2 and grounding capacitor C8 have the same capacitance value.

5. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 4, characterized in that, The inductors L1, L2, and L5 are arranged in a circular planar double-layer spiral winding form in the metal layer of the GaAs substrate. They are connected to the upper and lower metal layers and vias to form a double-layer spiral structure. The inductors L3 and L4 are arranged in a square planar double-layer spiral winding form.

6. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 5, characterized in that, The inductors L1 and L5 have the same inductance value, and the inductors L3 and L4 have the same inductance value.

7. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 6, characterized in that, With the straight line connecting coupling capacitor C3 and inductor L2 as the central axis, grounding capacitors C1 and C9, C2 and C8, coupling capacitors C4 and C5, resonant capacitors C6 and C7, inductors L1 and L5, and inductors L3 and L4 are arranged symmetrically with respect to this central axis. The input and output terminals are also arranged symmetrically with respect to this central axis.

8. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 7, characterized in that, Both the input and output terminals adopt a ground-signal-ground structure for RF pin routing.

9. A symmetrical source-load coupled bandpass filter based on GaAs IPD technology according to claim 8, characterized in that, The bandpass filter is suitable for the 2GHz-10GHz operating frequency band. The inductance values ​​of each inductor are selected in the range of 1nH-10nH, and the capacitance values ​​of each capacitor are selected in the range of 0.1pF-10pF.

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