CN115529016A - A High Rejection Bandpass Filter Based on Cascaded Structure - Google Patents

Abstract

The invention discloses a high-rejection band-pass filter based on a cascade structure. The filter is composed of a low-pass filter, a band-pass filter, an input port RFin and an output port RFout. The input signal enters the low-pass filter through the input port RFin, then passes through the band-pass filter, and finally is output through the output port RFout. The filter has the characteristics of low insertion loss and high out-of-band rejection.

Description

A High Rejection Bandpass Filter Based on Cascaded Structure

technical field

The invention belongs to the technical field of radio frequency integrated circuits.

Background technique

The filter is a frequency selective filter device, which allows the required frequency to pass and attenuates and suppresses other useless and harmful frequencies. With the rapid development of radio frequency integrated circuits, communication equipment puts forward higher requirements on the performance of filters, requiring filters with low insertion loss and high out-of-band rejection. The traditional filter structure is easy to realize the radio frequency filter, but its out-of-band suppression is poor, especially the suppression on the third harmonic and the fourth harmonic will be worse.

Contents of the invention

Purpose of the invention: In order to solve the above-mentioned problems in the prior art, the present invention proposes a high rejection bandpass filter based on a cascaded structure.

Technical solution: The present invention proposes a cascaded structure-based high-rejection band-pass filter, including a low-pass filter and a band-pass filter cascaded to each other.

Further, the low-pass filter includes a first resonant unit, a first capacitor and a second capacitor, one end of the first resonant unit is used as the input end of the entire high-rejection band-pass filter to receive a radio frequency signal, and is connected with the first One end of the capacitor is connected, and the other end of the first capacitor is grounded; the other end of the first resonant unit is connected to the band-pass filter and one end of the second capacitor; the other end of the second capacitor is grounded.

Further, the bandpass filter includes second to fifth resonance units and a third capacitor; one end of the second resonance unit is connected to the low-pass filter, and the other end is connected to one end of the third resonance unit and the fourth resonance unit One end, the other end of the fourth resonant unit is grounded, the other end of the third resonant unit is connected to one end of the fifth resonant unit and one end of the third capacitor, one end of the fifth resonant unit is grounded, and one end of the third capacitor serves as the entire high Rejection at the output of the bandpass filter.

Further, the resonant unit is composed of capacitors and inductors connected in parallel.

Beneficial effects: the filter of the present invention improves the suppression of the third harmonic and the fourth harmonic, and at the same time, the high suppression bandpass filter proposed by the present invention has the advantages of low insertion loss and high out-of-band suppression.

Description of drawings

Fig. 1 is the overall topological diagram of the present invention;

Fig. 2 is the emulation figure of the present invention;

Figure 3 is a simulation diagram of an uncascaded bandpass filter;

Fig. 4 is a comparison diagram of the simulation results of the present invention and the simulation results of the non-cascaded bandpass filter.

detailed description

The drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention.

As shown in Figure 1, the present embodiment provides a high-rejection band-pass filter based on a cascaded structure including a low-pass filter, a band-pass filter, an input port RFin and an output port RFout, and the input port RFin receives a radio frequency signal through a low-pass After the filter and the band-pass filter are output by the output port RFout, the low-pass filter includes a first resonant unit 1, a first capacitor and a second capacitor, and the band-pass filter includes a second resonant unit 2, a third resonant unit 3, The fourth resonant unit 4, the fifth resonant unit 5 and the third capacitor, one end of the first resonant unit is connected to the input port RFin, the other end is connected to the second resonant unit, one end of the first capacitor is connected to the input port RFin, and the other port is grounded, One end of the second capacitor is connected to the first resonant unit, the other end is grounded, one end of the third resonant unit is connected to the second resonant unit, the other end is connected to one end of the third capacitor, and the other end of the third capacitor is connected to the output port RFout , one end of the fourth resonant unit is grounded, the other end is connected to the second resonant unit and the third resonant unit, one end of the fifth resonant unit is grounded, the other end is connected to the third resonant unit and one end of the capacitor, the resonant unit consists of an inductor and a capacitor Composed of parallel connection, as shown in Figure 1, the first resonance unit includes inductor L1 and capacitor C1, one end of inductor L1 and capacitor C1 connected in parallel is connected to input port RFin, the second resonance unit includes inductor L2 and capacitor C2, inductor L2 and capacitor C2 After the parallel connection, one end is connected to the other end of the parallel connection of the inductor L1 and the capacitor C1, and the third resonance unit includes the inductor L3 and the capacitor C3. After the parallel connection of the inductor L3 and the capacitor C3, one end is connected to the other end of the parallel connection of the inductor L2 and the capacitor C2, and the fourth resonance unit includes the inductor L4 and capacitor C4, inductance L4 and capacitor C4 are connected in parallel, one end is connected to the other end of inductance L2 and capacitor C2 in parallel, and the other end is grounded, the fifth resonant unit includes inductance L5 and capacitor C5, inductance L5 and capacitor C5 are connected in parallel, and one end is connected to inductance L3 The other end connected in parallel with capacitor C3 is grounded, the first capacitor is C6, one end is grounded, the other end is connected to output port RFin, the second capacitor is C7, one end is connected to inductor L1, the other end is grounded, the third capacitor is C8, one end Connect the other end of the parallel connection of the inductor L3 and the capacitor C3, and connect the other end to the output port RFout.

In the bandpass filter of this embodiment, the fourth resonant unit (4) and the fifth resonant unit (5) form transmission poles, which determine the working frequency band of the filter and enhance the flatness in the band. The second resonant unit (2) A transmission zero point is formed on the high-frequency side of the passband to improve low-frequency out-of-band suppression, and the third resonant unit (3) forms a transmission zero point on the high-frequency side of the passband to enhance high-frequency out-of-band suppression. The low-pass filter is an elliptic low-pass filter, and the first resonance unit (1) forms a transmission zero point at the third harmonic to enhance the suppression of the filter at the third and fourth harmonics. Simulation result of the present invention is as shown in Figure 2, and dotted line represents the return loss of filter, and solid line represents the insertion loss of filter, and the operating frequency band of filter of the present invention is 3.3GHz-4.2GHz, and insertion loss is 1.5dB, in The suppression at 2.4GHz is -20dB, the suppression at DC-2.1GHz is less than -35dB, the suppression at 5.15GH is -16dB, the suppression at the second harmonic is less than -33dB, and the suppression at the third harmonic is less than -44dB. The suppression at the sub-harmonic is less than -43dB, achieving high suppression of the third and fourth harmonics.

Figure 3 shows the simulation results of the non-cascaded band-pass filter, and the high-frequency suppression performance is poor, especially at the third and fourth harmonics.

As shown in Figure 4, black solid line and dotted line are simulation results of the present invention, and gray solid line and dotted line are non-cascaded bandpass filter simulation results, and the present invention compared with prior art, its remarkable advantage Yes: The filter's rejection of the third and fourth harmonics is increased.

In addition, it should be noted that the various specific technical features described in the above specific implementation manners may be combined in any suitable manner if there is no contradiction. In order to avoid unnecessary repetition, various possible combinations are not further described in the present invention.

Claims (4)

1. A high-rejection band-pass filter based on a cascade structure is characterized by comprising a low-pass filter and a band-pass filter which are cascaded with each other.

2. The cascade structure-based high-rejection band-pass filter according to claim 1, wherein the low-pass filter includes a first resonant unit, a first capacitor and a second capacitor, one end of the first resonant unit is used as an input end of the whole high-rejection band-pass filter to receive a radio-frequency signal and is connected with one end of the first capacitor, and the other end of the first capacitor is grounded; the other end of the first resonance unit is connected with the band-pass filter and one end of the second capacitor; the other end of the second capacitor is grounded.

3. The high-rejection band-pass filter based on the cascade structure as claimed in claim 1, wherein the band-pass filter comprises second to fifth resonant units and a third capacitor; one end of the second resonance unit is connected with the low-pass filter, the other end of the second resonance unit is connected with one end of the third resonance unit and one end of the fourth resonance unit, the other end of the fourth resonance unit is grounded, the other end of the third resonance unit is connected with one end of the fifth resonance unit and one end of the third capacitor, one end of the fifth resonance unit is grounded, and one end of the third capacitor is used as the output end of the whole high-suppression band-pass filter.

4. A high-rejection band-pass filter based on a cascade structure according to any one of claims 2 and 3, wherein the resonance unit is composed of a capacitor and an inductor connected in parallel.

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