A high performance active low pass filter

Abstract

The present invention discloses a high-performance active low-pass filter, which relates to high-frequency communication front-end equipment. This solution is proposed to solve the shortcomings of the prior art, such as weak stopband suppression, poor stability, and insufficient bandwidth. A first MOS capacitor and a second MOS capacitor are provided; the first MOS capacitor is used to offset the parasitic capacitance between the signal input end and the signal output end of the P-way filter unit; the second MOS capacitor is used to offset the parasitic capacitance between the signal input end and the signal output end of the N-way filter unit. The advantage is that the MOS capacitor is used as a feedback loop to offset the main zero point of the circuit, improve the out-of-band suppression of the filter, and increase the circuit stability; and the low-pass filter is supplemented with a reasonable optimization design, so that the working bandwidth of the low-pass filter can eventually reach 100MHz to 5.1GHz, with good out-of-band suppression and stable filtering effect.

Description

Technical Field

[0001] The invention relates to high-frequency communication front-end equipment, and in particular to a high-performance active low-pass filter. Background Art

[0002] Filters are important units for signal processing. With the development of integrated circuit technology and communication technology, especially the development of mobile communication technology, the design of fully integrated active filters has become one of the frontier topics of concern to the international academic community. In recent years, the development of systems on a chip has also urgently needed to solve the problem of full integration of active filters. In millimeter-wave wireless communications or UWB, a large bandwidth is required to meet their speed requirements. At the same time, good stopband suppression and stability are indispensable parts of the filter. Therefore, the design and research of broadband high out-of-band suppression active low-pass filters is of great significance to the functional realization of the entire RF receiver system. Traditional source follower low-pass filters have the disadvantages of weak stopband suppression, poor stability, and insufficient bandwidth in millimeter-wave baseband applications. Summary of the invention

[0003] The present invention aims to provide a high-performance active low-pass filter to solve the problems existing in the above-mentioned prior art.

[0004] The present invention discloses a high-performance active low-pass filter, comprising a P-path filter unit and an N-path filter unit with the same structure, wherein the inputs of the two-path filter units are differential inputs; a first MOS capacitor and a second MOS capacitor are also provided; a substrate end of the first MOS capacitor is connected to a signal output end of the P-path filter unit, a gate end is connected to a signal input end of the N-path filter unit, and the first MOS capacitor is used to offset a parasitic capacitance between the signal input end of the P-path filter unit and its own signal output end; a substrate end of the second MOS capacitor is connected to a signal output end of the N-path filter unit, a gate end is connected to a signal input end of the P-path filter unit, and the second MOS capacitor is used to offset a parasitic capacitance between the signal input end of the N-path filter unit and its own signal output end.

[0005] The active low-pass filter is provided with a common-mode feedback unit; the P-path filtering unit comprises a P-path first MOS tube, a P-path second MOS tube, a P-path first capacitor array and a P-path second capacitor array; the P-path first MOS tube drain is connected to the P-path common-mode input signal of the common-mode feedback unit, the P-path first MOS tube source is used as a signal output end, and the P-path first MOS tube grid is used as a signal input end; the P-path second MOS tube drain is connected to the P-path first MOS tube source, the P-path second MOS tube source is grounded, and the P-path second MOS tube grid is connected to the P-path first MOS tube drain; the P-path first capacitor array is connected in parallel between the source and drain of the P-path first MOS tube, and the P-path second capacitor array is connected in parallel between the P-path second The N-way filtering unit comprises N-way first MOS tubes, N-way second MOS tubes, N-way first capacitor arrays and N-way second capacitor arrays; the drains of the N-way first MOS tubes are connected to the N-way common-mode input signals of the common-mode feedback unit, the sources of the N-way first MOS tubes are used as signal output ends, and the gates of the N-way first MOS tubes are used as signal input ends; the drains of the N-way second MOS tubes are connected to the sources of the N-way first MOS tubes, the sources of the N-way second MOS tubes are grounded, and the gates of the N-way second MOS tubes are connected to the drains of the N-way first MOS tubes; the N-way first capacitor arrays are connected in parallel between the sources and drains of the N-way first MOS tubes, and the N-way second capacitor arrays are connected in parallel between the sources and drains of the N-way second MOS tubes.

[0006] The high-performance active low-pass filter described in the present invention has the advantages of using MOS capacitors as feedback loops to offset the main zero point of the circuit, improve the filter's out-of-band suppression, and increase circuit stability; and the low-pass filter is supplemented with a reasonable optimization design, so that the working bandwidth of the low-pass filter can eventually reach 100MHz to 5.1GHz, and has good out-of-band suppression and stable filtering effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic structural diagram of the active low-pass filter of the present invention;

[0008] Figure 2 is a frequency response curve diagram of the active low-pass filter of the present invention;

[0009] Figure 3 is a graph of input impedance Z11 of the active low-pass filter of the present invention;

[0010] Figure 4 is a curve diagram of the stability coefficient Kf of the active low-pass filter of the present invention;

[0011] Figure 5 is the input 1 dB compression point of the active low-pass filter of the present invention;

[0012] Figure 6It is the input third-order intermodulation point of the active low-pass filter of the present invention.

[0013] Reference numerals:

[0014] S1-P path filter unit: C1P-P path first capacitor array, C2P-P path second capacitor array, VIP-P path input signal, VOP-P path output signal, VxP-P path common mode input signal, M1P-P path first MOS tube, M2P-P path second MOS tube;

[0015] S2-N-channel filter unit: C1N-N-channel first capacitor array, C2N-N-channel second capacitor array, VIN-N-channel input signal, VON-N-channel output signal, VxN-N-channel common mode input signal, M1N-N-channel first MOS tube, M2N-N-channel second MOS tube;

[0016] S3-feedback unit: MC1-first MOS capacitor, MC2-second MOS capacitor;

[0017] S4-common mode feedback unit: Vref-reference level, OPA-operational amplifier. DETAILED DESCRIPTION

[0018] like Figure 1 As shown, the high-performance active low-pass filter described in the present invention is provided with a P-way filtering unit S1, an N-way filtering unit S2, a feedback unit S3 and a common-mode feedback unit S4.

[0019] The P-path filter unit S1 includes a P-path first MOS tube M1P, a P-path second MOS tube M2P, a P-path first capacitor array C1P and a P-path second capacitor array C2P. The drain of the P-path first MOS tube M1P is connected to the P-path common-mode input signal VxP of the common-mode feedback unit S4, the source of the P-path first MOS tube M1P serves as a signal output terminal, and the gate of the P-path first MOS tube M1P serves as a signal input terminal. The drain of the P-path second MOS tube M2P is connected to the source of the P-path first MOS tube M1P, the source of the P-path second MOS tube M2P is grounded, and the gate of the P-path second MOS tube M2P is connected to the drain of the P-path first MOS tube M1P. The P-path first capacitor array C1P is connected in parallel between the source and drain of the P-path first MOS tube M1P, and the P-path second capacitor array C2P is connected in parallel between the source and drain of the P-path second MOS tube M2P.

[0020] The N-way filtering unit S2 includes N-way first MOS tubes M1N, N-way second MOS tubes M2N, N-way first capacitor arrays C1N and N-way second capacitor arrays C2N. The drain of the N-way first MOS tube M1N is connected to the N-way common mode input signal VxN of the common mode feedback unit S4, the source of the N-way first MOS tube M1N is used as a signal output end, and the gate of the N-way first MOS tube M1N is used as a signal input end. The drain of the N-way second MOS tube M2N is connected to the source of the N-way first MOS tube M1N, the source of the N-way second MOS tube M2N is grounded, and the gate of the N-way second MOS tube M2N is connected to the drain of the N-way first MOS tube M1N. The N-way first capacitor array C1N is connected in parallel between the source and drain of the N-way first MOS tube M1N, and the N-way second capacitor array C2N is connected in parallel between the source and drain of the N-way second MOS tube M2N.

[0021] The feedback unit S3 includes a first MOS capacitor MC1 and a second MOS capacitor MC2. The substrate end of the first MOS capacitor MC1 is connected to the signal output end of the P-path filter unit S1, and the gate end is connected to the signal input end of the N-path filter unit S2. The first MOS capacitor MC1 is used to offset the parasitic capacitance between the signal input end of the P-path filter unit S1 and its own signal output end. The substrate end of the second MOS capacitor MC2 is connected to the signal output end of the N-path filter unit S2, and the gate end is connected to the signal input end of the P-path filter unit S1. The second MOS capacitor MC2 is used to offset the parasitic capacitance between the signal input end of the N-path filter unit S2 and its own signal output end.

[0022] The common-mode feedback unit S4 mainly includes an operational amplifier OPA, and outputs a P-way common-mode input signal VxP to the P-way filter unit S1 and outputs an N-way common-mode input signal VxN to the N-way filter unit S2 through a common-mode detection resistor.

[0023] Principle description:

[0024] Any differential input signal will cause the main MOS tube of the path to generate a parasitic capacitance, which will affect the high-frequency stability and out-of-band suppression. Taking the P-path filter unit S1 as an example, the following explanation is given. From input to output, another signal path caused by the parasitic capacitance Cgs of the first MOS tube M1P of the P path is generated, causing the circuit to generate a main zero point in the right half plane, which seriously affects the stability of the circuit at high frequencies and reduces out-of-band suppression. By adding the first MOS capacitor MC1, the parasitic capacitance Cgs can be offset, thereby increasing the high-frequency stability and out-of-band suppression, so that the circuit can have a higher frequency bandwidth.

[0025] Technical effects such as Figure 2-Figure 6 shown.

[0026] In order to increase the stopband suppression, the first MOS capacitor MC1 and the second MOS capacitor MC2 of appropriate size are used to neutralize the parasitic capacitance Cgs of the P-way first MOS transistor M1P and the N-way first MOS transistor M1N, respectively, and offset the main zero point of the circuit, thereby increasing the out-of-band suppression of the filter. Figure 2 As shown in the figure, the out-of-band suppression can be increased by up to 25.3dB at high frequencies, and the -3dB bandwidth of high frequencies reaches 5.1GHz. Because the parasitic capacitance Cgs is offset, the input impedance in the 2.3GHz-9GHz band changes from negative to positive, as shown in the figure. Figure 3 The stability factor Kf increases from less than 1 at 2.2GHz-9.2GHz to greater than 40 at all times, as shown in Figure 4 As shown. By optimizing the filter's performance, the bandwidth can reach 100MHz to 5.1GHz, and it has good out-of-band suppression and stability. When the input single-tone signal is 2GHz, the input 1dB compression point is -4.33dBm, as shown Figure 5 When the input dual-tone signals are 1.9GHz and 2.1GHz respectively, the input third-order intermodulation point is 5.35dBm. Figure 6 shown.

[0027] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A high-performance active low-pass filter, comprising a P-way filter unit (S1) and an N-way filter unit (S2) of the same structure, wherein the inputs of the two-way filter units are differential inputs; It is characterized in that A first MOS capacitor (MC1) and a second MOS capacitor (MC2) are also provided; The substrate end of the first MOS capacitor (MC1) is connected to the signal output end of the P-path filter unit (S1), and the gate end is connected to the signal input end of the N-path filter unit (S2). The first MOS capacitor (MC1) is used to offset the parasitic capacitance between the signal input end of the P-path filter unit (S1) and its own signal output end; The substrate end of the second MOS capacitor (MC2) is connected to the signal output end of the N-way filter unit (S2), and the gate end is connected to the signal input end of the P-way filter unit (S1). The second MOS capacitor (MC2) is used to offset the parasitic capacitance between the signal input end of the N-way filter unit (S2) and its own signal output end; A common mode feedback unit (S4) is provided; The P-path filtering unit (S1) comprises a P-path first MOS tube (M1P), a P-path second MOS tube (M2P), a P-path first capacitor array (C1P) and a P-path second capacitor array (C2P); the drain of the P-path first MOS tube (M1P) is connected to the P-path common-mode input signal (VxP) of the common-mode feedback unit (S4), the source of the P-path first MOS tube (M1P) serves as a signal output end, and the gate of the P-path first MOS tube (M1P) serves as a signal input end; the drain of the P-path second MOS tube (M2P) is connected to the source of the P-path first MOS tube (M1P), the source of the P-path second MOS tube (M2P) is grounded, and the gate of the P-path second MOS tube (M2P) is connected to the drain of the P-path first MOS tube (M1P); the P-path first capacitor array (C1P) is connected in parallel between the source and drain of the P-path first MOS tube (M1P), and the P-path second capacitor array (C2P) is connected in parallel between the source and drain of the P-path second MOS tube (M2P); The N-channel filtering unit (S2) comprises N-channel first MOS tubes (M1N), N-channel second MOS tubes (M2N), N-channel first capacitor arrays (C1N) and N-channel second capacitor arrays (C2N); the drain electrodes of the N-channel first MOS tubes (M1N) are connected to the N-channel common-mode input signals (VxN) of the common-mode feedback unit (S4), the sources of the N-channel first MOS tubes (M1N) serve as signal output terminals, and the gate electrodes of the N-channel first MOS tubes (M1N) serve as signal input terminals; The drains of the N-way second MOS tubes (M2N) are connected to the sources of the N-way first MOS tubes (M1N), the sources of the N-way second MOS tubes (M2N) are grounded, and the gates of the N-way second MOS tubes (M2N) are connected to the drains of the N-way first MOS tubes (M1N); the N-way first capacitor arrays (C1N) are connected in parallel between the sources and drains of the N-way first MOS tubes (M1N), and the N-way second capacitor arrays (C2N) are connected in parallel between the sources and drains of the N-way second MOS tubes (M2N).

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