Low noise amplifier based on Butterworth band-pass filter

Abstract

The invention discloses a low-noise amplifier based on a Butterworth band-pass filter. The low-noise amplifier comprises an input matching module (1), a first-stage amplifier module (2), a Butterworth filter (3), a second-stage amplifier module (4) and an output matching module (5) which are connected in sequence, and a negative feedback network module (6) connected in parallel with the second-stage amplifier module (4) is also arranged between the Butterworth filter (3) and the output matching module (5). According to the invention, only signals in a working frequency range can be received, out-of-band low-frequency and out-of-band high-frequency signals outside the working frequency range can be suppressed, interference between the signals is reduced, and the communication quality of the system is improved.

Description

Technical Field

[0001] The invention relates to a low noise amplifier, in particular to a low noise amplifier based on a Butterworth bandpass filter. Background Art

[0002] In recent years, with the development of wireless communication technology, wireless communication systems are constantly being updated and upgraded, and the communication quality is constantly improving. Therefore, the requirements for transceivers in communication systems are also constantly increasing. As one of the key units of the transceiver, the low noise amplifier is located at the front end of the entire receiving system and is used to receive and amplify the electromagnetic wave signal sent from the antenna. Therefore, the frequency of the signal determines the operating frequency of the low noise amplifier, and also determines the performance of the receiving link and the quality of the entire wireless communication.

[0003] In the design process of traditional low-noise amplifiers, the matching structure is generally implemented using a low-pass structure. However, in some special applications, it is often desired to only receive signals within the required frequency range and suppress out-of-band high-frequency and out-of-band low-frequency signals outside the operating frequency to reduce interference between signals, thereby improving signal quality. These performances cannot be achieved by low-noise amplifiers with a low-pass structure.

[0004] Therefore, there is an urgent need to develop a low-noise amplifier that can only receive signals within the operating frequency range and can suppress out-of-band low-frequency and out-of-band high-frequency signals outside the operating frequency range, reduce interference between signals, and improve the communication quality of the system. Summary of the invention

[0005] The purpose of the present invention is to provide a low noise amplifier based on a Butterworth bandpass filter. The present invention has the characteristics of being able to receive only signals within the operating frequency range and being able to suppress out-of-band low-frequency and out-of-band high-frequency signals outside the operating frequency range, reducing interference between signals, and improving the communication quality of the system.

[0006] The technical solution of the present invention is a low-noise amplifier based on a Butterworth bandpass filter, comprising an input matching module, a first-stage amplifier module, a Butterworth filter, a second-stage amplifier module and an output matching module connected in sequence; a negative feedback network module connected in parallel with the second-stage amplifier module is also provided between the Butterworth filter and the output matching module.

[0007] In the aforementioned low noise amplifier based on Butterworth bandpass filter, the input end of the input matching module is connected to the radio frequency signal source, and the output end of the output matching module is connected to the radio frequency signal output end.

[0008] In the aforementioned low noise amplifier based on Butterworth bandpass filter, both the first-stage amplifier module and the second-stage amplifier module adopt a source negative feedback structure.

[0009] In the aforementioned low noise amplifier based on Butterworth bandpass filter, the first-stage amplifier module and the second-stage amplifier module both include transistors, and the source of the transistor is connected to a source feedback inductor.

[0010] In the aforementioned low noise amplifier based on Butterworth bandpass filter, the transistor is a gallium arsenide semiconductor compound field effect transistor.

[0011] In the aforementioned low noise amplifier based on Butterworth bandpass filter, the design process of the Butterworth filter includes the following steps:

[0012] S1. Determine the indicators of the Butterworth low-pass filter, including: Ω p , passband cutoff frequency; α p , minimum passband attenuation, unit: dB; Ω s , stopband start frequency; α s , maximum attenuation of stop band, unit: dB;

[0013] S2. Calculate the normalized frequency:

[0014]

[0015]

[0016] S3. Calculate the order N and parameter C according to the design requirements:

[0017]

[0018] in,

[0019] S4, obtaining the system function of the normalized Butterworth low-pass filter by looking up the N value table;

[0020] S5. Obtain the required bandpass filter according to the system function transformation.

[0021] In the aforementioned low noise amplifier based on Butterworth bandpass filter, the specific process of step S5 is: assuming that ω is the cutoff frequency of the low pass filter, ω1 and ω2 represent the boundaries of the band pass filter, then the operating frequency of the band pass filter can be obtained by substitution:

[0022]

[0023] Where Δ represents the relative width of the passband: ω0 is the center frequency.

[0024] Compared with the prior art, the present invention uses a Butterworth bandpass filter to perform inter-electrode matching between the first-stage amplifier and the second-stage amplifier, thereby completing the impedance change from the output impedance of the first-stage amplifier to the input impedance of the second-stage amplifier; at the same time, the output impedance of the input first-stage amplifier can be further filtered to suppress signals outside the working frequency band, reduce interference between signals, further improve signal quality, and improve the performance of the receiver.

[0025] The final simulation results of the circuit show that Figure 4-8 As shown, within the working frequency band of 5-6GHz, it is absolutely stable, the noise figure is less than 0.5, the gain is greater than 15dB, and the input and output reflection coefficients are less than -10; outside the working frequency band, the gain drops rapidly, effectively suppressing out-of-band signals and improving receiver performance.

[0026] In summary, the present invention has the characteristics of being able to receive only signals within the operating frequency range and being able to suppress out-of-band low-frequency and out-of-band high-frequency signals outside the operating frequency range, thereby reducing interference between signals and improving the communication quality of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a circuit schematic diagram of the present invention;

[0028] Figure 2 It is a structural block diagram of the present invention;

[0029] Figure 3 It is the equivalent circuit diagram of the source negative feedback structure;

[0030] Figure 4 is the frequency response graph of the Butterworth bandpass filter;

[0031] Figure 5 is the low noise amplifier gain diagram;

[0032] Figure 6 is the noise figure plot of a low noise amplifier;

[0033] Figure 7 is the reflection coefficient graph of the low noise amplifier;

[0034] Figure 8 It is the stability performance diagram of the low noise amplifier.

[0035] The markings in the attached drawings are: 1-input matching module, 2-first stage amplifier module, 3-Butterworth filter, 4-second stage amplifier module, 5-output matching module, 6-negative feedback network module, 401-transistor, 402-source feedback inductor. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0037] Embodiment. A low noise amplifier based on a Butterworth bandpass filter of the present invention has an overall schematic diagram as shown in FIG. Figure 1 As shown, the specific circuit connection method is as follows:

[0038] RFin is connected to the positive terminal of C1;

[0039] The negative end of C1, the positive end of C2, and the positive end of L3 are all connected to V1;

[0040] The negative terminal of C2 is connected to GND;

[0041] The negative terminal of L3, the negative terminal of L4 and the gate of M1 are all connected to V2;

[0042] The positive terminal of L4 is connected to the negative terminal of R1;

[0043] The positive end of R1, the negative end of C3 and VG are all connected to V3;

[0044] The positive terminal of C3 is connected to GND;

[0045] The source of M1 is connected to the positive terminal of L1;

[0046] The negative terminal of L1 is connected to GND;

[0047] The drain of M1, the negative terminal of L5, and the positive terminal of C5 are all connected to V4;

[0048] The positive end of L5, the negative end of C4 and VD are all connected to V5;

[0049] The positive terminal of C4 is connected to GND;

[0050] The negative end of C5, the positive end of L6, the positive end of C6, and the positive end of L7 are all connected to V7;

[0051] The negative terminal of L7 is connected to the positive terminal of C7;

[0052] The negative end of C7, the positive end of L8, the positive end of C8, and the positive end of C9 are all connected to V8;

[0053] The negative end of L6, the negative end of C6, the negative end of L8, the negative end of C8, and GND are all connected to V6;

[0054] The negative terminal of C9, the negative terminal of L9 and the gate of M2 are all connected to V9;

[0055] The positive terminal of L9 is connected to the negative terminal of R2;

[0056] The positive end of R2, the negative end of C10 and VG are all connected to V10;

[0057] The positive end of C10 is connected to GND;

[0058] The source of M2 is connected to the positive electrode of L2;

[0059] The negative terminal of L2 is connected to GND;

[0060] The drain of M2, the negative electrode of L10, and the positive electrode of C12 are all connected to V11;

[0061] The positive electrode of L10, the negative electrode of C11 and VD are all connected to V12;

[0062] The positive terminal of C11 is connected to GND;

[0063] The negative terminal of C12 is connected to RFout;

[0064] Among them, M1 and M2 are gallium arsenide semiconductor compound field effect transistors; R1 and R2 are metal resistors; L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10 are inductors; C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, and C12 are capacitors; RFin is the RF signal input terminal; RFout is the RF signal output terminal; VD is the drain bias voltage input terminal; and VG is the gate bias voltage input terminal.

[0065] The structural block diagram of a low noise amplifier based on a Butterworth bandpass filter of the present invention is as follows: Figure 2 As shown:

[0066] The structure of the low noise amplifier based on the Butterworth bandpass filter at least includes an input matching network, a first-stage amplifier, a Butterworth bandpass filter, a second-stage amplifier, an output matching network and a negative feedback network. Among them:

[0067] The input end of the input matching network is connected to the RF signal source, and the output end is connected to the first-stage amplifier to match the source impedance to the minimum noise input impedance of the transistor, so that the circuit obtains the minimum noise figure;

[0068] The input impedance of the first-stage amplifier is matched to the minimum noise coefficient of the transistor through the input matching network, achieving low-noise amplification of the signal; at the same time, the gain is taken into account to suppress the noise of the subsequent circuit;

[0069] The Butterworth filter acts as a first-stage and second-stage matching network, matching the input impedance of the first-stage amplifier to the input impedance of the second-stage amplifier. At the same time, the Butterworth acts as a bandpass filter, which can effectively suppress out-of-band high-frequency and out-of-band low-frequency signals, reduce interference between signals, and further improve communication quality.

[0070] The input impedance of the second-stage amplifier is matched to the output impedance of the first-stage circuit through a Butterworth filter to amplify the signal so that the circuit obtains the maximum signal gain; at the same time, the power of the low-noise amplifier is considered;

[0071] The input end of the output matching network is connected to the output end of the second-stage amplifier circuit, and the output end is connected to the RF signal output end and connected to the subsequent circuit. The output matching network matches the second-stage output impedance to the load impedance to ensure the effective output of the signal.

[0072] The negative feedback network is connected to the input and output of the secondary amplifier to achieve high gain flatness performance of the low noise amplifier;

[0073] Since the common source structure can provide a lower noise figure and a higher gain, the amplifier adopts a source negative feedback structure. Its equivalent circuit is as follows: Figure 3 As shown:

[0074] By introducing the source feedback inductor Ls at the source of the transistor, the input impedance Zin of the transistor can be expressed as:

[0075]

[0076] When ωL s <<R ds +R i When the input impedance can be approximated as

[0077]

[0078] It can be seen from formula (2) that after the feedback inductor is introduced, the real number of the input impedance is increased, and the imaginary part remains basically unchanged. By adjusting the source inductor Ls, the input impedance point of the transistor is made to coincide with the optimal noise coefficient impedance; at the same time, the source inductor will not introduce additional noise and will not deteriorate the circuit noise coefficient; in addition, the source inductor can also improve the stability of the circuit.

[0079] Butterworth filter is a kind of filter, and its frequency response in the passband is relatively flat, so it is also called the flattest response filter. Using Butterworth filter technology, all different types of filters can be designed, including low-pass, high-pass, band-pass, band-stop, etc. This application uses a band-pass filter.

[0080] There are three main factors to consider when designing a filter circuit:

[0081] Flat response within the operating frequency band; slow transition from passband to stopband; distortion-free transmission within the passband; in addition, rise and fall times also play a very important role.

[0082] The design process of Butterworth filter is as follows:

[0083] S1. Determine the Butterworth low-pass filter index:

[0084] Ω p : passband cutoff frequency; α p : minimum passband attenuation, unit: dB; Ω s , stopband start frequency; α s , maximum stopband attenuation, unit: dB.

[0085] S2. Calculate the normalized frequency:

[0086]

[0087]

[0088] S3. Calculate the order N and parameter C according to the design requirements:

[0089]

[0090] in,

[0091] S4, obtaining the system function of the normalized Butterworth low-pass filter by looking up the N value table;

[0092] S5, transform into the required bandpass filter:

[0093] Assuming ω is the cutoff frequency of the low-pass filter, ω1 and ω2 represent the boundaries of the passband filter, the operating frequency of the bandpass filter can be obtained by substitution:

[0094]

[0095] Where: Δ represents the relative width of the passband: ω0 is the center frequency.

[0096] The series inductor L k Replace with series L C Circuit, component values ​​are:

[0097]

[0098] Similarly, the parallel capacitor C k Replace with parallel L C The circuit, whose components are:

[0099]

[0100] The design results in a Butterworth bandpass filter.

Claims

1. A low noise amplifier based on a Butterworth bandpass filter, characterized in that: The invention comprises an input matching module (1), a first-stage amplifier module (2), a Butterworth filter (3), a second-stage amplifier module (4) and an output matching module (5) which are connected in sequence; a negative feedback network module (6) which is connected in parallel with the second-stage amplifier module (4) is also provided between the Butterworth filter (3) and the output matching module (5).

2. A low noise amplifier based on a Butterworth bandpass filter according to claim 1, characterized in that: The input end of the input matching module (1) is connected to a radio frequency signal source, and the output end of the output matching module (5) is connected to a radio frequency signal output end.

3. The low noise amplifier based on Butterworth bandpass filter according to claim 1, characterized in that: The first-stage amplifier module (3) and the second-stage amplifier module (4) both adopt a source negative feedback structure.

4. A low noise amplifier based on a Butterworth bandpass filter according to claim 3, characterized in that: The first-stage amplifier module (3) and the second-stage amplifier module (4) both include a transistor (401), and the source of the transistor (401) is connected to a source feedback inductor (402).

5. A low noise amplifier based on a Butterworth bandpass filter according to claim 4, characterized in that: The transistor (401) is a gallium arsenide semiconductor compound field effect transistor.

6. A low noise amplifier based on a Butterworth bandpass filter according to claim 1, characterized in that: The design process of the Butterworth filter includes the following steps: S1. Determine the indicators of the Butterworth low-pass filter, including: Ω p , passband cutoff frequency; α p , minimum passband attenuation, unit: dB; Ω s , stopband start frequency; α s , maximum attenuation of stop band, unit: dB; S2. Calculate the normalized frequency: S3. Calculate the order N and parameter C according to the design requirements: in, S4, obtaining the system function of the normalized Butterworth low-pass filter by looking up the N value table; S5. Obtain the required bandpass filter according to the system function transformation.

7. A low noise amplifier based on a Butterworth bandpass filter according to claim 6, characterized in that: The specific process of step S5 is: assuming that ω is the cutoff frequency of the low-pass filter, ω1 and ω2 represent the boundaries of the band-pass filter, then the operating frequency of the band-pass filter can be obtained by substitution: Where Δ represents the relative width of the passband: ω0 is the center frequency.

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