A medium filter-based L-band tuning amplification circuit

Abstract

This invention discloses an L-band tuned amplifier circuit based on a dielectric filter, belonging to the field of radio frequency front-end and wireless communication technology. The circuit includes a pre-stage tuning network, a low-noise amplifier, a post-stage tuning network, and a tuning control module. Both the pre-stage and post-stage tuning networks consist of a dielectric filter and a varactor diode capacitor bank. The resonant frequency of the dielectric filter is changed by adjusting the varactor diode capacitor, thus achieving radio frequency signal tuning. The tuning control module generates control voltage through an FPGA, a digital-to-analog converter (DAC), and an operational amplifier to achieve synchronous tuning of the pre- and post-stages. This invention utilizes the high quality factor and high stability characteristics of the dielectric filter to replace the inductor resonant unit in the traditional LC tuning structure, achieving frequency selection, amplification, and out-of-band interference suppression of signals within the L-band, thereby improving the anti-interference capability and overall reception performance of the receiver front-end.

Description

Technical Field

[0001] This invention relates to the fields of radio frequency front-end and wireless communication technology, specifically to an L-band tuned amplifier circuit based on a dielectric filter, used for frequency selection and low-noise amplification in the receiver front-end of communication equipment. Background Technology

[0002] Modern communication systems operating in complex electromagnetic environments are susceptible to interference from strong blocking signals, mutual interference from multiple devices operating in parallel, and the rapid frequency switching pressure caused by frequency hopping communication. To ensure that communication equipment maintains high receiving sensitivity under strong interference, a frequency-selective tuning filter is typically installed at the receiver front end and cascaded with a low-noise amplifier to achieve out-of-band interference suppression and low-noise amplification. However, the LC tuning structure commonly used in existing technologies has significant shortcomings in the L-band (approximately 1.7 GHz to 2 GHz).

[0003] Traditional LC tuned filters rely on a tuning coil and adjustable capacitor bank to form a resonant circuit. However, at high frequencies, the inductance of the tuning coil is extremely small (typically only a few nH), and manufacturing tolerances significantly affect the resonant frequency, resulting in poor stability of the filter's resonant point and insufficient batch consistency. During production and debugging, it is often necessary to repeatedly adjust the coil turn spacing to obtain the target inductance value, which is complex and difficult to guarantee consistency. In addition, due to the high flexibility of the coil structure, it is prone to deformation under external forces such as vibration and temperature changes, causing the resonant frequency to drift and affecting the receiver's frequency selection and long-term stability.

[0004] Meanwhile, LC-tuned structures have relatively low quality factors (Q values) at high frequencies, insufficient steepness of the resonance curve, and limited out-of-band rejection capabilities. When an LC-tuned filter is cascaded with a low-noise amplifier, the VSWR at the resonant point may abruptly change, easily causing input-output impedance mismatch, which deteriorates the noise figure of the low-noise amplifier and reduces the overall sensitivity of the receiver. In frequency-hopping communication systems, where frequency switching speeds are fast, the response speed and stability of LC-tuned structures are insufficient to meet the requirements of rapid tuning.

[0005] In existing technologies, dielectric filters are typically used in fixed-frequency bandpass filters, relying on the high stability and quality factor of the dielectric resonator to achieve excellent filtering performance. However, current publicly available technologies do not combine dielectric filters with varactor diodes to form a tunable structure, nor do they cascade them with low-noise amplifiers to form a tuned amplifier circuit. Therefore, in L-band communication equipment, there is still a lack of a front-end circuit structure that can simultaneously meet the requirements of high-frequency stability, tunability, strong interference suppression, and low-noise amplification.

[0006] Based on the shortcomings of the existing technology, it is necessary to propose a new tuned amplifier circuit structure. By utilizing the high stability and quality factor of the dielectric filter and combining it with a varactor diode to achieve tunability, and cascading it with a low-noise amplifier, a tuned amplifier circuit suitable for L-band communication equipment is formed to improve the receiver's frequency selection capability, anti-interference capability and overall reception performance. Summary of the Invention

[0007] The purpose of this invention is to provide an L-band tuned amplifier circuit based on a combination of a dielectric filter and a varactor diode. By utilizing the high quality factor and high stability of the dielectric filter to replace the traditional LC tuning structure, the frequency selection capability, anti-interference capability, and frequency stability of the receiver front end are improved.

[0008] To achieve the above objectives, the technical solution of the present invention is: an L-band tuned amplifier circuit based on a dielectric filter, comprising a pre-stage tuning network, a low-noise amplifier, a post-stage tuning network, and a tuning control module; The pre-amplifier tuning network is connected between the signal input terminal and the low-noise amplifier to tune and select the frequency of the input RF signal. The pre-amplifier tuning network includes a dielectric filter DR1 and a varactor diode capacitor group Cv1 connected to the dielectric filter DR1. The dielectric filter DR1 and the varactor diode capacitor group Cv1 form a tunable resonant circuit. The low-noise amplifier is connected between the pre-stage tuning network and the post-stage tuning network to amplify the radio frequency signal after frequency selection by the pre-stage tuning network with low noise. The post-stage tuning network is connected between the low-noise amplifier and the signal output terminal, and is used to re-tune and select the frequency of the RF signal after it has been amplified by the low-noise amplifier. The post-stage tuning network includes a dielectric filter DR2 and a varactor diode capacitor group Cv2 connected to the dielectric filter DR2. The dielectric filter DR2 and the varactor diode capacitor group Cv2 form a tunable resonant circuit. The tuning control module is connected to the pre-stage tuning network and the post-stage tuning network respectively. It is used to generate tuning control voltages Vt1 and Vt2, and change the resonant frequency of dielectric filters DR1 and DR2 by adjusting the equivalent capacitance of varactor diode capacitor banks Cv1 and Cv2, so that the pre-stage tuning network and the post-stage tuning network are tuned synchronously.

[0009] Compared with the prior art, the present invention has the following technical effects: First, the dielectric ceramic coaxial resonator used in this invention has a high quality factor and high processing precision. By strictly controlling its external dimensions, precise control of different operating frequencies can be achieved, with the highest operating frequency reaching 6GHz. The dielectric resonator has fine frequency steps and good processing consistency, enabling the tuned filter to maintain stable resonance characteristics during mass production. This avoids the manufacturing difficulties, complex debugging, and insufficient consistency problems caused by the extremely small inductance of traditional tuning coils (typically only a few nH), thereby reducing manual debugging steps and improving product manufacturability.

[0010] Secondly, the L-band tuned amplifier circuit based on dielectric filters of this invention achieves tuning and amplification functions in the same circuit by setting tunable filters before and after the low-noise amplifier and using λ / 4 dielectric resonators instead of traditional LC tuning coils. The cascaded design of the pre- and post-stage tuning filters and the low-noise amplifier, after joint debugging, effectively avoids the input-output impedance mismatch problem that easily occurs when traditional LC tuning structures are cascaded with low-noise amplifiers in the high-frequency band. This significantly reduces the VSWR, minimizes noise figure degradation, improves channel gain, and enhances the overall sensitivity and anti-interference capability of the receiver.

[0011] Furthermore, the tuning section of this invention uses a dielectric filter as the resonant core, which is connected in parallel with a varactor diode capacitor bank to form a tunable resonant circuit. The dielectric filter is made of a rigid ceramic material, featuring high mechanical strength, good dimensional stability, and low temperature drift. It will not deform due to external forces such as vibration or temperature changes, thus avoiding the problem of resonant frequency drift caused by the structural flexibility of traditional tuning coils in the high-frequency range. This significantly improves the long-term stability and environmental adaptability of the tuning filter, and enhances the reliability of the product.

[0012] In summary, this invention achieves high-stability frequency selection, strong interference suppression, and low-noise amplification in the L-band receiver front-end through the high stability and quality factor of the dielectric filter and its tunable combination with a varactor diode. The cascaded design of the pre- and post-stage tuning and low-noise amplifier improves impedance matching, reduces the noise figure, and increases receiver sensitivity. The high-consistency fabrication characteristics of the dielectric resonator enhance product reliability and mass production capabilities. This invention has a novel structure, effectively solves the various problems raised in the background art, and has significant technical effects and application value. Attached Figure Description

[0013] Figure 1 This is a comparison curve of the amplitude-frequency characteristics of different resonant structures of the dielectric filter of this invention; Figure 2 This is a schematic diagram of the equivalent RLC circuit model of the λ / 4 dielectric filter of this invention; Figure 3This is a block diagram of the overall circuit system of the present invention; Figure 4 This is a schematic diagram of the complete circuit principle of the present invention. Detailed Implementation

[0014] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are used to illustrate the technical solutions of the present invention and are intended to enable those skilled in the art to implement the present invention accordingly; they do not constitute a limitation on the scope of protection of the present invention.

[0015] Figure 1 The amplitude-frequency characteristics of the dielectric filter are illustrated, showing typical amplitude-frequency responses of the dielectric filter under different resonant structures, including the response curves of the pass-through structure, the λ / 2 structure, and the λ / 4 structure. The pass-through structure maintains a flat response across the entire frequency band, the λ / 2 structure exhibits attenuation at the resonant frequency, and the λ / 4 structure exhibits enhancement at the resonant frequency. This invention uses a λ / 4 dielectric filter as the resonant core of the tuning network to obtain a bandpass response, thereby improving the frequency selectivity of the receiver front-end.

[0016] Figure 2 The equivalent circuit of the dielectric filter is shown. The dielectric filter can be equivalently represented as a short stub structure with a characteristic impedance Z0, and its resonant behavior can be further equivalent to an RLC parallel circuit model, where R represents the equivalent loss of the dielectric filter, L represents the equivalent inductance of the dielectric filter, and C represents the equivalent capacitance of the dielectric filter. Near the resonant frequency, the dielectric filter exhibits significant frequency selectivity. By connecting a varactor diode capacitor bank in parallel with the dielectric filter, the equivalent capacitance can be changed by altering the junction capacitance of the varactor diode, thereby achieving continuous tuning of the resonant frequency. The tuning network of this invention is constructed based on this equivalent model. An λ / 4 resonant structure is formed internally within the dielectric filter, which can employ dielectric block resonators, coaxial dielectric resonators, or sheet dielectric resonators, exhibiting high quality factor and good frequency stability.

[0017] Figure 3 A block diagram of an L-band tuned amplifier circuit based on a dielectric filter is shown. The circuit includes a pre-stage tuning network, a low-noise amplifier, a tuning control module, and a post-stage tuning network. After the signal enters from the input terminal, it sequentially passes through the pre-stage tuning network, the low-noise amplifier, and the post-stage tuning network, and is finally output from the output terminal.

[0018] The pre-stage tuning network selects the frequency of the input signal. Internally, it consists of a dielectric filter and a varactor diode capacitor bank forming a resonant branch. The resonant frequency is adjustable via a tuning voltage provided by the tuning control module. The low-noise amplifier amplifies the signal after frequency selection by the pre-stage tuning network with low noise and provides stable RF drive capability to the subsequent tuning network. The subsequent tuning network corresponds in structure to the pre-stage tuning network, also consisting of a dielectric filter and a varactor diode capacitor bank forming a resonant branch. It further selects the frequency of the amplified signal to improve out-of-band rejection.

[0019] The tuning control module mainly consists of an FPGA, a dual-channel digital-to-analog converter (DAC), and operational amplifiers. The FPGA outputs the tuning control word and provides digital control signals to the dual-channel DAC via a serial interface. The dual-channel DAC converts the digital control word into two analog voltages. These two analog voltages are amplified by the operational amplifiers to form tuning control voltages Vt1 and Vt2, which are then fed into the bias branches of the pre-stage tuning network and the post-stage tuning network, respectively. These bias branches are used to change the junction capacitance of the varactor diode capacitor bank, causing the resonant frequencies of the dielectric filters DR1 and DR2 to switch between preset frequencies.

[0020] like Figure 4 As shown, this invention achieves tuning and amplification functions in the same circuit through the cascaded design of the pre- and post-stage tuning networks and the low-noise amplifier, as well as the synchronous tuning capability provided by the tuning control module. This constitutes the tuning amplifier circuit structure of this invention, as detailed below: The pre-amplifier tuning network includes a coupling capacitor Cc1, a dielectric filter DR1, a varactor diode capacitor bank Cv1, a bias resistor Rb1, a bias decoupling capacitor Cb1, a tuning control voltage Vt1, and a high-frequency ground. The varactor diode capacitor bank Cv1 is connected in parallel with the dielectric filter DR1, forming a tunable resonant circuit. The resonant frequency of the dielectric filter DR1 is adjusted by changing the equivalent capacitance of the varactor diode capacitor bank Cv1. The signal input is connected to node N1 via the coupling capacitor Cc1. Node N1 is connected to the input of the dielectric filter DR1, and the other end of DR1 is connected to RF ground. The varactor diode capacitor bank Cv1 consists of varactor diodes D1 and D2. One end of D1 and D2 is connected to node N1, and the other end of D1 and D2 is connected to the tuning control voltage Vt1 via the bias resistor Rb1 and grounded via the bias decoupling capacitor Cb1. Node N1 is connected to the input of the low-noise amplifier via the input matching network Cm1 and Lm1.

[0021] The low-noise amplifier is used to amplify the signal after frequency selection by the pre-stage tuning network with low noise. The input of the low-noise amplifier is connected to the output of the pre-stage tuning network via input matching networks Cm1 and Lm1, and the output is connected to the input of the post-stage tuning network via output matching networks Cm2 and Lm2. The power supply is connected to VDD via decoupling capacitor Cd, and the ground is connected to RF ground via an array of ground vias.

[0022] The post-stage tuning network corresponds to the pre-stage tuning network structure, including coupling capacitor Cc2, dielectric filter DR2, varactor diode capacitor bank Cv2, bias resistor Rb2, bias decoupling capacitor Cb2, tuning control voltage Vt2, and high-frequency ground. The output of the low-noise amplifier is connected to node N2 via coupling capacitor Cc2. Node N2 is connected to the input of dielectric filter DR2, and the other end of DR2 is connected to RF ground. The varactor diode capacitor bank Cv2 consists of varactor diodes D3 and D4. One end of D3 and D4 is connected to node N2, and the other end of D3 and D4 is connected to the tuning control voltage Vt2 via bias resistor Rb2, and grounded via bias decoupling capacitor Cb2. Node N2 is connected to the signal output terminal via output matching networks Cm2 and Lm2.

[0023] The tuning control module consists of an FPGA, a dual-channel digital-to-analog converter (DAC), and operational amplifiers A1 and A2. The FPGA outputs a serial control word and controls the dual-channel DAC to generate two analog output voltages, Vout1 and Vout2. Vout1 is amplified by operational amplifier A2 to form the tuning control voltage Vt1, and Vout2 is amplified by operational amplifier A1 to form the tuning control voltage Vt2. Vt1 is used to change the junction capacitance of D1 and D2 in the varactor diode capacitor bank Cv1, and Vt2 is used to change the junction capacitance of D3 and D4 in the varactor diode capacitor bank Cv2. By adjusting the equivalent capacitance value, the resonant frequencies of dielectric filters DR1 and DR2 are changed, thereby achieving frequency switching of the tuning network.

[0024] The working principle of the tuned amplifier circuit of this invention is as follows: The input signal first enters the pre-tuning network, which consists of a λ / 4 dielectric filter DR1 and a varactor diode capacitor bank Cv1 forming a resonant branch. The tuning control voltage Vt1 acts on varactor diodes D1 and D2, changing their junction capacitance and thus altering the equivalent capacitance of DR1, allowing its resonant frequency to continuously shift within a preset frequency range. When the input signal frequency matches the resonant frequency of DR1, the pre-tuning network exhibits a bandpass response, achieving target frequency selection and suppressing out-of-band blocking interference.

[0025] The signal, after frequency selection by the pre-tuning network, enters the low-noise amplifier through the input matching networks Cm1 and Lm1. The low-noise amplifier, through the combined action of the input and output matching networks, achieves low-noise, high-stability gain amplification of the RF signal.

[0026] The amplified signal enters the subsequent tuning network, which consists of a λ / 4 dielectric filter DR2 and a varactor diode capacitor bank Cv2 forming a resonant branch. The tuning control voltage Vt2 acts on varactor diodes D3 and D4, causing a change in their junction capacitance, thereby adjusting the resonant frequency of DR2. This ensures that the subsequent tuning network keeps pace with the preceding tuning network, further selecting the frequency of the amplified signal and improving overall out-of-band rejection.

[0027] The tuning control module mainly consists of a Field Programmable Gate Array (FPGA), a dual-channel Digital-to-Analog Converter (DAC), and operational amplifiers. The tuning control module outputs a tuning control word through the FPGA, which controls the dual-channel DAC to generate two analog control voltages. These voltages are amplified by the operational amplifier to form Vt1 and Vt2, which control the capacitance changes of Cv1 and Cv2 respectively, achieving synchronous adjustment of the resonant frequencies of DR1 and DR2. The entire circuit achieves rapid and continuous tuning of signals within the L-band, low-noise amplification, and out-of-band interference suppression through dynamic control of the dielectric filter's resonant frequency, thereby improving the receiver's anti-interference capability and overall reception performance.

[0028] Table 1 shows the performance test results of an embodiment of the tuned amplifier circuit of the present invention. The pre-stage tuning network first selects the frequency of the input signal, suppresses strong blocking interference, and maintains good impedance matching characteristics throughout the entire operating frequency band, with an input-output VSWR ≤ 1.8. The low-noise amplifier amplifies the frequency-selected signal with low noise, enabling the circuit to achieve a stable gain of 15 ± 0.5 dB in the 1.7 GHz to 2 GHz operating frequency band. The post-stage tuning network further enhances the out-of-band rejection capability, achieving an out-of-band rejection of over 22 dBc at a position ± 20% offset from the center frequency f0. By controlling the equivalent capacitance changes of the varactor diode capacitor banks Cv1 and Cv2 through tuning voltages Vt1 and Vt2, the resonant frequencies of the dielectric filters DR1 and DR2 change synchronously, achieving continuous tuning within the L-band range and keeping the frequency switching time within 10 μs, thereby meeting the application requirements of fast tuning.

[0029] Table 1 .

Claims

1. An L-band tuned amplifier circuit based on a dielectric filter, characterized in that, The system includes a pre-stage tuning network, a low-noise amplifier, a post-stage tuning network, and a tuning control module. The pre-stage tuning network is connected between the signal input terminal and the low-noise amplifier, and is used to tune and select the frequency of the input radio frequency signal. The pre-stage tuning network includes a dielectric filter DR1 and a varactor diode capacitor bank Cv1 connected to the dielectric filter DR1. The dielectric filter DR1 and the varactor diode capacitor bank Cv1 form a tunable resonant circuit. The low-noise amplifier is connected between the pre-stage tuning network and the post-stage tuning network, and is used to amplify the radio frequency signal after frequency selection by the pre-stage tuning network with low noise. The post-stage tuning network is connected between the low-noise amplifier and the signal output terminal, and is used to re-tune and select the frequency of the RF signal amplified by the low-noise amplifier. The post-stage tuning network includes a dielectric filter DR2 and a varactor diode capacitor bank Cv2 connected to the dielectric filter DR2. The dielectric filter DR2 and the varactor diode capacitor bank Cv2 form a tunable resonant circuit. The tuning control module is connected to the pre-stage tuning network and the post-stage tuning network respectively, and is used to generate tuning control voltages Vt1 and Vt2. By adjusting the equivalent capacitance of the varactor diode capacitor banks Cv1 and Cv2, the resonant frequencies of the dielectric filters DR1 and DR2 are changed, so that the pre-stage tuning network and the post-stage tuning network are tuned synchronously.

2. The L-band tuned amplifier circuit based on a dielectric filter according to claim 1, characterized in that: Both the dielectric filters DR1 and DR2 employ a λ / 4 dielectric resonant structure to achieve frequency selection of radio frequency signals.

3. The L-band tuned amplifier circuit based on a dielectric filter according to claim 1, characterized in that: A varactor diode capacitor bank Cv1 is connected to a dielectric filter DR1 to form a parallel tuning structure. The varactor diode capacitor bank Cv1 and the dielectric filter DR1 are connected in parallel to form a tuned resonant structure. The resonant frequency of the dielectric filter is adjusted by changing the equivalent capacitance value of the varactor diode capacitor bank.

4. The L-band tuned amplifier circuit based on a dielectric filter according to claim 1, characterized in that: The pre-tuning network also includes a coupling capacitor Cc1, a bias resistor Rb1, and a bias decoupling capacitor Cb1. The signal input terminal is connected to node N1 via the coupling capacitor Cc1. Node N1 is connected to the dielectric filter DR1 and the varactor diode capacitor bank Cv1. The varactor diode capacitor bank Cv1 is composed of varactor diodes D1 and D2. One end of D1 and D2 is connected to node N1, and the other end is connected to the tuning control voltage Vt1 via the bias resistor Rb1 and grounded via the bias decoupling capacitor Cb1.

5. The L-band tuned amplifier circuit based on a dielectric filter according to claim 1, characterized in that: The post-stage tuning network also includes a coupling capacitor Cc2, a bias resistor Rb2, and a bias decoupling capacitor Cb2. The output of the low-noise amplifier is connected to node N2 via the coupling capacitor Cc2. Node N2 is connected to the dielectric filter DR2 and the varactor diode capacitor bank Cv2. The varactor diode capacitor bank Cv2 is composed of varactor diodes D3 and D4. One end of D3 and D4 is connected to node N2, and the other end is connected to the tuning control voltage Vt2 via the bias resistor Rb2 and grounded via the bias decoupling capacitor Cb2.

6. The L-band tuned amplifier circuit based on a dielectric filter according to claim 1, characterized in that: The tuning control module includes a field-programmable gate array (FPGA), a dual-channel digital-to-analog converter (DAC), and operational amplifiers A1 and A2. The FPGA outputs a tuning control word to the dual-channel DAC, which outputs analog voltages Vout1 and Vout2 based on the tuning control word. Vout1 and Vout2 are amplified by operational amplifiers A2 and A1, respectively, to form tuning control voltages Vt1 and Vt2, which control varactor diode capacitor banks Cv1 and Cv2, respectively, to achieve synchronous tuning between the front-stage tuning network and the rear-stage tuning network.

7. The L-band tuned amplifier circuit based on a dielectric filter according to claim 1, characterized in that: An input matching network is set between the low-noise amplifier and the pre-amplifier tuning network. The input matching network includes a capacitor Cm1 and an inductor Lm1. An output matching network is set between the low-noise amplifier and the post-amplifier tuning network. The output matching network includes a capacitor Cm2 and an inductor Lm2. The input matching network and the output matching network are used to achieve impedance matching between the low-noise amplifier and the tuning network.

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