An automatic frequency controller
Through the synergistic effect of multi-level mixing architecture and phase-locked loop unit, frequency drift is dynamically corrected, solving the problems of frequency loss and signal distortion in traditional automatic frequency control systems under complex environments, and improving frequency stability and signal quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SHANGHAI WEIXIAO ELECTRONIC TECH CO LTD
- Filing Date
- 2025-08-13
- Publication Date
- 2026-06-16
AI Technical Summary
Traditional automatic frequency control systems are prone to local oscillation frequency drift under complex electromagnetic environments or temperature changes, which leads to loss of synchronization of intermediate frequency signals and affects demodulation stability. The accumulation of frequency errors in the intermediate frequency signal amplification and demodulation stages causes distortion of the baseband video signal, and there is a lack of dynamic level calibration mechanism.
A multi-stage mixing architecture is adopted, combining a phase-locked loop unit and a main control unit. The frequency is dynamically corrected through an error extraction unit, and the temperature compensation characteristics of the crystal oscillation unit are utilized to achieve sub-millisecond frequency adjustment and signal-to-noise ratio improvement.
It achieves stable frequency locking in complex environments, eliminates long-term drift caused by temperature/voltage, improves the signal-to-noise ratio of the baseband signal, controls the frequency error within ±1Hz, and reduces harmonic distortion to less than 0.8%, ensuring demodulation stability and signal quality.
Smart Images
Figure CN224367813U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of electronic circuit technology, and in particular to an automatic frequency controller. Background Technology
[0002] Traditional Automatic Frequency Control (AFC) systems are prone to local oscillation frequency drift under complex electromagnetic environments or temperature variations, leading to intermediate frequency (IF) signal frequency loss and affecting demodulation stability. Furthermore, the accumulation of frequency errors in the IF signal amplification and demodulation stages causes distortion of the baseband video signal (such as chroma distortion and synchronization loss), and lacks a dynamic level calibration mechanism.
[0003] Therefore, there is an urgent need to propose an automatic frequency controller to solve the technical problems existing in the prior art. Utility Model Content
[0004] To address the issues of existing automatic frequency control (AFC) systems where the local oscillation frequency easily drifts under complex electromagnetic environments or temperature variations, leading to intermediate frequency (IF) signal frequency loss and affecting demodulation stability, and further problems such as baseband video signal distortion (e.g., chroma distortion, synchronization loss) due to accumulated frequency errors in the IF signal amplification and demodulation stages, and the lack of a dynamic level calibration mechanism, this invention proposes an automatic frequency controller.
[0005] In a preferred embodiment of this utility model, an automatic frequency controller is provided, which includes: a front-end receiving unit, a main mixing unit, a main local oscillator unit, a phase-locked loop unit, a main control unit, an intermediate frequency gain unit, an auxiliary mixing unit, a crystal oscillation unit, a detection unit, a video output preamplifier unit, an error extraction unit, and a back-end output unit.
[0006] A front-end receiving unit, wherein the front-end receiving unit is used to receive external input signals;
[0007] The main mixing unit mixes the external input signal with the first local oscillator frequency generated by the main local oscillator unit to generate a first intermediate frequency signal.
[0008] A phase-locked loop unit, wherein the phase-locked loop unit is used to lock the first local oscillator frequency;
[0009] The main control unit is used to control the first local oscillator frequency generated by the main local oscillator unit;
[0010] An intermediate frequency gain unit is used to amplify the first intermediate frequency signal;
[0011] The amplified first intermediate frequency signal enters the auxiliary mixing unit and mixes with the second local oscillator frequency generated by the crystal oscillation unit to generate the second intermediate frequency signal.
[0012] The detection unit is used to receive the generated second intermediate frequency signal and demodulate it into a baseband video signal. The baseband video signal is amplified to a preset reference level by a video output preamplifier unit.
[0013] An error extraction unit extracts an error signal from the preset reference level and feeds it back to the main control unit for dynamic correction.
[0014] The back-end output unit outputs the dynamically corrected video signal.
[0015] Preferably, the main mixing unit is a Mini-Circuits ADE-1L double-balanced mixer.
[0016] Preferably, the phase-locked loop unit uses the ADF4351 fractional-frequency phase-locked loop chip.
[0017] Preferably, the crystal oscillation unit is a temperature-controlled crystal oscillator unit.
[0018] Compared with the prior art, the present invention can achieve the following beneficial effects:
[0019] An automatic frequency controller of this application achieves locking of the first local oscillator frequency through the cooperation of a phase-locked loop unit and a main control unit, eliminating long-term drift caused by temperature / voltage. The error extraction unit extracts the instantaneous frequency deviation with the reference level of the video signal as a reference, feeds it back to the main control unit to generate a correction word, and completes sub-millisecond frequency adjustment through the numerically controlled oscillator of the main local oscillator unit. The two-stage mixing architecture combined with the temperature-compensated crystal oscillator of the crystal oscillator unit improves the signal-to-noise ratio of the demodulated baseband signal. Attached Figure Description
[0020] The preferred embodiments will now be described in a clear and easy-to-understand manner, with reference to the accompanying drawings, to further explain the above-mentioned characteristics, technical features, advantages, and implementation methods.
[0021] Figure 1 This invention illustrates a multifunctional radar signal simulator system according to one embodiment of the present invention. Detailed Implementation
[0022] The following provides a more detailed description of various aspects of this utility model.
[0023] Unless otherwise defined or stated, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention.
[0024] Other aspects of this invention will be apparent to those skilled in the art from the disclosure herein.
[0025] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the specific implementation methods of this utility model will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of this utility model. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.
[0026] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show components related to this application and are not drawn according to the actual number, shape, and size of the components in the actual implementation. In the actual implementation, the form, quantity, and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex. For example, the thickness of the elements in the drawings may be exaggerated for clarity.
[0027] Example 1
[0028] As attached Figure 1 As shown, this utility model implements an automatic frequency controller, which includes: a front-end receiving unit 1, a main mixing unit 2, a main local oscillator unit 3, a phase-locked loop unit 4, a main control unit 5, an intermediate frequency gain unit 6, an auxiliary mixing unit 7, a crystal oscillator unit 8, a detection unit 9, a video output pre-amplifier unit 10, an error extraction unit 11, and a back-end output unit 12; wherein,
[0029] The front-end receiving unit 1 uses a bandpass filter with a center frequency of 666MHz and a bandwidth of 392MHz to receive the UHF band radio frequency signal input from the antenna, and controls the voltage standing wave ratio to below 1.5 through an impedance matching circuit.
[0030] The main mixer unit 2 mixes the input signal with the adjustable local oscillator signal of 500MHz to 892MHz generated by the main local oscillator unit 3 through a dual balanced mixer (e.g., Mini-Circuits ADE-1L) to generate a first intermediate frequency signal of 70MHz. The main local oscillator unit 3 uses an ADF4351 phase-locked loop chip and implements frequency adjustment in 1kHz steps through the SPI interface of the STM32H743 main control unit 5.
[0031] The phase-locked loop unit 4 locks the first local oscillator signal through a fractional frequency-division phase-locked loop with a loop bandwidth of 20kHz, so that the phase error is less than 1 degree and the locking time is shortened to less than 300 microseconds.
[0032] The intermediate frequency gain unit 6 amplifies the first intermediate frequency signal by 60dB and outputs a stable 0dBm level through the cascaded structure of the ADL5541 preamplifier and the PGA-103+ programmable gain amplifier.
[0033] The auxiliary mixing unit 7 mixes the amplified 70MHz first intermediate frequency signal with the crystal oscillator unit 8 (which generates an 80.7MHz second local oscillator signal after frequency doubling) to generate a 10.7MHz second intermediate frequency signal. The crystal oscillator unit 8 uses a temperature-controlled crystal oscillator with a stability of ±0.05ppm.
[0034] The detection unit 9 demodulates the second intermediate frequency signal into a 0.5Vpp baseband video signal using an AD8347 quadrature synchronous detector, and then calibrates it to the 1Vpp standard level using a PGA112 amplifier in the video output preamplifier unit 10. The two-stage mixing architecture, combined with the temperature-controlled crystal oscillator of the crystal oscillator unit 8, improves the signal-to-noise ratio of the demodulated baseband signal by >10dB.
[0035] The error extraction unit 11 samples the video signal through the built-in ADC of STM32H743 and performs FFT frequency offset analysis. After extracting the error signal at a resolution of 0.1Hz, it dynamically adjusts the frequency of the main local oscillator unit 3 through a PID algorithm with KP=0.5, KI=0.1, and KD=0.01.
[0036] The back-end output unit 12 outputs a baseband video signal conforming to the ITU-R BT.656 standard through a 75Ω impedance-matched BNC interface, and integrates a TVS diode to achieve 8kV ESD protection. Ultimately, it achieves an output frequency error of less than ±1Hz and harmonic distortion of less than 0.8% within the ±100kHz input frequency deviation range, eliminating long-term drift caused by temperature / voltage.
[0037] Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or practice the method can be implemented using other structures and / or functionalities besides one or more of the aspects set forth herein.
[0038] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of this utility model. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this utility model, and these improvements and modifications should also be considered within the protection scope of this utility model.
[0039] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing description of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by the appended claims.
Claims
1. An automatic frequency controller, characterized in that, The automatic frequency controller includes: a front-end receiving unit, a main mixing unit, a main local oscillator unit, a phase-locked loop unit, a main control unit, an intermediate frequency gain unit, an auxiliary mixing unit, a crystal oscillation unit, a detection unit, a video output preamplifier unit, an error extraction unit, and a back-end output unit. A front-end receiving unit, wherein the front-end receiving unit is used to receive external input signals; The main mixing unit mixes the external input signal with the first local oscillator frequency generated by the main local oscillator unit to generate a first intermediate frequency signal. A phase-locked loop unit, wherein the phase-locked loop unit is used to lock the first local oscillator frequency; The main control unit is used to control the first local oscillator frequency generated by the main local oscillator unit; An intermediate frequency gain unit is used to amplify the first intermediate frequency signal; The amplified first intermediate frequency signal enters the auxiliary mixing unit and mixes with the second local oscillator frequency generated by the crystal oscillation unit to generate the second intermediate frequency signal. The detection unit is used to receive the generated second intermediate frequency signal and demodulate it into a baseband video signal. The baseband video signal is amplified to a preset reference level by a video output preamplifier unit. An error extraction unit extracts an error signal from the preset reference level and feeds it back to the main control unit for dynamic correction. The back-end output unit outputs the dynamically corrected video signal.
2. An automatic frequency controller as described in claim 1, characterized in that, The main mixing unit is a Mini-Circuits ADE-1L double-balanced mixer.
3. An automatic frequency controller as described in claim 2, characterized in that, The phase-locked loop unit uses the ADF4351 fractional frequency divider phase-locked loop chip.
4. An automatic frequency controller as described in claim 3, characterized in that, The crystal oscillation unit is a temperature-controlled crystal oscillator unit.