Variable Frequency Filter Calibration With Temperature Compensation
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Solution Overview
Problem
Calibration of voltage-tractable band-pass filters in radio chains is challenging due to varying central frequencies with temperature changes, requiring individual calibration and external devices, which are not adaptable to conventional radio channels and towable filters.
Innovation Solution
A method and system using a digital-to-analog converter driven by a programmable device, such as an FPGA, to generate voltage for the filter, with a temperature sensor and power measurement devices to create a calibration table for optimal frequency settings, allowing self-calibration without external devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external measuring devices are used for calibration, then calibration can be performed, but device complexity increases and calibration time is extended
Solution Approach 1:
The filter calibration system performs self-calibration using its own internal components (signal generator, power meter, and control unit) without requiring external measuring devices. The control unit automatically adjusts the filter's central frequency by generating test signals, measuring output power, and iteratively optimizing the frequency setting based on the measured responses, thereby eliminating the need for external calibration equipment.
Solution Approach 2:
The system implements a feedback mechanism where the power meter measures the output signal power after it passes through the filter, and this measurement is fed back to the control unit. The control unit uses this feedback information to adjust the filter's central frequency setting, creating a closed-loop calibration process that achieves precise calibration without external devices.
2Measurement precision
If traditional calibration methods are used, then calibration can be performed, but calibration time is extended and productivity decreases
Solution Approach 1:
The system performs preliminary actions by pre-configuring the signal generator to automatically generate test signals at frequencies surrounding the filter's central frequency, and pre-positioning the power meter to measure output power. This automated preparation eliminates manual setup time and enables rapid iterative calibration, significantly improving calibration speed while maintaining accuracy.
Solution Approach 2:
The calibration process operates continuously through automated iterative adjustments. The control unit continuously generates test signals, the power meter continuously measures output power, and the control unit continuously adjusts the filter frequency based on measurements. This continuous automated operation eliminates idle time between calibration steps, dramatically increasing calibration productivity compared to manual methods.
3Adaptability or versatility
If voltage is applied to adjust filter frequency, then central frequency can be changed, but temperature variations cause frequency drift
Solution Approach 1:
The system uses feedback to continuously monitor and correct temperature-induced frequency drift. The power meter measures the actual output power at known test frequencies, and the control unit compares these measurements against expected values to detect frequency drift caused by temperature variations. The control unit then applies corrective voltage adjustments to restore the filter's central frequency to its intended value, maintaining frequency stability despite temperature changes.
Solution Approach 2:
The system replaces manual mechanical frequency adjustment with an automated electronic control system. Instead of physically adjusting the filter, the control unit automatically applies voltage to the filter's tuning elements based on power measurements, enabling precise and rapid frequency correction that compensates for temperature drift more effectively than manual adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid and precise calibration of variable frequency filters within radio chains, adapting to temperature changes and eliminating the need for external calibration equipment, ensuring accurate central frequency adjustment.
Implementation Method 1
use is made of a code value contained in a calibration table... a digital-to-analog converter connected to a signal amplifier and to a filter positioned upstream of an antenna
Implementation Method 2
a temperature sensor, a device emitting a signal, a device adapted to measure the value of the power of the signal after passing through said filter
Data Source
Figure 1~2
Figure 3
Figure 4A~4B
AI summary
The invention relates to a method and a system for calibrating a filter whose center frequency value is variable, characterized in that it comprises at least the following steps: - initialization of the steps with a code value, - measurement of the power value after passing through the filter to be calibrated for each frequency contained in the calibration table, - execution of an iterative process of the secant method on all rejection frequencies associated with said filter to determine the code value allowing the filter to be balanced for each of the frequency and temperature values, leading to a calibration table.