FM-CW Radar Modulation Circuit for VCO Linearity Correction
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Solution Overview
Problem
Conventional FM-CW radar systems face challenges in achieving high linearity of frequency modulation due to the nonlinear frequency characteristics of Voltage Controlled Oscillators (VCOs), which affect measurement accuracy and require complex correction mechanisms.
Innovation Solution
A frequency modulation circuit that includes a digital-analog converter, voltage control oscillator, frequency divider, frequency converter, single-phase differential converter, analog-digital converter, and signal processing circuit to generate and correct modulation control voltage data, ensuring high linearity of frequency modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a VCO is used for frequency modulation in FM-CW radar, then the circuit configuration remains relatively simple, but the frequency modulation linearity deteriorates due to nonlinear voltage-frequency characteristics
Solution Approach 1:
The patent implements feedback control by measuring the actual oscillation frequency of the VCO and comparing it with the target frequency, then adjusting the modulation control voltage to minimize frequency deviation. This closed-loop feedback mechanism compensates for the nonlinear voltage-frequency characteristics of the VCO, achieving high frequency modulation linearity while maintaining circuit simplicity.
Solution Approach 2:
The patent changes the parameter being controlled from direct voltage control to frequency-based control with feedback. By measuring the actual frequency output and using it to adjust the control voltage dynamically, the system transforms the open-loop voltage control into a closed-loop frequency control system, resolving the linearity issue without complicating the overall circuit architecture.
2Manufacturing precision
If feedback control is implemented to correct VCO frequency characteristics, then frequency modulation linearity improves, but inspection time increases due to additional measurement and adjustment work
Solution Approach 1:
The patent performs frequency measurement and feedback adjustment during the shipment inspection process itself, rather than requiring separate characterization and correction steps. By integrating the frequency measurement and feedback control into the inspection workflow, the system achieves high frequency modulation linearity without adding significant inspection time, as the correction is performed proactively during the mandatory inspection phase.
3Ease of operation
If quadrature demodulation with frequency division is used to measure oscillation frequency, then the measurement process is simplified, but measurement accuracy deteriorates
Solution Approach 1:
The patent applies partial frequency division (dividing the VCO output frequency by a factor N) before measurement, rather than measuring the full frequency directly. This partial action approach allows the use of simpler measurement circuits while maintaining sufficient accuracy for feedback control, as the divided frequency is lower and easier to measure precisely with standard ADC equipment.
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
The solution enables high linearity of frequency modulation, improving measurement accuracy and reducing the complexity of correction processes, thereby enhancing the precision of distance and speed calculations in radar systems.
Implementation Method 1
a voltage control oscillator to oscillate, based on the modulation control time-dependent voltage data output from the digital-analog converter, an oscillation frequency signal
Implementation Method 2
a frequency divider to perform frequency division of the oscillation frequency signal of the voltage control oscillator and output the oscillation frequency signal
Implementation Method 3
a frequency converter to down-convert a frequency division signal output from the frequency divider
Implementation Method 4
a single-phase differential converter to convert an intermediate frequency signal of single-phase output from the frequency converter into differential signals and output the differential signals
Implementation Method 5
an analog-digital converter to convert, concerning the differential signals output from the single-phase differential converter, analog signals of the differential signals into digital signals
Data Source
AI summary
A frequency modulation circuit includes a VCO, a DIV, a MIX, a single-phase differential converter, and a signal processing circuit. The signal processing circuit performs differential arithmetic processing of an intermediate frequency signal with a program of a microcomputer according to a quadrature demodulation scheme and, thereafter, measures a frequency from phase information, performs n-th order polynomial (n is an integer equal to or larger than 2) approximation on time-frequency data of an IF signal output by a chirp modulation control voltage after inverse function correction, and performs modulation correction for correcting a time error.