Chirp Signal Circuit With Real-Time VCO Frequency Correction
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Solution Overview
Problem
Conventional signal generating circuits for FMCW radar systems cannot compensate for errors in chirp signals when the voltage-frequency characteristics of the voltage-controlled oscillator (VCO) suddenly change due to disturbances, such as temperature variations, and require multiple chirp signal generations to update these characteristics.
Innovation Solution
A signal generating circuit that includes a control voltage setting unit, a voltage-controlled oscillator, a quadrature demodulator, and a frequency detector, which generates a chirp signal by correcting the control voltage using derived voltage-frequency characteristics from inphase and quadrature signals obtained through quadrature demodulation, allowing for real-time compensation of VCO frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the conventional signal generating circuit uses a lookup table to store voltage-frequency characteristics and updates it by generating chirp signals multiple times while varying local frequency, then the V-F characteristics can be obtained, but the circuit cannot compensate for errors when VCO characteristics suddenly change and cannot update V-F characteristics during the multiple signal generations
Solution Approach 1:
The patent implements a feedback mechanism where the measured frequency information from the chirp signal is fed back to update the lookup table. The system measures the actual frequency of the chirp signal generated by the VCO, compares it with the expected frequency from the lookup table, and uses this feedback to correct and update the V-F characteristics stored in the lookup table, enabling continuous compensation without requiring multiple signal generations.
Solution Approach 2:
The patent performs preliminary measurement and correction of the V-F characteristics by generating a test chirp signal before normal operation. The system pre-measures the actual frequency characteristics of the VCO and pre-updates the lookup table with corrected values, so that when actual chirp signal generation is needed, the lookup table already contains accurate characteristics and no time-consuming updates are required during operation.
2Reliability
If the circuit generates chirp signals multiple times to obtain V-F characteristics, then the characteristics can be derived, but the chirp signal generation efficiency decreases and linearity deteriorates due to inability to compensate for sudden VCO changes
Solution Approach 1:
The system continuously monitors the actual frequency output of the VCO and feeds this information back to update the lookup table. This feedback loop ensures that the V-F characteristics in the lookup table always reflect the current state of the VCO, maintaining high linearity of generated chirp signals while enabling rapid, single-shot signal generation without repeated updates.
Solution Approach 2:
The patent dynamically adjusts the voltage-frequency characteristics parameters in the lookup table based on measured deviations. By changing the stored V-F characteristic parameters to match actual VCO behavior, the system maintains accurate frequency control and linearity in generated chirp signals while avoiding the need for multiple generation cycles.
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 real-time compensation of chirp signal errors even with sudden changes in VCO characteristics, allowing for continuous and accurate generation of chirp signals without the need for multiple signal generations, thereby improving the linearity and stability of the chirp signal.
Implementation Method 1
a voltage controlled oscillator configured to alter a frequency of an output signal in response to the control voltage
Implementation Method 2
a quadrature demodulator configured to carry out quadrature demodulation of part of the output signal of the voltage controlled oscillator using a local signal generated by a local oscillator, to generate an inphase signal and a quadrature signal
Data Source
AI summary
A signal generating circuit includes a control voltage setting unit (CVSU) configured to set a control voltage for a chirp signal using voltage-frequency characteristics indicating characteristics of an output frequency versus voltage; a VCO configured to alter the frequency of its output signal by the control voltage; a quadrature demodulator configured to perform quadrature demodulation of the output signal of the VCO to generate an inphase signal and a quadrature signal orthogonal to each other; and a frequency detector configured to detect the frequency of the output signal of the VCO on the basis of the inphase signal and quadrature signal. The CVSU corrects the control voltage by using the voltage-frequency characteristics derived from relationships between the control voltage and the frequency of the output signal of the VCO. The VCO generates the chirp signal based on the control voltage corrected by the CVSU.