Chirp Generator Feedback Multiplication for Wideband Low-Noise Sweeps
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Solution Overview
Problem
Chirp generators in radar applications face challenges in achieving high bandwidth while maintaining low phase noise, as increasing the VCO gain to achieve larger chirp bandwidths typically results in increased phase noise.
Innovation Solution
A chirp-generator design incorporating a phase-locked loop with a switched-varactor-bank, where varactors are sequentially controlled to contribute to the VCO circuit capacitance at controlled rates, allowing for a lower effective VCO gain and improved phase noise performance without increasing the VCO gain factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the VCO gain is increased to achieve larger chirp bandwidth, then the bandwidth is improved, but the phase noise increases
Solution Approach 1:
The varactor bank is divided into multiple segments (first varactor, second varactor, etc.) that are switched on and off sequentially during the chirp cycle. Each varactor contributes to the total capacitance at different time intervals, allowing the bandwidth to be increased through cumulative capacitance changes while keeping the instantaneous VCO gain lower, thereby reducing phase noise.
Solution Approach 2:
The varactors are controlled to switch on and off periodically according to a chirp cycle. The controller activates the first varactor during a first time interval and the second varactor during a second time interval, creating a periodic modulation pattern that generates the chirp signal. This periodic switching enables bandwidth expansion through time-varying capacitance while maintaining lower peak VCO gain.
2Speed
If the VCO gain factor is increased to provide larger chirp bandwidth, then the bandwidth is improved, but the phase noise performance deteriorates
Solution Approach 1:
The system uses dynamic switching of varactors to change the total capacitance of the VCO circuit over time. The controller dynamically adjusts which varactors are active during different time intervals of the chirp cycle, creating a time-varying capacitance profile that generates the desired chirp bandwidth without requiring a permanently high VCO gain factor, thus preserving phase noise performance.
Solution Approach 2:
The capacitance parameter of the VCO circuit is changed over time by selectively switching varactors on and off. The total capacitance varies during the chirp cycle, with different varactors contributing at different times. This parameter modulation achieves the required chirp bandwidth while keeping the instantaneous capacitance changes small enough to maintain low VCO gain and good phase noise characteristics.
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
This approach enables the generation of chirp signals with increased bandwidth while maintaining low phase noise, effectively addressing the trade-off between bandwidth and noise in existing technologies.
Implementation Method 1
a varactor circuit (448) that is configured to change a capacitance of the VCO-circuit based on a sequence of different control-voltages
Implementation Method 2
a phase-detector configured to: receive a clock-input-signal; receive a feedback-signal; and provide a phase-difference-signal representative of a phase difference between the clock-input-signal and the feedback-signal
Data Source
AI summary
A chirp-generator comprising a phase-detector for providing a phase-difference-signal representative of a phase difference between a clock-input-signal and a feedback-signal. A VCO-circuit is configured to provide a chirp-generator-output-signal based on the phase-difference-signal. The VCO-circuit comprises a switched-varactor-bank, which includes a plurality of varactors, and a varactor-switch associated with each of the plurality of varactors. The varactor-switch is configured to selectively control whether or not the associated varactor contributes to the capacitance of the VCO-circuit, based on the state of a varactor-control-signal. The chirp-generator also includes a feedback-component configured to: receive the chirp-generator-output-signal; and apply a variable-multiplication-factor to the chirp-generator-output-signal in order to provide the feedback signal for the phase-detector. A controller provides a sequence of different variable-multiplication-factors to the feedback-component; and provides varactor-control-signals to the plurality of varactors such that the varactors are sequentially controlled such that they contribute to the capacitance of the VCO-circuit.