Tunable Oscillator Circuit With Switched Capacitance for Low Phase Noise
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Solution Overview
Problem
Conventional voltage-controlled oscillators in phase-locked loop circuits for FMCW radar systems face challenges in achieving a wide tuning range while maintaining low phase noise, as large varactors used for wide frequency ranges result in high phase noise and power consumption.
Innovation Solution
A tunable resonant circuit with a biasing circuit and control circuitry that includes a voltage divider network and hysteretic comparators, allowing for fast and continuous coarse tuning using small varactors, reducing power consumption and phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If large varactors are used to achieve wide frequency tuning range, then the tuning range is improved, but phase noise and power consumption increase
Solution Approach 1:
The patent divides the frequency tuning process into two independent stages: coarse tuning and fine tuning. The coarse tuning stage uses a set of switched capacitances to provide large frequency steps across a wide range, while the fine tuning stage uses a small varactor for continuous small adjustments. This segmentation allows each component to be optimized for its specific function, avoiding the need for a single large varactor that would generate high phase noise.
Solution Approach 2:
The patent introduces a flash analog-to-digital converter (ADC) as an intermediary component that converts the control voltage into digital signals to control the switched capacitances. This ADC acts as a mediator between the continuous control voltage and the discrete capacitance switching, enabling precise coarse tuning without requiring large varactor adjustments that would increase phase noise.
2Adaptability or versatility
If large varactors are used to achieve wide frequency tuning range, then the tuning range is improved, but power consumption increases
Solution Approach 1:
The patent segments the tuning function into coarse and fine stages, allowing the use of small, low-power varactors for fine tuning while the coarse tuning is handled by switched capacitances that consume minimal power. This eliminates the need for a single large varactor that would consume excessive power to achieve the same tuning range.
Solution Approach 2:
The patent changes the operating parameters by using a flash ADC to convert the control voltage into discrete digital levels that control the switched capacitances. This parameter transformation allows the system to achieve wide tuning range through digital switching of small capacitances rather than analog adjustment of large varactors, significantly reducing power consumption.
3Speed
If coarse quantized tuning is performed using switched capacitances, then tuning speed is improved, but continuity of tuning is reduced
Solution Approach 1:
The patent merges two tuning mechanisms into a unified system: the flash ADC-controlled switched capacitances provide fast coarse tuning, while the continuously controllable small varactor provides smooth fine tuning. The combination of these two mechanisms achieves both fast response and continuous tuning coverage across the entire frequency range, with the varactor filling in the gaps between the discrete capacitance steps.
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 solution enables fast and continuous coarse tuning suitable for automotive radar sensors, reducing power consumption and phase noise while maintaining a wide tuning range, suitable for automotive radar applications.
Implementation Method 1
a tunable resonant circuit having a first node and a second node. The tunable resonant circuit may include an inductance coupled between the first node and the second node, a variable capacitance coupled between the first node and the second node
Implementation Method 2
a voltage divider network configured to generate a set of different voltage thresholds
Implementation Method 3
a set of comparator circuits with hysteresis configured to compare the input control signal to the set of different voltage thresholds to generate a respective set of control signals
Data Source
AI summary
Disclosed herein is a tunable resonant circuit including an inductance directly electrically connected in series between first and second nodes, a variable capacitance directly electrically connected between the first and second nodes, and a set of switched capacitances coupled between the first and second nodes. The set of switched capacitances includes a plurality of capacitance units, each capacitance unit comprising a first capacitance for that capacitance unit directly electrically connected between the first node and a switch and a second capacitance for the capacitance unit directly electrically connected between the switch and the second node. Control circuitry is configured to receive an input control signal and connected to control the switches of the set of switched capacitances. A biasing circuit is directly electrically connected to the tunable resonance circuit at the first and second nodes.