LC Digitally Controlled Oscillator With Temperature-Compensated Capacitance
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Solution Overview
Problem
Digitally controlled oscillators (DCOs) face significant temperature sensitivity issues, making it difficult to achieve low temperature drift rates, especially with LC-based DCOs, as existing methods using temperature sensors and compensation capacitors are inaccurate and insufficient.
Innovation Solution
A device comprising a voltage reference supply with a programmable slope, a temperature sensor, and a switched capacitor bank in an LC-DCO, where the voltage reference varies linearly with temperature, and the switched capacitor bank adjusts capacitance to correct both linear and non-linear frequency errors, using a combination of PTAT and IPTAT currents for precise temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a temperature sensor and temperature compensation capacitor bank are used to correct temperature variation in DCO output frequency, then temperature sensitivity is improved, but measurement precision and reliability are degraded due to sensor inaccuracies and temperature dependence of analog varactors
Solution Approach 1:
The patent replaces the mechanical/analog temperature compensation system (temperature sensor + analog varactor capacitor bank) with a digital system. A temperature compensation lookup table stored in memory contains pre-calculated capacitance values for different temperatures. The microcontroller reads the temperature, queries the lookup table, and switches the corresponding digital capacitor bank, eliminating analog component inaccuracies and temperature dependencies.
Solution Approach 2:
The patent changes the capacitance parameter of the LC resonator by switching in different capacitor bank configurations based on temperature. Instead of relying on analog varactor tuning which has temperature dependence, the system discretizes the capacitance adjustment by switching between predefined capacitor values stored in a lookup table, achieving accurate frequency compensation without analog component issues.
2Ease of operation
If analog varactors are used for temperature compensation, then frequency adjustment is achieved, but reliability is worsened due to temperature dependence of the varactors themselves
Solution Approach 1:
The patent substitutes analog varactors with digital switches controlling fixed capacitors. The capacitor bank is controlled by digital signals from a microcontroller that reads temperature from a sensor and queries a lookup table. This digital approach eliminates the temperature dependence inherent in analog varactors while maintaining frequency adjustment capability through discrete capacitance switching.
Solution Approach 2:
The patent creates a digital copy of the temperature-compensation function through a lookup table stored in memory. Instead of relying on the physical characteristics of analog varactors that change with temperature, the system uses a digital representation (lookup table) that contains pre-calculated compensation values, which are then applied through digital switching of the capacitor bank.
3Device complexity
If ring oscillator topology is used for DCO, then device complexity is reduced, but temperature sensitivity increases making low temperature drift difficult to achieve
Solution Approach 1:
The patent merges the advantages of ring oscillator simplicity with LC oscillator temperature stability. The system uses a ring oscillator as the core frequency-generating element for low complexity, but combines it with an LC resonator and temperature-compensated capacitor bank to achieve low temperature sensitivity. This hybrid approach consolidates the simplicity of ring oscillators with the temperature stability of LC-based systems.
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 effectively minimizes frequency variation across temperature ranges, achieving stable output frequencies with reduced temperature sensitivity, even in high-temperature conditions, by synergistically combining supply voltage compensation and switched capacitor bank adjustments.
Implementation Method 1
a voltage reference supply, configured to provide a reference voltage that varies in response to temperature according to a predefined relationship
Implementation Method 2
a temperature sensor providing a temperature signal indicating a temperature
Implementation Method 3
the LC-DCO comprising a switched capacitor bank configured to provide temperature compensation by varying an effective capacitance in the LC circuit in response to the control signal
Implementation Method 4
an LC-DCO receiving the reference voltage and providing an output signal with a frequency from an LC circuit
Data Source
AI summary
A device comprising: a voltage reference supply, configured to provide a reference voltage that varies in response to temperature according to a predefined relationship; a temperature sensor providing a temperature signal indicating a temperature; a first controller configured to receive the temperature signal and to output a control signal; an LC-DCO receiving the reference voltage and providing an output signal with a frequency from an LC circuit, the LC-DCO comprising a switched capacitor bank configured to provide temperature compensation by varying an effective capacitance in the LC circuit in response to the control signal.