Injection-Locked Oscillator LC Tank Calibration for Robust Frequency Locking
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Solution Overview
Problem
Existing injection locked oscillators face challenges in maintaining robust locking over process, voltage, and temperature variations, leading to frequency deviations and increased power and area consumption due to the need for multiple oscillators and complex frequency tracking loops.
Innovation Solution
A calibration circuit that adjusts the capacitance of the LC tank in an injection locked oscillator to maximize the amplitude of the output signal, selecting the optimal capacitance value to ensure the oscillation frequency aligns with the target frequency, thereby achieving robust locking without additional oscillators or complex loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a frequency tracking loop with main VCO and replica VCO is used to maintain precise target frequency, then frequency precision is improved, but device complexity and power consumption increase due to the presence of two VCOs
Solution Approach 1:
The patent uses a simplified copying approach where a single VCO is copied once to create the injection-locked oscillator, rather than maintaining two full VCOs with complex frequency tracking loops. This single copying event followed by injection locking achieves frequency precision while dramatically reducing device complexity compared to traditional dual-VCO frequency tracking loops
Solution Approach 2:
The patent extracts the frequency tracking function from the complex dual-VCO system and implements it through a simpler injection locking mechanism. By taking out the frequency tracking loop complexity and replacing it with injection locking, the system maintains frequency precision while reducing device complexity and power consumption
2Measurement precision
If two quadrature VCOs are used with frequency tracking loop to achieve correct central frequency, then frequency precision is improved, but area consumption increases due to the presence of two oscillators
Solution Approach 1:
The patent employs a single copying operation to generate the injection-locked oscillator from one VCO, eliminating the need for two quadrature VCOs. This approach achieves the required frequency precision while significantly reducing the area consumption that would result from implementing two full oscillators with quadrature relationships
3Adaptability or versatility
If locking range is made wide to accommodate process variations and frequency drifts, then adaptability is improved, but frequency precision deteriorates due to deviation from target frequency
Solution Approach 1:
The patent implements a feedback mechanism through the injection locking process itself, where the injected signal provides continuous frequency correction to the VCO. This feedback approach allows the system to maintain a wide locking range for adaptability while simultaneously keeping frequency precision high by continuously correcting drifts and variations
Solution Approach 2:
The injection-locked oscillator dynamically adjusts its frequency in response to the injected signal, allowing it to adapt to process variations and maintain a wide locking range. At the same time, the dynamic locking mechanism ensures that the oscillator remains precisely locked to the target frequency, resolving the contradiction between wide adaptability and frequency precision
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 allows for simple and effective calibration, ensuring proper locking over process, voltage, and temperature variations while reducing power and area consumption, and achieving high harmonic rejection.
Implementation Method 1
LC oscillator 22 is tuned at N×flo by the combination of inductors L1, L2 and capacitors C1, C2. Inductors L1, L2 and capacitors C1, C2 form a LC tank.
Implementation Method 2
Injection transistors 30 and 32 convert a voltage at the gates thereof to a voltage at the drain terminals thereof. The drain terminals of injection transistors 30 and 32 are coupled to injection nodes IN1 and IN2 of LC oscillator 22.
Data Source
AI summary
A circuit for calibrating an injection locked oscillator is provided. The injection locked oscillator includes an injection locking input, an LC tank and an oscillator output to output an oscillator output signal. The circuit is configured to adjust a capacitance of the LC tank to different values, detect an amplitude of the oscillator output signal for each value of the different values of the capacitance while an input signal having a target frequency is applied to the injection locking input, determine a maximum amplitude of the detected amplitudes, and select a value for operating the injection locked oscillator based on the determined maximum amplitude.