Cross-Coupled Oscillator Tuning Without Varactor Frequency Drift
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional oscillators in electronic circuits face challenges in maintaining accurate and stable frequency due to temperature variations, process variations, and electromagnetic interference, which can cause frequency drift, and the use of varactors can introduce non-ideal second-order effects and parasitic capacitance, affecting circuit operation and reliability.
Innovation Solution
An oscillator design featuring a cross-coupled transistor pair and another transistor pair mutually coupled through inductors, with current sources having adjustable transconductance in response to input voltage, temperature, and process parameters, allowing for compensation of frequency drift without the need for crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a varactor is used to adjust capacitance for frequency compensation, then the oscillation frequency accuracy is improved, but non-ideal second order effects and parasitic capacitance are introduced that affect circuit operation and reliability
Solution Approach 1:
The patent removes the varactor component from the oscillator circuit entirely. Instead of using a varactor to adjust capacitance for frequency compensation, the invention employs a different architecture that achieves frequency stability without this problematic component, thereby eliminating the source of parasitic capacitance and second-order effects.
Solution Approach 2:
The patent uses a cross-coupled transistor pair configuration that replicates the frequency adjustment function through transconductance control rather than direct capacitance modulation. This alternative implementation achieves the same frequency compensation goal without the harmful side effects of varactor-based approaches.
2Stability of the object's composition
If temperature variation and process variation are compensated through conventional methods, then frequency stability is improved, but device complexity increases due to additional compensation circuits
Solution Approach 1:
The oscillator circuit is designed to automatically compensate for temperature and process variations through its inherent cross-coupled transistor architecture. The transconductance of the transistors naturally adjusts with temperature changes, providing self-compensation without requiring external temperature sensors or complex compensation circuits.
Solution Approach 2:
The patent exploits the natural variation of transistor transconductance parameters with temperature and process conditions. By designing the circuit to utilize these parameter changes rather than fight them, the system achieves frequency stability without adding complexity. The oscillation frequency is determined by the transconductance ratio, which remains relatively stable despite individual parameter drifts.
Data Source
AI summary
An oscillator configured to generate an oscillation signal is provided. The oscillator includes a transistor pair and a cross-coupled transistor pair. The transistor pair is coupled to a first current source and has a first transconductance. The first transconductance is changed in response to a current value of the first current source. The cross-coupled transistor pair is coupled to a second current source and has a second transconductance. The second transconductance is changed in response to a current value of second current source. The transistor pair and the cross-coupled transistor pair are mutually coupled by a plurality of inductors. A frequency of the oscillation signal is determined according to the first transconductance and the second transconductance. Furthermore, a clock generator and a method for generating a clock signal thereof are also provided.