Oscillator Switchover Circuit for Stable External-Resistor Transition
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Solution Overview
Problem
Oscillators with on-chip resistor components face accuracy issues due to temperature-dependent and non-linear variations, leading to frequency deviations from target frequencies, and switching to an external-resistor mode can cause unstable charging currents, potentially resulting in system failures during transitions.
Innovation Solution
A three-phase transition method is implemented to switch from internal-resistor mode to external-resistor mode, involving charging an external capacitor with the internal resistor connected, disconnecting the internal resistor and connecting the external resistor, and then disconnecting the bias current source while connecting the current mirror, to stabilize the oscillator frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an internal resistor is used in the oscillator circuit, then the oscillator can operate with integrated components, but frequency accuracy deteriorates due to temperature-dependent and non-linear variations
Solution Approach 1:
The patent extracts the resistor component from the integrated oscillator circuit and places it externally. The oscillator circuit on the chip is configured to work with an external resistor, removing the temperature-dependent and non-linear variation issues associated with on-chip resistors. This allows the oscillator to achieve better frequency accuracy while maintaining the benefits of integration for other components.
2Measurement precision
If the oscillator switches from internal-resistor mode to external-resistor mode, then frequency accuracy can be improved, but unstable charging currents occur during transition
Solution Approach 1:
The patent implements a three-phase transition method where preliminary actions are taken before the actual mode switching. Phase 1 prepares the circuit by connecting the external resistor while the internal resistor is still active. Phase 2 performs the actual switching. Phase 3 completes the transition by disconnecting the internal resistor fully. This staged approach prevents unstable charging currents by ensuring smooth transitions between modes.
Solution Approach 2:
The patent uses switch circuits as intermediary elements to manage the transition between internal-resistor and external-resistor modes. The switches act as mediators that control the connection and disconnection of resistors in a controlled manner, preventing direct abrupt changes that would cause unstable charging currents. The switch circuitry ensures that transitions occur smoothly without causing system failures.
3Device complexity
If a direct switch from internal-resistor to external-resistor mode is implemented, then the transition is simple, but sharp frequency changes occur causing system failures
Solution Approach 1:
The patent segments the mode transition process into three distinct phases instead of implementing a direct single-step switch. Phase 1 involves connecting the external resistor while maintaining internal resistor operation. Phase 2 performs the actual mode switching. Phase 3 completes the transition by fully disconnecting the internal resistor. This segmentation of the transition process prevents sharp frequency changes while managing the complexity through structured control.
Solution Approach 2:
Before the actual mode switching occurs, the patent performs preliminary actions in Phase 1 where the external resistor is connected to the oscillator circuit while the internal resistor remains active. This preliminary connection allows the circuit to prepare for the transition smoothly, preventing abrupt frequency changes that would occur with direct switching. The preliminary action ensures that all components are ready for the mode change without causing system failures.
Data Source
AI summary
In an example, a system includes an oscillator circuit on a chip. The oscillator circuit includes a charging current generator including a current mirror and an amplifier, where the amplifier is coupled to a pin of the chip. The oscillator circuit also includes a first switch coupled to the pin, a second switch coupled to the pin and to a charging resistor, and a third switch coupled to the amplifier and an internal resistor, where the internal resistor is internal to the chip. The oscillator circuit includes a bias current source coupled to the current mirror. The system includes an external resistor coupled to the pin, where the external resistor is external to the chip. The system also includes an external capacitor coupled to the pin and coupled in parallel to the external resistor, where the external capacitor is external to the chip.