Oscillator Resistor Switchover for Stable Frequency Transition
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Solution Overview
Problem
Oscillators with on-chip resistor components face accuracy issues due to temperature-dependent variations and drift over time, leading to frequency deviations from target frequencies, and transitioning from internal-resistor mode to external-resistor mode can cause unstable charging currents, potentially resulting in system failures.
Innovation Solution
A three-phase transition method is implemented, where the external capacitor is first charged with the internal resistor connected, then the internal resistor is disconnected and the external resistor is connected, and finally, the bias current source is disconnected, ensuring a controlled transition and stable oscillator frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the oscillator uses on-chip resistor components, then the device complexity is reduced and ease of manufacture is improved, but the accuracy and frequency stability deteriorate due to temperature-dependent variations and drift over time
Solution Approach 1:
The oscillator circuit is divided into two operational modes: internal-resistor mode using on-chip resistors for ease of manufacture, and external-resistor mode using off-chip resistors for higher accuracy. The circuit can be segmented to use different resistor sources based on application requirements.
Solution Approach 2:
The oscillator allows changing the resistance parameter by switching between internal and external resistors. This parameter change enables the system to adapt between convenience (internal) and precision (external) requirements.
2Measurement precision
If the oscillator transitions from internal-resistor mode to external-resistor mode, then the frequency accuracy is improved, but the charging current stability deteriorates potentially causing system failures
Solution Approach 1:
Before transitioning to external-resistor mode, the circuit performs preliminary actions including: charging the external capacitor through the internal resistor first, then gradually switching to the external resistor. This preliminary charging prevents sudden current spikes that would cause system failures.
Solution Approach 2:
The circuit provides beforehand cushioning by using the internal resistor as a buffer during the transition phase. The internal resistor cushions the charging current before the external resistor takes over, preventing harmful current surges that would compromise system reliability.
3Device complexity
If a direct transition from internal-resistor mode to external-resistor mode is performed, then the device complexity is reduced, but the charging current stability deteriorates causing frequency deviations
Solution Approach 1:
The transition process includes preliminary steps: first charging the external capacitor through the internal resistor, then switching to external resistor for accurate frequency generation. This preliminary action sequence maintains charging current stability without requiring complex additional circuitry.
Solution Approach 2:
The transition is performed as a periodic sequence of operations: internal resistor charging phase, switching phase, and external resistor operation phase. This periodic structured transition maintains stability while keeping the device complexity manageable.
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 method provides a controlled transition from internal-resistor mode to external-resistor mode, reducing the risk of system failures by stabilizing the oscillator frequency and ensuring accurate operation.
Implementation Method 1
a charging current generator including a current mirror and an amplifier
Implementation Method 2
an external capacitor coupled to the pin and coupled in parallel to the external resistor
Implementation Method 3
disconnecting an internal resistor of the oscillator chip and connecting an external resistor to the oscillator chip
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.