RC Oscillator Bias Current Compensation for Low Temperature Drift
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Solution Overview
Problem
Existing RC oscillators exhibit significant temperature drift due to the temperature-sensitive delay in internal comparator and digital logic circuits, leading to variations in oscillation frequency across different temperatures.
Innovation Solution
The RC oscillator incorporates a bias circuit that generates two bias currents with a specific ratio having a positive temperature coefficient, which compensates for the temperature-dependent logic delay, thereby stabilizing the oscillation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the existing RC oscillator structure is used, then the circuit is simple and low cost, but the oscillation frequency has large temperature drift due to temperature-sensitive delay in comparator and digital logic circuits
Solution Approach 1:
The bias circuit is segmented into multiple current sources with different temperature coefficients. The first bias current has a positive temperature coefficient while the second has a negative temperature coefficient, allowing independent optimization of each current's temperature characteristics to achieve overall frequency stability.
Solution Approach 2:
The patent changes the temperature dependence parameter of the bias currents by designing currents with opposite temperature coefficients. By adjusting the ratio and magnitude of these currents, the overall system's temperature drift is compensated, transforming the temperature sensitivity parameter from harmful to beneficial.
2Reliability
If the ratio of the first bias current to the second bias current is optimized, then the temperature drift is reduced, but the bias circuit complexity increases
Solution Approach 1:
The patent introduces an intermediary mechanism where the ratio of two bias currents with opposite temperature coefficients serves as the mediator to compensate for temperature drift. This intermediary approach allows temperature compensation without requiring complex active control circuits, maintaining relative simplicity while achieving the desired temperature stability.
3Reliability
If temperature compensation is implemented, then frequency stability improves, but the power consumption increases
Solution Approach 1:
The bias circuit is designed to self-regulate temperature compensation through the inherent temperature coefficients of the current sources. The circuit automatically adjusts the effective bias current ratio based on temperature without requiring external control signals or additional power-intensive temperature sensing and control mechanisms, achieving power-efficient temperature compensation.
Data Source
AI summary
Disclosed is an RC oscillator comprising: a bias circuit, generating first and second bias currents, and outputting a charging current proportional to a total bias current that is the sum of the first and second bias currents, wherein the ratio of the first bias current to the second bias current has a positive temperature coefficient; and an oscillation circuit, for periodically charging a capacitor using the charging current output by the bias circuit, and using a voltage across a resistor through which the second bias current or a current proportional thereto flows as a reference voltage to compare with a charging voltage on the capacitor, so as to obtain a periodically oscillating clock signal. Thus, the present disclosure can compensate the positive temperature coefficient of the subsequent delay and realize the RC oscillator with low temperature drift by making the charging time of the capacitor have a negative temperature coefficient.