RC Oscillator Bias Current Compensation for Low Temperature Drift
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Solution Overview
Problem
Existing RC oscillators suffer from significant temperature drift due to the temperature sensitivity of the internal comparator and digital logic circuit delays, affecting the oscillation frequency and overall chip performance.
Innovation Solution
An RC oscillator design that generates two bias currents with a specific ratio, where one has a positive temperature coefficient and the other has a negative temperature coefficient, compensating for the temperature sensitivity by adjusting the ratio to achieve a negative temperature coefficient for the charging time of the capacitor, thereby reducing temperature drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional RC oscillator is used, then the circuit is simple and low cost, but the oscillation frequency has large temperature drift due to temperature-sensitive delays in the comparator and digital logic circuits
Solution Approach 1:
The bias circuit is divided into two independent modules: a first bias current module generating a bias current with positive temperature coefficient, and a second bias current module generating a bias current with negative temperature coefficient. This segmentation allows each module to be optimized for specific temperature compensation functions, resolving the contradiction between frequency stability and circuit complexity by organizing the compensation mechanism into modular, manageable segments.
Solution Approach 2:
The patent changes the temperature coefficient parameter of bias currents by using different circuit topologies in the two modules. The first module uses a configuration that produces positive temperature coefficient current, while the second module uses a different configuration producing negative temperature coefficient current. By adjusting these parameters and their ratio, the overall system achieves temperature-compensated frequency stability without excessive complexity.
2Reliability
If temperature compensation is implemented using existing schemes, then frequency stability improves, but the circuit complexity and power consumption increase
Solution Approach 1:
The patent merges the temperature compensation function with the existing bias circuit structure by integrating two bias current modules that work together to compensate for temperature effects. Instead of adding separate compensation circuits, the solution combines temperature compensation directly into the bias generation mechanism, achieving frequency stability while minimizing additional power consumption and circuit complexity.
Solution Approach 2:
The bias circuit performs self-temperature-compensation by using its own internal current modules to generate compensating currents. The first bias current module and second bias current module work autonomously to counteract temperature drift effects, eliminating the need for external temperature sensing or additional control circuits, thereby reducing power consumption while maintaining frequency stability.
3Reliability
If the ratio of first bias current to second bias current is optimized, then temperature drift is reduced, but the design complexity increases
Solution Approach 1:
The patent optimizes the ratio parameter between the first bias current and second bias current to achieve effective temperature compensation. By carefully selecting and adjusting this ratio parameter during design, the system minimizes temperature drift while maintaining a relatively simple circuit structure. This parameter optimization approach resolves the contradiction by finding the optimal balance point rather than requiring complex adaptive mechanisms.
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
Disclosed is an RC oscillator (300) comprising: a bias circuit (310), generating first and second bias currents (Ia, Ib), and outputting a charging current (IL) proportional to a total bias current that is the sum of the first and second bias currents, wherein the ratio (Ia/Ib) of the first bias current to the second bias current has a positive temperature coefficient; and an oscillation circuit (320), for periodically charging a capacitor (C0, C1) using the charging current output by the bias circuit, and using a voltage across a resistor (R2) through which the second bias current or a current proportional thereto flows as a reference voltage to compare with a charging voltage (Vcap) on the capacitor, so as to obtain a periodically oscillating clock signal (CLK, CLKB). 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.