Oscillator Comparator Delay Compensation
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Solution Overview
Problem
In switching power supplies, the intrinsic delay of the comparator in traditional oscillators leads to a mismatch between the theoretical and actual oscillating frequency, especially for high-frequency oscillators above 2.2 MHz, due to parasitic inductance and temperature effects.
Innovation Solution
The introduction of an error amplifier that regulates the average or peak value of the capacitor voltage to match the reference voltage, eliminating the influence of the comparator's intrinsic delay by generating a regulation voltage used for comparison, thereby improving oscillator precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traditional comparator-based oscillator is used, then the circuit structure is simple, but the oscillating frequency cannot match the theoretical value due to comparator delay
Solution Approach 1:
An error amplifier is introduced as an intermediary component between the voltage generation path and the comparator. This error amplifier dynamically adjusts the voltage across the capacitor to compensate for the comparator's intrinsic delay, ensuring that the oscillating frequency matches the theoretical value calculated from the reference voltage, current source, and capacitor values.
Solution Approach 2:
The error amplifier implements a feedback mechanism by continuously monitoring the voltage across the capacitor and adjusting it based on the difference between the actual and desired oscillation timing. This feedback loop eliminates the frequency deviation caused by comparator delay, achieving precise frequency control without requiring complex circuit modifications.
2Productivity
If the oscillating frequency is increased above 2.2 MHz, then the productivity is improved, but the frequency deviation caused by comparator delay becomes more significant
Solution Approach 1:
The error amplifier performs preliminary adjustment of the capacitor voltage before the comparison operation occurs. By proactively compensating for the known comparator delay effect, the system prevents frequency deviation from occurring in the first place, enabling high-frequency operation above 2.2 MHz while maintaining accurate frequency control.
Solution Approach 2:
The feedback mechanism in the error amplifier becomes increasingly important at higher frequencies, where the comparator delay has a larger impact on the oscillation period. The continuous adjustment ensures that even at frequencies above 2.2 MHz, the actual oscillating frequency remains precisely matched to the theoretical value.
Data Source
AI summary
There is provided an oscillator which includes a current source, a capacitor coupled between the current source and a reference ground, a first switch coupled to the capacitor in parallel, an error amplifier, a comparator and a one-shot circuit. The error amplifier is coupled to the capacitor and configured to generate a regulation voltage based on a reference voltage and the voltage across the capacitor. The comparator is configured to compare the voltage across the capacitor with the regulation voltage and generate a comparison signal. The one-shot circuit is coupled to the comparator, wherein based on the comparison signal, the one-shot circuit generates a trigger signal to control the first switch.