DC-DC Converter Hysteresis Control for RF Spur Reduction
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Solution Overview
Problem
Pulse frequency modulation (PFM) DC-DC converters face challenges in managing the spectral content of their output, leading to undesirable tones in radios, which are dependent on load current, input voltage, output voltage, and external components, affecting efficiency and RF performance.
Innovation Solution
Implementing a system with a resistor divider, plurality of switches, and a controller to adjust hysteresis levels and control the switching sequence of a PFM DC-DC converter, allowing for dynamic variation of hysteresis levels and randomization of switch control to manage output ripple and fundamental frequency, thereby reducing spurs and improving spectral content predictability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PFM mode is used to improve efficiency at light loads, then quiescent current is reduced to 20 μA, but spectral content becomes unpredictable causing undesirable tones in radios
Solution Approach 1:
The patent applies dynamics by making the hysteresis levels adjustable and variable over time. The controller dynamically switches between different hysteresis level sets based on operating conditions, transforming the static hysteresis comparator into a dynamic system that can adapt to different load and frequency requirements, thereby reducing spectral content while maintaining efficiency benefits
Solution Approach 2:
The patent changes the hysteresis level parameters to control the switching frequency and spectral content. By adjusting the hysteresis levels in the comparator, the system modifies the switching characteristics of the PFM converter to reduce undesirable tones in the spectral output while maintaining the efficiency advantages of PFM operation
2Device complexity
If hysteresis levels are fixed to simplify control, then circuit complexity is reduced, but spectral content cannot be managed effectively
Solution Approach 1:
The patent segments the hysteresis control into multiple discrete levels that can be independently selected. Instead of a continuous variable hysteresis control, the system uses segmented hysteresis levels (first set and second set) that are switched by the controller, simplifying the control architecture while still enabling effective spectral content management
Solution Approach 2:
The patent implements periodic action by alternating between different hysteresis level sets in a controlled manner. The controller periodically switches between the first and second sets of hysteresis levels, creating a modulated switching pattern that reduces spectral content through frequency modulation while maintaining relatively simple control circuitry
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 approach enhances efficiency and maintains RF performance by spreading harmonic content over multiple frequencies with reduced magnitude, achieving efficient power delivery in hysteretic mode while maintaining predictable spectral output, switching between PFM and PWM modes as needed.
Implementation Method 1
a resistor divider
Implementation Method 2
adjust hysteresis levels of the feedback of an output of a pulse frequency modulated DC-DC converter
Data Source
AI summary
Two hysteresis levels, a high level and a low level, may be used to set a period (and the switching frequency) of the output voltage of a DC-DC converter, as well as the output ripple of the converter. These two thresholds may be changed using pairs of switches. By controlling the sequence and the duration of the on-time of the switches, spectral spurs in the output can be controlled and the amplitude and the frequency band of interest can be reduced. Additional spur reduction may be possible by randomizing the control of the switches.