Pulse Pair Shaping for RF Interference in DC-DC Converters
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Solution Overview
Problem
Pulse frequency modulation (PFM) DC-DC converters cause interference in radio frequency (RF) circuits due to unpredictable and wide frequency band energy spread, which is difficult to control.
Innovation Solution
A PFM voltage converter with a pulse generator that produces pulse pairs with a predetermined pulse separation interval, based on the frequency of a local oscillator's mixing signal, to reduce interference around RF and mixing signal frequencies, using a table to determine the interval for specific RF channels and threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PFM converter is used to maximize efficiency over wider load current range, then power efficiency is improved, but RF interference becomes difficult to control due to wide and unpredictable frequency band spread
Solution Approach 1:
The patent applies periodic action by generating pulse pairs with a predetermined separation interval that corresponds to the period of the RF signal or its harmonics. This periodic structure creates constructive and destructive interference patterns in the frequency domain, producing spectral nulls at specific frequencies. The pulse separation interval is calculated based on the RF signal frequency to ensure that the second pulse cancels the interference from the first pulse at the target frequency, thereby reducing RF interference while maintaining PFM efficiency benefits
Solution Approach 2:
The patent converts the harmful RF interference into a beneficial effect by deliberately structuring the pulse pairs to create spectral nulls at interfering frequencies. The interference energy is not simply suppressed but redirected through constructive interference at non-critical frequencies and destructive interference at critical frequencies. This transforms the unpredictable wideband noise into a controlled spectrum with targeted attenuation at RF frequencies while maintaining overall power conversion efficiency
2Object-generated harmful factors
If pulse pairs with predetermined separation interval are generated, then RF interference is reduced through spectral nulls, but device complexity increases due to additional control logic and timing requirements
Solution Approach 1:
The patent implements multi-functionality by integrating the pulse pair generation logic into the existing PFM control circuitry. The same control logic that determines when to generate pulses based on voltage thresholds also calculates and applies the pulse separation interval based on RF frequency. This unified approach allows a single control block to perform both power management and RF interference mitigation functions, avoiding the need for separate dedicated circuits and reducing overall system complexity
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the pulse separation interval based on the detected RF signal frequency. Rather than using a fixed timing structure, the system modifies the temporal parameter (separation interval) in response to changing RF conditions. This allows the converter to adapt to different RF environments and maintain spectral nulls at the correct frequencies without requiring complex reconfiguration of the entire control architecture
Data Source
AI summary
In one aspect, an apparatus includes: a pulse frequency modulation (PFM) voltage converter to receive a first voltage and provide a second voltage to a load; and a pulse generator. The PFM voltage converter may include an inductor to store energy based on the first voltage and a switch controllable to switchably couple the first voltage to the inductor. The pulse generator may be configured to generate at least one pulse pair to control the switch, where this pulse pair is formed of a first pulse and a second pulse substantially identical to the first pulse, where the second pulse is separated from the first pulse by a pulse separation interval, when the second voltage is less than a first threshold voltage.