DC-DC Converter Spur Control via Frequency Shifting
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Solution Overview
Problem
The integration of DC-DC converters with sensitive analog circuits is hindered by high switching noise, which causes spur-related issues, preventing their integration on the same chip due to uncontrollable harmonic distortion and magnetic coupling, leading to increased size and cost when kept as off-chip components.
Innovation Solution
An integrated circuit that digitally controls switching noise by shifting the switching frequency to a clock frequency, using a spur-controlled clock to drive power switches, ensuring that none of the harmonics fall within the channel of interest, with the frequency shift calculated to place the channel of interest between two consecutive harmonics, thereby minimizing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If DC-DC converter is integrated with analog circuits on the same chip, then die area is reduced and cost is lowered, but switching noise causes unacceptable spur levels in the analog circuit frequency band
Solution Approach 1:
The patent changes the switching frequency parameter of the DC-DC converter to a frequency that is not an integer multiple of the analog circuit's operating frequency, thereby moving the spurs away from the sensitive frequency band. This allows integration without the spurs falling into the analog circuit's frequency range.
Solution Approach 2:
The patent implements dynamic adjustment of the switching frequency based on the operating state of the analog circuit. By dynamically changing the switching frequency when the analog circuit is active, the spurs are moved away from the sensitive band only when needed, enabling integration while maintaining analog performance.
2Object-affected harmful factors
If physical separation between DC-DC converter and analog circuits is increased, then magnetic coupling is reduced, but die area increases and integration becomes difficult
Solution Approach 1:
Instead of changing the physical layout, the patent changes the frequency parameter of the DC-DC converter to avoid integer multiples of the analog circuit frequency. This allows close physical proximity without significant magnetic coupling affecting the analog circuit's frequency band.
Solution Approach 2:
The patent converts the potential harmful magnetic coupling into a non-problematic situation by frequency tuning. The spurs are moved away from the sensitive band, so even though magnetic coupling exists, it does not cause harmful effects in the analog circuit's operating range.
3Object-affected harmful factors
If off-chip capacitors are added to filter noise, then switching noise is reduced, but current loop size increases and magnetic coupling to RF circuits increases
Solution Approach 1:
The patent changes the switching frequency parameter to avoid generating spurs in the analog circuit's frequency band. This eliminates the need for additional filtering capacitors and their associated large current loops, as the spurs are prevented from occurring in the first place.
Solution Approach 2:
The patent extracts the noise filtering function from the physical domain (capacitors and large current loops) and moves it to the frequency domain (by tuning the switching frequency). This eliminates the need for large off-chip capacitors and their associated magnetic coupling problems.
4Use of energy by moving object
If switching frequency is kept at integer multiples of analog circuit frequency, then power conversion efficiency is maintained, but spurs fall into the frequency band of interest causing performance degradation
Solution Approach 1:
The patent changes the switching frequency parameter from integer multiples of the analog circuit frequency to a frequency that avoids these multiples. This maintains power conversion efficiency while preventing spurs from falling into the sensitive frequency band.
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 effectively reduces switching noise coupling, allowing for the integration of DC-DC converters with analog circuits, maintaining performance and reducing overall solution size and cost by minimizing magnetic coupling and ensuring the channel of interest is free from spurs.
Implementation Method 1
The DC-DC converter is very noisy due to the fact that it switches large current values in order to supply the total current of all digital and analog circuits supplied by its output
Implementation Method 2
Several coupling mechanisms (e.g. substrate, magnetic, power supply, etc.) cause these spurs to reach the sensitive analog circuits. One major form of coupling is magnetic (inductive). Unlike resistive and capacitive coupling, inductive coupling does not depend on material type or material depth.
Implementation Method 3
digitally controlling switching noise spurs in a receiver by shifting a switching frequency (fs) to a clock frequency (fs+Δf) to move a Kth harmonic of the switching frequency
Data Source
AI summary
An integrated circuit for digital controlling switching noise spurs in a receiver by shifting a switching frequency (fs) to a clock frequency (fs+Δf) to move a Kth harmonic of the switching frequency (fs) is provided. The integrated circuit includes a spur controlled clock that operates the clock frequency (fs+Δf), and a DC-DC converter circuitry that includes a first power switch, and a second power switch. The first power switch and the second power switch are driven by the clock frequency (fs+Δf). Δf ranges from(fRF-Kfs)+BWKto(fRF-(K-1)fs)-BWK-1,and fRF is center frequency of a received channel. None of the harmonics of the clock frequency (fs+Δf) is present in a channel of interest. The switching frequency is larger than the channel bandwidth 2BW.