SMPS Dither Control Circuit for Ripple and Spurious Energy Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Switch mode power supplies (SMPS) generate periodic ripple voltage that can interfere with radio frequency signals, leading to spurious side band signals, and existing methods to mitigate this either reduce efficiency or increase power consumption, making them unsuitable for efficient operation in cellular phone transmitter applications.
Innovation Solution
A control circuit and dithering method that uses a random number generator to form an optimized n-degree polynomial for uniform signal distribution, a switch control block to manage output stages, and a dither control block to generate a synchronized dither current, minimizing glitches and combining it with a reference current from a voltage ramp generator to reduce ripple voltage while maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If switching frequency is increased to reduce ripple voltage, then ripple voltage is reduced, but efficiency decreases due to increased dynamic power consumption
Solution Approach 1:
The patent applies dynamics by modulating the switching frequency dynamically rather than using a fixed frequency. A dither signal is added to the nominal switching frequency, causing the frequency to vary over time. This dynamic frequency modulation spreads the spectral energy of the ripple voltage across a wider bandwidth, reducing peak spurious emissions while maintaining the average switching frequency and thus preserving efficiency.
Solution Approach 2:
The patent changes the frequency parameter by introducing a dither component to the switching frequency. The switching frequency becomes f_sw(t) = f_nominal + dither_signal(t), where the dither signal varies the frequency within a certain range. This parameter change transforms the concentrated spectral energy into distributed spectral energy, reducing spurious emissions without requiring a significant increase in average switching frequency.
2Object-generated harmful factors
If external filtering is used to reduce ripple voltage, then ripple voltage is reduced, but cost increases
Solution Approach 1:
The patent replaces the mechanical/electrical filtering approach with a control-based approach. Instead of adding external passive filtering components (inductors, capacitors, resistors) to attenuate ripple voltage, the patent uses active frequency modulation through a dither signal injected into the switching frequency control. This substitution eliminates or reduces the need for additional filtering hardware, thereby reducing cost while achieving the same ripple reduction effect.
3Object-generated harmful factors
If a linear regulator is added for power control to reduce ripple, then ripple issues are reduced, but efficiency decreases and battery life shortens
Solution Approach 1:
The patent replaces the linear regulator approach with a switching-based frequency modulation approach. Instead of using a linear regulator to smooth the power supply and reduce ripple (which dissipates excess power as heat), the patent modulates the switching frequency of the existing SMPS to spread spectral energy. This maintains the high efficiency of switching regulation while achieving ripple reduction, thus preserving battery life.
Solution Approach 2:
The patent applies dynamics by continuously modulating the switching frequency with a dither signal rather than using a static linear regulation approach. This dynamic frequency variation spreads the ripple energy spectrally without the power loss associated with linear regulation, maintaining efficiency while reducing ripple issues.
Data Source
AI summary
There is provided a control circuit of a switch mode power supply including a random number generator configured to form an optimized n-degree polynomial based on the minimum power-on cycle time in order to form a uniform distribution of output signals, a switch control block configured to control output signals of the switch control block such that the complementary output stages of the switch control block conduct at different times on the basis of the output signals received from the random number generator. and a dither control block configured to generate a synchronized dither current by minimizing glitches at each differential stage of a default reference current based on the output signals received from the switch control block, and to combine the generated synchronized dither current with a reference current of a voltage ramp generator.