PWM Frequency Control for Low-Noise ADC Signal Conversion

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Solution Overview

Problem

Existing electronic apparatuses face challenges in reducing the influence of noise from pulse width modulation (PWM) signals, particularly in the context of analog-to-digital conversion, where aliasing noise is generated due to overlapping frequencies of PWM and sampling frequencies.

Innovation Solution

The electronic apparatus sets the frequency of the PWM signal to specific ranges relative to the sampling frequency, such as NFs+Fs/4≤Fn≤(N+1)Fs−Fs/4, and adjusts the phases of multiple PWM signals to cancel noise superimpositions, using ground connections and phase shifts to minimize noise interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the PWM frequency is set close to the sampling frequency to improve power conversion efficiency, then the power conversion efficiency is improved, but aliasing noise increases and overlaps with the signal band

Engineering Contradiction:

Improvepower conversion efficiencyVSAvoidaliasing noise

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent divides the frequency spectrum into distinct segments: the signal band (0 to Fs/4), the transition band (Fs/4 to Fs/2), and the PWM frequency region (above Fs/2). By segmenting the frequency allocation, the PWM frequency can be positioned in a region that does not overlap with the signal band, thereby reducing aliasing noise while maintaining power conversion efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the PWM frequency parameter to satisfy the condition Fn ≥ Fs/2 + Fs/4, which shifts the PWM frequency away from the signal band. This parameter change ensures that the aliased noise components fall outside the usable signal range, effectively reducing noise interference while preserving conversion efficiency.

Inventive Principle:

Principle #35Parameter changes

2Power

If multiple PWM signals are used to improve power conversion performance, then the power conversion performance is improved, but noise superimposition increases

Engineering Contradiction:

Improvepower conversion performanceVSAvoidnoise superimposition

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent introduces asymmetric phase shifting among multiple PWM signals, where each PWM signal has a different phase offset. This asymmetric phase distribution causes the noise components to cancel each other out through destructive interference, reducing noise superimposition while maintaining the power conversion performance benefits of multiple PWM signals.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent employs periodic phase shifting of PWM signals, where the phase offsets are set to specific values (e.g., 180 degrees for two signals, 120 degrees for three signals). This periodic action ensures that noise components from multiple PWM signals align in opposite phases, causing them to cancel each other out and reducing overall noise superimposition.

Inventive Principle:

Principle #19Periodic action

3Device complexity

If the PWM frequency is reduced to simplify filter design, then the filter design is simplified, but the noise component falls within the Nyquist frequency and increases aliasing noise

Engineering Contradiction:

Improvefilter design complexityVSAvoidaliasing noise in Nyquist region

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the PWM frequency parameter to a specific range (Fs/2 + Fs/4 ≤ Fn < Fs) that positions the fundamental PWM frequency and its harmonics above the Nyquist frequency. This parameter change ensures that aliasing noise does not fold back into the signal band, simplifying filter design requirements while effectively reducing aliasing noise in the Nyquist region.

Inventive Principle:

Principle #35Parameter changes

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 aliasing noise and noise superimposition, ensuring that the output signal of the analog-to-digital converter maintains a low noise level within the desired frequency band, enhancing signal quality.

Implementation Method 1

a low-pass filter circuit that outputs a voltage based on the pulse width modulation signal

Methodology Applied

Scientific EffectLow-pass filtering: Filter (electronic)

Implementation Method 2

a third electronic circuit that converts the analog signal into a digital signal

Methodology Applied

Scientific EffectAnalog-to-digital conversion:

Implementation Method 3

the processor sets a frequency of the pulse width modulation signal to a frequency at which a noise component included in the digital signal is reduced in relation to a sampling frequency of the third electronic circuit

Methodology Applied

Scientific EffectFrequency domain separation:

Data Source

PatentUS12609710B2Electronic apparatus

Publication Date: 2026.04.21 FUJIFILM CORP

AI summary

An electronic apparatus includes: a processor; a first electronic circuit that outputs a pulse width modulation signal; a low-pass filter circuit that outputs a voltage based on the pulse width modulation signal; a second electronic circuit that outputs an analog signal by using the output voltage of the low-pass filter circuit; and a third electronic circuit that converts the analog signal into a digital signal, and the processor sets a frequency of the pulse width modulation signal to a frequency at which a noise component included in the digital signal is reduced in relation to a sampling frequency of the third electronic circuit.