Differential PWM for Switching Amplifiers With Reduced Frequency Pulling
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Solution Overview
Problem
The integration of communication and audio sub-systems on a single chip in communication devices is hindered by frequency pulling, a phenomenon caused by mutual inductive coupling between the class-D amplifier and the oscillator, leading to spurious signals and interference in adjacent frequency bands, violating data transmission standards.
Innovation Solution
A pulse width modulation scheme that generates differential pulse width modulated waveforms with a pre-determined non-zero minimum pulse width, reducing frequency pulling by adjusting the duty cycle of PWM waveforms to minimize interference while maintaining amplifier performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the communication sub-system and audio sub-system are integrated on a single chip, then device size and cost are reduced, but frequency pulling occurs causing spurious signals and interference in adjacent frequency bands
Solution Approach 1:
The patent introduces an isolation circuit as an intermediary element between the class-D amplifier and the oscillator. This isolation circuit acts as a buffer that blocks the mutual inductive coupling responsible for frequency pulling, while still allowing the systems to be integrated on the same chip. The isolation circuit effectively mediates the interaction between the two subsystems, preventing harmful frequency pulling without requiring physical separation.
2Use of energy by moving object
If the class-D amplifier operates at high switching speed, then power efficiency is improved, but time varying interference loops are created causing frequency pulling in the oscillator
Solution Approach 1:
The isolation circuit serves as a mediator that allows the class-D amplifier to operate at high switching speeds for power efficiency while preventing the generation of time-varying interference loops from affecting the oscillator. The isolation circuit blocks the coupling path that would otherwise transmit these interference loops to the oscillator, thus maintaining both high power efficiency and oscillator stability.
3Power
If the switching amplifier drives the modulated waveform to saturation and cut-off modes, then amplification performance is improved, but mutual inductive coupling varies the operating frequency of the oscillator
Solution Approach 1:
The isolation circuit acts as a protective intermediary between the high-power class-D amplifier and the oscillator. It allows the amplifier to operate in saturation and cut-off modes for optimal amplification performance while preventing the mutual inductive coupling from varying the oscillator's operating frequency. The isolation circuit effectively decouples the frequency modulation effects while maintaining power transfer efficiency.
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
Significantly reduces frequency pulling in the oscillator for both idling and non-idling conditions without compromising amplifier performance, ensuring compliance with data transmission standards and preventing data loss for low amplitude signals.
Implementation Method 1
the class-D amplifier drives the modulated waveform to saturation and cut-off modes at a high switching speed, generating a rectangular waveform with fast moving transition edges as an output
Implementation Method 2
These interference loops vary the operating frequency of the oscillator due to mutual inductive coupling
Data Source
AI summary
A device and a method for implementing pulse width modulation for switching amplifiers (120) is described herein. In one embodiment, the device includes a sampling signal generator (202) to generate a sampling signal (208) and a modulation unit (102) operatively coupled to the sampling signal generator (202). The modulation unit (102) generates differential pulse width modulated waveforms based on the sampling signal (208) and differential input signals (220-1 and 220-2) such that at least one differential pulse width modulated waveform has a duty cycle equivalent to a pre-determined non-zero minimum pulse width at all values of the differential input signals (220-1 and 220-2).