Differential Class D Amplifier for Common-Mode Noise Rejection
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Solution Overview
Problem
Conventional class D amplifiers are susceptible to noise interference when noise signals of equal magnitude and phase are present, as they cannot accurately match the gains of their amplifiers, leading to output noise in the load.
Innovation Solution
A class D amplifier design where a pulse generating circuit determines the gain for both output signals, and a differential pulse generating circuit inverts and shifts the pulse signal by half a period, ensuring that noise signals of equal amplitude and phase are cancelled out, resulting in no output noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate amplifiers are used for positive and negative output signals in a conventional class D amplifier, then the amplifier can deliver pulse width modulated signals to the load, but noise signals of equal magnitude and phase cannot be rejected due to gain mismatch between the amplifiers
Solution Approach 1:
The patent merges the gain determination function into a single pulse generating circuit that controls both the positive and negative output signals. Instead of having separate amplifiers with independently set gains, the invention uses one pulse generating circuit to generate pulse signals that are then differentially processed, ensuring both output paths share the same gain reference and thereby achieving noise rejection.
Solution Approach 2:
The invention creates a copied and inverted version of the pulse signal for the negative output path. The differential pulse generating circuit generates a second pulse signal that is the logical inverse of the first pulse signal, ensuring symmetric noise characteristics that can be rejected at the output. This copying approach ensures both paths experience identical noise conditions.
2Power
If conventional class D amplifier circuits are used, then power amplification can be achieved, but the circuit complexity increases with separate feedback paths and multiple integrating amplifiers
Solution Approach 1:
The pulse generating circuit serves multiple functions simultaneously: it generates the pulse width modulated signal, determines the gain for both output channels, and provides the reference for differential processing. This multi-functionality reduces the number of separate components needed, simplifying the overall circuit structure while maintaining power amplification capability.
Solution Approach 2:
The invention segments the amplifier into distinct functional blocks: a pulse generating circuit for signal generation and gain determination, a differential pulse generating circuit for creating complementary signals, and output stages for delivering the amplified signals. This segmentation allows each block to be optimized independently while reducing overall complexity through modular design.
Data Source
AI summary
Class D amplifier is resistant to interferences. Binary output signals y1 and y2, are generated from input signal s1, delivered to input terminal IN, to drive a load connected across output terminals OUTP and OUTN. Pulse generating circuit 10 generates a pulse width modulated pulse signal y0 from input signal s1, inverted signal of the output signal y1 and output signal y2. Differential pulse generating circuit 14 receives pulse signal y0 and inverts low and high levels of pulse signal y0, while shifting the resulting signal by half period from the pulse signal y0, to generate a pulse signal y3. Pulse amplifier 11a receives pulse signal y0 and generates output signal y1 supplied to output terminal OUTP. Pulse amplifier 11b receives pulse signal y3 and generates output signal y2 delivered to output terminal OUTN.