Soft Common Return Multi-Channel Amplifier for Common-Mode Noise Control

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Solution Overview

Problem

Existing multi-channel amplifiers face challenges in minimizing noise and distortion, particularly due to common mode noise issues that arise when amplifiers are driven by different signals, affecting signal integrity and frequency response.

Innovation Solution

A system comprising channel switching amplifiers with a shared capacitor and a signal processor that processes input signals to regulate the common mode signal, ensuring isolation between amplifiers and maintaining a flat frequency response by controlling the voltage range of the common terminal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If amplifiers share a common decoupling capacitor, then device complexity is reduced, but common mode noise and distortion increase affecting signal integrity

Engineering Contradiction:

Improveamplifier structure complexityVSAvoidcommon mode noise

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent divides the common return path into separate segments for each amplifier channel by introducing individual return path resistors (R1, R2) and a summing resistor (R3). This segmentation isolates the current paths of different amplifiers, preventing their interaction through the shared capacitor while maintaining the benefit of a shared power supply connection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces intermediate elements (return path resistors and summing resistor) between the amplifiers and the shared capacitor. These intermediaries act as mediators that control and regulate the current flow, preventing direct interaction between amplifier channels while still allowing the shared capacitor to function for power supply decoupling.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If amplifiers share a common decoupling capacitor, then manufacturing cost is reduced, but frequency response flatness deteriorates

Engineering Contradiction:

Improvemanufacturing costVSAvoidfrequency response flatness

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent segments the return path currents through individual resistors for each channel, allowing independent control of current distribution. This segmentation enables precise control over the frequency response characteristics while maintaining a cost-effective shared capacitor architecture.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses parameter changes in the return path resistors (R1, R2, R3) to optimize frequency response flatness. By carefully selecting resistor values, the system achieves flat frequency response across the operating range while maintaining the economical shared capacitor configuration.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If amplifiers are driven by different signals, then versatility is improved, but common mode noise increases due to capacitor integration of current differences

Engineering Contradiction:

Improvesignal processing flexibilityVSAvoidcommon mode noise

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The summing resistor (R3) acts as an intermediary that combines the return path currents from different amplifier channels in a controlled manner. This intermediary element allows the amplifiers to process different signals independently while preventing the integration of current differences that would otherwise create common mode noise through the shared capacitor.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent uses parameter changes in the return path resistors to optimize the balance between versatility and noise reduction. By adjusting resistor values, the system can accommodate different signal configurations (mono, stereo, differential) while maintaining low common mode noise through proper current distribution.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250105803A1Multi-channel amplifier with soft common return point

Publication Date: 2025.03.27 CIRRUS LOGIC INT SEMICON LTD

AI summary

A system may include a signal processor that receives a first input signal from a first channel switching amplifier of a multi-channel amplifier and a second input signal from a second channel switching amplifier of the multi-channel amplifier, wherein the first channel switching amplifier and the second channel switching amplifier share a capacitor that has a first terminal coupled to a common terminal that is coupled to a first negative polarity of the first channel switching amplifier and a second positive polarity of the second channel switching amplifier and a second terminal that is coupled to a ground. The signal processor may be configured to receive the first input signal and the second input signal and modify the first input signal into the first channel switching amplifier and the second input signal into the second channel switching amplifier to regulate a common mode signal at the common terminal.