Common-Mode Headset Driver Circuit for Differential Noise Cancellation

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Solution Overview

Problem

Existing stereo headset amplifier driving units face challenges in noise reduction due to DC bias power dissipation and audible hum, with current solutions like capacitive and common mode amplifier schemes either increasing power consumption or requiring additional processing masks, and capacitive schemes necessitating bulkier components.

Innovation Solution

A driver circuit configuration with a common mode amplifier, first and second driver amplifiers, and feedback circuits that replicate noise to cancel it differentially across speakers, using equal gain amplifiers and a reference voltage derived from the common mode voltage to eliminate DC bias and reduce noise power.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a capacitive scheme is used to decouple DC bias from audio output, then DC bias is removed, but noise across the speaker increases and bulky capacitors are required

Engineering Contradiction:

ImproveDC bias power dissipationVSAvoidnoise across speaker

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a common mode amplifier as an intermediary component that generates a common mode voltage equal to the DC bias voltage. This mediator allows the DC bias to be replicated and subtracted from the audio output through differential signaling, effectively removing DC power dissipation while avoiding the noise and bulk issues associated with capacitive coupling schemes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If a negative voltage scheme is used to enable audio output to swing below ground, then DC bias is eliminated, but power consumption increases and additional processing masks are required

Engineering Contradiction:

ImproveDC bias power dissipationVSAvoidpower consumption from positive supply voltage

Core Design Contradiction:

Loss of energyVSUse of energy by moving object

Solution Approach 1:

The patent creates a copy of the DC bias voltage through the common mode amplifier, which generates a common mode voltage that replicates the bias level. This copied voltage is then used in the differential output stage to eliminate the need for negative voltage generation, thereby reducing power consumption and avoiding the need for additional processing masks while still achieving DC bias elimination.

Inventive Principle:

Principle #26Copying

3Loss of energy

If a CM amplifier scheme is used to generate CM voltage equal to DC bias, then DC bias is removed, but an extra amplifier is required increasing device complexity

Engineering Contradiction:

ImproveDC bias power dissipationVSAvoidnumber of amplifiers

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent designs the common mode amplifier to serve multiple functions: it generates the common mode voltage equal to DC bias, provides the reference voltage for the differential output stage, and enables noise cancellation through its feedback circuitry. By making this single amplifier multi-functional, the patent reduces the overall device complexity compared to schemes requiring separate dedicated circuits for each function.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges the DC bias elimination function, noise cancellation function, and output driving function into a unified circuit architecture centered around the common mode amplifier. The feedback circuits of the common mode and differential output amplifiers are combined to achieve noise cancellation, thereby reducing the total number of discrete components and simplifying the overall device structure.

Inventive Principle:

Principle #5Merging (Combining)

4Object-affected harmful factors

If feedback circuits are configured to replicate noise at CM amplifier output, then noise cancellation is achieved, but circuit complexity increases

Engineering Contradiction:

Improvenoise across speakerVSAvoidfeedback circuit configuration

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent implements feedback circuits in both the common mode amplifier and the differential output amplifiers that are configured to replicate and cancel noise. The feedback mechanism automatically adjusts the signal levels to ensure that noise generated at the common mode amplifier output is precisely replicated at the differential outputs and then canceled through differential signaling, achieving noise reduction while maintaining manageable circuit complexity through systematic feedback design.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8792650B2CM amplifier divided output supplying first, second, CM amplifier inputs

Publication Date: 2014.07.29 TEXAS INSTRUMENTS INC

AI summary

A driver circuit includes a first driver amplifier that is configured to generate a first output in response to a first reference voltage input and a first audio input; a second driver amplifier that is configured to generate a second output in response to the first reference voltage and a second audio input; and a common mode (CM) amplifier, coupled to the first driver amplifier and the second driver amplifier. The CM amplifier is configured to generate an output in response to a second reference voltage input, the first reference voltage input being a divided version of the output. Gains of the first driver amplifier, second driver amplifier and the CM amplifier are equal. Noise at the output appears across a plurality of resistors coupled at the outputs of the first driver amplifier, second driver amplifier and the CM amplifier and cancels with respect to the output of the CM amplifier.