VCO-Based DC Offset Compensation for Multiplexed Audio Amplifiers
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Solution Overview
Problem
Existing audio amplifier circuitry faces challenges in efficiently compensating for DC offset voltages, leading to audible artifacts and power wastage, particularly in battery-powered devices, due to the large size and cost of conventional ADC-based compensation circuits, which also hinder fast settling times when multiplexing across multiple audio outputs.
Innovation Solution
The implementation of a DC offset compensation circuit using a voltage controlled oscillator (VCO) and counter to generate pulse counts from both the amplified output signal and a reference signal, allowing for accurate compensation without the need for a conventional ADC, thereby reducing silicon area and enabling faster settling times across multiple audio outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an ADC-based feedback path is used for DC offset compensation, then measurement precision is improved, but area of stationary object increases
Solution Approach 1:
The patent replaces the ADC (analog-to-digital converter) with a VCO (voltage-controlled oscillator) and counter combination. The VCO converts the analog output voltage into a frequency signal, which is then counted and compared digitally. This substitution eliminates the need for a large ADC while maintaining DC offset measurement capability through frequency-based measurement.
Solution Approach 2:
The patent changes the measurement parameter from direct voltage measurement (requiring ADC) to frequency measurement (using VCO and counter). By converting the DC offset voltage into a frequency deviation of the VCO output, the system achieves equivalent measurement precision using smaller, more area-efficient components.
2Measurement precision
If separate DC offset compensation circuits are provided for multiple audio outputs, then measurement precision is improved, but area of stationary object increases
Solution Approach 1:
The patent implements a universal DC offset compensation circuit that can serve multiple audio outputs (headphone, line-out, internal speaker, noise cancellation speaker) through time-multiplexed operation. The single VCO-based compensation circuit is sequentially applied to different outputs, providing accurate DC offset correction for each without requiring separate dedicated circuits for each output channel.
Solution Approach 2:
The patent merges multiple DC offset compensation functions into a single unified compensation circuit. Instead of having separate compensation paths for each audio output, the system combines them into one shared VCO-based compensation mechanism that operates in a time-multiplexed manner, significantly reducing the total chip area required.
3Area of stationary object
If ADC-based compensation circuitry is multiplexed between multiple audio signal lines, then area of stationary object is reduced, but speed decreases
Solution Approach 1:
The patent employs periodic action through the VCO's oscillating output, which naturally provides periodic signals for counting and comparison. The VCO is driven by the output signal and reference signal in alternating periods, enabling continuous monitoring and rapid adjustment of DC offset across multiple outputs without requiring sequential multiplexing of a single compensation resource.
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 solution provides accurate DC offset compensation with reduced silicon area and cost, enabling faster compensation across multiple audio outputs, thus minimizing power wastage and audible artifacts, while maintaining efficiency in battery-powered devices.
Implementation Method 1
a voltage controlled oscillator (VCO) configured to provide, over time, a first VCO output signal based on said amplified output signal and a second VCO output signal based on a reference signal
Data Source
AI summary
An apparatus and method for DC offset compensation. An amplifier receives an input signal (AIN) and provides an amplified output signal (SOUT) and a feedback path provides DC offset compensation. The feedback path comprises at least one voltage controlled oscillator (VCO) and a counter. The VCO provides, over time, a first VCO output signal based on said amplified output signal and a second VCO output signal based on a reference signal (VREF). The counter generates first pulse counts based upon the first VCO output signal and second pulse counts based upon the second VCO output signal and provides a compensation signal based on a comparison of the first and second pulse counts. One voltage controlled oscillator may sequentially receive a signal based on said amplifier output signal and the reference signal from a multiplexer so as to sequentially produce the first and second VCO output signals.