PWM Quantizer Gain Calibration for Stable Class-D Speaker Drive
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Solution Overview
Problem
Class-D amplifiers in personal audio devices face challenges in maintaining a fixed combined gain across different operating modes, leading to undesirable variations in ramp voltage swing range and associated sensitivity issues due to changes in speaker voltage, which complicates the design of voltage-to-time conversion circuits.
Innovation Solution
The implementation of a closed-loop pulse width modulation (PWM) modulator with a quantizer having adjustable analog gain, allowing for calibration to compensate for non-ideal characteristics and maintain a consistent combined gain across modes by adjusting the analog gain of the quantizer in response to changes in speaker voltage, thereby reducing the variation in ramp voltage swing range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the speaker driver operates with different PWM drive voltage swing ranges in different modes, then power efficiency is improved, but the combined gain varies across modes causing sensitivity issues
Solution Approach 1:
The quantizer's analog gain is made dynamically adjustable based on the operating mode. When the speaker driver switches between different PWM drive voltage swing ranges (first mode with first voltage range, second mode with second voltage range), the analog gain of the quantizer is correspondingly adjusted to compensate for gain variations, thereby maintaining stable combined gain across modes while preserving power efficiency benefits
Solution Approach 2:
The analog gain parameter of the quantizer is changed in response to mode transitions. By detecting which mode the speaker driver is operating in (based on PWM drive voltage swing range), the system adjusts the analog gain parameter to compensate for the different voltage ranges, ensuring that the product of quantizer gain and driver gain remains substantially constant across operating modes
2Stability of the object's composition
If the analog gain of the quantizer is adjusted to compensate for speaker voltage changes, then combined gain stability is improved, but device complexity increases
Solution Approach 1:
The system employs feedback by monitoring the operating mode of the speaker driver (first mode or second mode based on PWM drive voltage swing range) and using this information to adjust the analog gain of the quantizer. This feedback mechanism enables automatic compensation for gain variations without requiring complex external control circuits, as the mode detection and gain adjustment are integrated within the existing modulator architecture
Data Source
AI summary
A PWM modulator has a quantizer that generates a PWM output signal to speaker driver. When a first voltage swing range is supplied to the speaker driver, the quantizer analog gain is controlled to be a first gain value. When a second PWM drive voltage swing range is supplied to the speaker driver, the analog gain is controlled to be a second gain value. The first and second gain values of the analog gain of the quantizer cause the combined gain of the quantizer and driver to be approximately equal in the two modes. The quantizer has at least two gain-affecting measurable non-ideal characteristics. The quantizer is adjustable using measured first and second values to correct for first and second of the at least two non-ideal characteristics. The gain of the quantizer is calibratable while the quantizer is adjusted using the measured first and second measured values.