PWM Playback Path Gain Control During Impedance Switching
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Solution Overview
Problem
Existing audio amplifier technologies face challenges in maintaining constant overall path gain during transitions between high and low impedance modes, leading to audio artifacts such as audible pops and clicks.
Innovation Solution
A signal path with an analog and digital portion, where the output impedance and variable digital gain are adjusted continuously or in steps to maintain constant overall path gain during impedance mode transitions, using a control circuit to manage the impedance and gain in a pulse width modulation amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the output impedance is switched between high and low impedance modes, then the amplifier can adapt to different load conditions and improve power efficiency, but audio artifacts such as audible pops and clicks occur due to gain variations during transition
Solution Approach 1:
The control circuit performs preliminary action by adjusting the digital gain in advance before the impedance mode transition occurs. This preemptive gain adjustment ensures that the overall path gain remains constant throughout the transition, preventing audio artifacts from occurring during the impedance switching event.
Solution Approach 2:
The system implements feedback by continuously monitoring the overall path gain and using the control circuit to adjust the digital gain accordingly. This closed-loop control ensures that any gain variations during impedance transitions are compensated, maintaining constant overall path gain and eliminating audio artifacts.
2Reliability
If the output impedance is transitioned continuously or in steps between high and low impedance modes, then the amplifier maintains constant overall path gain, but the device complexity increases due to the control circuit requirements
Solution Approach 1:
The control circuit acts as an intermediary between the impedance switching mechanism and the digital gain adjustment. It coordinates the timing and magnitude of gain changes to match impedance transitions, enabling smooth impedance mode switching while maintaining constant overall path gain without requiring complex hardware modifications to the amplifier itself.
3Object-generated harmful factors
If the variable digital gain is adjusted contemporaneously with output impedance transition, then audio artifacts are reduced, but the manufacturing precision requirements increase for coordinating impedance and gain changes
Solution Approach 1:
The control circuit is designed to adjust the digital gain in advance of the impedance transition, with predetermined timing and magnitude relationships. This approach reduces the need for high-precision real-time coordination during manufacturing, as the gain adjustment sequence can be programmed and tested in advance rather than requiring precise hardware synchronization.
Data Source
AI summary
In a signal path comprising an analog path portion configured to operate in a plurality of output impedance modes including a high impedance mode with a first impedance and a low impedance mode with a second impedance, and a digital path portion having a variable digital gain and configured to convert a digital input signal and into an analog signal provided to the analog path portion, a method may include responsive to a condition for switching between the high impedance mode and the low impedance mode or vice versa, transitioning the output impedance continuously or in a series of steps between the first impedance and the second impedance or vice versa and, contemporaneously with transitioning the output impedance, transitioning the variable digital gain continuously or in a series of steps such to maintain a substantially constant overall path gain for the signal path remains substantially constant during transition.