Class-D Amplifier Common-Mode Control for Safe Input Voltage
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Solution Overview
Problem
Conventional class-D amplifier circuits face challenges in maintaining the input common-mode voltage at a low level due to disturbances from the output common-mode voltage, which can exceed the maximum rating voltage, potentially damaging the amplifier.
Innovation Solution
A class-D amplifier circuit with a common-mode control circuit that generates first and second high-bandwidth transconductance currents to regulate the input common-mode voltage, using a combination of non-operational-amplifier and operational-amplifier transconductance circuits to manage the common-mode control signals and maintain the input common-mode voltage within a predetermined level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback circuits are used to feedback the differential output signal, then the amplifier circuit can maintain stability and reduce distortion, but the input common-mode voltage is disturbed by the output common-mode voltage and cannot be maintained at the low voltage setting
Solution Approach 1:
A common-mode control circuit is introduced as an intermediary between the feedback circuits and the differential input signal. This control circuit generates a common-mode control signal that actively counteracts the disturbance from the output common-mode voltage, allowing the feedback mechanism to maintain stability while the control circuit preserves the low input common-mode voltage setting.
Solution Approach 2:
The common-mode control circuit dynamically adjusts the common-mode control signal based on the output common-mode voltage level. When the output common-mode voltage exceeds a predetermined threshold, the control circuit activates to regulate the input common-mode voltage back to the low voltage setting, effectively changing the operating parameter to prevent damage.
2Reliability
If the input common-mode voltage is allowed to rise to match the output common-mode voltage, then the feedback mechanism works more effectively, but the voltage may exceed the maximum rating and damage the amplifier circuit
Solution Approach 1:
The common-mode control circuit performs preliminary anti-action by detecting when the output common-mode voltage rises and preemptively generating a control signal to counteract the disturbance before it can damage the amplifier. This prevents the harmful voltage rise from occurring in the first place, rather than merely responding after damage occurs.
Solution Approach 2:
The common-mode control circuit implements a secondary feedback mechanism that specifically targets the common-mode voltage component. This additional feedback loop works in conjunction with the main feedback circuits to maintain both stability and voltage safety, creating a layered control system that addresses both objectives simultaneously.
Data Source
AI summary
A class-D amplifier circuit includes an amplifier circuit, a PWM circuit, a power stage circuit, a pair of feedback circuits, and a common-mode control circuit. The amplifier circuit receives a differential input signal at differential input ends to generate a differential intermediate signal. The PWM circuit generates a PWM signal according to the differential intermediate signal. The power stage circuit generates a differential output signal at differential output ends according to the PWM signal. The common-mode control circuit controls first and second high bandwidth transconductance circuits according to the output common-mode voltage of the differential output signal, so as to generate first and second common-mode control currents, thereby providing a common-mode control signal at the differential input ends to regulate the input common-mode voltage of the differential input signal at a predetermined input common-mode level.