Amplifier Input Stage Compensation for Class D Supply Mismatch
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Solution Overview
Problem
Class D power amplifiers face issues due to high voltage output stages, leading to malfunctions and undesired effects when the difference between supply voltages PVDD and VDD is significant, causing instability at node N1.
Innovation Solution
A transconductance (gm) circuit is introduced to compare the input voltage with a common mode voltage, generating a compensate current to stabilize the voltage at the input stage, eliminating the need for sensing PVDD and allowing for a compact amplifier design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high voltage output stage is used in class D power amplifier, then the output power capability is improved, but the circuit stability deteriorates due to voltage variation at node N1
Solution Approach 1:
The patent implements a feedback mechanism where the voltage at node N1 is continuously monitored and fed back to the input stage. This feedback loop allows the circuit to automatically adjust and compensate for voltage variations, maintaining stability despite the high voltage output stage. The feedback signal is combined with the input signal to correct deviations in real-time.
Solution Approach 2:
The patent introduces an intermediate voltage node (node N1) between the input stage and output stage that acts as a mediator. This node buffers the voltage transitions and isolates the input stage from direct exposure to high voltage variations, thereby maintaining circuit stability while enabling high power output.
2Adaptability or versatility
If the difference between supply voltages PVDD and VDD is increased, then the output voltage range is improved, but the malfunction rate increases
Solution Approach 1:
The patent dynamically adjusts the voltage parameters at different stages of the amplifier. By controlling the voltage at node N1 to track variations in PVDD while maintaining appropriate voltage differences, the circuit achieves a wide output voltage range without exceeding safe operating limits that would cause malfunctions.
Solution Approach 2:
The patent employs dynamic voltage adjustment where the operating points of various stages are continuously adapted based on the supply voltage conditions. This dynamic operation allows the amplifier to maintain reliability across a wide range of supply voltages by preventing static operating conditions that could lead to malfunctions.
3Stability of the object's composition
If voltage sensing circuitry is added to compensate for PVDD-VDD difference, then the circuit stability is improved, but the chip area increases
Solution Approach 1:
The patent designs the input stage to perform multiple functions: it serves as both the signal amplifier and the voltage sensing element. The existing input transistors and biasing circuits are utilized to detect voltage variations at node N1, eliminating the need for separate dedicated sensing circuits and reducing overall chip area.
Solution Approach 2:
The circuit uses its own internal components to perform the sensing and compensation functions. The input stage components naturally respond to voltage variations at node N1, and this response is directly utilized for compensation without requiring external or additional specialized sensing circuitry.
Data Source
AI summary
An amplifier circuit with novel design is provided. The amplifier circuit includes an input stage, a resistor, an output stage, an intermediate stage and a gm circuit. The input stage is coupled to a first supply voltage, and is arranged to receive an input voltage and a feedback current. The resistor is coupled between the input voltage and the input stage. The output stage is coupled to a second supply voltage, and is arranged to provide an output voltage for driving a load. The intermediate stage is coupled between the input stage and the output stage, and includes a level shifter. The gm circuit is coupled to the input stage, and is arranged to compare the input voltage with a common mode voltage, and thereby generates a compensate current for the input stage.