Amplifier Circuit Common-Mode Compensation Without DC-Blocking Capacitors
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Solution Overview
Problem
Existing audio amplifier circuits require external capacitors and increased pin count on integrated circuits to decouple DC signals from AC signals, leading to increased component count, PCB space requirements, and noise sensitivity issues, which are not adequately addressed by current noise reduction solutions.
Innovation Solution
Incorporating a compensation circuit that injects a DC current representative of the difference between unequal common mode voltages into the power amplifier, eliminating the need for external decoupling capacitors and optimizing common mode voltage at the output, while reducing pin count and PCB space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external capacitors are used to decouple DC signals from AC signals, then DC decoupling is achieved, but component count and PCB space increase
Solution Approach 1:
The patent merges the DC decoupling function with the existing amplifier circuitry by using the common mode voltage difference between stages. The compensation circuit integrates DC current injection directly into the amplifier stages, eliminating the need for separate external decoupling capacitors while achieving the same DC blocking effect.
Solution Approach 2:
The patent extracts the DC decoupling function from external passive components and implements it within the active amplifier circuit itself. By removing the requirement for external capacitors and focusing on the essential amplification function, the design achieves DC decoupling through internal circuit mechanisms.
2Reliability
If external capacitors are used to decouple DC signals from AC signals, then DC decoupling is achieved, but PCB space requirements increase
Solution Approach 1:
The patent combines multiple functions (amplification and DC decoupling) into a single integrated circuit package. The compensation circuit is implemented within the IC, using the voltage difference between amplifier stages to generate compensating DC currents that block DC signals without requiring external capacitor components that would occupy PCB space.
3Reliability
If compensation circuit injects DC current to compensate for common mode voltage difference, then common mode voltage is optimized, but circuit complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the compensation circuit continuously monitors the common mode voltage difference between amplifier stages and automatically adjusts the DC current injection accordingly. This feedback loop maintains optimal common mode voltage levels without requiring complex external control circuits.
Solution Approach 2:
The compensation circuit is self-regulating, using the inherent voltage difference between amplifier stages to generate the necessary compensating DC currents. The circuit automatically adjusts itself based on operating conditions without requiring external intervention or complex control logic.
Data Source
Figure 1~2
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Figure 5
AI summary
An amplifier circuit (400, 500, 600) on a single die comprises a low voltage amplifier with a first common mode voltage (Vreg/2) and having an input and an output. A power amplifier has a second common mode voltage (Vbatt/2) whose input is operably coupled to an output of the low voltage amplifier. The first common mode voltage (Vreg/2) and second common mode voltage (Vbatt/2) are unequal. A compensation circuit (465, 545, 645) is operably coupled to an input of the power amplifier (455, 582, 584) and arranged to inject a DC-current (594) or apply a common mode voltage (AREF) into the power amplifier (455, 582, 584) that is representative of a difference between the first common mode voltage and the second common mode voltage.