Audio Measurement Amplifier with Nested Feedback Loops

The patent extracts the sense resistor from the direct signal path to the acoustic transducer. By placing the sense resistor only in the feedback path of the amplifier and using differential amplification, the current measurement function is retained while the harmful damping effect on the transducer is eliminated. The sense resistor is effectively 'taken out' from the path that directly affects the transducer dynamics.

The patent introduces a differential amplifier as an intermediary element that measures the voltage across the sense resistor without directly connecting the sense resistor to the transducer. This intermediary mechanism allows current measurement while isolating the transducer from the damping influence of the sense resistor, resolving the contradiction between measurement capability and dynamic performance.

The patent employs a servo mechanism with feedback to accurately control and measure DC offsets. The system uses a feedback loop that continuously monitors the output offset and adjusts the input signal to achieve the desired offset level. This feedback approach enables precise DC offset control while maintaining a relatively simple overall circuit structure, resolving the contradiction between simplicity and measurement precision.

The patent segments the amplifier circuit into distinct functional blocks: an inner feedback loop for basic amplification, an outer servo loop for DC offset control, and separate filter circuits. This segmentation allows each block to be optimized for its specific function while keeping the overall design manageable. The modular approach enables accurate DC offset measurement without requiring a completely complex redesign of the entire amplifier.

The patent uses a nested feedback structure where an inner feedback loop (for AC signal amplification) is contained within an outer feedback loop (for DC offset control). This nesting allows the simpler inner loop to handle high-frequency signals while the outer loop manages DC and low-frequency offsets. The nested structure achieves high measurement precision across the full frequency range without requiring completely separate independent circuits, thus managing complexity efficiently.

The patent implements dynamic filtering where the inner feedback loop handles high-frequency AC signals and the outer servo loop handles low-frequency DC signals. The filters are designed with appropriate time constants that allow each loop to dynamically respond to its designated frequency range. This dynamic separation of functions enables accurate DC offset measurement while maintaining circuit simplicity through frequency-based task allocation rather than requiring complex multi-functional circuits.