Switching Amplifier Back-EMF Recovery During Zero-Voltage Sampling
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Solution Overview
Problem
Switching amplifiers, used for efficient power delivery to transducers, face challenges in measuring current flow due to their low output impedance, making it difficult to separate the small back-EMF signal from the large driving signal, which is essential for full-duplex operation.
Innovation Solution
A method and apparatus that temporarily disconnect the transducer from the switching amplifier during its zero voltage state to measure the residual current flow, using a signal capture circuit to capture both the output signal and the back-EMF signal, and then subtract the prediction of the output signal to isolate the back-EMF signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a switching amplifier is used to drive the transducer, then power efficiency is improved, but the ability to measure current flow and separate the back-EMF signal deteriorates
Solution Approach 1:
The patent introduces an intermediary measurement circuit that couples to the transducer during the amplifier's zero-voltage state. This intermediary circuit allows current measurement without directly loading the switching amplifier output, thus preserving power efficiency while enabling back-EMF signal extraction. The measurement circuit acts as a mediator that accesses the transducer current indirectly through the amplifier's natural zero-voltage intervals.
Solution Approach 2:
The patent performs current measurement during the preliminary zero-voltage state that naturally occurs in switching amplifier operation before the next power delivery phase. By capturing the back-EMF signal during this brief interval when the amplifier output is already at zero voltage, the system prepares the measurement data before the next power cycle begins, avoiding interference from the large driving signal.
2Productivity
If the transducer is continuously driven by the switching amplifier, then audio output quality is improved, but the ability to capture back-EMF signal deteriorates
Solution Approach 1:
The patent employs periodic switching between power delivery mode and measurement mode, utilizing the natural periodic zero-voltage states in switching amplifier operation. During each switching cycle, the amplifier delivers power during active phases and enters zero-voltage states periodically, allowing the measurement circuit to capture back-EMF signals at these regular intervals without continuous interruption of audio output.
Solution Approach 2:
The patent uses only a small portion of the total time (the brief zero-voltage intervals) for measurement purposes, while the majority of time is dedicated to continuous audio power delivery. This partial action approach ensures that audio output quality is maintained at high levels while still obtaining sufficient measurement data during the available zero-voltage windows.
3Productivity
If the output signal is continuously applied to the transducer, then audio output is improved, but the dynamic range for back-EMF measurement deteriorates
Solution Approach 1:
The patent extracts the back-EMF signal measurement opportunity by taking advantage of the zero-voltage state intervals that are inherently present in switching amplifier operation. During these extracted time windows when the output signal is naturally absent, the measurement circuit captures the back-EMF signal without the overwhelming presence of the large audio driving signal, thus achieving sufficient dynamic range for accurate measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables full-duplex operation by effectively separating and measuring the back-EMF signal, improving the dynamic range and allowing simultaneous audio output and input, even with high-efficiency switching amplifiers.
Implementation Method 1
when such a transducer is subjected to an external sound, it in turn produces an electrical signal, a back Electromotive Force or 'back-EMF' signal
Implementation Method 2
driven by a pulse width modulated output signal from a switching amplifier
Implementation Method 3
the transducer having a reactance that causes a current to continue to flow momentarily in the transducer when the output signal ceases
Data Source
AI summary
An apparatus and method for determining signals representative of events in the environment of a reactive transducer while being driven by a switching amplifier is disclosed. While the switching amplifier is in a zero voltage state, a signal capture circuit that is also in a zero voltage state is connected to the transducer for a relatively brief period of time during which a measurement is made of the residual current flow due to the inductance of the transducer. A prediction of the output signal is then subtracted from the signal measured across the transducer, reducing the overall range of the signal and increasing the relative size of the back-EMF signal compared to any remaining output signal. If desired, conventional echo cancellation can then be performed. The back-EMF signal can then be subjected to further processing by an analog-to-digital converter as known in the art.