Speaker Current Sensing Circuit With Common-Mode Voltage Rejection
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Solution Overview
Problem
Conventional techniques for measuring electric current in loudspeakers are sensitive to common mode voltage, leading to high costs and reduced accuracy, especially in the electroacoustic field where high-frequency measurements are challenging and heat dissipation needs to be monitored accurately.
Innovation Solution
A device with a shunt resistor and voltage-current converters, including current mirrors and a bias current generator, that transforms voltage differences into signal intensity, operating in a linear mode and canceling bias currents to reject common mode voltage, thereby improving sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional differential amplifier with input resistor is used for current measurement, then current intensity can be converted to potential difference, but the device becomes intrinsically sensitive to common mode voltage requiring expensive precision differential amplifier
Solution Approach 1:
The patent introduces an intermediary current mirror circuit between the shunt resistor and the measurement system. This current mirror acts as a mediator that transfers the current signal while rejecting common mode voltage, eliminating the need for expensive precision differential amplifiers and resolving the contradiction between measurement accuracy and device complexity
Solution Approach 2:
The patent replaces the conventional voltage-based differential amplifier measurement system with a current-based measurement system using current mirrors. This substitution changes the fundamental measurement approach from voltage differential to current copying, which inherently rejects common mode voltage and reduces the need for high-precision components
2Power
If high common mode voltage is present in the system, then voltage can reach about a hundred volts, but measurement accuracy deteriorates due to sensitivity to common mode voltage
Solution Approach 1:
The patent converts the harmful effect of high common mode voltage into a beneficial feature by using current mirrors that inherently copy current signals while automatically rejecting common mode voltage. The high voltage environment, which would normally degrade measurement accuracy, becomes irrelevant to the measurement process because the current mirror responds only to differential current changes
Solution Approach 2:
The patent changes the measurement parameter from voltage differential to current copying. By using current mirrors that operate with current signals rather than voltage signals, the system becomes insensitive to common mode voltage variations, allowing accurate measurements even when common mode voltage reaches hundred volts
3Adaptability or versatility
If bidirectional current measurement is required regardless of current direction and common mode voltage polarity, then measurement versatility improves, but device complexity increases
Solution Approach 1:
The patent implements a universal current measurement system using current mirrors that can handle bidirectional currents and both polarities of common mode voltage through a single circuit configuration. The current mirror inherently adapts to signal direction and voltage polarity without requiring additional components or reconfiguration, achieving multi-functionality and resolving the contradiction between versatility and complexity
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
The device achieves high sensitivity and accuracy in measuring bidirectional currents with reduced cost, capable of handling wide frequency ranges and high common mode voltage rejection, ensuring precise current control and heat monitoring in loudspeakers.
Implementation Method 1
a shunt resistor (1) positioned in series between the acoustic amplifier and the acoustic enclosure
Implementation Method 2
a voltage-current converter whose inputs are connected to the poles of the shunt resistor, said converter being adapted to proportionally transform the voltage difference at the poles of the shunt into a signal intensity
Implementation Method 3
a first current mirror whose input is connected to the output of the voltage-to-current converter and whose output is connected to a current-to-voltage converter
Implementation Method 4
whose output is connected to a current-to-voltage converter such that the voltage at the output of the current-to-voltage converter is proportional to the current signal
Implementation Method 5
said bias current generator being adapted to generate a bias current such that the device operates in linear mode and without saturation regardless of the electric current generated by the acoustic amplifier
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention relates to a device for measuring an electric current generated by an acoustic amplifier to drive a loudspeaker comprising: • a resistor (1) positioned in series between the amplifier and the loudspeaker; • a voltage-current converter (3) whose inputs are connected to the poles of the resistor (1) and which proportionally transforms the voltage difference across the shunt poles into a signal intensity; • a first current mirror (7) whose input is connected to the output of the voltage-current converter (3) and whose output is connected to • a current-voltage converter (5);• a constant bias current generator (9) connected to an input of the voltage-current converter (3) and whose output is connected to the current-voltage converter (5) via a second current mirror (11), and adapted to generate a bias current such that the device operates in linear mode and without saturation regardless of the electrical current generated by the acoustic amplifier.