Load Sensing Switch Techniques for Impedance Measurement
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Solution Overview
Problem
Existing systems for measuring load impedance in miniature speakers face accuracy issues due to significant differences in signal path gains caused by the much smaller sense resistor, leading to relative gain errors and power dissipation challenges.
Innovation Solution
Implementing a single sense amplifier and ADC to perform time-multiplexed measurements using three switches, allowing for improved matching between signal paths and reducing gain errors, with a digital processor calculating the load impedance from the measured voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a sense resistor much smaller than the load is used to avoid power dissipation, then power dissipation is reduced, but the gain characteristics of the signal paths become very different leading to degraded measurement accuracy
Solution Approach 1:
The patent implements time-multiplexed measurements where the system periodically alternates between measuring the load voltage and the sense resistor voltage using switches. This periodic switching allows both voltage measurements to be performed sequentially through a single signal path, eliminating the need for continuous parallel measurement paths with different gain characteristics. The measurement cycle includes: (1) switching to connect the load voltage to the measurement circuit, (2) switching to connect the sense resistor voltage to the same measurement circuit, and (3) repeating the cycle to obtain both voltage values for impedance calculation.
2Productivity
If separate signal paths are used to process load voltage and sense resistor voltage, then simultaneous measurement is enabled, but the large difference in signal path gains degrades measurement accuracy
Solution Approach 1:
The patent merges the measurement of both load voltage and sense resistor voltage into a single signal path by using time-multiplexing with switches. Instead of maintaining separate parallel signal paths with different gain characteristics, the system combines both measurement functions through one common measurement circuit. The switches dynamically connect either the load voltage or the sense resistor voltage to the same measurement amplifier and ADC, ensuring that both measurements share identical gain characteristics and are subject to the same environmental conditions, thereby eliminating gain mismatch errors.
Data Source
AI summary
Techniques for sensing the resistance of a load. In an aspect, a sense resistor is provided in series with the load. Each terminal of the sense resistor is alternately coupled via switches to a sense amplifier. A second input of the sense resistor is coupled to a terminal of the load. The voltage drop across the load and the voltage drop across the load plus sense resistor are alternatively measured. These voltage drops may be digitized and used to compute a resistance of the load using, e.g., a digital processor.