Differential Amplifier Battery Sensing Below Common-Mode Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Personal electronic devices face challenges in accurately measuring battery voltage across a wide range using circuitry with a lower supply voltage, requiring costly special circuitry and reducing dynamic range due to the need for matched resistors and difficulty in creating a low-noise reference voltage.
Innovation Solution
A differential measurement circuit with a differential amplifier and current source is used to generate a differential output signal proportional to the battery voltage, where the current source subtracts the midpoint of the battery voltage range, and a common mode biasing circuit adjusts the input common mode voltage to operate within the circuit supply voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If resistors are used to divide battery voltage to a lower range, then the voltage is compatible with device circuitry, but manufacturing precision deteriorates due to difficulty in fabricating well-matched integrated resistors
Solution Approach 1:
The patent extracts the voltage division function from the measurement circuit by using a separate biasing circuit that generates a reference voltage equal to the midpoint of the battery voltage range. This reference voltage is then subtracted from the battery voltage at the differential amplifier inputs, eliminating the need for precision-matched resistors within the measurement circuit itself.
Solution Approach 2:
The patent introduces a midpoint voltage reference as an intermediary element. This reference voltage, generated by a dedicated biasing circuit, serves as a mediator that allows the differential amplifier to measure the battery voltage accurately without requiring precision-matched resistors. The reference voltage bridges the gap between the high battery voltage and the lower circuit supply voltage.
2Measurement precision
If a reference voltage is created for differential measurement, then measurement accuracy improves, but noise performance deteriorates due to difficulty in creating a low-noise reference
Solution Approach 1:
The patent segments the voltage reference generation function into a separate biasing circuit that operates independently from the differential measurement circuit. This segmentation allows the reference voltage to be generated with optimized noise characteristics, using current mirrors and biasing networks that are specifically designed to minimize noise while providing the required midpoint voltage.
3Adaptability or versatility
If special circuitry is used to measure high voltage, then measurement capability improves, but device complexity and cost increase
Solution Approach 1:
The patent creates equipotential conditions at the differential amplifier inputs by applying the battery voltage to both inputs and subtracting the midpoint reference voltage through current sources. This approach allows the differential amplifier, which operates at lower voltages, to accurately measure the full battery voltage range without requiring special high-voltage circuitry.
Data Source
AI summary
An apparatus comprises a differential amplifier circuit and a current source. The differential amplifier circuit is configured to receive a voltage at an input, wherein the differential amplifier circuit generates an output voltage having a magnitude proportional to the received voltage over a voltage range to be measured at a specified output common mode voltage. The current source is electrically connected to an input of the differential amplifier circuit and is configured to subtract a midpoint of a voltage range of the battery voltage to be measured at the input of the differential amplifier, wherein a circuit supply voltage provided to the differential amplifier circuit and the current source is less than the voltage at the input.