Differential Amplifier Offset Correction Using Input DAC Injection
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Solution Overview
Problem
Differential amplifiers and magnetic field sensing elements often exhibit undesirable offset voltages, leading to inaccuracies in sensing magnetic fields, especially when the field is zero, and existing methods to reduce these offset voltages require additional amplifier stages that can negatively impact system parameters like noise, offset, and bandwidth.
Innovation Solution
A circuit that adjusts the offset voltage of a differential amplifier or a combination of a differential amplifier and a magnetic field sensing element using a resistor network, current generators, and a switching network, allowing for offset correction without adding extra amplifier stages in the sensing element's signal path, utilizing matched R-2R digital-to-analog converters to inject currents into the differential amplifier's input nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional amplifier stages are added to reduce offset voltage, then offset voltage is reduced, but noise increases and bandwidth decreases
Solution Approach 1:
The patent extracts the offset correction function from a separate amplifier stage and integrates it directly into the differential amplifier's input stage. By placing resistor networks and current sources at the input nodes, the offset is corrected at the source without requiring additional amplification stages, thereby avoiding the noise and bandwidth penalties associated with extra stages.
Solution Approach 2:
The patent applies preliminary action by correcting the offset voltage at the very input stage of the differential amplifier, before the signal undergoes further amplification. The resistor networks and current sources are configured to generate compensating currents that cancel offset voltages at the input nodes, ensuring clean signal processing throughout the subsequent stages.
2Measurement precision
If additional amplifier stages are added to reduce offset voltage, then offset voltage is reduced, but device complexity increases
Solution Approach 1:
The patent merges the offset correction function with the differential amplifier's input stage by integrating resistor networks and current sources directly at the input nodes. This consolidation eliminates the need for separate amplifier stages dedicated to offset correction, reducing device complexity while maintaining offset correction capability.
Solution Approach 2:
The input stage of the differential amplifier is designed to serve multiple functions simultaneously: it performs the primary differential amplification function while also incorporating offset correction through integrated resistor networks and current sources. This multi-functionality reduces the overall number of components and stages required in the circuit.
3Measurement precision
If additional amplifier stages are added to reduce offset voltage, then offset voltage is reduced, but system bandwidth decreases
Solution Approach 1:
The patent extracts the offset correction function from subsequent amplifier stages and implements it directly at the input stage. By placing the correction mechanism at the beginning of the signal path, the signal spends less time passing through multiple amplification stages, thereby preserving bandwidth while still achieving offset correction.
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
This solution effectively cancels offset voltages without requiring additional amplifier stages, maintaining system parameters and improving the accuracy of magnetic field sensing by ensuring equal emitter currents when the offset voltage is corrected, thus enhancing the precision of magnetic field detection.
Implementation Method 1
a Hall Effect element 24 coupled between a current generator 22 and a voltage reference (e.g., ground), can generate a differential signal 24a, 24b
Implementation Method 2
four magnetoresistance elements 12, each having a resistance proportional to a magnetic field
Data Source
AI summary
An electronic circuit has a differential amplifier with a differential transistor pair having two transistors. The electronic circuit also has two digital-to-analog converters, a respective one of the two digital-to-analog converters coupled to each respective one of the two transistors. Control bits adjust the DACs to provide an offset voltage adjustment of the differential amplifier.