Chopper Current Sensing Circuitry for Low-Noise Precision Measurement
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Solution Overview
Problem
Existing current sensing techniques in electronic systems face challenges in achieving high sensitivity, accuracy, wide bandwidth, low temperature drift, and strong common mode rejection, particularly in consumer electronic devices where current measurement is crucial for safety and power management.
Innovation Solution
The proposed current sensing circuitry employs a differential amplifier with a switch network that alternates first and second current sources between input and output phases, combined with a differential chopper amplifier and a current-to-voltage converter, utilizing synchronized chopping frequencies to reduce noise and offset drift, and an analogue-to-digital converter for precise current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensing techniques are used with operational amplifiers and sense resistors, then current measurement capability is achieved, but noise performance and offset drift deteriorate
Solution Approach 1:
The patent applies periodic chopping action to modulate the differential amplifier and current sources at a chopping frequency. This periodic modulation transfers the DC offset and low-frequency noise to AC domain, allowing them to be filtered out while preserving the current measurement signal. The chopper amplifier alternates between active and reset phases periodically, achieving low noise and low offset drift performance.
2Measurement precision
If high sensitivity and wide bandwidth are achieved in current sensing, then measurement capability is improved, but temperature drift increases
Solution Approach 1:
The patent employs automatic offset cancellation through feedback mechanisms. The chopper amplifier continuously monitors and cancels its own offset voltage through feedback loops. Additionally, the system uses feedback to maintain stable operating points despite temperature variations, ensuring that sensitivity and bandwidth remain constant while compensating for temperature-induced drift.
3Measurement precision
If common mode rejection is improved in current sensing, then measurement accuracy is enhanced, but circuit complexity increases
Solution Approach 1:
The patent merges the differential amplifier with chopper stabilization circuits into a single integrated chopper amplifier unit. The current sources are also integrated with the amplification stage, allowing common mode rejection to be achieved through the differential architecture itself rather than requiring separate common mode rejection circuits. This integration maintains high common mode rejection while controlling overall circuit complexity.
Data Source
AI summary
The present application relates to current sensing circuitry (100) that comprises a differential amplifier (110) comprising first and second inputs configured to sense a current across a sense resistance, and an output configured to output a current sense signal. The circuitry (100) further comprises a first current source, a second current source and a switch network operable in: a first phase in which the first current source is connected to the first input and disconnected from the output, and the second current source is connected to the output and disconnected from the first input; and a second phase in which the first current source is connected to the output and disconnected from the first input, and the second current source is connected to the first input and disconnected from the output.