Current Sensing Circuit Using Shunt and Transformer Segmentation
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Solution Overview
Problem
Conventional current sensing circuits face challenges in measuring rapid current changes in wireless communication devices, such as those using Bluetooth Low Energy protocols, due to high noise levels, limited dynamic range, and slow response times, which hinder the observation of current shifts within 1 μs or less.
Innovation Solution
A current sensing circuit configuration that combines a shunt resistor sensing circuit with a current transformer (CT) sensing circuit, utilizing a low-pass filter and an adder to minimize noise and achieve a wide dynamic range from 1 μA to 200 mA, with a fast response capable of tracking changes under 1 μs, and high input impedance for high-side current sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used to measure current, then current measurement is achieved, but noise increases and measurement precision deteriorates for low current levels
Solution Approach 1:
The patent divides the current measurement function into two separate circuits: a shunt resistor circuit for high current measurement and a current transformer circuit for low current measurement. This segmentation allows each circuit to be optimized for its specific current range, reducing noise impact on low current measurements while maintaining measurement capability for high currents.
Solution Approach 2:
The patent introduces a current transformer as an intermediary device to measure low current levels without the noise problems associated with shunt resistors. The current transformer provides galvanic isolation and transforms the current into a measurable signal with much lower noise, acting as a mediator between the high current source and the measurement instrument.
2Stability of the object's composition
If bypass capacitors are installed in the measurement circuit, then circuit stability is improved, but response time increases due to long time constant
Solution Approach 1:
The patent separates the measurement into two independent circuits with different time constant requirements. The shunt resistor circuit can use larger bypass capacitors for stability, while the current transformer circuit is designed with smaller capacitors to maintain fast response time for low current measurements, thus resolving the contradiction between stability and speed.
Solution Approach 2:
The patent changes the electrical parameters of the measurement circuits by using different resistance and capacitance values optimized for each current range. The current transformer circuit uses parameters that result in a shorter time constant, enabling fast response while the shunt circuit uses parameters optimized for stability, allowing each circuit to operate in its optimal parameter regime.
3Adaptability or versatility
If a single sensing circuit is used, then device complexity is reduced, but dynamic range is limited and cannot cover five orders of magnitude
Solution Approach 1:
The patent merges two different sensing circuits (shunt resistor and current transformer) into a unified measurement system. Both circuits share common components such as the oscilloscope input and ground reference, allowing the system to achieve a wide dynamic range of five orders of magnitude while avoiding the full complexity of two completely independent measurement systems.
Solution Approach 2:
The patent creates a universal current measurement system that can handle both high and low current levels through a single integrated circuit configuration. The system uses a current transformer that can operate across a wide current range, making it multi-functional for both low current precision measurement and high current measurement, reducing the need for separate specialized circuits.
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 solution provides low-noise performance, a wide dynamic range, and fast response characteristics, enabling accurate measurement of current changes across five orders of magnitude, from 1 μA to 200 mA, with a signal-to-noise ratio of 1,000, effectively capturing current waveforms with high fidelity.
Implementation Method 1
a current transformer (CT) sensing circuit, wherein a primary-side winding of the current transformer is connected in parallel to both ends of the shunt resistor and a secondary-side winding of the current transformer is connected to an input terminal of a transimpedance amplifier
Data Source
AI summary
A current sensing circuit for sensing current in a DUT includes first and second input terminals; a shunt resistor connected to the first input terminal; a shunt resistor sensing circuit that amplifies voltage between terminals of the shunt resistor; a low pass filter coupled to an output of the shunt resistor sensing circuit; a current transformer having a primary winding connected between a terminal of the shunt resistor and the second input terminal; a current transformer sensing circuit connected to a secondary winding of the current transformer and configured to amplify current from the secondary winding; and an adder configured to add outputs of the low pass filter and the first current transformer sensing circuit. The current transformer sensing circuit includes a first transimpedance amplifier and a first input resistor. The current transformer has a low frequency-side cutoff frequency equal to a cutoff frequency of the low pass filter.