Current Sense Amplifier Circuit for Beyond-Rail Common-Mode Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current sense amplifiers face challenges in measuring high-voltage currents due to limited common mode voltage range, offset, noise, and increased die size and cost, especially when operating with modern integrated circuits that require amplification of small differential voltages while rejecting large common mode voltages.
Innovation Solution
A current sense amplifier with an extended common mode voltage range is designed using a silicon-on-insulator (SOI) high-voltage technology, incorporating an open-loop feedback amplifier, level shifter resistors, and a transconductance stage to amplify and level shift the differential input signal, allowing operation beyond the supply rails and intrinsic process limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a shunt resistor with small value is used to minimize power loss, then power loss is reduced, but the voltage across the shunt resistor becomes smaller requiring more stringent measurement requirements
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary device between the shunt resistor and the measurement system. The op-amp amplifies the small differential voltage across the shunt resistor, making it measurable by standard ADCs while allowing the shunt resistor to maintain its low value for minimal power loss. The non-inverting and inverting inputs of the op-amp connect to the shunt resistor terminals, and the output provides the amplified signal to the ADC.
2Device complexity
If current sense amplifiers are implemented using resistive dividers, then the circuit is simple, but offset, noise, and speed/bandwidth problems occur requiring precise trimming
Solution Approach 1:
The patent employs feedback mechanisms through the operational amplifier configuration. The op-amp continuously monitors the differential voltage across the shunt resistor and adjusts its output to maintain accuracy. This feedback approach eliminates the need for precise resistor trimming while reducing offset and noise issues associated with resistive divider implementations. The feedback loop ensures that the amplified output accurately represents the input differential voltage.
3Reliability
If current sense amplifiers are implemented in high-voltage fabrication process technologies, then they can handle high common mode voltages, but the die size increases and costs increase
Solution Approach 1:
The patent changes the voltage domain parameters by using level shifting techniques. The operational amplifier circuit is designed to accept high common mode voltages at its inputs while producing a low-voltage output suitable for standard 5V or 3.3V ADCs. This parameter transformation allows the use of standard low-voltage fabrication processes while maintaining the ability to measure high-voltage currents, thereby reducing die size and cost compared to high-voltage process implementations.
4Adaptability or versatility
If the common mode voltage range is extended beyond supply rails, then high-voltage current measurement capability is achieved, but circuit complexity increases
Solution Approach 1:
The operational amplifier serves as an intermediary that mediates between the high common mode voltage environment and the low-voltage digital system. The op-amp's input stage is designed to tolerate high common mode voltages while its output stage provides a standardized low-voltage signal. This intermediary approach extends the common mode voltage range without requiring complex high-voltage circuitry throughout the entire measurement system, thus limiting the increase in overall circuit complexity.
Data Source
AI summary
A circuit includes an input stage configured to receive and amplify an input signal to produce an amplified signal, where the input signal is referenced to a higher voltage and is associated with a common mode voltage. The circuit also includes level shifter resistors configured to level shift the amplified signal to produce a shifted signal. The level shifter resistors are configured to provide a voltage drop so that the shifted signal is referenced to a lower voltage. The input stage may include multiple transistors floating in one or more isolated portions of a substrate, where the transistors perform amplification in the input stage. The circuit may also include circuitry configured to control current through the level shifter resistors so that the voltage drop depends on the common mode voltage of the input signal. In addition, the lower voltage may be between supply rails of the circuit.