Current Mirror Sense Circuit for Bidirectional Zero-Crossing Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing current sense circuits are limited to unidirectional current measurement, suffer from errors due to common-mode voltage dependency, and struggle with bidirectional current sensing across zero levels, requiring complex and costly operational amplifiers with high common-mode rejection ratio.
Innovation Solution
A current sense circuit with a differential amplifier, a controllable current mirror, and a biasing circuit that sets the common-mode voltage at the amplifier inputs to a predefined DC voltage, allowing bidirectional current measurement by sinking or sourcing currents based on differential amplifier outputs and generating corresponding currents in the output branch, while compensating for bias currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a difference amplifier is used to measure current through a sense resistor, then the current measurement function is achieved, but the measurement precision deteriorates due to common-mode voltage dependency causing offset voltage variations
Solution Approach 1:
The patent connects both inputs of the difference amplifier to the same potential (common-mode voltage) through the sense resistor, ensuring that common-mode voltage variations affect both inputs equally and are rejected by the differential amplifier, thereby eliminating offset voltage variations caused by common-mode voltage changes
Solution Approach 2:
The patent implements a feedback mechanism where the output of the difference amplifier is fed back through a feedback resistor to the inverting input, creating a virtual ground that stabilizes the common-mode voltage at the amplifier inputs and compensates for any drift, thereby improving measurement stability
2Measurement precision
If operational amplifiers with high CMMR and very low offset voltage are used to reduce common-mode voltage dependency, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses the equipotentiality principle to ensure both amplifier inputs experience identical common-mode voltage, making the measurement independent of CMMR specifications and allowing the use of standard operational amplifiers rather than requiring high-performance, complex, and expensive devices
Solution Approach 2:
The patent creates a symmetric circuit configuration where both inputs of the difference amplifier are treated identically with respect to common-mode voltage connection, effectively copying the same potential reference to both inputs, which simplifies the amplifier selection criteria
3Productivity
If a difference amplifier is used for current sensing, then unidirectional current measurement is achieved, but adaptability deteriorates because the circuit cannot measure bidirectional current smoothly across zero level
Solution Approach 1:
The patent introduces asymmetry in the feedback network by using different resistor values in the feedback path versus the input path, which allows the circuit to handle both positive and negative current directions while maintaining stable operation and smooth zero-crossing behavior, thereby enabling bidirectional measurement capability
Data Source
AI summary
A current sense circuit may comprise a first circuit node and a second circuit node configured to be coupled to a first terminal and a second terminal of a current sense resistor, respectively; differential amplifier including a first input and a second input which are coupled to the first circuit node and the second circuit node via a first input resistor and a second input resistor; a voltage source, configured to set the voltage at the first input of the differential amplifier; and a controllable current mirror configured to sink or source a first current in its input branch based on one or more outputs of the differential amplifier and to generate a corresponding second current in its output branch. The input branch is coupled to the second input of the differential amplifier. A biasing circuit is coupled to the controllable current mirror.