Replica-Biased Current Sensing With Offset Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current sensor accuracy is challenged by offset, temperature dependence, and bandwidth limitations in high-switching-frequency applications, particularly in advanced FinFET process nodes, where maintaining accuracy across a wide dynamic range is difficult due to noise, ringing, and power supply voltage reliability issues.
Innovation Solution
A capacitively sampled replica-biased current sensor design with an amplifier having capacitively coupled inputs in feedback, which compensates for input offset and operates from a clean supply voltage, reducing disruption to the power grid and allowing operation independent of input voltage, using a switched capacitor circuitry and DC level-shifter to sense and measure current with improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a classic current sensor design is used, then it can operate with simple structure, but it suffers from offset errors, temperature dependence, and limited bandwidth at high switching frequencies
Solution Approach 1:
The current sensor is divided into multiple functional blocks: replica switch circuitry, feedback amplifier, offset compensation circuitry, and switched capacitor circuitry. Each block performs a specific function, allowing the overall system to achieve high accuracy while maintaining manageable complexity through modular design.
Solution Approach 2:
A feedback amplifier is employed to sense the voltage across the replica switch and adjust the replica gate voltage accordingly. This feedback mechanism ensures accurate current sensing by continuously correcting for variations and maintaining the desired operating point, thereby improving measurement precision.
Solution Approach 3:
The offset compensation circuitry automatically detects and corrects amplifier input offset voltages without requiring external calibration or trimming. The circuit uses the amplifier's own output to generate compensation signals, enabling self-calibration and eliminating the need for manual adjustment while maintaining high accuracy.
2Speed
If the current sensor operates at high switching frequencies, then it achieves better responsiveness, but offset errors and bandwidth limitations worsen accuracy
Solution Approach 1:
Offset compensation is performed continuously or periodically before current measurement to eliminate offset errors in advance. The compensation circuitry pre-adjusts the amplifier operating point, ensuring that when high-frequency current signals are measured, the offset has already been corrected, thereby maintaining accuracy at high switching frequencies.
Solution Approach 2:
The circuit dynamically adjusts operating parameters such as amplifier gain and bandwidth to optimize performance at different switching frequencies. By changing these parameters adaptively, the sensor maintains high accuracy whether operating at low or high frequencies, resolving the trade-off between speed and precision.
3Measurement precision
If calibration is performed to improve accuracy, then measurement precision increases, but the number of trims and settings increases complexity
Solution Approach 1:
The offset compensation circuitry automatically detects and corrects amplifier input offset voltages without requiring external calibration or trimming. The circuit uses the amplifier's own output to generate compensation signals, enabling self-calibration and eliminating the need for manual adjustment while maintaining high accuracy.
Solution Approach 2:
A replica switch is created that copies the electrical characteristics of the actual power switch. By sensing current through the replica instead of the power switch directly, the system achieves accurate measurement without disrupting the power grid or requiring complex calibration procedures, as the replica inherently matches the power switch behavior.
4Measurement precision
If the sensor operates from a clean supply voltage, then accuracy improves, but power overhead increases
Solution Approach 1:
The feedback amplifier serves multiple functions: it senses the voltage across the replica switch, generates the compensation signal for offset correction, and drives the replica gate. This multi-functionality reduces the need for separate dedicated circuits, thereby lowering overall power consumption while maintaining the clean supply voltage requirement for accurate operation.
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 highly accurate current sensing with reduced trims and settings, robustness across various applications, and independence from input voltage, enabling better energy metering and performance in energy-constrained systems.
Implementation Method 1
an amplifier having capacitively coupled inputs in feedback, which compensates for input offset
Implementation Method 2
using a switched capacitor circuitry and DC level-shifter to sense and measure current with improved accuracy
Data Source
AI summary
A current sensing topology uses an amplifier with capacitively coupled inputs in feedback to sense the input offset of the amplifier, which can be compensated for during measurement. The amplifier with capacitively coupled inputs in feedback is used to: operate the amplifier in a region where the input common-mode specifications are relaxed, so that the feedback loop gain and/or bandwidth is higher; operate the sensor from the converter input voltage by employing high-PSRR (power supply rejection ratio) regulators to create a local, clean supply voltage, causing less disruption to the power grid in the switch area; sample the difference between the input voltage and the controller supply, and recreate that between the drain voltages of the power and replica switches; and compensate for power delivery network related (PDN-related) changes in the input voltage during current sensing.