MOSFET Current Sensor Bias Control for Low-Current Accuracy
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Solution Overview
Problem
Current sensing in Smart Power ICs faces challenges in minimizing the scatter of the current ratio (K) at low currents due to threshold voltage mismatch and source voltage offset, which existing techniques fail to adequately address.
Innovation Solution
A controller circuit is implemented that optimizes the biasing of power MOSFET transistors based on the ratio of source voltage offset and threshold voltage mismatch distributions, introducing a new operation mode called proportional regulation to minimize the standard deviation of the current ratio, thereby enhancing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If normal operation mode is used with constant gate voltage, then the circuit operates simply, but source voltage offset causes linear increase of scatter in K with decreasing drain current
Solution Approach 1:
The patent transitions from static constant gate voltage operation to dynamic gate voltage control through a control circuit that adjusts the gate voltage based on drain current level. This dynamic adjustment compensates for source voltage offset effects, maintaining measurement precision across varying current conditions while adding controlled complexity to the operation mode.
Solution Approach 2:
The patent changes the operating parameters by adjusting gate voltage dynamically rather than keeping it constant. The control circuit modifies gate voltage as a function of drain current to counteract the linear increase in scatter caused by source voltage offset, thereby improving current ratio accuracy without requiring fundamental operational changes.
2Reliability
If gate-back regulation is used with constant drain voltage, then the circuit provides regulation control, but threshold voltage mismatch leads to linear increase of scatter in K with decreasing drain current
Solution Approach 1:
The patent modifies the gate voltage parameter dynamically based on drain current conditions rather than maintaining constant drain voltage as in gate-back regulation. This parameter change strategy compensates for threshold voltage mismatch effects, reducing scatter in the current ratio while preserving regulation functionality through adaptive control.
Solution Approach 2:
The patent implements a feedback mechanism where the control circuit continuously monitors drain current and adjusts gate voltage accordingly. This feedback loop compensates for threshold voltage mismatch by adapting the gate voltage to counteract its effects, thereby improving measurement precision while maintaining the regulatory function.
3Measurement precision
If proportional regulation is implemented with optimized biasing, then measurement precision improves at low currents, but device complexity increases due to additional control circuitry
Solution Approach 1:
The patent introduces a control circuit as an intermediary element that mediates between the power MOSFET and the measurement system. This intermediary component implements proportional regulation by adjusting gate voltage based on drain current, improving measurement precision at low currents while containing complexity through a dedicated control module rather than redesigning the entire system.
Data Source
AI summary
An integrated circuit device comprises a first transistor having a gate coupled to an output of a first operational amplifier, a second transistor having a threshold voltage proportional to a threshold voltage of the first transistor, the second transistor having a gate coupled to an inverting input of a second operational amplifier, an output of the second operational amplifier coupled to an inverting input of the first operational amplifier, a first resistor coupled between the second transistor gate and the inverting input of the second operational amplifier, and a second resistor coupled between the output of the second operational amplifier and the inverting input of the second operational amplifier, a ratio of the second resistor to the first resistor selected based upon a ratio of a production distribution of a transistor source voltage offset to a production distribution of a transistor threshold voltage mismatch.