MOSFET Threshold Voltage Sensor Using Current Mirror Bias Control
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Solution Overview
Problem
Existing threshold voltage sensors are affected by resistor and mobility variations, leading to inaccuracies in device transconductance estimation.
Innovation Solution
A low-cost threshold voltage sensor design utilizing a metal-oxide-semiconductor field-effect transistor (MOSFET) current mirror with an active device and diode-connected MOSFET, which generates an output voltage containing threshold voltage information while eliminating non-ideal process factors through bias voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional threshold voltage sensors are used, then device transconductance can be estimated, but the measurement precision deteriorates due to resistor and mobility variations
Solution Approach 1:
The patent extracts and eliminates the harmful factors (resistor variations and mobility variations) from the threshold voltage measurement process. By using a differential pair configuration where one transistor is diode-connected and another is in linear region, the measurement system selectively extracts only the threshold voltage information while rejecting the unwanted process variations through careful circuit topology design.
Solution Approach 2:
The patent changes the operating parameters of the MOSFETs to achieve immunity from process variations. Specifically, by biasing transistors in different regions (saturation, linear, triode) and controlling their operating points, the circuit transforms the relationship between current, voltage, and threshold voltage to eliminate dependence on mobility and resistor values, leaving only threshold voltage as the determining factor.
2Measurement precision
If active devices and bias voltage control are added to remove process factors, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent makes the MOSFETs perform multiple functions simultaneously. The same transistors used for current mirroring also serve as the sensing elements for threshold voltage measurement. The diode-connected transistor and linear-region transistor both contribute to process variation rejection while enabling the measurement function, reducing the need for separate dedicated components.
Solution Approach 2:
The circuit uses itself to compensate for process variations. The differential pair configuration inherently compares the two transistor paths, and through the self-biasing arrangement, the circuit automatically adjusts to cancel out mobility and resistor variations without requiring external calibration or additional compensation components.
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 sensor achieves high accuracy and stability by removing the impact of resistor and mobility variations, providing a reliable estimation of threshold voltage.
Implementation Method 1
The operational amplifier has an output terminal coupled to a gate terminal of the first MOSFET and a gate terminal of the second MOSFET... the constant current that is mirrored from the first MOSFET to the second MOSFET
Implementation Method 2
The constant current flows through the diode-connected MOSFET to generate an output voltage that contains information about a threshold voltage of a MOSFET
Implementation Method 3
The active device is coupled between the drain terminal of the first MOSFET and a ground terminal to determine a constant current that is mirrored from the first MOSFET to the second MOSFET
Implementation Method 4
The first bias voltage, second bias voltage, third bias voltage, and fourth bias voltage make the third MOSFET, the fourth MOSFET, and the diode-connected MOSFET operating in a saturation region, and the fifth MOSFET operating in a linear region. All non-ideal process factors are removed from the sensed threshold voltage
Data Source
AI summary
A low-cost and high-accuracy threshold voltage (Vth) sensor is shown. In addition to a current mirror implemented by an operational amplifier and two metal-oxide-semiconductor field-effect transistors (MOSFETs), the Vth sensor uses an active device and a diode-connected MOSFET. The active device is provided to determine a constant current that is mirrored from the first MOSFET to the second MOSFET of the current mirror. The diode-connected MOSFET is coupled between the drain terminal of the second MOSFET and the ground terminal. The constant current flows through the diode-connected MOSFET to generate an output voltage that contains information about a threshold voltage (Vth) of a MOSFET.