MOSFET Threshold Voltage Sensor Using Current Mirror Bias Control
Find Innovative SolutionsGenerate Solutions
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 removing 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 sensing accuracy is degraded due to resistor and mobility variations
Solution Approach 1:
The patent changes the operating parameters by biasing the third MOSFET in saturation region and the fifth MOSFET in linear region, while keeping the fourth MOSFET in saturation. This specific parameter configuration enables the cancellation of mobility variation effects. Additionally, the diode-connected MOSFET configuration transforms the relationship between drain-source voltage and gate-source voltage, eliminating resistor variation impacts on the threshold voltage measurement.
Solution Approach 2:
The patent uses a current mirror configuration where the third and fourth MOSFETs replicate the same current, and the fifth MOSFET mirrors this current to the diode-connected MOSFET. By copying the current through multiple paths with different bias conditions, the system can compare and cancel out process variations, achieving immunity to resistor and mobility variations while maintaining accurate threshold voltage sensing.
2Ease of manufacture
If a simple current mirror is used, then the device is low-cost, but the measurement is affected by non-ideal process factors
Solution Approach 1:
The patent merges a standard current mirror with additional biasing circuits and a diode-connected MOSFET into a single integrated sensor unit. This combination allows the circuit to simultaneously perform current mirroring and process variation cancellation, achieving high measurement precision without requiring separate compensation circuits, thus maintaining cost-effectiveness and ease of manufacture.
Solution Approach 2:
The sensor circuit performs multiple functions: it acts as a current mirror, a threshold voltage sensor, and a process variation compensator all in one configuration. The same MOSFETs and biasing circuits that enable low-cost implementation also provide immunity to non-ideal process factors, making the design universally applicable and cost-effective without sacrificing accuracy.
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 is not affected by resistor and mobility variations, providing stable and precise threshold voltage sensing.
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, a first input terminal receiving a first constant voltage, and a second input terminal coupled to the drain terminal of the first MOSFET
Implementation Method 2
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 3
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 of a 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 operate in a saturation region, and the fifth MOSFET operate in a linear region. All non-ideal process factors are removed from the sensed threshold voltage
Data Source
Figure 1
Figure 2
Figure 3A
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.