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US 2011/0031945 A1Published application
Threshold voltage extraction circuit
AssigneeNXP B.V.
InventorJonah E. Nuttgens
Life of this patent
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Abstract
A pair of MOS transistors (10,12) are arranged as a potential divider. As the MOS transistors (10,12) pass from a weak inversion regime to a strong inversion regime, the voltage at the midpoint of the threshold divider changes from being substantially constant to varying. A difference amplifier (14) is used to detect this voltage, and a feedback loop (16) through a further transistor (18) is also provided.
Claims12
A threshold voltage extraction circuit comprising:
- a potential divider formed from first and second MOS transistors, the first and second MOS transistors having gates connected together, wherein the MOS transistors change from a weak inversion regime to a strong inversion regime as the gate-source voltage of the MOS transistors crosses a threshold voltage, wherein the output voltage of the potential divider changes between a substantially constant value and a value that varies with the applied gate-source voltage as the gate-source voltage crosses the threshold voltage;
- and
- a difference amplifier arranged to compare the voltage output from the potential divider with a reference voltage to detect the threshold voltage of the MOS transistors.
A method of extracting a threshold voltage, including:
- providing a first MOS transistor of a first conductivity type connected in series with a second MOS transistor of the same conductivity type between a plus voltage node and a minus voltage node, the first and second MOS transistors having a central node between them, wherein as the voltage between the plus node and the minus node rises towards the threshold voltage of the first and second MOS transistors the voltage on the central node has a sub-threshold plateau;
- and
- comparing the voltage on the central node with the reference voltage, wherein the reference voltage is from 1% to 50% higher than the sub-threshold plateau.
Dependencies are inferred from the claim text.