Electric circuit
AssigneeSemiconductor Energy Laboratory Co., Ltd.
InventorsHajime Kimura, Yasuko Watanabe
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Abstract
A transistor has variation in a threshold voltage or mobility due to accumulation of factors such as variation in a gate insulating film which is caused by a difference of a manufacturing process or a substrate to be used and variation in a crystal state of a channel formation region. The present invention provides an electric circuit which is arranged such that both electrodes of a capacitance device can hold a voltage between the gate and the source of a specific transistor. Further, the present invention provides an electric circuit which has a function capable of setting a potential difference between both electrodes of a capacitance device so as to be a threshold voltage of a specific transistor.
Claims1
An electric circuit for outputting an output voltage from an output-terminal based on an input voltage to be inputted from an input terminal, characterized by comprising:
- a first transistor and a second transistors transistor connected in series;
- a first capacitance device connected between a gate electrode and a source electrode of said first transistor;
- a second capacitance device connected between a gate electrode and a source electrode of said second transistor;
- a first switch for making a value of a sum of a first potential difference between both electrodes of said first and second capacitance devices device and a second potential difference between both electrodes of said second capacitance device into a power supply voltage;
- a second switch for making a potential difference between said both electrodes of said first capacitance device into a threshold voltage of said first transistor;
- a third switch for making a potential difference between said both electrodes of said second capacitance device into a threshold voltage of said second transistor;
- and
- a fourth switch for outputting said output voltage from said source electrode of said first transistor when a first voltage is inputted in said gate electrode of said first transistor and a bias second voltage is inputted in said gate electrode of said second transistor.
Dependencies are inferred from the claim text.