As for a transistor, overlapped are factors such as a variation of a gate insulation
film which occurs due to a difference of a manufacturing process and a substrate
used and a variation of a crystalline state in a channel forming region and thereby,
there occurs a variation of a threshold voltage and mobility of a transistor.
This invention provides an electric circuit which used a rectification type
device in which an electric current is generated only in a single direction, when
an electric potential difference was applied to electrodes at both ends of the
device. Then, the invention provides an electric circuit which utilized a fact
that, when a signal voltage is inputted to one terminal of the rectification type
device, an electric potential of the other terminal becomes an electric potential
offset only by the threshold voltage of the rectification type device.
