Patent ID: 8022728

Claim:
A common-mode voltage controller comprising: a first buffer in a signal transmission circuit; a second buffer arranged a subsequent stage or a preceding stage of the first buffer in a signal transmission circuit; a first reference voltage generation unit to generate a common-mode voltage corresponding to the first buffer; a second reference voltage generation unit to generate a common-mode voltage corresponding to the second buffer at the subsequent stage or the preceding stage; and a control signal generation unit to generate a control signal to control a common-mode voltage of the first buffer according to a difference voltage between an output of the first reference voltage generation unit and an output of the second reference voltage generation unit, and to give the control signal to the first buffer and first reference voltage generation unit, wherein said control signal generation unit generates a control signal for lowering an output voltage of said first reference voltage generation unit if the output voltage of the first reference voltage generation unit is higher than an output voltage of said second reference voltage generation unit, and for raising the output voltage of the first reference voltage generation unit if the output voltage of the first reference voltage generation unit is lower than the output voltage of the second reference voltage generation unit, said control signal generated by said control signal generation unit is an analog signal, and an analog/digital conversion unit for converting said analog signal generated by said control signal generation unit into a digital signal and giving it to said first buffer and first reference voltage generation unit.