Patent ID: 7180310

Claim:
An amplitude varying driver circuit operable to output an output signal, which is an amplified input signal being directly supplied to said driver circuit, comprising: a plurality of differential amplifiers provided in parallel with one another, wherein a signal corresponding to the input signal is input into each base terminal thereof; a pre-driver circuit connected with each base terminal of said plurality of differential amplifiers, receiving said input signal and providing the signal corresponding to said input signal to each base terminal of said plurality of differential amplifiers; a resistor section, which is provided in series with said plurality of differential amplifiers, operable to establish potential of the output signal according to a total current flowing to said plurality of differential amplifiers; and an amplitude control transistor, which is provided in series with said plurality of differential amplifiers, operable to define the total current flowing to said plurality of differential amplifiers by varying a current flowing to said amplitude control transistor.