Patent ID: 7010008

Claim:
A driver circuit suitable for use in an electro-optical modulator driver, comprising: an output stage, comprising: first and second bipolar transistors arranged as a first differential pair, the emitters of said transistors connected together at a first common node, said first transistor's collector coupled to ground; a first current source connected between said first common node and a first supply voltage which provides bias current to said first differential pair; said second transistor's collector coupled to a second supply voltage via an impedance and providing said driver circuit's output; a reference voltage provided to said second transistor's base; and a capacitor connected between said second transistor's base and ground such that said second transistor's base is at AC ground; such that said output stage amplifies an input signal applied to said first transistor's base and provides said amplified input signal at said driver circuit's output; a third bipolar transistor, the base of which provides said driver circuit's input and the emitter of which is connected to said first transistor's base; and a second current source connected between said third transistor's emitter and said first supply voltage which provides bias current to said third transistor, said third transistor and second current source forming an emitter-follower circuit which presents a low impedance to said first transistor's base.