Fast high-swing modulator driver circuit

A electro-optical modulator driver, comprising:

• first and second bipolar transistors (M5,M6) arranged as a first differential pair, the emitters of said first and second transistors connected together at a first common node;
• a first current source (54) connected between said first common node and a first supply voltage which provides bias current to said first differential pair, the collectors of said first and second transistors coupled to ground via respective resistances, the bases of said first and second transistors providing differential inputs for said driver circuit;
• a third bipolar transistor (M4) having its base connected to the collector of one of said first and second transistors;
• a second current source (48) 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;
• a fourth bipolar transistor (M3), the base of which is connected to the emitter of said third transistor;
• a third current source (46) connected between said fourth transistor's emitter and said first supply voltage which provides bias current to said fourth transistor, said fourth transistor and third current source forming an emitter-follower circuit;
• fifth and sixth bipolar transistors (M1,M2) arranged as a second differential pair, the emitters of said transistors connected together at a second common node;
• a fourth current source (44) connected between said second common node and said first supply voltage which provides bias current to said first differential pair;
• said fifth transistor's collector coupled to ground via a diode (38) and said fifth transistor's base connected to the emitter of said fourth transistor;
• said sixth transistor's collector coupled to a supply voltage via a resistance;
• a reference voltage provided to said sixth transistor's base;
• a capacitor connected between said sixth transistor's base and ground such that said sixth transistor's base is at AC ground;
• and
• a bias-T network having a DC input, a signal input and an AC output, said bias-T network connected at its signal input to said sixth transistor's collector and connected at its DC input to a supply voltage, said bias-T network's AC output providing said driver circuit's output;
• such that said driver circuit amplifies a differential input signal applied to said differential inputs and provides said amplified input signal as a single-ended output signal at said driver-circuit's output.