10Gbps EAM Driver with Integrated Bias Network

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The MAX3940 is designed to drive an electro-absorption modulator (EAM) at data rates up to 10.7Gbps. It incorporates the functions of a biasing circuit and a modulation circuit, with integrated control op amps externally programmed by DC voltages.

The integrated bias circuit provides a programmable biasing current up to 50mA. This bias current reflects a bias voltage of up to 1.25V on an external 50Ω load. The bias and modulation circuits are internally connected on chip, eliminating the need for an external bias inductor.

A high-bandwidth, fully differential signal path is internally implemented to minimize jitter accumulation. When a clock signal is available, the integrated data-retiming function can be selected to reject input-signal jitter.

The MAX3940 receives differential CML signals (ground referenced) with on-chip line terminations of 50Ω. The output has a 50Ω resistor for back termination and is able to deliver a modulation current of 40mA_P-P to 120mA_P-P, with an edge speed of 23ps (typical, 20% to 80%). This modulation current reflects an EAM modulation voltage of 1.0V_P-P to 3.0V_P-P.

The MAX3940 also includes an adjustable pulse-width control circuit to precompensate for asymmetrical EAM characteristics.

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