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US 8,009,709 B2Granted
DC coupled driver with active termination
AssigneeJDS Uniphase Corporation
InventorDavid A. Nelson
Life of this patent
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Abstract
A DC coupled driver is described for modulating a vertical cavity surface emitting laser at high speeds with active termination. High speed and low total power dissipation is achieved by improving the driver immunity to pulse reflections, which can arise due to impedance mismatch between the driver output impedance and the VCSEL impedance. The rise and fall times of the driver may be adjusted for particular applications. The driver may be fabricated using a choice of bipolar, NMOS and PMOS technologies.
Claims6
A DC-coupled driver for driving a vertical cavity surface emitting laser (VCSEL) diode comprising:
- a first positive voltage supply for providing a supply voltage to the driver during operation;
- a ground rail for providing a current return path to the first positive voltage supply;
- a differential input stage for receiving data and complementary data signals from a signal source, the differential input stage comprising a first and a second transistor, a first and a second output terminal, each connected to the first and a second transistor, respectively, and a modulation current source for biasing the first and second transistors;
- a termination resistor having a first and a second terminal;
- a first current source connected to the first terminal on the termination resistor for providing a current bias to at least one of the VCSEL diode and the first transistor of the differential input stage;
- a low frequency differential input feedback amplifier for sensing a voltage drop across the termination resistor, and operational to maintain a predetermined voltage drop across the termination resistor;
- wherein the VCSEL diode is connected directly to the termination resistor for actively controlling a driving voltage on the VCSEL diode;
- a shunt feedback transimpedance amplifier comprising a bias diode for providing a bias voltage offset, a third transistor for providing gain, and a feedback resistor;
- a second current source connected to the second terminal on the termination resistor for providing a current bias to the second transistor of the differential input stage;
- and
- an inverting voltage to current converter having an output terminal that is coupled to an input of the shunt feedback transimpedance amplifier;
- wherein the low frequency feedback amplifier further comprises:
- a first operational amplifier having an inverting input terminal, a non-inverting input terminal, and an output that is connected to an input of the inverting voltage to current converter;
- a bypass capacitor connecting the non-inverting input terminal to the ground rail;
- a first input resistor connecting the non-inverting input terminal to the first terminal on the termination resistor;
- a second input resistor connecting the inverting input terminal to the second terminal on the termination resistor;
- an integrating capacitor connecting the inverting input terminal to the output terminal of the first operational amplifier;
- and
- wherein the first output of the differential input stage is connected to the first terminal on the termination resistor;
- and the second output of the differential input stage is connected to the input of the shunt feedback transimpedance amplifier.
17 more elements
Dependencies are inferred from the claim text.