New CMOS Class AB Transmitter for 10 Gb/s Serial Links

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This paper presents a new fully differential CMOS class AB transmitter for 10 Gb/s serial links. The transmitter consists of a fully differential multiplexer, a rail-to-rail configured pre-amplification stage, and a push-pull output stage. The multiplexer achieves a high multiplexing speed by using modified pseudo-NMOS logic where pull-up networks are replaced with self-biased active inductors. The rail-to-rail configured pre-amplification stage with active inductors amplifies the signals from the multiplexer. The fully differential output current is generated by a class AB output stage operated in a push-pull mode. High data rates of the transmitter are obtained by ensuring that the transistors in both the pre-amplification and output stages are always in saturation and the voltage swing of all critical nodes is small. The fully differential configuration of the transmitter effectively suppresses common-mode disturbances, particularly those coupled from the power and ground rails, the electro-magnetic interference exerted from channels to neighboring devices is also minimized. The transmitter minimizes switching noise by drawing a constant current from the supply voltage.

The transmitter has been implemented in TSMC 0.18 μm 1.8 V 6-metal CMOS technology and analyzed using Spectre from Cadence Design Systems with BSIM3.3 device models. Simulation results demonstrate that the transmitter provides a 5 mA peak-to-peak differential output current with 100 ps eye-width and >5 mA eye-height at 10 Gb/s. The transmitter consumes 18 mW with a total transistor area of 100 μm2 approximately.

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