A 5 Gb/s Radiation Tolerant Laser Driver

A laser driver for data transmission at 5 Gb/s has been developed as a part of the Giga Bit Transceiver (GBT) project. The Giga Bit Laser Driver (GBLD) targets High Energy Physics (HEP) applications for which radiation tolerance is mandatory. The GBLD ASIC can drive both VCSELs and some types of edge emitting lasers. It is essentially composed of two drivers capable of sinking up to 12 mA each from the load at a maximum data rate of 5 Gb/s, and of a current sink for the laser bias current. The laser driver include also pre-emphasis and duty cycle control capabilities

Wireline equalization using pulse-width modulation

Abstract-High-speed data links over copper cables can be effectively equalized using pulse-width modulation (PWM) pre-emphasis. This provides an alternative to the usual 2-tap FIR filters. The use of PWM pre-emphasis allows a channel loss at the Nyquist frequency of ~30dB, compared to ~20dB for a 2-tap symbol-spaced FIR filter. The use of PWM fits well with future high-speed low-voltage CMOS processes. The filter has only one ‘knob’, which is the duty-cycle. This makes convergence of an algorithm for automatic adaptation straightforward. Spectral analysis illustrates that, compared to a 2-tap FIR filter, the steeper PWM filter transfer function fits better to the copper channel. This applies to both half-symbol-spaced and symbol-spaced 2-tap FIR filters. Circuits for implementation are as straightforward as for FIR pre-emphasis. In this paper new measurements are presented for a previous transmitter chip, and a new high-swing transmitter chip is presented. Both coaxial and differential cables are used for the tests. A bit rate of 5 Gb/s (2-PAM) was achieved with all cable assemblies, over a cable length of up to 130 m. Measured BER at this speed is <10-12