A CMOS 18 THzΩ 248 Mb/s transimpedance amplifier and 155 Mb/s LED-driver for low cost optical fiber links

The realization of a complete low cost CMOS optical fiber link using a LED and PIN as optical components is presented. The driver and receiver are realized in a standard 0.8 μm digital CMOS process which makes integration with a DSP possible. The driver is a current steering transistor combined with a small quiescent current source. The modulation current is 60 mA which allows a 155 Mb/s optical data-rate. The receiver is a three-stage transimpedance amplifier followed by a signal converter which provides digital output signal levels. The three-stage configuration makes possible the realization of a high transimpedance (150 kΩ), necessary to obtain a high sensitivity, combined with a high bandwidth. The achieved optical data-rate is 240 Mb/s for 1 μA input modulation currents. This results in a transimpedance bandwidth of 18 THzΩ, which is one order of magnitude higher than recently published circuits. The speed performance of the total link is limited by the optical time-constant of the LED, leading to a 155 Mb/s optical link, designed for use in four-fiber interboard connections in 622 Mb/s B-ISDN systems