A 40 Gbps Broadband Amplifier for Modulator-Driver Applications Using a GaAs HBT Technology

Published in:
IEEE BCTM Bipolar/BiCMOS Circuits and Technology Meeting Dig., 2004, pp. 281-284.
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Abstract:
A broadband amplifier suitable for high-bitrate modulator driver applications is fabricated using a GaAs-HBT process with f_T and f_max of 45 and 170 GHz, respectively. The design takes optimum advantage of the available technology, to obtain a broadband gain of 12 dB and a 3 dB cut-off-frequency of 24 GHz. A smooth decrease around f_c is chosen in order to keep a positive gain value at higher frequencies and a relatively flat group delay, which is a key condition for the eye-diagram opening. This appears to be the best way to combine high bitrate signal amplification with sufficiently high output voltage for a relatively low f_T HBT technology, compared to others, as InP HEMT or GaAs pHEMT. According to the NRZ power spectra, 40 Gb/s signal amplification is possible with such characteristics since the smooth slope condition is fulfilled. Eye diagram measurements at 40 Gb/s with several input signal swings are presented. A 4 V_pp output well-opened 40 Gb/s eye diagram is obtained with a large signal gain of 12 dB. This is a promising result for 40 Gb/s modulator driver applications using low-cost standard technologies and an interesting performance in terms of a maximum broadband f_c to (f_T , f_max) ratio.

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