A 40 Gbps broadband amplifler for modulator- driver applications using a GaAs HBT technology

Abstract

A broadband amplifier suitable for high-bitrate modulator driver applications is fabricated using a GaAs-HBT process with f r and fmu of 45 and I 7 0 GHr, respectively. The design takes optimum advantage of the available technology, to obtain a broadband gain of 12 dB and a 3dB cut-off-frequency of 24 GHL A smooth decrease around f c is chosen in order to keep a positive gain value at higher frequencies and a relatively frat 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 sujj7ciently high output voltage for a relatively low f r 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 Vpp output well-opened 40 Gb/s eye diagram is obtained with a large signalgain of 12 dB. This is a promising resuit for 40 Gb/s modulator driver applications using low-cost standard technologies and an interesting perfomiance in terms of a marimurn broadband5 to (f7, fnp3 ratio.