An over-67-GHz-bandwidth 2 Vppd linear differential amplifier with gain control in 0.25-µm InP DHBT technology

In this report, a differential linear amplifier for high-symbol-rate multilevel transmission is presented. We designed and fabricated the amplifier IC by using newly developed in-house 0.25-μm InP DHBT technology, which yields peak f
_t
and f
_max
of over 400 GHz. This amplifier consists of lumped variable-gain amplifier and distributed output buffer for achieving large gain control range and ultra-broadband performance. The -3 dB bandwidth and the differential gain are over 67 GHz and 10.7 dB, respectively. Output return loss is better than -10 dB up to 63 GHz. In addition to the ultra-broadband characteristics, nearly 10-dB variable gain range are obtained. The amplifier provides clear output waveform at a symbol rates up to 100 Gbaud with NRZ signal, and up to 56 Gbaud with PAM4 signal respectively.