A 64-GHz Optical Receiver for 128-GBd Links Using a 55-nm SiGe BiCMOS Traveling-Wave Linear Transimpedance Amplifier

Abstract

We present an optical receiver using a SiGe BiCMOS transimpedance amplifier (TIA) chip with a 3 dB bandwidth over 67 GHz and a transimpedance gain up to 77 dBΩ. This TIA consists of a single-ended input stage and two differential gain stages followed by a differential output stage. These traveling-wave stages feature variable gain and peaking. A TIA channel consumes 487.5 mW, or 2.2 pJ/bit operating at 112 GBd PAM-4, and occupies a chip area of 1.125 mm2. The THD at 1 GHz (10 GHz) is kept below 2% (5%) for input swings up to 1.6 mApp (1.3 mApp) by reducing the gain. After wire bonding the input of this TIA to a silicon photonic germanium photodiode, a bandwidth of 64 GHz and a group delay variation of 20.3 ps are obtained. Using a 10-tap feedforward equalizer (FFE), opto-electrical eye diagrams are captured and for 128 GBd NRZ, a sensitivity of −5.9 dBm is measured at a bit error rate (BER) of 1E-12. For 112 GBd PAM4, the KP4 sensitivity level is −4.8 dBm. The input-referred noise is measured at 18.8pA/Hz−−−√.