A Low-Noise Linear TIA With 42-GHz Bandwidth for Single-Ended Coherent Optical Receivers

This letter demonstrates a low-noise linear transimpedance amplifier (TIA) for single-ended coherent optical receivers (ORXs) in 0.13- $\mu $ m SiGe BiCMOS. The TIA achieves relatively low noise, excellent linearity, and approximately unchanged bandwidth (BW) within a wide gain dynamic range by employing a cascade structure of an improved shunt-feedback (SFB) high- $R_{F}$ TIA Core optimized for high linearity and a variable-gain single-to-differential (VG-S2D) circuit with adjustable peaking. The measured results of the TIA exhibit 42-GHz −3-dB BW at 74-dB $\Omega $ maximum transimpedance gain $(Z_{T}) {_{,}}~37$ -dB gain dynamic range, 12.5-pA/ $\sqrt {\mathrm {(Hz)}}$ input reference noise (IRN) current density, and <3% total harmonic distortion (THD) at 2-mApp input photodiode (PD) current and 600-mVpp output swing. The TIA can function up to 60-GBaud PAM4 eye diagrams when the pseudo-random bit sequence (PRBS) length is $2{^{{31}}} -1$ . The TIA draws 72-mA current from a 3.3-V voltage supply and takes up 1 mm2 of the chip area with all its testing pads.

I. Introduction

With the increased transmission capacity of wavelength-division multiplexed (WDM) systems, coherent technologies, which can deal with multilevel modulation formats and have post-processing functions, such as compensation for group-velocity dispersion (GVD) and polarization-mode dispersion (PMD) of fibers [1], have renewed interest since 2000 and are now widely used in long-haul optical transmission systems, as well as some short-haul communications [2]. Several balanced coherent optical receivers (ORXs) with data rates exceeding 100 Gb/s/wavelength have recently been proposed for ultrahigh-speed coherent applications [3], [4], [5]. The balanced photodiode (BPD) with a high-common mode rejection ratio (CMRR) is commonly used to mitigate signal-to-signal beat interference (SSBI) due to the square-law detection process [1]. However, as the symbol rate exceeds 100 GBaud per transimpedance amplifier (TIA), the deterioration of the matching between the two single photodiodes (PDs) of the BPD, as well as the unbalance of the optical hybrid, will lead to a decrease in the single port rejection ratio (SPRR) [6], thereby deteriorating the sensitivity of the ORX. Single-ended receivers (SERs) [7], [8], [9], [10], [11] are one solution to the issues with balanced receivers (BRs) mentioned above. By using an SER, an 882-Gb/s transmission over 100 km standard single mode fiber (SSMF) with a low-LO-to-signal-power ratio (LOSPR) of 12 dB has been demonstrated in [11]. Compared to the conventional BR, the SER provides comparable performance and thus is an attractive option for ultrahigh-speed applications. In a SER, BPD is substituted by the single-ended PD. The obvious advantages of SER over BR are the simplicity of construction and the low cost. Furthermore, the problem of the deterioration in SPRR due to the imbalance between the two single PDs in the BPD and optical hybrid is eliminated. Note that SSBI is not removed in an SER owing to the single-ended PD and should be dealt with by the latter digital signal processor (DSP) in the digital domain. This paper proposes a low-noise linear SiGe BiCMOS TIA for single-ended coherent ORXs and is structured as follows: Section II illustrates the proposed TIA’s analysis and design. The measurement results that validate the design are discussed in Section III. Finally, this letter is concluded in Section IV.