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.