Design of a 56-GBaud Low Noise PAM-4 Optical Receiver in 90-nm SiGe BiCMOS

A 56 GBaud low noise PAM-4 transimpedance amplifier(TIA) is proposed in this paper. An shunt-feedback topology transimpedance amplifier(SF-TIA) integrated with a front-end auto gain control circuit(AGC1) can tolerant up to 1.5 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$mA_{pp}$</tex> input current without distortion. A variable gain amplifier(VGA) with post AGC loop can maintain the amplitude of output swing at approximately 500 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$mV_{pp}$</tex>. An output buffer designed with T-coil can provide good output matching performance. Designed in 90 nm SiGe BiCMOS technology, the low noise PAM-4 optical receiver has a maximum transimpedance gain of 79 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{dB}\Omega$</tex> while -3 dB bandwidth is 36 GHz and input referred noise current is 2.33 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu A_{rms}$</tex>.