High Sensitivity and Dynamic-Range 25 Gbaud Silicon Receiver Chipset With Current-Controlled DC Adjustment Path and Cube-Shape Ge-on-Si PD

Abstract

This paper presents a high sensitivity and dynamic range 25 Gbaud optical receiver including the CMOS transimpedance amplifier (TIA) and Ge-on-Si photodetector. In the TIA with a DC bypassing path, instead of deploying a voltage-controlled path with a fixed feedback strength, a current-controlled path with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{\mathrm {m}}$ </tex-math></inline-formula> -adjusting ability is proposed to minimize the noise amplified by the feedback loop and achieve high sensitivity. In addition, in the optical part, a Ge-on-Si photodetector with cube-shape Ge is proposed to boost the responsivity, which therefore overcomes the noise contribution from the TIA and enhance the overall sensitivity of the cascaded optical receiver. The CMOS transimpedance amplifier includes a 3-stage transimpedance pre-amplifier, a 4-stage post amplifier, a CML buffer stage and a DC offset cancellation block. Measurement results show a transimpedance of 66–71 dB <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> , a SDD21 bandwidth of 18.5 GHz, an input-referred noise current density of 11.1 pA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz, a BER of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{-{12}}$ </tex-math></inline-formula> @ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$26~\mu \text{A}$ </tex-math></inline-formula> and a power consumption of 105 mW. The FOM is 5.2 which is the lowest, to the best of the authors’ knowledge. The photodetector achieves a responsivity of 0.57 A/W at 1550 nm and a bandwidth of 40 GHz. The optical receiver achieves an optical sensitivity of −11.7 dBm. Compared with the prior arts, the proposed receiver demonstrates distinct sensitivity and FOM enhancement.