A 25Gbaud PAM-4 Linear Burst-Mode Receiver With Analog Gain- and Offset Control in 0.25μm SiGe:C BiCMOS

We present a burst-mode receiver (BMRx) whose architecture and design is optimized for linear operation up to 25Gbaud modulation rates. The linear burst-mode receiver (LBMRx) consists of a fixed-gain transimpedance amplifier, followed by a three-stage post-amplifier and a 50-ohm output buffer. The gain of the post-amplifier stages and dc-offsets of the datapath can be quickly adjusted from one burst to the next through combined feedforward (providing rapid settling) and feedback (providing accurate gain and offset control) automaticgain-control (AGC) and automatic-offset-control (AOC) loops. When receiving 25G NRZ and assembled with a PIN photodetector, a sensitivity of -18.1 dBm and overload of at least 3.5 dBm was measured at a bit-error-rate (BER) of 1E-2, thus supporting a 21.6 dB input dynamic range. When receiving 4-level pulse amplitude modulation (PAM-4), a sensitivity of -11.4 dBm and overload of at least 4.4 dBm was measured at a low-densityparity-check (LDPC) BER reference of 1E-2, supporting 15.8 dB dynamic range. Between -10 up to 3.5 dBm the LBMRx also features internal start-of-burst (SOB) and end-of-burst (EOB) detection. Over the specified input dynamic range, the total harmonic distortion (THD) remains below 5%. The receiver was designed in a 0.25 μm SiGe:C BiCMOS technology, occupying an area of 1.32 × 1.05 mm
²
and consumes 280 mW from a 2.5 V supply. This LBMRx can be used as front-end for new upcoming passive optical networks (PONs) that may require, e.g., electronic equalization (to overcome bandwidth limitations of opto-electronic components) or dispersion compensation; or may be used to support advanced modulation formats requiring linear operation.