A low-noise programmable-gain amplifier for 25 Gb/s multi-mode fiber receivers in 28nm CMOS FDSOI

Wide bandwidth, very low noise and high gain, finely adjustable, are key features in programmable-gain amplifiers (PGA) employed in multi-mode fiber (MMF) receivers. High frequency boost at Nyquist is also desirable to partially recover ISI and relax the requirements of electronic dispersion compensation. In this work, a PGA for 25Gb/s MMF receivers is proposed. Shunt and series inductors between cascaded stages are exploited to achieve programmable high-frequency boost independent from in-band gain and with a sharp out-of-band roll-off. Compared to typical RC-degenerated gain stages, the adopted solution enables very low noise operation. Realized in 28nm CMOS FDSOI technology the PGA has a programmable gain ranging from 15dB to 29dB with 0.15 dB fine steps and up to 14.2dB boost at Nyquist frequency. Power consumption is 32mW and equivalent input noise, at maximum high-frequency boost, is 300μV_rms only.