A 50-Gb/s Multicarrier Transmitter Using DAC-Based Polar Drivers in 22-nm FinFET

A digital-to-analog converter (DAC)-based polar transmitter (TX) is proposed for multicarrier signaling in wireline applications. The proposed TX achieves a 50-Gb/s total data rate with maximized spectral efficiency by using three parallel 5-GS/s DAC-based drivers and two orthogonal carriers of 5 and 10 GHz. The three DAC-based drivers operating with baseband (BB) four-level pulse amplitude modulation (PAM-4) and mid-band (MB) and high-band (HB) 16-state complex modulation have 7-bit amplitude modulation along with an extra 2-bit predistortion (PD) to compensate for the driver nonlinearity. In addition, the MB and HB polar drivers have 7-bit phase modulation. Because the amplitude and phase modulations are performed independently in the polar drivers, the proposed TX can support arbitrary modulation formats such as QAM-16 or APSK-4 <tex-math notation="LaTeX">$+$</tex-math> 12 for MB and HB. For TX equalization, an eight-tap finite-impulse response (FIR) filtering is implemented in the digital domain using lookup tables (LUTs). The fabricated TX in 22-nm FinFET has 1.2-Vppd output swing and achieves 50-Gb/s data rate, bit error rate (BER) <tex-math notation="LaTeX">$<$</tex-math> 10 <tex-math notation="LaTeX">$-$</tex-math> 4 , and 1.68-pJ/b energy efficiency with a channel having 21.5-dB loss at 12.5 GHz for both QAM-16 and APSK-4 <tex-math notation="LaTeX">$+$</tex-math> 12 modulations.