Analysis and Design of a DC-12-GHz Distribution Power Amplifier for Quantum Key Distribution Application

A CMOS distributed power amplifier (DPA) for quantum key distribution (QKD) system to drive an electro-optical phase modulator is developed. Due to the requirement of amplifying high-speed non-return-to-zero (NRZ) signal, our design is supposed to provide enough bandwidth, including dc. To achieve sharp roll-off performance, the m-derived filter section is applied to realize the artificial transmission line rather than the constant-k section. Combining the theory analysis and simulation, the bridges between gain ripple, group delay fluctuation, or maximum linear output power and the parameters of time domain waveform are established. Furthermore, through analyzing the attenuation and delay of the transmission line, approaches to improving the frequency performance, such as gain variation and group delay fluctuation, are provided. The DPA is implemented in the 0.25- $\mu \text{m}$ CMOS process and achieves a bandwidth of dc-12 GHz, a gain of 11.54 dB with variation of ±1.34 dB, a group delay of 400 ps with fluctuation of about 100 ps, and a maximum output 1-dB compression point of 20.6 dBm. When a 1-Gb/s NRZ signal is applied to the DPA, the rise and fall times are both about 90 ps. The amplifier occupies an area of 2.8 mm $\times0.94$ mm including pads and adopts the flip-chip package with low-temperature co-fired ceramic (LTCC) substrate.