As represented in widespread diffusion of smartphones, the internet traffic continues to increase day by day, and an increase in the capacities of optical fiber communications, wireless communications, line telecommunications, and the like as well as their advanced functionalities are required. As an elemental technique for realizing the increased capacities and advanced functionalities of systems, development of efficient network configurations, advanced digital modulation and demodulation systems, optical and electronic devices operable at high speed, and the like are currently underway. For instance, focusing on a circuit on a transmission side of a communication device, processing such as advanced multi-level modulation and waveform shaping is vigorously examined in the level of digital signals using a digital signal processor (DSP), which is a processor dedicated to digital signal processing.
In introducing such a digital signal processing technology using the DSP, a digital-to-analog converter (DAC) which converts a digital signal generated by the DSP into a final high-speed analog signal and which is operable at high speed is essential. However, the DAC fabricated by using a current CMOS platform has an analog output bandwidth of about 15 GHz, which is insufficient and causes one of bottlenecks in realizing the increase of capacity for communication systems.