Most of today’s CMOS/BiCMOS designs for terahertz applications target the circuit blocks. This is especially true of the terahertz fundamental-frequency oscillators. In an impressive feat, however, substrate-integrated-waveguide (SIW) antennas have been integrated with active terahertz circuits in CMOS/BiCMOS by a group of researchers at Singapore’s Institute of Microelectronics, A*STAR. The team includes Sanming Hu; Yong-Zhong Xiong (now with MicroArray Technologies); Bo Zhang (now with Xi’an University of Posts and Telecommunciations); Lei Wang (now with the University of Electronic Science and Technology of China); Teck-Guan Lim (now with JDS Uniphase Corp.); Minkyu Je; and Mohammad Madihian.
The researchers’ terahertz transmitter (Tx) and receiver (Rx) chipset operates at roughly 400 GHz in 0.13-μm silicon-germanium (SiGe) BiCMOS technology. In the transmit chip, the SIW antenna also works as a high-pass filter. In doing so, it keeps the unwanted harmonics from being radiated out of the chip. The key is the SIW antenna’s high-pass filtering characteristic, which enables it to suppress the unwanted fundamental and second harmonic signals by 50 and 30 dB, respectively. In addition to the SIW antenna, the transmit chip houses a voltage-controlled oscillator (VCO), buffer, modulator, power amplifier (PA), and frequency tripler.
For its part, the receive chip contains an SIW antenna with a tunable bandwidth. It is integrated with a two-mode subharmonic mixer, which achieves conversion loss that is ~5 dB lower than the loss suffered by conventional designs. The receive chip consumes 50 nA from a 1.2-V supply.
To improve performance, the researchers created some novel function blocks. For instance, they found that the transmitter’s output power could be raised to ~0 dBm or higher by using a high-power VCO and their redesigned amplifier, which provided gain of ~20 dB at 140 GHz. See “A Si-Ge BiCMOS Transmitter/Receiver Chipset with On-Chip SIW Antennas for Terahertz Applications,” IEEE Journal of Solid-State Circuits, Nov. 2012, p. 2654.