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In this article, a set of oscillators and a heterodyne image receiver operating near 600 GHz have been developed, each based on a 250-nm InP heterojunction bipolar transistor (HBT) technology and a 130-nm SiGe HBT technology, respectively. The oscillators are based on the common-base cross-coupled push–push topology, which employed coupled-line loads for improved output power and efficiency with a small area. The measured oscillation frequency ranges of the three oscillators with different coupled-line lengths were 628–682, 556–610, and 509–548 GHz, respectively, with a tuning capability achieved with bias variation. The maximum output power and the dc-to-RF efficiency achieved with the oscillators were −10 dBm and 0.19%, respectively. The heterodyne receiver, which consists of a mixer, an IF amplifier, and an IF detector, exhibited a maximum responsivity of 469 kV/W and a minimum noise equivalent power (NEP) of 0.64 pW/Hz1/2. A transmission-mode 3-D THz tomography imaging setup was established with one of the fabricated oscillators and the heterodyne receiver employed as the signal source and the image detector, respectively. With the imaging setup, a successful reconstruction of 3-D images of a target object was demonstrated based on the filtered back-projection algorithm.

A 300-GHz quadrature voltage-controlled oscillator (QVCO) integrated with a pair of mixers based on an InP heterojunction bipolar transistor (HBT) technology has been developed. A super-harmonic coupling technique was applied to generate the quadrature signal in the QVCO. The oscillation frequency tuning range is 24.8 GHz (from 286.1 to 310.9 GHz), and the frequency range maintaining the quadrature operation (within ±10°) is 4.8 GHz (297.2–302.0 GHz). The maximum output power of the QVCO was measured as 0.46 dBm at 286.3 GHz. The measured phase noise is −91.4 dBc/Hz with 10 MHz offset at 294.2 GHz. The integrated QVCO-mixer consumes a dc power of 167.5 mW.

A 24-48 GHz wideband frequency tripler has been developed based on a 130-nm SiGe BiCMOS technology. The 2-stage tripler employs a compact wideband matching technique for the inter-stage and output matching, leading to a measured 3-dB bandwidth of 24 GHz (24-48 GHz), or 67 % with reference to the center frequency. The obtained peak conversion gain is -2.5 dB at 27 GHz with a -5-dBm input power, and the saturated output power is -0.87 dBm at 33 GHz with a 4.8-dBm input power. The tripler consumes 6.8 mW. The circuit occupies 460 × 300 μm2, excluding probing pads.

This paper presents a high efficiency gate inductive feedback Colpitts Voltage Controlled Oscillator (VCO) operating near 90 GHz. It includes multi-way transformers at the load, which helps to enhance the DC-to-RF efficiency with boosted impedance and extended voltage swing through drain-buffer and drain-source magnetic couplings. The proposed VCO is fabricated in a 65-nm CMOS process, and showed an oscillation frequency tuning range of 87.5-92.0 GHz (4.5 GHz). Over the frequency range, the output power and the dc power consumption exhibited values of −2.8 −1.7 dBm and 6-22.5 mW, respectively. The peak DC-to-RF efficiency was 9.4 %, and the corresponding phase noise was −107.4 dBc/Hz at 10-MHz offset. The lowest phase noise at the optimum bias condition was −116.7 dB/Hz at 10-MHz offset. The chip size is 400 ⨯ 300 μm2 excluding DC and RF pads.

THz oscillators operating up to 680 GHz have been developed in this work based on a 250-nm InP heterojunction bipolar transistor (HBT) technology. This work shows that the common-base cross-coupled push-push oscillator topology is improved by adopting a coupled-line structure, in which DC blocking capacitors and other transmission lines are replaced by a pair of coupled lines. The coupled lines enable efficient impedance and phase matching with a small area, resulting in improved output power and efficiency. Three types of oscillators with a slight dimensional variation were fabricated. The measured oscillation frequency of the three oscillators are 628 - 682 GHz, 556 - 610 GHz and 509 - 548 GHz, respectively, with bias-based tuning. The maximum output power and DC-to-RF efficiency of oscillators are up to -10 dBm and 0.19 %, respectively. The circuit occupies only around 0.014 mm2 excluding the probing pads.

A 300-GHz integrated transmitter has been developed based on a 250-nm InP HBT technology. The transmitter is composed of a voltage-controlled oscillator (VCO) and a switch, which serve as a signal generator and a modulator, respectively. The VCO adopts a common-base cross coupled topology to acquire a high output power near 300 GHz. The output power and the frequency tuning range of the VCO are 3.8 dBm and 298 - 316.1 GHz, respectively. The switch, which employs a conventional traveling wave topology with three shunt transistor stages, exhibits an insertion loss of 2.4 dB and an isolation of 9.0 dB, both measured at 300 GHz. The integrated transmitter exhibits a peak output power of 0 dBm and −7 dBm for on- and off-state, respectively. The measured tuning range is 301.3 - 312.5 GHz.

A 130-GHz OOK transmitter has been developed based on a 65-nm CMOS technology in this work. The transmitter is composed of a 130-GHz fundamental oscillator and a switch-based OOK modulator. The oscillator is based on an LC cross-coupled differential pair with a tapered buffer, while the switch adopts a 3-stage shunt configuration. The on/off power ratio of the switch is over 20 dB, and the transmitter exhibits an output power of −5.1 dBm with the switch turned on. The 3-dB bandwidth of the transmitter measured with a frequency domain technique is 16 GHz. The transmitter consumes 55.2 mW, mostly arising from the oscillator.