Choul-Young Kim

Design of a 24-GHz CMOS VCO With an Asymmetric-Width Transformer

A K-band CMOS voltage-controlled oscillator (VCO) is implemented with a 0.18- ¿m radio frequency CMOS process. For low supply voltage operation, a transformer-feedback topology using a transformer is proposed. The analysis of the transformer-feedback VCO is presented. This shows that the inductance ratio of the transformer must be optimized, and asymmetric-width transformers allow the easy optimization and the high Q-factor. Based on this analysis, the transformer design consideration of the transformer feedback VCO is presented. The VCO operates at 24.27 GHz with the phase noise of -100.33 dBc/Hz at 1-MHz offset, and it consumes 7.8 mW from a 0.65-V supply voltage.

A Quadrature Radar Topology With Tx Leakage Canceller for 24-GHz Radar Applications

A quadrature radar topology with a Tx leakage canceller is presented. The canceller is composed of four branch-line hybrid couplers, a 90deg delay line, and a Wilkinson combiner. It has high Tx-to-Rx isolation and wide bandwidth characteristics. The isolation is 35.27 dB at 24 GHz and does not drop below 30 dB over a 2-GHz bandwidth. Given that the isolation of the branch-line hybrid coupler is 21.5 dB, the enhancement of the isolation is expected to be 13.77 dB. A quadrature Doppler radar front-end with the canceller was implemented. The noise level in the mixer output is lower by 9 dB compared with that of a conventional quadrature radar. This radar can measure speed as low as 0.76 mm/s, which correspond to a 0.12-Hz Doppler shift. It is also able to detect signs of the Doppler shift from a moving target due to its quadrature topology.

A K-Band CMOS Voltage Controlled Delay Line Based on an Artificial Left-Handed Transmission Line

A K-band voltage controlled delay line based on a left-handed transmission line (LHTL) with cascaded metal-oxide-semiconductor (MOS) varactors and shunt inductors using CMOS technology is demonstrated for the first time. A variable time delay can be obtained by changing the capacitance of MOS varactors without any power consumption. The figure of merit is 10.9deg/dB at 18 GHz. This result is better than other variable LHTL in similar frequency band. A time delay ranging from 56.8 ps to 76.4 ps is achieved at 18 GHz. It allows about 30 times longer time delay than that of a traditional right-handed one with the same length. The chip size, including the pads, is 410 mum times 640 mum.

Tx Leakage Cancellers for 24 GHz and 77 GHz Vehicular Radar Applications

Tx leakage cancellers for 24 and 77 GHz vehicular radar systems are presented. These have high Tx-to-Rx isolation and wideband characteristics. Tx leakage cancellers are composed of four Lange couplers, a 90deg delay line, and a Wilkinson combiner. Tx leakage cancellers are implemented on GaAs substrate. A 24 GHz Tx leakage canceller shows the transmitting loss of 5.7 dB and Tx leakage cancellation of 28.1 dB. Also a 77 GHz Tx leakage canceller shows the transmitting loss of 3.6 dB and Tx leakage cancellation of 28.2 dB. Isolations due to Lange coupler are 15.1 dB in 24 GHz Tx leakage cancellers and 13.1 dB in 77 GHz Tx leakage cancellers, respectively. The isolations due to the topology of the Tx leakage canceller are expected to be 13 dB and 15.1 dB, respectively. These compact Tx leakage cancellers show wideband characteristics of bandwidth beyond 4 GHz

A Circularly Polarized Balanced Radar Front-End With a Single Antenna for 24-GHz Radar Applications

In this paper, we propose a circularly polarized balanced radar front-end topology with a Tx leakage canceller. This radar is composed of a dual-orthogonal fed microstrip patch antenna, a 90deg delay line, a differential cross-coupled oscillator, two Lange couplers, a Wilkinson combiner, and a mixer. We implemented circularly polarized balanced Doppler radars by using a printed circuit board and InGaP/GaAs heterojunction bipolar transistor technologies. The front-end chip and module with antenna are 1 mm times 1 mm and 3 cm times 3 cm, respectively. The average Tx-to-Rx isolation is about 36 dB. This radar can measure speeds as low as 0.5 mm/s, which corresponds to a 0.076-Hz Doppler shift. The received signals of the circularly polarized balanced Doppler radar are about two times larger than those of a linearly polarized balanced Doppler radar due to the topology. This result occurs because the proposed radar has an intrinsic loss of only 3 dB in the receiving path.

A K-band quadrature VCO based on asymmetric coupled transmission lines

A K-band quadrature voltage-controlled oscillator (QVCO) based on asymmetric coupled transmission lines is presented. Asymmetric coupled transmission lines are used to couple two identical LC tank oscillators for generation of a quadarature signal with comparable phase noise with reported QVCOs at the frequencies. The fabricated QVCO using InGaP/GaAs HBT technology shows the oscillation frequencies from 22.07 to 22.9 GHz. The frequency tuning range is about 830 MHz. The peak output power is 6 dBm. The phase noise of − 121.17 dBc/Hz at 1 MHz offset and 185.6 of FOM are achieved at the operating frequency of 22.83 GHz.

InP/InGaAs heterojunction bipolar transistors with low-resistance contact on heavily doped InP emitter layer

InP/InGaAs heterojunction bipolar transistors (HBTs) with low-resistance Ti/Pt/Au contact directly on heavily doped InP emitter layer have been demonstrated. A specific contact resistance of Ti/Pt/Au to n-type InP with doping concentration of 2×1019 cm−3 was investigated with the tunneling model theoretically and transmission line model (TLM) experimentally, revealing that it depends greatly on the doping level. TLM measurements exhibited a low specific contact resistance of 3.5×10−7 Ω cm2, which can be applicable to the fabrication of HBTs. InP/InGaAs HBTs with n+-InP emitter layer have been demonstrated with excellent dc characteristics, including a low offset voltage of 0.12 V, a knee voltage of 0.5 V, and a current gain of 28. These results verify that the heavily doped InP emitter layer allows a low-resistance contact.

Monolithic Integration of InP-Based HEMT and MSM Photodiode Using InGaAsP (λ=1.3 µm) Buffer

A new epitaxial layer structure for the integration of a high-electron-mobility transistor (HEMT) and a metal-semiconductor-metal photodiode (MSM PD) is proposed. With the aid of an InGaAsP (?=1.3 ?m) buffer, this epitaxial layer structure has an additional function of light absorption without performance degradation of the HEMT. With this light absorption ability, the epitaxial layer structure can support a MSM PD structure and makes the fabrication process of the MSM PD identical to that of a HEMT. The characteristics of a monolithically integrated HEMT and MSM PD are presented and discussed. Measured ft and fmax are 18.7 GHz and 47 GHz, respectively, for the 1.5?100 ?m2 gate HEMT, and a responsivity of 0.7 A/W at a wavelength of ?=1.3 ?m has been acquired for the MSM PD.

Design and Fabrication of Ka-Band Microstrip to Waveguide Transitions Using E-Plane Probes

In this paper, two kinds of E-plane microstrip-to-waveguide transitions are optimally designed and fabricated for combining output power from multiple small-power amplifiers in a WR-28 waveguide because conventional K connectors cause unnecessary insertion loss and adaptor loss. The transition design is based on target specifications such as a center frequency of 35 GHz, bandwidth of , 0.1 dB insertion loss and 20 dB return loss. Performance variation caused by mechanical tolerance and assembly deviation is fully evaluated by three dimensional electromagnetic simulation. The fabricated back-to-back transitions with 16 mm and 26.57 mm interstage microstrip lines show insertion loss per transition of ~0.1 dB at 35 GHz and average 0.2 dB over full Ka band. Also the back-to-back transition shows return loss greater than 15 dB, which implies that the transition itself has return loss better than 20 dB.

A Ka-Band 8 W Power Amplifier Module Using 4-Way Waveguide Power Combiners with High Isolation

In this paper, a Ka-band 8 W power amplifier module with WR-28 waveguide input and output ports is implemented and measured using four 2 W power amplifier modules and 4:1 waveguide power combiners with high isolation of 25 dB at 35 GHz. The 2 W power amplifier modules are fabricated using waveguide-to-microstrip transitions and show output power of 32.5~33.3 dBm and power gain of 26.9~28.7 dB at 35 GHz. Four 2 W power amplifier modules are combined through 4:1 waveguide power combiners with resistive septum and the combined power shows 39.0 dBm(8 W) under 6 V drain bias and 39.6 dBm(9.1 W) under 6.5 V drain bias at 35 GHz.