Development of RTD-based oscillators with improved RF power performances by using RTD pair topology

Abstract

Low-power monolithic oscillator and amplifier are critical building blocks in the short-range wireless transceiver systems for wireless sensor network (WSN) and implantable biomedical applications. In these wireless systems, the low dc power consumption is a key design issue because of the limited capacity of the small size battery source. Among various low-power electronic devices, a resonant tunneling diode (RTD) has been developed for ultra-low power MMICs due to inherent negative differential resistance (NDR) characteristics arising from quantum-effect tunneling phenomenon achieved at a low bias voltage. However, the RTD based MMICs produce relatively low output power due to the narrow NDR voltage span of the RTD, which is inherent characteristic of the epitaxial layer structure. To enhance the output power characteristics of RTD MMICs, various power combining techniques, such as the resonant cavity-based combiners and circuit-level technologies, have been conducted. In this thesis, to improve the output performances of RTD MMICs, among various techniques for improving output power characteristics, the RTD-pair topology has been proposed to improve the output power performances along with good dc-to-RF conversion efficiency. In order to conduct the topology research for the RTD-pair based MMICs, a reflection-type amplifier, a voltage controlled oscillator (VCO), and an on-off keying (OOK) oscillator were designed and fabricated with an InP-based RTD/HBT MMIC technology. For the developed InP-based RTD/HBT MMIC technology, representative characteristics of the fabricated active devices are as follows. The RTD shows a peak voltage of 0.30 V and current density of 0.73 kA/$cm^2$, respectively, with a peak-to-valley current ratio (PVCR) of 13. The cutoff frequency of the RTD was 70 GHz. The HBT with an emitter area of 1.5x4$\mu m^2$ shows the maximum $f_t/f_{max}$ of 100/63 GHz, respectively, with a dc current gain of 50. As for passive devices, spiral inductors, MIM capacitors, thin film resistors, and varactor diodes have been implemented for realizing the high performance LC tank of the proposed oscillator and the hybrid coupler of RTD amplifier. For topology research of the RTD-pair configuration, the communication blocks such as low-power amplifier, VCO, and on-off keying oscillator operated in the 5.8 GHz band have been developed. Firstly, an improved RF-power amplifier using RTD-pairs has been investigated. The fabricated IC dissipated a low dc power of 284 $\mu$W with a power gain of 9.1 dB and a return loss of -15.1 dB at a 5.64 GHz frequency. By using RTD-pair configuration, the maximum linear $P_{OUT}$ was increased up to -18.7 dBm. Secondly, the RTD based VCO using RTD-pair topology was proposed to improve the output power performances. The fabricated single VCO showed -0.53 dBm of the output power with high DC-to-RF efficiency of 12.7 % at an oscillation frequency of 5.7 GHz. Thirdly, a prototype of RTD-pair based on-off keying oscillator has been proposed and demonstrated with the direct modulation of RTD-pair based VCO. The fabricated oscillator shows a high data-rate of 500 Mb/s with a good FOM of 13.7 pJ/bit. In order to employ the RTD-pair based OOK oscillator to practical WSN applications, an RTD oscillator integrated with the HBT switch has been proposed for a 24 GHz ISM band transmitter. The fabricated IC showed the high-speed switching capability of 5 Gb/s with a good phase noise characteristic of -118.17 dBc/Hz at 1 MHz offset. The maximum RF output power was obtained to be -1.76 dBm at a carrier frequency of 24.1 GHz. It consumes 15.8 mW, resulting in a good figure-of-merit (FOM) value of 3.2 pJ/bit. The obtained results demonstrate its potential as a high performance on-off mode oscillator for high data rate OOK transceiver systems.