Design, implementation and measurement of low voltage microwave oscillators and frequency synthesizers

Abstract

The development of broadband wireless communication driven by the fast growing market has been progressing rapidly in recent years. Owing to the overcrowded spectrum at 900MHz, 1.8GHz and 2.4GHz, data transmission are migrating towards 5.8GHz and even higher bands. Recently, much attention has been drawn to the applications of wireless local area network (WLAN) standards, including IEEE 802.11a and HIPERLAN. Driven by portability reason, the market keeps pushing the development of low-voltage operated and low-power consumption wireless transceivers for handheld applications for 900MHz to 5GHz frequency bands. The voltage-controlled oscillator (VCO) is a critical component in a wireless transceiver. In microwave VCO design, it is difficult to achieve high output power with low phase noise at low supply voltage, such as below 3V. The difficulty will be more profound when the oscillating frequency approaches the cut-off frequency of the active device due to the decrease of gain and the increase of noise. In this thesis, various design approaches of microwave VCO are investigated. The results recommend the use of distributed oscillator for low voltage operation. A distributed voltage-controlled oscillator (DVCO) can operate at frequencies close to the cut-off frequencies of active devices by absorbing the parasitic capacitance of the transistors into the artificial transmission lines. To demonstrate the design concept, a 5.8GHz DVCO based on bipolar transistors has been developed. A prototype was implemented successfully on low cost FR4 fiber glass printed circuit board. The prototype delivers −3dBm output power with −100dBc/Hz phase noise at 100kHz offset while operating at 1.8V. Injection locking technique is also developed to control a distributed oscillator by using a subharmonically injection source. The proposed DVCO can be applied in phase locked loop frequency synthesizers. Two novel frequency synthesizers adopting dual phase locked loop (PLL) and direct memory access technique are studied. These frequency synthesizers achieve fast channel acquisition and high channel efficiency. The frequency accuracy and channel switching performance are presented. Measurement results show that the proposed techniques are suitable for low voltage handheld applications. To study the phase noise characteristic, two systems for close-in phase noise measurement of free-running VCOs and open-loop modulation transceivers using a spectrum analyzer has been developed. One of the systems applies charge pump PLL technique to track the drifting frequency automatically. The system needs no calibration and alignment process. A prototype demonstrated the accuracy and repeatability. The other system uses subharmonic injection locking technique to lock the frequency of the device-under-test. Compared with the conventional delay line and PLL method, the proposed systems is much more convenient and cost-effective. The achievements of the work are as follows: 1. A 1.8V, 5.8GHz distributed voltage controlled oscillator module has been designed and implemented successfully. Detail study and practical implementation of a 5.2GHz frequency synthesizer with a subharmonically injection locked distributed oscillator reveals that the solution is promising for low voltage operation. 2. Two frequency synthesizers are specially designed for low voltage operate handheld devices: 1. dual PLL frequency synthesizer; and 2. direct memory access frequency synthesizer. The two frequency synthesizers are successfully implemented. 3. Automatic frequency tracking and subharmonic injection locking techniques for phase noise measurement of free-running VCOs and frequency synthesizers are studied and implemented successfully.

Date of Award	4 Oct 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kim Fung TSANG (Supervisor)