Design Of Wide Range Voltage Controlled Ring Oscillator

VCO is a kind of oscillator whose oscillation frequency changes with the outside voltage, and widely used in high speed serial data communication, clock generator, data transceiver and other related fields. The biggest advantage of the VCO is able to provide a stably and accurately clock signal. The tuning range and phase noise performance decided whether the oscillator generates a clock signal with high performance. With the rapid development of 4G net-work, high frequency and wide range VCO becomes more and more important in the wireless communication devices. In the conventional CMOS process, designers often use the LC structure to design the oscillator, but it will raise the requirement of the process. The best worse is that using LC structure will greatly increased the area of the chip, thereby increasing the cost of design. In a word, in the conventional CMOS process, the research of high frequency and wide range in the ring-VCO is important.This paper first introduces the background, significance and development status of the VCO, analyzes the basic working principle of the oscillator, then briefly describes the typical topology of the oscillator and two kinds of typical phase noise model to further understand the structure of the oscillator. This paper explained the negative feedback theory in detail, and explained the condition of the normal operation of the oscillator in three aspects. The oscillator used to includes crystal oscillator, LC oscillator and so on. The phase theory is point out that the amplitude and phase of the sinusoidal signal can be affected by the interference of the outside noise when the interference of the external noise is disturbed. On the basis of this theory, the paper studies the mathematical model, the main performance index of the VCO and three methods to increase the frequency regulation range including center frequency, power supply voltage, adjusting range, adjusting linearity and so on. The paper then studies three methods of broadband tuning including capacitive switch, variable inductance, multiple narrowband VCO and so on. At the end of this paper, elaborating the design concept of the system block diagram, the design method of operational amplifier and the delay unit. Also we finish the simulation of the circuit system under Cadence platform.The design of Ring voltage-controlled oscillator in this paper is based on SMIC 0.18um CMOS Process. And the frequency of this VCO is range from 1.468GHz to 10.13GHz. The simulation result shows that when the operating frequency is 5GHz, the phase noise is -23.55dBc/Hz@10KHz,-51.91dBc/Hz@100KHz, and in the 1MHz offset, the phase noise is -80.27dBc/Hz.