The explosive growth in wireless communication has driven research into low-cost, low-power and miniaturised wireless receivers. A low power and low phase noise voltage controlled oscillator (VCO) is one of the key components of transceiver systems. Close-in phase noise, responsible for jitter in time domain, is the most important parameter of a VCO as it results in inter-symbol interferences in high speed analogue to digital converters (ADCs). VCO phase noise also degrades system sensitivity and selectivity of wireless receivers. To improve battery life, VCO designs for wireless receivers must consume the least possible power. Hence, the primary aims of this research are to achieve a VCO with very low close-in phase noise and with low power consumption. Substantial research into VCO topologies and the design of on-chip passive elements has made on-chip complementary metal oxide semiconductor (CMOS) implementation of LC-tank VCO possible. However, the principle issues with CMOS LC-VCOs have been the unavailability of a high quality factor (Q) on-chip inductor and high flicker noise of active devices.
This work covers the design of CMOS fully integrated low power low phase noise voltage controlled oscillators for telecommunication or datacommuni- tion systems. The need for low power is obvious, as mobile wireless telecommunications are battery operated. As wireless telecommunication systems use oscillators in frequency synthesizers for frequency translation, the selectivity and signal to noise ratio of receivers and transmitters depend heavily on the low phase noise performance of the implemented oscillators. Datacommunication s- tems need low jitter, the time-domain equivalent of low phase noise, clocks for data detection and recovery. The power consumption is less critical. The need for multi-band and multi-mode systems pushes the high-integration of telecommunication systems. This is o?ered by sub-micron CMOS feat- ing digital ?exibility. The recent crisis in telecommunication clearly shows that mobile hand-sets became mass-market high-volume consumer products, where low-cost is of prime importance. This need for low-cost products - livens tremendously research towards CMOS alternatives for the bipolar or BiCMOS solutions in use today.
Abstract: The design of voltage-controlled Oscillators nowadays is all about being capable of operating at higher clock frequencies for the purpose of higher data rate, consuming less power for the purpose of longer battery life, and having better phase noise performance for the purpose of higher quality of wireless service and more efficient use of the available frequency spectrum since most of the wireless and mobile terminals that these VCOs work in are required to be able to operate in multiple RF standards to serve new generations of standards while being backward compatible with existing ones, leading to a demand for multi-standard multi-band radio operation that deals with high frequency RF signals that undergo different modulation schemes of different standards in different channels over a wide range of frequency band. A top-down system design from the PLL to the VCO is carried out to determine the specifications for a fully integrated dual-band voltage-controlled oscillator (VCO) designed for a Zero-IF WiMAX/WLAN receiver in a O.18tm CMOS technology with 1.8V supply voltage. A VCO employing a differential cross-coupled inductance-capacitance (LC) tank architecture is proposed to cover twice the desired frequency bands for WiMAX and WLAN standards in order to avoid load pulling between VCO frequency and incoming RF frequency. The switching between two bands is implemented by using two binary-weighted capacitor arrays while switching inside each sub-band is implemented by different digital control signal combinations for the binary-weighted capacitances. A phase noise of -120.7dB/Hz at 1MHz offset frequency is demonstrated for an oscillation frequency of 4.84GHz. The average power consumption of this VCO is 8.1mW. This VCO is developed as an IP (Intellectual Property) to be used in a fully integrated CMOS multi-standard WiMAX/WLAN radio allowing seamless roaming of handheld mobile devices between hotspots in future Wireless Metropolitan Area Network (WMAN). To compare the performance of ring oscillators to that of LC tank oscillators, the designs of two three-stage multiple-pass voltage-controlled ring oscillators with dual-delay paths are demonstrated where the differential delay cell utilizes both the primary loop delay and the negative skewed delay to increase the frequency of oscillation substantially and retain or even increase tuning range. Their phase noise performance is also improved by switching in and out the transistors periodically. In design I, the covered frequency range is from 0.74 GHz to 1.96 GHz, which translates to a tuning range of 90 % A phase noise of -104.995dBc/Hz is demonstrated for an oscillation frequency of 1.8535 GHz. Each stage draws a current of 4.963mA on average from a 1.8V power supply, resulting in a power consumption of 26.8mW. In design II, the covered frequency range is from 1.0478 GHz to 2.0022 GHz, which translates to a tuning range of 63%. The frequency-voltage curve is almost a perfect linear curve for V between OV and 0.9V. A phase noise of -110.O45dBc/Hz is demonstrated for an oscillation frequency of 2.00216 GHz. Each stage draws a current of 10.179mA on average from a 1.8V power supply, resulting in a power consumption of 55mW.
Design of High-Performance CMOS Voltage-Controlled Oscillators presents a phase noise modeling framework for CMOS ring oscillators. The analysis considers both linear and nonlinear operation. It indicates that fast rail-to-rail switching has to be achieved to minimize phase noise. Additionally, in conventional design the flicker noise in the bias circuit can potentially dominate the phase noise at low offset frequencies. Therefore, for narrow bandwidth PLLs, noise up conversion for the bias circuits should be minimized. We define the effective Q factor (Qeff) for ring oscillators and predict its increase for CMOS processes with smaller feature sizes. Our phase noise analysis is validated via simulation and measurement results. The digital switching noise coupled through the power supply and substrate is usually the dominant source of clock jitter. Improving the supply and substrate noise immunity of a PLL is a challenging job in hostile environments such as a microprocessor chip where millions of digital gates are present.
Design of High-Performance CMOS Voltage-Controlled Oscillators presents a phase noise modeling framework for CMOS ring oscillators. The analysis considers both linear and nonlinear operation. It indicates that fast rail-to-rail switching has to be achieved to minimize phase noise. Additionally, in conventional design the flicker noise in the bias circuit can potentially dominate the phase noise at low offset frequencies. Therefore, for narrow bandwidth PLLs, noise up conversion for the bias circuits should be minimized. We define the effective Q factor (Qeff) for ring oscillators and predict its increase for CMOS processes with smaller feature sizes. Our phase noise analysis is validated via simulation and measurement results. The digital switching noise coupled through the power supply and substrate is usually the dominant source of clock jitter. Improving the supply and substrate noise immunity of a PLL is a challenging job in hostile environments such as a microprocessor chip where millions of digital gates are present.
The book discusses the latest developments and outlines future trends in the fields of microelectronics, electromagnetics and telecommunication. It contains original research works presented at the International Conference on Microelectronics, Electromagnetics and Telecommunication (ICMEET 2018), organised by GVP College of Engineering (A), Andhra Pradesh, India. The respective papers were written by scientists, research scholars and practitioners from leading universities, engineering colleges and R&D institutes from all over the world, and share the latest breakthroughs in and promising solutions to the most important issues facing today’s society.
Two kinds of voltage-controlled oscillators (VCO)--active inductor based VCO and LC cross-coupled VCO--are studied in this work. Although the phase noise performance is not competitive, the proposed active inductor based VCO provide an alternative method to VCO design with very small chip area and large tuning range. The measurement shows a test oscillator based on active inductor topology successfully oscillates near 530MHz band. The phase noise of the widely used LC cross-coupled VCO is extensively investigated in this work. Under the widely used power dissipation and chip area constraints, a novel optimization procedure in LC oscillator design centered on a new inductance selection criterion is proposed. This optimization procedure is based on a physical phase noise model. From it, several closed-form expressions are derived to describe the phase noise generated in the LC oscillators, which indicate that the phase noise is proportional to the L2· gL3 factor. The minimum value of this factor for an area-limited spiral inductor is proven to monotonically decrease with increasing inductance, suggesting a larger inductance is helpful to reduce the phase noise in LC VCO design. The validity of the optimization procedure is proven by simulations. Two test chips are designed and measured.
