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voltage controlled oscillator


VCO Introduction

The fast emerging wireless technology, such as 5GHz Wireless LAN (WLAN) in US, or High Performance Radio LAN (HIPERLAN) in Europe demands low cost integrated RF transceiver. As an alternative to traditional high cost GaAs, BJT RF technologies, CMOS technology has been proven to be suitable for RF application when the MOS device is scaled down to submicron regime. The benefit of using standard CMOS process is its potential possibility of integrating the whole RF transceiver on a single chip at lower cost. In order to achieve a single chip radio on bulk CMOS, we may face lots of design challenges. One of the challenges is to design an integrated CMOS VCO at microwave frequency with low phase noise. The phase noise of a VCO is a very critical specification for many wireless communication systems. However, different modulation schemes have different phase noise requirements. For 5GHz WLAN, OFDM (Orthogonal Frequency Division Multiplexing) is expected to be the modulation scheme. Since OFDM system performance is very sensitive to phase error, as a result, the phase noise requirement of this system is very stringent even at low offset frequency, such as 10kHz and 100kHz.

Close in carrier phase noise of CMOS VCO is usually dominated by two components. One is thermally induced phase noise, which is originated from thermal noise sources inside a VCO and has 1/f2 characteristics; the other is 1/f induced phase noise, which is due to 1/f noise up-conversion and has 1/f3 characteristics. When deep sub-micron MOS devices are used for high frequency VCO, 1/f induced phase noise could be very significant at 10kHz and 100kHz. In recent years, low phase noise LC type integrated CMOS VCO is a very active research topic. Since phase noise is inversely proportional to Q2, where Q is the loaded Q of an LC tank, thus, increasing Q is the main focus of current research. However, due to the substrate loss of bulk CMOS, the Q factor of on chip inductor and varactor has limited room to improve at microwave frequency. Therefore, further phase noise improvement, particularly the 1/f induced phase noise needs some alternative methods. In this paper, a low frequency feedback concept originated from discrete microwave community was first applied and implemented in high frequency integrated LC CMOS VCOs for 1/f induced phase noise suppression.

Practical Harmonic Oscillator Design”, in “ Low-Power Design Techniques and CAD Tools for Analog and RF Integrated Circuits ”,

A Comparison between Two 1.8GHz CMOS VCOs Tuned by Different Varactors

Oscillator Design by A.W.Dearn – Paper presented at the The IEE Training Event -How to Design RF Circuits

TUNING AND CONTROL OF AN ON-CHIP PIEZOELECTRIC RESONATOR, Matthew J. Volkar, Thesis

Fully Integrated RF VCO for Wireless Transceivers, International Symposium on Signals, Systems,

understanding on vco function inside PLL

Design of VCO

Fully Integrated RF VCO for Wireless Transceivers, International Symposium on Signals, Systems, and Electronics

RF-CMOS Oscillators with Switched Tuning , Custom IC Conf

RF-CMOS Oscillators with Switched Tuning Custom IC Conf, presentation slides

How Phase Noise Appears in Oscillators

A 900 MHz CMOS LC-Oscillator With Quadrature Outputs

More links

Wide band VCO for Set-Top TV Tuner

voltage to frequncy and frequency to voltage conversion

lecture notes on VCO

VCO design application notes

VCO-Voltage Controlled Oscillator

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Voltage controlled oscillators and varactors

Voltage controlled oscillator ; LC and var cap

articles from ofc.com

Oscillators ;epanorama.net

Oscillator Design ; links on vco sss.mag


information on oscillator design ;RF avenue

History of Crystal Oscillators

Crystal theory of operation

An Introduction to Oscillator Design

Frerking crystal history paper

tutorial on oscillator design

oscillator design

PLL and oscillator articles

Oscillator

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oscillator design articles

2.4 GHz VCO

VCO design
Voltage Controlled Oscillator application note, This application note explores the design fundamentals needed to implement a trimless, fixed-frequency, IF voltage-controlled oscillator (VCO) and points out the challenges in guaranteeing proper circuit operation

VCO Phase noise
The term phase noise is widely used for describing short term random frequency fluctuations of a signal. Frequency stability is a measure of the degree to which an oscillator maintains the same value of frequency over a given time

Using a VCXO as a Clock Generator
VCXO (Voltage Controlled Crystal Oscillator) is an oscillator whose frequency is determined by a crystal, but can be adjusted by a small amount by changing a control voltage.

VCXO’s Voltage Controlled Crystal Oscillators
VCXO’s Voltage Controlled Crystal Oscillators, A VCXO (voltage controlled crystal oscillator) is a crystal oscillator which includes a varactor diode and associated circuitry allowing the frequency to be changed by application of a voltage across that diode,

Quartz oscillators free download papers

Introduction to Quartz Frequency Standard
More than one billion (i.e., 109) quartz crystal oscillators are produced annually for applications ranging from inexpensive watches and clocks to radionavigation and spacecraft tracking systems. The fundamentals of quartz oscillators are reviewed in this report, with emphasis on quartz frequency standards (as opposed to inexpensive clock oscillators). The subjects discussed include: crystal resonators and oscillators, oscillator types, and the characteristics and limitations of temperature-compensated crystal oscillators (TCXO) and oven-controlled crystal oscillators (OCXO). The oscillator instabilities discussed include: aging, noise, frequency vs. temperature, warmup, acceleration effects, magnetic field effects, atmospheric pressure effects, radiation effects, and interactions among the various effects. Guidelines are provided for oscillator comparison and selection. Discussions of specifications are also included, as are references and suggestions for further reading

This specification covers the general requirements for quartz crystal oscillators used in electronic equipment. The crystal oscillators covered by this specification are unique due to the fact that these devices must be able to operate satisfactorily in systems under demanding conditions such as: 20 g’s vibration, 100 g’s of shock, 24 hours of salt spray, wide temperature range (e.g., -55°C to +85°C) and low noise under vibration. In addition, these requirements are verified under a qualification system. Commercial components are not designed to withstand these Environmental conditions.

FIFTY YEARS OF PROGRESS IN QUARTZ CRYSTAL FREQUENCY STANDARDS, Marvin E. Frerking, Proceedings of the 1996 research International Frequency Control Symposium, pp. 33 – 46.

INVESTIGATIONS IN LOW DRIVE LEVEL SENSITIVITY OF QUARTZ RESONATORS AFFECTING THEIR MOTIONAL PARAMETERS, R. Brendel, M. Addouche, P. Salzenstein, E. Rubiola, and Y. S. Shmaliy.

Hysteresis Effects after Reflow Soldering of Surface-Mount Crystal Devices, Bernd Neubig, Proceedings research International Frequency Control Symposium Pasadena May 1998.

Das Grosse Quarzkochbuch, Bernd Neubig & Wolfgang Briese Feldkirchen: Franzis-Verlag, 1997, in German. Available per chapter at http://www.axtal.com/info/buch.html, merged into one file with complete bookmarks.

Quartz
Crystal Equivalent Circuit, Peter Daborn, (48 KB) Mathcad 2000.

RECENT DEVELOPMENT OF QUARTZ OSCILLATORS, Norio TABUCHI, Minoru TAKEDA, Toru MATSUMOTO, Masatoshi SATO, NIPPON PRECISION CIRCUITS Inc.

Study on ELID grinding for quartz blank, Kiyoshi Sawada e.a., RIKEN Review No. 34 (April, 2001): Focused on Advances on Micro-mechanical Fabrication Techniques.





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  1. Guru

    WITH the constant shrinking of feature sizes and increasing clock speeds in integrated circuit (IC) technology, designers are approaching a widespread use of digital systems with clock speeds in the gigahertz range. One of the major challenges in the distribution and synchronization of these gigahertz clocks is on-chip phase-locked loop (PLL) clock multipliers which rely on the oscillation amplitude of LC voltage-controlled oscillator (VCOs) . Since the oscillation amplitude of current-biased LC VCOs varies over its tuning range , an amplitude control scheme is needed to set the amplitude to a predefined level so the operation of the frequency dividers in the PLL is not compromised

    On the other hand, to ensure a clock with very low jitter, a high-quality LC tank is needed. However, the quality factor of practical on-chip inductors is typically very low and frequency dependent. The low quality factor and frequency dependence is mainly due to a lossy silicon substrate and thin metal layers. A great deal of attention has been focused on improving the performance of lossy LC tanks by introducing a negative transconductance to compensate its resistive loss . By tuning this loss, and thus the factor of the LC tank, it is possible to control the amplitude of oscillation in an LC VCO implementation. The tuning results in a fast and reliable start up with an optimal bias point in terms of phase noise performance [6]. However, the bias current required by the oscillator depends on the amplitude of oscillation, the losses in the tank, and also other process and environment parameters. Consequently, if the VCO circuit is biased with a fixed current, oscillations over all conditions may not be guaranteed, nor can an optimum value to minimize power and ensure fixed amplitude of oscillation be found .

    Therefore, having a stable, efficient, and cost-effective mechanism to control the resistive loss of the LC tank can also be used to tune the quality factor of on-chip LC filters . The PLL circuit locks the oscillation frequency of the VCO and thus the center frequency of the slaved filter. Assuming identical tanks for both VCO and filter, the control loop locks the oscillation amplitude to a reference signal, and feeds the same control voltage to the slaved resonator. In other words, the same concept used to tune the quality factor of the LC filters has been modified to regulate the oscillation amplitude. However, the main problem of using a VCO is its amplitude regulation during the tuning process.

  2. Guru

    In practical implementations of LC oscillators in which the quality factor of the tank is dominated by the quality factor of the inductor, due to dependence of the oscillation amplitude on the square of the oscillation frequency and the bias current of the LC tank, a stable amplitude control loop is essential to maintain a constant oscillation amplitude over the tuning range of the voltage-controlled oscillator (VCO) and to optimally bias the VCO over different conditions. In this paper, an enhanced loss control scheme incorporating an integral feedback to automatically tune the oscillation amplitude of LC oscillators is proposed. The proposed loss control feedback (LCF) loop is conditionally stable with an easy stability requirement to meet and its stability is examined: 1) by linearizing the system around the stable point using a perturbation method; and 2) by numerically solving the nonlinear differential equation of the LCF loop describing the transient behavior of the step response of the loop.

    • Guru

      Understanding Phase Noise from Digital Components in PLL Frequency Synthesizers
      The article explains how the phase noise from the digital components in a PLL synthesizer (dividers, phase detector and charge pump) can be understood in terms of timing jitter in these devices. This simple physical model is shown to predict the observed variation of phase noise with PLL parameters and provides further insight into sources of significant phase noise.

      full download at http://www.radiolab.com.au/DesignFile/dn006a.pdf

  3. admin

    good tutorial on vco design






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