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Voltage Controlled Oscillators Prepared by : Yasmin Mohamed Salma fareed Maryam Magdy Supervised by : Dr.Mohamed Abdelghany 1 Slide 2 Introduction VCO VCO Types Specs & Data sheet Applications Limitations and Trade- offs Latest Research Questions 2 Slide 3 VCO People want to be connected all the time. High bandwidth needed. Quartz crystal used for frequencies less than 100 MHZ Higher than 300 MHZ, physical limitation occur. 3 Slide 4 VCO A Voltage Controlled Oscillator is an oscillator whose oscillation frequency is controlled by a voltage input. The output frequency can be sinusoidal or Sawtooth. Frequency synthesizers, navigation systems, instrumentation systems, and telecommunication devices Oscillators are electronic circuits designed to produce a repetitive electronic signal. 4 Slide 5 5 Varactor Diode Abrupt Hyper- Abrupt Slide 6 Varactor Diodes A diode that has a variable capacitance which is a function of the voltage that is impressed on its terminals. Tuning / varactor diodes are operated reverse-biased, and therefore no current flows. The width of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. 6 [1] Slide 7 Varactor Diodes Relations : capacitance is inversely proportional to the depletion region thickness depletion region thickness is proportional to the square root of the applied voltage the capacitance is inversely proportional to the square root of the voltage applied to the diode. 7 [1] Slide 8 Varactor Diodes Different varactor diodes,have different values and parameters of PN junction. Abrupt varactors and hyperabrupt varactors have different properties as detailed below. Different doping profiles could be applied to the pn junction of the varactor diode, to achieve certain c-v relations. 8 [1] Slide 9 Abrupt Diodes For an abrupt varactor diode the doping concentration is held constant, i.e constant doping level as far as reasonably possible. Disadvantage : In applications where a linear dependence is required, a lineariser is needed. This takes additional circuitry that may be an additional burden for some applications, not only in terms of circuitry, but also the slower response speed caused by the lineariser. 9 [1] Slide 10 Hyper-abrupt varactor diodes This provides a narrow band linear frequency variation. much greater capacitance change for the given voltage change Disadvantage : Low Q factor, only used for microwave appilcations. Up to a few GHZ at most. 10 [1] Slide 11 Introduction VCO VCO Types Specs & Data sheet Limitations and Trade- offs Latest Research Questions 11 Slide 12 VCO Specifications 1)Control Voltage :: This is the voltage applied at the input terminal of the oscillator. This varying voltage cause a change in frequency. 2) Deviation : This refers to the amount of change in frequency due to change in voltage. A 5 volt control voltage might result in deviation of 100 ppm. 12 Slide 13 VCO Specifications 3)Transfer Function : Denotes the direction of frequency change vs control voltage Positive transfer function : increase in frequency with increase in voltage negative transfer function : decrease in frequency with decrease in voltage 13 [2] Slide 14 VCO Specifications 4) Linearity The ratio between frequency error and total deviation, expressed in percent. Frequency error : maximum line away from best straight line plot through output frequency and control voltage. 14 [2] Slide 15 VCO Specifications 15 [2] Slide 16 VCO Specifications Center Frequency: is the output frequency f0 of the VCO with its control voltage at its center value and is expressed in [Hz]. Tuning Range: is the range of output frequencies that the VCO oscillates at over the full range of the control voltage. Tuning Sensitivity: is the change in output frequency per unit change in the control voltage, typically expressed in [Hz/V]. 16 Slide 17 VCO Specifications Load Pulling: quanties the sensitivity of the output frequency to changes in its output load Supply Pulling: quanties the sensitivity of the output frequency to changes in the power supply voltage and is expressed in [Hz/V]. Power Consumption: species the DC power drain by the oscillator and its output buffer circuits. 17 Slide 18 VCO Specifications Output Power: is the power the oscillator can deliver to a specied load. Harmonic suppression: species how much smaller the harmonics of the output signal are compared to the fundamental component and is typically expressed in [dBc]. Spectral Purity: can be specied depending on the application, in the time domain in terms of jitter or in the frequency domain in terms of phase noise or carrier/noise ratio. 18 Slide 19 Introduction VCO VCO Types Specs & Data sheet Applications Limitations and Trade- offs Latest Research Questions 19 Slide 20 Limitations Spectral purity Time domain : Amplitude variation and that the zero-crossings of the output waveform are not perfectly spaced in time,but exhibit random variation around a nominal value called jitter. 20 [3] Slide 21 Limitations Frequency domain : Phase noise : frequency stability of a signal. 21 [3] Slide 22 Limitations Q Factor : High Q factor implies that there is a small damping factor and the signal is better able to maintain oscillation. Higher Q more resistant to noise. 22 [3] Slide 23 Introduction VCO VCO Types Specs & Data sheet Applications Limitations and Trade- offs Latest Research Questions 23 Slide 24 VCO Latest Research 24 The two LC-VCOs are designed in 0.25-m BiCMOS process provides 67.3% tuning-range (4856- 9779 -116 dBc/Hz 20 mW power consumption from 1.2 V supply The first oscillator provides 67.3% tuning-range (4856- 9779 MHz), below than -116 dBc/Hz phase noise at 1- MHz offset and 20 mW power consumption from 1.2 V supply voltage. The second oscillator offers 68.7% tuning-range (4821- 9867 MHz), a phase noise -121 dBc/Hz to -115 dBc/Hz. The maximum power consumption is 18.6 mW 1.2 V supply voltage. The maximum power consumption is 18.6 mW from a 1.2 V supply voltage. Wideband LCVCO design for LTE/LTE-A standards - 2-5 Sept. 2013 - Mediterranean Microwave Symposium (MMS), 2013 13th Fahs, B. et. Al. Slide 25 Theoretical Questions Why cant we use a crystal oscillator in high frequency operations? Because its quality degrades over high frequencies due to physical limitations. What are the types of VCO? Abrupt Varactor-Based VCO, Hyper abrupt Varactor Based VCO. What are relations of Capacitance and voltage ? capacitance is inversely proportional to the depletion region thickness depletion region thickness is proportional to the square root of the applied voltage the capacitance is inversely proportional to the square root of the voltage applied to the diode. 25 Slide 26 Theoretical Questions Mention two VCO specifications. Spectral Purity -Tuning Range. How are Varactor diodes used in c-v relations ? Different doping profiles could be applied to the pn junction of the varactor diode. Mention two applications of a VCO. Electronic Jamming equipment, Frequency synthesizer. What happens if we increase Quality factor ? phase-noise and Power consumption will be reduced. 26 Slide 27 Theoretical Questions 3)What is the base circuit design of a VCO? Oscillator Circuit with oscillation frequency = What are two components of spectral purity ? Jitter and phase noise 27 Slide 28 Oscillators Feedback Concept = 1 Phase ( ) = 0 Conditions of oscillations: [4] Slide 29 Most Popular VCOs LC Oscillator: low phase noise, large area Ring Oscillator: easy to integrate, higher phase noise [5] Slide 30 LC Oscillators -LC Oscillators are prone to losses which causes oscillations to decay exponentially. -losses are caused by the series resistances in the inductors and capacitors. -The challenge is to compensate these losses using a negative resistance, thats why they are called Negative Resistance Oscillators. -Transistors are used for the purpose of creating this negative resistance. Basic Idea: Slide 31 Analysis of Negative Resistance Oscillator [5] Slide 32 Analysis of Negative Resistance Oscillator (Step 1) Typically, losses are dominated by series resistance in the inductor. [5] Slide 33 Analysis of Negative Resistance Oscillator (Step 2) -Split oscillator circuit into half circuits to simplify analysis -We can approximate Vs as being incremental ground -Transistor can be represented with a negative resistor Note: Gm is large signal transconductance value. [5] Slide 34 Ways of Improving Design -Design tank components (inductors and capacitors) to achieve high Q Resulting Rp value is as large as possible -Choose bias current (Ibias) for large swing (without going far into saturation). -Choose transistor size to achieve adequately large gm1 (Usually twice as large as 1/Rp1 to guarantee startup) Slide 35 Calculation of Oscillator Swing - By symmetry, assume I1(t) is a square wave -We are interested in determining fundamental component (DC and harmonics filtered by tank) [5] [2] Slide 36 Calculation of Oscillator Swing [5] Slide 37 Different Configurations for LC VCOs [5] Slide 38 Problems [3 ] Slide 39 Slide 40 Applications of VCO Function Generators (low frequency oscillators). High-frequency VCOs are usually used in phase-locked loops for radio receivers. Voltage-to-frequency converters, with a highly linear relation between voltage and frequency. They are used to convert a slow analog signal into a digital signal over a long distance. [7] Slide 41 [8] Slide 42 -Harmonic (Tuned) Oscillators: Resonator + amplifier The amplifier replaces the resonator losses and isolates the resonator from the output. A varactor is used to change the capacitance and hence the resonant frequency. [7], [8] Slide 43 -Relaxation (Untuned) Oscillators: They can provide wide range of optional frequencies with a minimal number of external components. They are used in monolithic ICs. Three topologies of relaxation oscillators: 1. Ground-Capacitor VCOs. 2. Emitter-Coupled VCOs. 3. Delay-Based Ring VCOs. [7], [8] Slide 44 -Relaxation Oscillators Types: Both ground-capacitor and emitter-coupled VCOs operate similarly. The Time spent in each state depends on the rate of charge or discharge of a capacitor. For the ring oscillator, the output frequency is a function of each delay stage. [7] Slide 45 Advantages of Harmonic Oscillators over Relaxation Oscillators: Frequency stability with respect to temperature, noise, and power supply. They have good accuracy for frequency control, since the frequency is controlled by a crystal or tank circuit. [7] Slide 46 Disadvantages of Harmonic Oscillators: They cannot be easily implemented in monolithic ICs, relaxation oscillator VCOs are better suit for this technology. Unlike harmonic VCOs, relaxation VCOs are tunable over wider range of frequencies. [7], [8] Slide 47 VCOs Comparison [9] Slide 48 Square Wave Generator(SQWG): [10] Slide 49 [10] Slide 50 [10] Slide 51 [10] Slide 52 [10] Slide 53 [10] Slide 54 [10] Slide 55 [10] Slide 56 Triangular Wave Generator(TRW): [10] Slide 57 [10] Slide 58 [10] Slide 59 [10] Slide 60 [10] Slide 61 [10] Slide 62 Linear Voltage Controlled Oscillator: [10] Slide 63 [10] Slide 64 [10] Slide 65 [10] Slide 66 [10] Slide 67 [10] Slide 68 References: 1] http://www.cbtricks.com/handyandy/PC-122/Clarifier.htm (varactor)http://www.cbtricks.com/handyandy/PC-122/Clarifier.htm [2]Vectron International 267 Lowell Road, Hudson, NH 03051 Tel: 1-88-VECTRON-1 http://www.vectron.com http://www.vectron.com [3] Analog Circuit Design,Sansen, WillyHuijsing, Johan van de Plassche, Rudy 10.1007/978-1-4757-3047-0_17 Integrated GHz Voltage Controlled OscillatorsU [4] http://eee.guc.edu.eg/CorsMain/Electronics/ELCT1003%20High%20Speed%20Electronic%20Circuits/schedule.html [5] http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-976-high-speed- communication-circuits-and-systems-spring-2003/lecture-notes/lec11.pdf [6] http://users.ece.gatech.edu/pallen/Academic Slide 69 [7] http://en.wikipedia.org/wiki/Voltage-controlled_oscillatorhttp://en.wikipedia.org/wiki/Voltage-controlled_oscillator [8]http://users.ece.gatech.edu/pallen/Academic/ECE_6440/Summer _2003/L130-VCO-I(2UP).pdf [9]http://trace.tennessee.edu/cgi/viewcontent.cgi?article=3582&con text=utk_gradthes [10]http://eee.guc.edu.eg/Courses/Electronics/ELCT703%20Microe lectronics/lectures_pdf/ch04-wavefunction_generators.pdf