DOCSLIB.ORG

Homebrew RF Siganl Generator Colpitts FET Oscillator

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Homebrew RF Siganl Generator Colpitts FET Oscillator HomeBrew RF Siganl Generator Colpitts FET Oscillator THE OSCILLATOR V1 is 9.0 Volts dc Purpose and Function Create a signal which can be amplified for use in an RF frequency Generator. Theory and Design I have lost the reference for this circuit o But very similar to the Colpitts in the 2007 ARRL1 C1-C2 and L1 form the Resonator circuit C3 provides coupling/ isolation to J1g Positive feedback is provide by the C2 J1d connection Many texts claim component selection is more black art than science using calculations 2 C1 –C2 were picked by available variable capacitors with typical ranges of 30- 110pf William R. Robinson Jr. p1of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator C3 was picked for best response Scope must be on 10x to keep from overloading William R. Robinson Jr. p2of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator Calculated Frequency C1, C2, and L1 determine the frequency 1 o Ceq 1 1 CC1 2 o C1,C2 represent a ganged variable capacitor =33 to110pf and c2=220 pF . When C1, C2 = 33pf Ceqmin = 1/(1/33 +1/33) Ceqmin = 16.5 pf . When C1, C2 = 68pf Ceqmax = 1/(1/68+1/68) Ceqmin = 34 pf 1 Resonate Frequency F 0 3 2 LC o L = 1 uH 1 o Fmax = 2 1.0uH *16.5pF o Fmax = 39.2 Mhz 1 o Fmin = 2 1.0uH *34pF o Fmin = 27.3 Mhz By similar means we calculate for their values of L1 o L1 = 10 uH . Fmax = 12.3 Mhz . Fmin = 8.63 Mhz o L1 = 100 uH . Fmax = 3.92 Mhz . Fmin = 2.73 Mhz Bias The FET forms a classic Source follower Because there is little or no current into the Gate o There is no voltage drop across R1 o Using Kirkoffs voltage law we get Vgs = - Vs = -Id Rs . (Rs = R2)Vgs Vgs Id Idss 1( 4 Vp William R. Robinson Jr. p3of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator . Idss and Vp are dependent on the FET and can be found in the data sheets Vp is between 8.0 and 0 Volts 5 I will use the average of 4.0 volts Idss is between 2.0 and 20.0 mA 5, I will use the average of 11.0 ma Vgs o Vgs = needs to be less Vp to keep Id less than Idss o Vgs and therefore Vs needs to be high enough to allow for sufficient swing of the output signal . I choose Vgs = -1.5 Volts for max swing 5.1 Now we can compute Id11 ma (1 0.4 o Id = 8.69 ma Rs = Vs/Id = 1.5V/7.78 = 192 ohms Vg = 0 by design Vd = 9V power supply NOTE: The R required to achieve Vgs = -1.5V in simulation was 3.3K ohms o So these calculations are off by an order of magnitude o The model FET is not an exact match o Looking at the Data sheet 5 we see a large variance for Vgs and Idss. This and Reference 6 show that it is very difficult to calculate the biases for and FET with any degree of certainty Amplitude I was not able to calculate the amplitude of the output. Harmonic Noise I was not able to calculate the Harmonic noise of the output. William R. Robinson Jr. p4of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator Simulation Simulations were over optimistic about magnitude and the ability to oscillate than a real circuit until the C1-C3 were made non- ideal by adding 10ohm series resistance, however this is then to pessimistic! Frequency C1, C2 = 33pf , L1 = 1uh => 36.8 Mhz Series1 550.000m Series2 500.000m 450.000m 400.000m 350.000m 300.000m 250.000m 200.000m 150.000m 100.000m 50.000m 0.0 -50.000m 0.0 10.000M 20.000M 30.000M 40.000M 50.000M 60.000M 70.000M 80.000M 90.000M 100.000M C1, C2 = 33pf , L1 = 1uh => 36.8 Mhz C1, C2 = 68pf , L1 = 1uh => 26.6 Mhz C1, C2 = 33pf , L1 = 10uh => 11.6 Mhz C1, C2 = 68pf , L1 = 10uh => 8.34 Mhz C1, C2 = 33pf , L1 = 100uh => 3.75 Mhz C1, C2 = 68pf , L1 = 100uh => 2.54 Mhz Bias Vd = 9.0 Vg = 0.0 Vs = 1.5 Amplitude C1, C2, C1 = 33pf , L1 = 1uh => 2.0 Vp-p C1, C2, C1 = 110pf , L1 = 1uh => 0.4 Vp-p C1, C2, C1 = 33pf , L1 = 10uh => 11.0 Vp-p (Clipping) C1, C2, C1 = 110pf , L1 = 10uh => 5.6 Vp-p C1, C2, C1 = 33pf , L1 = 100uh => 11.0 Vp-p (Clipping) William R. Robinson Jr. p5of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator C1, C2, C1 = 110pf , L1 = 100uh => 11.0 Vp-p (Clipping) Harmonic Noise The values below are Vdb to the nearest peak in the frequency domain (harmonic distortion) C1, C2, C1 = 33pf , L1 = 1uh => -24.5 db C1, C2, C1 = 110pf , L1 = 1uh => -29.5 db C1, C2, C1 = 33pf , L1 = 10uh => -25.8 db C1, C2, C1 = 110pf , L1 = 10uh => -22.6 db C1, C2, C1 = 33pf , L1 = 100uh => -28.0 db C1, C2, C1 = 110pf , L1 = 100uh => -28.0 db William R. Robinson Jr. p6of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator Real Circuit Frequency C1, C2 = 33pf , L1 = 1uh => 27.8 Mhz C1, C2 = 68pf , L1 = 1uh => 25.0 Mhz C1, C2 = 33pf , L1 = 10uh => 10.9 Mhz C1, C2 = 68pf , L1 = 10uh => 7.14 Mhz C1, C2 = 33pf , L1 = 100uh => 3.50 Mhz C1, C2 = 68pf , L1 = 100uh => 2.34 Mhz Bias I failed to measure these. Amplitude C1, C2, C1 = 33pf , L1 = 1uh => 3.0 Vp-p C1, C2, C1 = 110pf , L1 = 1uh => 4.0 Vp-p C1, C2, C1 = 33pf , L1 = 10uh => 8.0 Vp-p (Clipping) C1, C2, C1 = 110pf , L1 = 10uh => 9.0 Vp-p C1, C2, C1 = 33pf , L1 = 100uh => 9.0 Vp-p (Clipping) C1, C2, C1 = 110pf , L1 = 100uh => 10.0 Vp-p (Clipping) Harmonic Noise The values below are Vdb to the nearest peak in the frequency domain (harmonic distortion) C1, C2, C1 = 33pf , L1 = 1uh => -14 db C1, C2, C1 = 110pf , L1 = 1uh => -14 db C1, C2, C1 = 33pf , L1 = 10uh => -15 db C1, C2, C1 = 110pf , L1 = 10uh => -20 db C1, C2, C1 = 33pf , L1 = 100uh => -12 db C1, C2, C1 = 110pf , L1 = 100uh => -30 db William R. Robinson Jr. p7of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator C1, C2 = 68pf L1 = 1uh o Top trace is Vosc o Bottom trace is FFT(Vosc) C1, C2 = 68pf L1 = 10uh o Top trace is Vosc o Bottom trace is FFT(Vosc) William R. Robinson Jr. p8of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator William R. Robinson Jr. p9of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator C1, C2 = 68pf L1 = 100uh o Top trace is Vosc o Bottom trace is FFT(Vosc) C1, C2 = 33pf L1 = 1uh o Top trace is Vosc o Bottom trace is FFT(Vosc) William R. Robinson Jr. p10of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator William R. Robinson Jr. p11of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator C1, C2 = 33pf L1 = 10uh o Top trace is Vosc o Bottom trace is FFT(Vosc) C1, C2 = 33pf L1 = 100uh o Top trace is Vosc o Bottom trace is FFT(Vosc) William R. Robinson Jr. p12of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator William R. Robinson Jr. p13of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator Comparison Comparison is at best reasonable o I attribute the decreased frequency in simulation to the capacitance of the other components o I attribute the decreased frequency in the real circuit to the capacitance of the set up (used a prototype board) Real-Measured Simulation Calculated Frequency in Mhz C1, C2 = 33pf , L1 = 1uh 27.8 36.8 39.2 C1, C2 = 86pf , L1 = 1uh 25.0 26.6 27.3 C1, C2 = 33pf , L1 = 10uh 10.9 11.6 12.3 C1, C2 = 86pf , L1 = 10uh 7.14 8.34 8.63 C1, C2 = 33pf , L1 = 100uh 3.50 3.75 3.92 C1, C2 = 86pf , L1 = 100uh 2.34 2.54 2.73 Amplitude Vp-p C1, C2 = 33pf , L1 = 1uh 3.0 2.0 N/A C1, C2 = 86pf , L1 = 1uh 4.0 0.4 N/A C1, C2 = 33pf , L1 = 10uh 8.0 11.0 clipping N/A C1, C2 = 86pf , L1 = 10uh 9.0 8.5 N/A C1, C2 = 33pf , L1 = 100uh 9.0 11.0 clipping N/A C1, C2 = 86pf , L1 = 100uh 10.0 11.0 clipping N/A Harmonic Noise db C1, C2 = 33pf , L1 = 1uh -14 -24.8 N/A C1, C2 = 86pf , L1 = 1uh -14 -29.5 N/A C1, C2 = 33pf , L1 = 10uh -15 -25.8 N/A C1, C2 = 86pf , L1 = 10uh -20 -22.6 N/A C1, C2 = 33pf , L1 = 100uh -12 -28 N/A C1, C2 = 86pf , L1 = 100uh -30 -28 N/A Ve N/A 9.0 9.0 Vb N/A 0.0 0.0 Ve N/A 1.5 1.5 William R. Robinson Jr. p14of 28 2008 All rights Reserved HomeBrew RF Siganl Generator Colpitts FET Oscillator Conclusion This proved to my satisfaction that I wanted to use an FET in the Oscillator instead of a BJT because of the lower Harmonic Noise When I discovered that the frame of the gang capacitor was had to be isolated from ground ans that it suffered frequency changes even when touching an insulated knob I dropped the Colpitts in favor of the Hartley Oscillator References 1.
Load more

Recommended publications
  • Analysis of BJT Colpitts Oscillators - Empirical and Mathematical Methods for Predicting Behavior Nicholas Jon Stave Marquette University
    Marquette University e-Publications@Marquette Master's Theses (2009 -) Dissertations, Theses, and Professional Projects Analysis of BJT Colpitts Oscillators - Empirical and Mathematical Methods for Predicting Behavior Nicholas Jon Stave Marquette University Recommended Citation Stave, Nicholas Jon, "Analysis of BJT Colpitts sO cillators - Empirical and Mathematical Methods for Predicting Behavior" (2019). Master's Theses (2009 -). 554. https://epublications.marquette.edu/theses_open/554 ANALYSIS OF BJT COLPITTS OSCILLATORS – EMPIRICAL AND MATHEMATICAL METHODS FOR PREDICTING BEHAVIOR by Nicholas J. Stave, B.Sc. A Thesis submitted to the Faculty of the Graduate School, Marquette University, in Partial Fulfillment of the Requirements for the Degree of Master of Science Milwaukee, Wisconsin August 2019 ABSTRACT ANALYSIS OF BJT COLPITTS OSCILLATORS – EMPIRICAL AND MATHEMATICAL METHODS FOR PREDICTING BEHAVIOR Nicholas J. Stave, B.Sc. Marquette University, 2019 Oscillator circuits perform two fundamental roles in wireless communication – the local oscillator for frequency shifting and the voltage-controlled oscillator for modulation and detection. The Colpitts oscillator is a common topology used for these applications. Because the oscillator must function as a component of a larger system, the ability to predict and control its output characteristics is necessary. Textbooks treating the circuit often omit analysis of output voltage amplitude and output resistance and the literature on the topic often focuses on gigahertz-frequency chip-based applications. Without extensive component and parasitics information, it is often difficult to make simulation software predictions agree with experimental oscillator results. The oscillator studied in this thesis is the bipolar junction Colpitts oscillator in the common-base configuration and the analysis is primarily experimental. The characteristics considered are output voltage amplitude, output resistance, and sinusoidal purity of the waveform.
    [Show full text]
  • Lec#12: Sine Wave Oscillators
    Integrated Technical Education Cluster Banna - At AlAmeeria ‎ © Ahmad El J-601-1448 Electronic Principals Lecture #12 Sine wave oscillators Instructor: Dr. Ahmad El-Banna 2015 January Banna Agenda - © Ahmad El Introduction Feedback Oscillators Oscillators with RC Feedback Circuits 1448 Lec#12 , Jan, 2015 Oscillators with LC Feedback Circuits - 601 - J Crystal-Controlled Oscillators 2 INTRODUCTION 3 J-601-1448 , Lec#12 , Jan 2015 © Ahmad El-Banna Banna Introduction - • An oscillator is a circuit that produces a periodic waveform on its output with only the dc supply voltage as an input. © Ahmad El • The output voltage can be either sinusoidal or non sinusoidal, depending on the type of oscillator. • Two major classifications for oscillators are feedback oscillators and relaxation oscillators. o an oscillator converts electrical energy from the dc power supply to periodic waveforms. 1448 Lec#12 , Jan, 2015 - 601 - J 4 FEEDBACK OSCILLATORS FEEDBACK 5 J-601-1448 , Lec#12 , Jan 2015 © Ahmad El-Banna Banna Positive feedback - • Positive feedback is characterized by the condition wherein a portion of the output voltage of an amplifier is fed © Ahmad El back to the input with no net phase shift, resulting in a reinforcement of the output signal. Basic elements of a feedback oscillator. 1448 Lec#12 , Jan, 2015 - 601 - J 6 Banna Conditions for Oscillation - • Two conditions: © Ahmad El 1. The phase shift around the feedback loop must be effectively 0°. 2. The voltage gain, Acl around the closed feedback loop (loop gain) must equal 1 (unity). 1448 Lec#12 , Jan, 2015 - 601 - J 7 Banna Start-Up Conditions - • For oscillation to begin, the voltage gain around the positive feedback loop must be greater than 1 so that the amplitude of the output can build up to a desired level.
    [Show full text]
  • Oscillator Circuits
    Oscillator Circuits 1 II. Oscillator Operation For self-sustaining oscillations: • the feedback signal must positive • the overall gain must be equal to one (unity gain) 2 If the feedback signal is not positive or the gain is less than one, then the oscillations will dampen out. If the overall gain is greater than one, then the oscillator will eventually saturate. 3 Types of Oscillator Circuits A. Phase-Shift Oscillator B. Wien Bridge Oscillator C. Tuned Oscillator Circuits D. Crystal Oscillators E. Unijunction Oscillator 4 A. Phase-Shift Oscillator 1 Frequency of the oscillator: f0 = (the frequency where the phase shift is 180º) 2πRC 6 Feedback gain β = 1/[1 – 5α2 –j (6α – α3) ] where α = 1/(2πfRC) Feedback gain at the frequency of the oscillator β = 1 / 29 The amplifier must supply enough gain to compensate for losses. The overall gain must be unity. Thus the gain of the amplifier stage must be greater than 1/β, i.e. A > 29 The RC networks provide the necessary phase shift for a positive feedback. They also determine the frequency of oscillation. 5 Example of a Phase-Shift Oscillator FET Phase-Shift Oscillator 6 Example 1 7 BJT Phase-Shift Oscillator R′ = R − hie RC R h fe > 23 + 29 + 4 R RC 8 Phase-shift oscillator using op-amp 9 B. Wien Bridge Oscillator Vi Vd −Vb Z2 R4 1 1 β = = = − = − R3 R1 C2 V V Z + Z R + R Z R β = 0 ⇒ = + o a 1 2 3 4 1 + 1 3 + 1 R4 R2 C1 Z2 R4 Z2 Z1 , i.e., should have zero phase at the oscillation frequency When R1 = R2 = R and C1 = C2 = C then Z + Z Z 1 2 2 1 R 1 f = , and 3 ≥ 2 So frequency of oscillation is f = 0 0 2πRC R4 2π ()R1C1R2C2 10 Example 2 Calculate the resonant frequency of the Wien bridge oscillator shown above 1 1 f0 = = = 3120.7 Hz 2πRC 2 π(51×103 )(1×10−9 ) 11 C.
    [Show full text]
  • A 20 Mv Colpitts Oscillator Powered by a Thermoelectric Generator
    A 20 mV Colpitts Oscillator powered by a thermoelectric generator Fernando Rangel de Sousa∗, Marcio Bender Machado∗†, Carlos Galup-Montoro ∗ ∗Integrated Circuits Laboratory-LCI Federal University of Santa Catarina-UFSC Florianopolis-SC, Brazil, Tel.: +55-48-3721-7640 Email:[email protected] † Sul-Rio-Grandense Federal Institute Charqueadas-RS, Brazil Email:[email protected] Abstract—In this paper, we present a MOSFET-based Colpitts of around 13 mV , only seven milivolts far from the voltage oscillator based on a “zero-threshold” transistor operating at a supply value for which the circuit sustained oscillations at 130 supply voltage below 20 mV. The circuit was carefully analyzed mV(peak-to-peak)/97 kHz. Moreover, the circuit was powered and expressions relating the start-up conditions and the voltage supply, as well as the oscillation frequency were developed. by a thermoelectric generator which supplied a DC voltage of Measurement results obtained on a discrete prototype confirmed around 22 mV when it was installed on the arm of a person the low-voltage operation of the oscillator, which sustained in a 24oC room. oscillations of 130 mV (peak-to-peak) at 97 kHz when the voltage supply was 19.8 mV. The circuit was also powered from a II. COLPITTS OSCILLATOR thermoelectric generator (TEG) connected to a persons arm in a room with temperature of 24oC room. Under these conditions, A Colpitts oscillator can be broken in two main blocks : i) the TEG supplied 22 mV and the circuit operated as expected. a potentially unstable one-port and ii) a load network, as it is shown in Fig.
    [Show full text]
  • A Study of Phase Noise in Colpitts and LC-Tank CMOS Oscillators
    Downloaded from orbit.dtu.dk on: Oct 02, 2021 A study of phase noise in colpitts and LC-tank CMOS oscillators Andreani, Pietro; Wang, Xiaoyan; Vandi, Luca; Fard, A. Published in: I E E E Journal of Solid State Circuits Link to article, DOI: 10.1109/JSSC.2005.845991 Publication date: 2005 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Andreani, P., Wang, X., Vandi, L., & Fard, A. (2005). A study of phase noise in colpitts and LC-tank CMOS oscillators. I E E E Journal of Solid State Circuits, 40(5), 1107-1118. https://doi.org/10.1109/JSSC.2005.845991 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 40, NO. 5, MAY 2005 1107 A Study of Phase Noise in Colpitts and LC-Tank CMOS Oscillators Pietro Andreani, Member, IEEE, Xiaoyan Wang, Luca Vandi, and Ali Fard Abstract—This paper presents a study of phase noise in CMOS phase noise itself.
    [Show full text]
  • Oscilators Simplified
    SIMPLIFIED WITH 61 PROJECTS DELTON T. HORN SIMPLIFIED WITH 61 PROJECTS DELTON T. HORN TAB BOOKS Inc. Blue Ridge Summit. PA 172 14 FIRST EDITION FIRST PRINTING Copyright O 1987 by TAB BOOKS Inc. Printed in the United States of America Reproduction or publication of the content in any manner, without express permission of the publisher, is prohibited. No liability is assumed with respect to the use of the information herein. Library of Cangress Cataloging in Publication Data Horn, Delton T. Oscillators simplified, wtth 61 projects. Includes index. 1. Oscillators, Electric. 2, Electronic circuits. I. Title. TK7872.07H67 1987 621.381 5'33 87-13882 ISBN 0-8306-03751 ISBN 0-830628754 (pbk.) Questions regarding the content of this book should be addressed to: Reader Inquiry Branch Editorial Department TAB BOOKS Inc. P.O. Box 40 Blue Ridge Summit, PA 17214 Contents Introduction vii List of Projects viii 1 Oscillators and Signal Generators 1 What Is an Oscillator? - Waveforms - Signal Generators - Relaxatton Oscillators-Feedback Oscillators-Resonance- Applications--Test Equipment 2 Sine Wave Oscillators 32 LC Parallel Resonant Tanks-The Hartfey Oscillator-The Coipltts Oscillator-The Armstrong Oscillator-The TITO Oscillator-The Crystal Oscillator 3 Other Transistor-Based Signal Generators 62 Triangle Wave Generators-Rectangle Wave Generators- Sawtooth Wave Generators-Unusual Waveform Generators 4 UJTS 81 How a UJT Works-The Basic UJT Relaxation Oscillator-Typical Design Exampl&wtooth Wave Generators-Unusual Wave- form Generator 5 Op Amp Circuits
    [Show full text]
  • W9HE Amplifiers
    Introduction Rather than try to give you the material so that you can answer the questions from “first principles," I will provide enough information that you can recognize the correct answer to each question. Chapter 6 Notes In no particular order, the necessary “nuggets:” 1. Junction transistors are current controlled and therefore have relatively low input impedance. Field effect devices, including vacuum tubes, are voltage controlled and therefore have relatively high input impedance. Vacuum tubes are implicitly diodes as well. Transistor input and output elements can be reversed and the device would operate somewhat. 2. See attached amplifier circuits sheet. Another phrase for “common word" amplifer is “grounded word" amplifer. The key is determining which lead is at signal ground level. The lead may not be at DC ground for bias reasons. If a lead is connected to the power supply via a capacitor in parallel with a resistor then that lead is at signal ground. 3. See attached oscillators circuits sheet. Oscillators can be built using any type of amplifier. All that is required is a gain greater than 1 with positive feed back. The major classes of oscillators are named according to the method of providing that feedback. If the feedback circuit is a divided capacitor, then the oscillator is a Colpitts oscillator. The memory key is C for capacitance. If the feedback circuit is a divided inductor, then the oscillator is a Hartley oscillator. The memory key is H for Henries of inductance. If the feedback circuit is a crystal, then the oscillator os a Pierce oscillator.
    [Show full text]
  • 5 Frequency Measurement and Manipulation
    EE3.02/A04 Instrumentation 5. Frequency generation and measurement 5 Frequency Measurement and manipulation By the end of this section you will be able to: • Describe and quantify the operation of frequency measuring instruments. • Describe a phase locked loop, and its principles of operation. • Compute the centre frequency, capture and tracking range of a phase locked loop • Describe several methods for frequency multiplication. 5.1 Frequency as a state variable The generation and measurement of frequency is related to the ancient problem of determining time by building clocks. The importance of clocks to navigation on earth, on the sea and recently in air and in space means that enormous resources have been allocated over the centuries in resolving it. In our days time measurement is by far the most exact branch of metrology, and time is known (at least to the Standards organisations) with an estimated error of 1 part in 1014. Techniques to further improve time determination by another 2 orders of magnitude are known and are being implemented. Suffice it to say that the theoretical accuracy of time determined by GPS is better than 1 part in 108 which corresponds to an uncertainty of a fraction of a second /year. It is counter intuitive that the frequency of a signal can be considered as a state variable, a quantity which not only can be measured, but also can be manipulated. Figure 5-1: Historical development of clock accuracy (after HP application note 1289: The science of timekeeping) CP IC-EEE Autumn 2007 1 EE3.02/A04 Instrumentation 5.
    [Show full text]
  • Electronic PRINCIPLES
    MALVINO & BATES Electronic PRINCIPLES SEVENTH EDITION Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 2323 Oscillators Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Topics Covered in Chapter 23 • Theory of sinusoidal oscillation • The Wien-bridge oscillator • Other RC oscillators • The Colpitts oscillator • Other LC oscillators Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Topics Covered in Chapter 23 (Continued) • Quartz crystals • The 555 timer • Astable operation of the 555 timer • 555 circuits • The phase-locked loop • Function generator ICs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinusoidal oscillation requires both the correct phase and loop gain. φφφ = 0° = positive. feedback A v V . out B AVB = 1 AVB < 1 AVB > 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinusoidal oscillators • The starting signal is thermal noise. • AVB > 1 at startup (A VB is the loop gain). • The feedback network determines B and the phase of the feedback. • Only one frequency arrives at the input as an in-phase signal (positive feedback). • Either A V or B is eventually decreased so that A VB = 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Wien-bridge oscillator • Used for low to moderate frequencies (5 Hz to 1 MHz) • Produces an almost perfect sine wave • Nonlinear resistance is used to decrease loop gain to 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Wien-Bridge oscillator circuit .. vout 1 . fr = RL 2πππRC 2R ’ R’ Tungsten lamp Resistance of lamp C R increases until .
    [Show full text]
  • CHAPTER Feedback Amplifier & Oscillators
    Analog Circuits Day-12 Oscillators Introduction to Feedback: The phenomenon of feeding a portion of the output signal back to the input circuit is known as feedback. The effect results in a dependence between the output and the input and an effective control can be obtained in the working of the circuit. Feedback is of two types. • Negative Feedback • Positive Feedback Negative or Degenerate feedback: • In negative feedback, the feedback energy (voltage or current), is out of phase with the input signal and thus opposes it. • Negative feedback reduces gain of the amplifier. It also reduce distortion, noise and instability. • This feedback increases bandwidth and improves input and output impedances. • Due to these advantages, the negative feedback is frequently used in amplifiers. NegativeFeedback Positive or regenerate feedback: • In positive feedback, the feedback energy (voltage or currents), is in phase with the input signal and thus aids it. Positive feedback increases gain of the amplifier also increases distortion, noise and instability. • Because of these disadvantages, positive feedback is seldom employed in amplifiers. But the positive feedback is used in oscillators. Positive Feedback In the above figure, the gain of the amplifier is represented as A. The gain of the amplifier is the ratio of output voltage Vo to the input voltage Vi. The feedback network extracts a voltage Vf = β Vo from the output Vo of the amplifier. This voltage is subtracted for negative feedback, from the signal voltage Vs. Now, Vi=Vs + Vf =Vs+βVo The quantity β = Vf/Vo is called as feedback ratio or feedback fraction. The output Vo must be equal to the input voltage (Vs + βVo) multiplied by the gain A of the amplifier.
    [Show full text]
  • Chapter.8: Oscillators
    www.getmyuni.com Chapter.8: Oscillators • Objectives: – To understand • The basic operation of an Oscillator • the working of low frequency oscillators – RC phase shift oscillator – Wien bridge Oscillator • the working of tuned oscillator – Colpitt’s Oscillator, Hartley Oscillator – Crystal Oscillator • the working of UJT Oscillator Basic operation of an Oscillator • An amplifier with positive feedback results in oscillations if the following conditions are satisfied: – The loop gain ( product of the gain of the amplifier and the gain of the feedback network) is unity – The total phase shift in the loop is 0 • If the output signal is sinusoidal, such a circuit is referred to as sinusoidal oscillator. 1 www.getmyuni.com When the switch at the amplifier input is open, there are no oscillations. Imagine that a voltage Vi is fed to the circuit and the switch is closed. This results in Vo = AV Vi and Vo = Vf is fed back to the circuit. If we make Vf = Vi, then even if we remove the input voltage to the circuit, the output continues to exist. Vo = AV Vi Vo = Vf AV Vi = Vf If Vf has to be same as Vi, then from the above equation, it is clear that, AV =1. Thus in the above block diagram, by closing the switch and removing the input, we are able to get the oscillations at the output if AV =1, where AV is called the Loop gain. Positive feedback refers to the fact that the fed back signal is in phase with the input signal. This means that the signal experiences 0 phase shift while traveling in the loop.
    [Show full text]
  • Lab 4. Crystal Oscillator
    Lab 4. Crystal Oscillator Modeling the Piezo Electric Quartz Crystal Most oscillators employed for RF and microwave applications use a resonator to set the frequency of oscillation. It is desirable to use a resonator with the highest possible Q (lowest possible loss). Use of a high Q resonator generally guarantees that the phase of the loop gain will exhibit rapid variation near the frequency where it passes through 0. This means that the frequency of oscillation will be tightly constrained such that environmental changes that tend to alter the phase of the loop gain will not cause significant frequency shifts. In general, both the long-term and short-term stability of the oscillator is improved when the resonator has high Q. Resonators constructed using lumped inductors and capacitors typically have Q’s on the order of 100 or so. This is sufficient for some applications, but a much higher Q can be obtained if a quartz crystal is used as an element of the feedback network. To the circuit engineer the quartz crystal is a two-terminal passive network. The device is an electro- mechanical transducer which converts electric energy to mechanical energy and vice versa. The unit usually consists of a small quartz wafer sandwiched between two metal electrodes. In practice a quartz crystal will exhibit many resonance frequencies. It can be modeled electrically by the equivalent circuit shown in Figure 1.1 at frequencies near one set of resonance frequencies fs and fp. The capacitance Co is due to the parallel plate capacitor formed by the metal contacts that are used to hold the quartz wafer.
    [Show full text]