Oscillator, and the colpitts oscillator design example in these lecture notes are design. The rf choke is intended to present a high impedance to the node between the two backtoback varactor diodes so that the oscillator signal does not leak out the tuning port. Homebrew rf siganl generator colpitts fet oscillator william r. Lc oscillators can be designed by using different methods. Bjt oscillator design say we desire an oscillation amplitude of v0 100mv at. Design and simulation of rf cmos oscillators in advanced design system ads by.
Colpitts, is one of a number of designs for lc oscillators, electronic oscillators that use a combination of inductors l and capacitors c to produce an oscillation at a certain frequency. The designguide is applicable to any oscillator, but is especially useful for rf board. Final oscillator common base colpitts oscillator but sometimes simply called a reflection oscillator with transmission line in base providing feedback. Tuned oscillators radio frequency oscillators 17 tuned oscillator is a circuit that generates a radio frequency output by using lc tuned resonant circuit. Ese319 introduction to microelectronics 2008 kenneth r. Colpitts family if we remove the explicit ground connection on the oscillator, we have the template for a generic oscillator. A valuable reference for practising rf and microwave designers and engineers, rf and microwave transistor oscillator design is also useful for lecturers, advanced students and research and design. In this tutorial you will build and test a high frequency colpitts oscillator using a parallel resonant lc circuit. This tutorial is a quick guide for new ads users to design cmos rf oscillators and do the post processing on their simulation data in ads. Lc tank circuits and the colpitts oscillator youtube. Among these two, the frequently used design is colpitts oscillator designed by and named after an american engineer edwin h colpitts in 1918. Resonator enables slope of the admittance to be set. In this tutorial, we are going to explain colpitts oscillator circuit, basics in brief. It is a variation of the colpitts oscillator and uses the crystal in its series resonant mode to create the positive feedback from the transistors collector to the base.
Apr 09, 2017 in this video we discuss the basic physics of a simple lc tank circuit and the role it plays in the colpitts oscillator. Although both these oscillators oscillator use an lc tuned tank circuit to control the oscillator frequency, the hartley design can be recognised by its use of a tapped inductor l1 and l2 in fig. Before i dropped the colpitts oscillator i did addition design on the other stages of a rf frequency generator. Oscillators theory and practice ed messer ki4nna october 2009 rev b. Because of high frequencies, small inductance can be used for the radio frequency of oscillation. The frequency of oscillation can be calculated in the same way as any parallel resonant circuit, using. Because of high frequencies, small inductance can be. Colpitts the resonant circuit is an inductor and two capacitors.
A colpitts oscillator design technique using sparameters. This manuals provides reference information on the use of the oscillator designguide. Oscillator design for vhfuhf phase noise in oscillators, along with frequency stability and efficiency, is an important parameter in oscillator design. Voltage controlled oscillators are electronic circuits designed to produce a periodic sinusoidal signal whose frequency is dependent on the voltage applied at the input 1. Aug 21, 2015 a colpitts oscillator consists of two capacitive reactances and one inductive reactance in the tank circuit or feedback network. R represents total resistance in collector circuit, i. In this video we discuss the basic physics of a simple lc tank circuit and the role it plays in the colpitts oscillator. The open loop gain will be set by the gm of the device, by rp and the capacitive divider. The colpitts, hartly and clapp circuits are examples of negative resistance oscillators shown here using bipolars as the active devices. Lopresti 2006 updated 03nov08 krl 1 colpitts oscillator basic positive feedback oscillator the colpitts lc oscillator circuit openloop analysis closedloop analysis root locus stability limit colpitts design. With the colpitts oscillator the connection between these two capacitors is used as the centre tap for the circuit. Hartley the resonant circuit is a tapped inductor or two inductors and one capacitor.
Figure 1 shows a typical colpitts oscillator with a tank circuit in which an inductor l is connected in parallel to the serial combination of capacitors c 1 and c 2 shown by the red enclosure. In particular, he discusses the effect of largesignal transconductance big gm on the colpitts oscillator and sums up nicely why you get distortion with large signals because the resistance to the fundamental frequency of the. Colpitts used in oscore biasing point, which is shown in the oscore subcircuit which you can see from. Rf and microwave oscillator design using phemt transistor. In our previous articles, we explain about oscillator circuit and hartley oscillator in detail. To expound on various oscillator architectures for mw and rf frequencies. A colpitts oscillator design technique using sparameters 1986 timothy k. Since the colpitts oscillator is a type of tank circuit lc. Rf radio frequency snr signaltonoise ratio soi silicon on insulator. The main objective of this book is to present all relevant information necessary for rf and microwave transistor oscillator design including wellknown and new theoretical approaches and practical circuit schematics and designs, as well as to suggest optimum design approaches, which combine effectively analytic calculations and computeraided. Im trying to build a common base colpitts oscillator for a project in my university. The colpitts oscillator is a type of high frequency oscillator consisting of a lc tank within the feedback loop of a classa commonemitter bipolar junction transistor bjt circuit.
It is another type of sinusoidal lc oscillator and is basically a harmonic oscillator, which has a lot of applications. To design and develop hartley, colpitts and differential. Positive feedback amplifiers oscillators lc and crystal. Colpitts oscillator simulated with ansys rf option shows a variety of pertinent results such as phase noise and transient response.
To design a circuit that detects and counts the zero. Colpitts oscillator basic schematic emphasizing feedback emphasizing loop gain assumptions. In particular, he discusses the effect of largesignal transconductance big gm on the colpitts oscillator and sums up nicely why you get distortion with large signals because the resistance to the fundamental frequency of the sine wave is greater than its harmonics big gm is lower for the fundamental frequency and you end up with a wave. There is a reason for everything the reason may not be obvious first presented at. How to design rf circuits oscillators andrew dearn introduction oscillators can generally be categorised as either amplifiers with positive feedback satisfying the wellknown barkhausen criteria ref. Leads to lower phase noise and overall improved oscillator performance. Niknejad university of california, berkeley eecs 142 lecture 22 p. Rf oscillator simulation and analysis in multisim 12 weijie tang. In many ways, the colpitts oscillator is the exact opposite of the hartley oscillator we looked at in the previous tutorial. Rf and microwave oscillator design using phemt transistor bhavana benakaprasad, salah sharabi, and dr. Lc tuned tank circuit to control the oscillator frequency, the hartley design can be recognised by. Common base colpitts oscillator all about circuits.
How to design rf circuits oscillators andrew dearn. A harmonicoscillator design methodology based on describing functions jesper bank. Pdf design and simulation of high frequency colpitts oscillator. Tunedinput and tunedoutput oscillator tunedoutput tunedinput feedback coupling ci rf. This major qualifying project involves the design of a voltage controlled oscillator vco for radio frequency rf applications. Colpitts oscillator in this configuration the active device is in a common base configuration. By watching this video, you will learn the following topics. Most of the rf circuits we have discussed to date are based on crystal oscillators. Colpitts oscillator is generally used in rf applications and the typical operating range is 20khz to 300mhz.
The tank circuit usually consists of a pair of capacitors in series joining to an inductance coil. The main use of colpitts oscillator is in mobile or other radio frequency controlled communications devices. Common base colpitts oscillator but sometimes simply called a reflection oscillator with transmission line in base providing feedback. This colpittscrystal oscillator is ideal for low frequency crystal oscillator circuits. Tuned oscillator circuits tuned oscillators use a parallel lc resonant circuit lc tank to provide the oscillations. Using the microwave chaotic signals generated from colpitts oscillator, the advantage of the direct chaotic radar is, by varying the operating condition, the dynamics in a colpitts oscillator can. Rf oscosc ato sillators practical considerations example 12. The well known lc oscillators are hartley oscillator and colpitts oscillator. The design of vhfuhf oscillators has been described in many books and journals with most of the emphasis on frequency stability and to some smaller part on outputefficiency. An optimized grounded base oscillator design for vhfuhf. In this video, the design and working of colpitts oscillator have been explained with derivation and example. Pdf rf and microwave oscillator design using phemt. When the crystals internal l and c have equal reactances, they cancel, leaving only.
Schematic for smallsignal oscillator design figure 4. Laker updated 10nov09 krl 1 colpitts oscillator basic positive feedback oscillator the colpitts lc oscillator circuit openloop analysis closedloop analysis root locus stability limit colpitts design. You must isolate the tuning port from the resonator. A colpitts oscillator, invented in 1918 by american engineer edwin h. The circuit of colpitts oscillator is similar to that of hartley oscillator except the difference that rather than making tapped connection at the inductor junctions, it is made at the capacitor junction. Similarly, change the values of capacitors and inductor in the frequency selective filter. Frequency selective networks for typical rf and microwave oscillators, the following oscillator types are commonly used. In this project, you will build and analyze a colpitts oscillator with an lc tank circuit. To design an oscillator, we must have knowledge of the properties and the operation of oscillators. The colpitts oscillator is a particularly good circuit for producing fairly low distortion sine wave signals in the rf range, 30khz to 30mhz. May 25, 2019 colpitts oscillator is a type of lc oscillator which falls under the category of harmonic oscillator and was invented by edwin colpitts in 1918. This is a short look at how transistors can be used to create colpitts oscillators. Khaled elgaid electronics and nanoscale engineering, school of engineering, university of glasgow, glasgow g12 8lt, united kingdom abstractthis paper presents a systematic approach to designing. The colpitts configuration can be recognized by its use of a tapped capacitor divider c 1 and c 2 in figure 1.
In this research, a colpitts oscillator is comprised from a bipolar junction transistor bjt amplifier with lc tank. First, the colpitts oscillator may be redrawn as an lc amplifier with positive feedback figure 3. Colpitts oscillators are somewhat similar to the shunt fed hartley circuit except the colpitts oscillator, instead of having a tapped inductor, utilises two series capacitors in its lc circuit. Rs is needed to deq the rfc in case it resonates with a diode. In colpitts oscillator, the capacitive voltage divider setup in the tank circuit works as the feed back source and this arrangement gives better frequency stability when compared to the hartley oscillator which uses an inductive voltage.
Homebrew rf siganl generator colpitts fet oscillator. Just like the hartley oscillator, the tuned tank circuit consists of an lc resonance subcircuit connected between the collector and the base of a single stage. Colpitts oscillator is a type of lc oscillator which falls under the category of harmonic oscillator and was invented by edwin colpitts in 1918. Frequency sensitivity and drift in short and long terms. Experimental methods in rf design wes hayward et al first edition p 2. This oscillator uses an lc resonator to set the oscillation frequency and a capacitive. Temperature bias and decoupling circuitry with a of 100. Just like the hartley oscillator, the tuned tank circuit consists of an lc resonance subcircuit connected between the collector and the base of a single stage transistor amplifier producing a sinusoidal output waveform.
Equivalent circuit of the colpitts oscillator 1 2 1 2 1 c c c c l wo complete circuit for a colpitts oscillator. In this colpitts oscillator circuit, the feedback factor. Oct 24, 2018 in this video, the design and working of colpitts oscillator have been explained with derivation and example. Colpitts,1is one of a number of designs for lc oscillators, electronic oscillatorsthat use a combination of inductorsl and capacitorsc to produce an oscillation at a certain frequency. Crystals provide excellent stability in an oscillator circuit, but are limited to a single operating frequency or a limited frequency set. Measured result of colpitts oscillator rf and microwave oscillator design using phemt transistor b.
Various models such as, common source and common gate configuration in negativeresistance oscillators, common source series. Build your own transistor radios and ive come to the section where ron is analyzing the oscillator circuits used in his designs. Colpitts oscillator circuit diagram working and applications. The following is more of the details of the analysis and design of the colpitts. The most common type of crystal oscillator is the pierce circuit shown in figure 4. For typical rf and microwave oscillators, the following oscillator. Colpitts oscillator is another type of oscillator design used to produce an oscillation at a certain frequency. This paper presents a systematic approach to designing negativeresistance and colpitts oscillators using phemt transistor. Design and simulation of rf cmos oscillators in advanced. Oscillator, and the colpitts oscillator design example in these lecture notes are design examples which follows this process. Due to the difficulties in a smooth variation of inductor and capacitor, the colpitts oscillator is mainly used for fixed frequency generation. It can be shown that the colpitts family of oscillator never squegg. Wideband voltage controlled oscillator vco for rf applications. Oscillator is an amplifier with the positive feedback and it converts dc input signal into ac output waveform with certain variable frequency drive and certain shape of output waveform like sine wave or square wave, etc by using the positive feedback instead of input signal.
In highfrequency oscillation, colpitts oscillator is an excellent choice. The primary objective of this tutorial lesson is to underline the challenges of analyzing oscillator circuits. Ive tried various times to build the actual circuit, but the oscilloscope isnt reading anything from my circuit. Since the colpitts oscillator is a type of tank circuit lc combination and works on feedback of energy, the. Alternatively, the colpitts oscillator can be analyzed in a simpler but less accurate manner, which provides a set of design equations that are clearer, more insightful, and useful for firstorder oscillator design. Tuned oscillator is a circuit that generates a radio frequency output by using lc tuned resonant circuit.
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