Hartley oscillator ppt

The Web This site. The Hartley Oscillator is a particularly useful circuit for producing good quality sine wave signals in the RF range, 30kHz to 30MHz although at the higher limits of this range and above, The Colpitts oscillator is usually preferred. 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. The frequency of oscillation can be calculated in the same way as any parallel resonant circuit, using:.

This basic formula is adequate where the mutual inductance between L 1 and L 2 is negligible, but needs to be modified when the mutual inductance between L 1 and L 2 is considerable. Mutual inductance is an additional effective amount of inductance caused by the magnetic field created around one inductor or one part of a tapped inductor inducing a current into the other inductor. When both inductors are wound on a common core, as shown in Fig.

The actual value of M depends on how effectively the two inductors are magnetically coupled, which among other factors depends on the spacing between the inductors, the number of turns on each inductor, the dimensions of each coil and the material of the common core. With separate fixed inductors, as shown in Fig. In practice the small values of inductance of the inductors needed at RF create very little magnetic field outside the component, and only when mounted within a couple of millimetres of each other is the mutual inductance effect noticeable, as shown in Fig.

The amount of mutual inductance in a circuit using two small fixed inductors such as the circuit featured in Oscillators module 2. Whether the mutual inductance between small inductors of just a few micro Henrys add or subtract from the calculated oscillator frequency of a RF Hartley oscillator, this will generally only change the operating frequency by an amount similar to that which may be caused by the normal component value variation due to the tolerances of the oscillator components.

Calculating a theoretical value for k involves some quite complex math due to the number of factors affecting the mutual coupling, and the process is often reduced to deciding whether there is little mutual coupling, so that less than half of the magnetic flux produced by one coil affects the other coil. If so, then k is assumed to have a value less than 0.

Module 2.1

In practice the core shared by such a tapped inductor working at RF frequencies will often be found to be a variable type as shown in Fig. This gives the amplifier a high gain only at the resonant frequency Method 2 in Introduction to Oscillators.

This particular version of the Hartley circuit uses a common base amplifier, the base of TR1 being connected directly to 0V as far as AC the signal is concerned by C1. In this mode the output voltage waveform at the collector, and the input signal at the emitter are in phase. This ensures that the fraction of the output signal fed back from the tuned circuit collector load to the emitter via the capacitor C2 provides the necessary positive feedback.

C2 also forms a long time constant with the emitter resistor R3 to provide an average DC voltage level proportional to the amplitude of the feedback signal at the emitter of Tr1.

This is used to automatically control the gain of the amplifier to give the necessary closed loop gain of 1. The emitter resistor R3 is not decoupled because the emitter terminal is used as the amplifier input. The base being connected to ground via C1, which will have a very low reactance at the oscillator frequency.

Its operation is supposed to be rather like a water tank or cistern that can supply a continuous flow of water from an intermittently flowing external supply.

hartley oscillator ppt

The tank circuit in the oscillator contains high values of circulating current topped up regularly by smaller amounts of current from the amplifier. Because most of the current flowing in the oscillator is flowing just around the resonant tank circuit rather than though the amplifier section of the oscillator, LC oscillators generally produce a sine wave with very little amplifier sourced distortion.

Another feature of the tank circuit is to provide the correct amount of positive feedback to keep the oscillator running. This is done by dividing the inductive branch of the circuit into two sections, each having a different value, the inductor therefore works in a similar manner to an autotransformer, the ratio of the two windings providing the appropriate amount of signal to be fed back to the input of the amplifier.

Because in Fig. Therefore waveform X across L1, and waveform Y across the whole circuit are in phase. As a common base amplifier is being used, the collector and emitter signals are also in phase, and the tank circuit is therefore providing positive feedback.

In other Hartley designs, using common emitter amplifiers for example, similar tank circuits are used but with different connections, so that the feedback signal is always in phase with the input signal, therefore providing the necessary positive feedback. It is common in LC sine wave oscillators to use automatic class C bias.

In class C the bias voltage, that is the base voltage of the transistor is more negative than the emitter voltage, making V be negative so that the average centre voltage of the input wave is located on the negative portion of the V be axis of the characteristic curve shown in Fig.Hartley oscillator was invented in by the american engineer Ralph Hartley while he was working for the Western Electric company. The original design was tube based and he got a patent for it in the year The inductors are connected in series and the capacitor is connected across them in parallel.

Hartley oscillators are commonly used in radio frequency RF oscillator applications and the recommended frequency range is from 20KHz to 30MHz. Hartley oscillators can be operated at frequencies lower than 20KHz, but for lower frequencies the inductor value need to be high and it has a practical limit. In the circuit diagram resistors R1 and R2 give a potential divider bias for the transistor Q1. Re is the emitter resistor, whose job is to provide thermal stability for the transistor.

Ce is the emitter by pass capacitors, which by-passes the amplified AC signals. If the emitter by-pass capacitor not there, the amplified ac voltages will drop across Re and it will get added on to the base-emitter voltage of Q1 and will disrupt the biasing conditions. The task of a DC decoupling capacitor is to prevent DC voltages from reaching the succeeding stage.

Inductor L1, L2 and capacitor C1 forms the tank circuit. When the power supply is switched ON the transistor starts conducting and the collector current increases.

This charging and discharging creates a series of damped oscillations in the tank circuit and it is the key. The output voltage of the transistor voltage across collector and emitter will be in phase with the voltage across inductor L1.

The typical arrangement of a Hartley oscillator using opamp in shown in the figure above. In transistorized versions the gain will be equal to or faintly greater than the ratio of L1 and L2. In opamp version the gain is less dependent on the tank circuit elements and so it provides better frequency stability. Very good Circuit. I got it this working with a 9V cell and it produced a pretty clean sine wave of about 1 MHz that could be seen on a scope, and heard by placing an AM radio next to the circuit.

C out, C in, Ce —. Author jojo. FM Radio jammer January 13, Sweep Frequency Generator March 28, Signal Generators February 22, Nick 3 years ago. Rahul Krishnan 4 years ago. In answer are not current pls give the correct value…. Richelle 5 years ago. What are some interfaces of Hartley?

I need theory for single tuned voltage amplifier. Submit Type above and press Enter to search. Press Esc to cancel.The Hartley oscillator is an electronic oscillator circuit in which the oscillation frequency is determined by a tuned circuit consisting of capacitors and inductorsthat is, an LC oscillator.

The circuit was invented in by American engineer Ralph Hartley. The distinguishing feature of the Hartley oscillator is that the tuned circuit consists of a single capacitor in parallel with two inductors in series or a single tapped inductorand the feedback signal needed for oscillation is taken from the center connection of the two inductors.

Hartley invented and patented the design in while overseeing Bell System's transatlantic radiotelephone tests; it was awarded patent number 1, on October 26, In Hartley was awarded the IRE medal of honor "For his early work on oscillating circuits employing triode tubes and likewise for his early recognition and clear exposition of the fundamental relationship between the total amount of information which may be transmitted over a transmission system of limited band-width and the time required.

The original version used a triode as the amplifying device in common plate cathode follower configuration, with three batteries, and separate adjustable coils. The simplified circuit shown to the right uses a JFET in common-drain configurationan LC tank circuit here the single winding is tapped and a single battery.

The circuit illustrates the Hartley oscillator operation: [ dubious — discuss ]. Variations on the simple circuit often include ways to automatically reduce the amplifier gain to maintain a constant output voltage at a level below overload; the simple circuit above will limit the output voltage due to the gate conducting on positive peaks, effectively damping oscillations but not before significant distortion spurious harmonics may result.

Changing the tapped coil to two separate coils, as in the original patent schematic, still results in a working oscillator but now that the two coils are not magnetically coupled the inductance, and so frequency, calculation has to be modified see belowand the explanation of the voltage increase mechanism is more complicated than the autotransformer scenario.

A quite different implementation using a tapped coil in an LC tank feedback arrangement is to employ a common-grid or common-gate or common-base amplifier stage, [3] which is still non-inverting but provides voltage gain instead of current gain ; the coil tapping is still connected to the cathode or source or emitterbut this is now the low impedance input to the amplifier; the split tank circuit is now dropping the impedance from the relatively high output impedance of the plate or drain or collector.

The Hartley oscillator is the dual of the Colpitts oscillator which uses a voltage divider made of two capacitors rather than two inductors. Although there is no requirement for there to be mutual coupling between the two coil segments, the circuit is usually implemented using a tapped coil, with the feedback taken from the tap, as shown here.

The frequency of oscillation is approximately the resonant frequency of the tank circuit. If the capacitance of the tank capacitor is C and the total inductance of the tapped coil is L then.

If two uncoupled coils of inductance L 1 and L 2 are used then. However, if the two coils are magnetically coupled the total inductance will be greater because of mutual inductance k [4]. The actual oscillation frequency will be slightly lower than given above, because of parasitic capacitance in the coil and loading by the transistor. From Wikipedia, the free encyclopedia. Common-drain Hartley circuit. United States Office Patent. Retrieved 22 March Learnabout electronics.

Archived from the original on Retrieved CS1 maint: archived copy as title link. Electronic oscillators. Barkhausen stability criterion Harmonic oscillator Leeson's equation Nyquist stability criterion Oscillator phase noise Phase noise. Phase-shift oscillator Twin-T oscillator Wien bridge oscillator. Butler oscillator Pierce oscillator Tri-tet oscillator. Blocking oscillator Multivibrator ring oscillator Pearson—Anson oscillator basic Royer.

Cavity oscillator Delay-line oscillator Opto-electronic oscillator Robinson oscillator Transmission-line oscillator Klystron oscillator Cavity magnetron Gunn oscillator.It seems a mysterious and even a magical force.

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Online questionnaire for Nodal Centre.Toggle navigation. Help Preferences Sign up Log in. Featured Presentations. Hartley Oscillator Circuit Theory Working and Application - This article discusses about an hartley oscillator circuit, circuit using operational amplifier, uses LC tank circuit, advantages, disadvantages and its applications. This article discusses about an hartley oscillator circuit, circuit using operational amplifier, uses LC tank circuit, advantages, disadvantages and its applications.

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hartley oscillator ppt

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hartley oscillator ppt

Description: This article discusses about an hartley oscillator circuit, circuit using operational amplifier, uses LC tank circuit, advantages, disadvantages and its applications — PowerPoint PPT presentation.

Latest Highest Rated. The circuit was invented in by American engineer Ralph Hartley. Hartley oscillator is inductively coupled. It's a variable frequency oscillators where the oscillator may be a series or shunt fed. Hartley oscillators is the advantage of having one tuning capacitor and one center tapped inductor. This processor simplifies the construction of a Hartley oscillator circuit. It works as the active device in amplifier stage.

R1 and R2 are biasing resistors. At high frequencies, the reactance value of this choke is very high. So, it can be treated as an open circuit. RE is also be a biasing resistor. The CC1 and CC2 are the coupling capacitors. The collector current starts raising and begins with the charging of the capacitor C. Once capacitor C is fully charged, it starts discharging through L1 and L2 and again starts charging.

This back-and-fourth voltage waveform is a sine wave which is a small and leads with its negative alteration. It will eventually die out unless it is amplified. The sine wave generated by the tank circuit is coupled to the base of the transistor through the capacitor CC1.

Since the transistor is configured as common-emitter, It takes the input from tank circuit and inverts it to a standard sine wave with a leading positive alteration. The mutual inductance between L1 and L2 provides the feedback of energy from collector-emitter circuit to the base-emitter circuit. This type of circuit facilitates the gain adjustment by using feedback resistance and input resistance. Whereas in Op-amp oscillator gain is less depends on the tank circuit element.

Hence provides greater frequency stability. The operation of this circuit is similar to the transistor version of Hartley oscillator. Then this wave is stabilized and inverted by the amplifier.Toggle navigation. Help Preferences Sign up Log in. View by Category Toggle navigation. Products Sold on our sister site CrystalGraphics. Description: This article discusses about an hartley oscillator circuit, circuit using operational amplifier, uses LC tank circuit, advantages, disadvantages and its applications — PowerPoint PPT presentation.

Latest Highest Rated. The circuit was invented in by American engineer Ralph Hartley. Hartley oscillator is inductively coupled. It's a variable frequency oscillators where the oscillator may be a series or shunt fed. Hartley oscillators is the advantage of having one tuning capacitor and one center tapped inductor. This processor simplifies the construction of a Hartley oscillator circuit. It works as the active device in amplifier stage. R1 and R2 are biasing resistors.

At high frequencies, the reactance value of this choke is very high. So, it can be treated as an open circuit. RE is also be a biasing resistor. The CC1 and CC2 are the coupling capacitors. The collector current starts raising and begins with the charging of the capacitor C. Once capacitor C is fully charged, it starts discharging through L1 and L2 and again starts charging. This back-and-fourth voltage waveform is a sine wave which is a small and leads with its negative alteration.

hartley oscillator ppt

It will eventually die out unless it is amplified. The sine wave generated by the tank circuit is coupled to the base of the transistor through the capacitor CC1. Since the transistor is configured as common-emitter, It takes the input from tank circuit and inverts it to a standard sine wave with a leading positive alteration. The mutual inductance between L1 and L2 provides the feedback of energy from collector-emitter circuit to the base-emitter circuit. This type of circuit facilitates the gain adjustment by using feedback resistance and input resistance.

Whereas in Op-amp oscillator gain is less depends on the tank circuit element. Hence provides greater frequency stability. The operation of this circuit is similar to the transistor version of Hartley oscillator. Then this wave is stabilized and inverted by the amplifier. The frequency of an oscillator is varied by using a variable capacitor in the tank circuit. Keeping the feedback ratio and the amplitude of the output is constant for over a frequency range.

By using a variable capacitor or by making core movable varying the inductancefrequency of oscillations can be varied. Very few components are needed, including either two fixed inductors or a tapped coil. The amplitude of the output remains constant over the working frequency range.

The harmonic content in the output of this oscillator is very high. Hence it is not suitable for the applications which require a pure sine wave.


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