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    colpitt oscillator

    first i want to ask that are hartley and colpitts oscillators made on ICs. if not then please tell me the reason. and if yes then which one is better and why??

    any references will also be helpful

    •   Alt14th November 2004, 09:32

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  2. #2
    v_naren
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    hartely oscillator

    colpitt is better as its phase noise performance is the best
    and mostly people use the LC cross coupled oscillator for IC implementations as it helps reducing the external noise sources such as bulk noise due to its differential nature

    reference

    http://www.edaboard.com/ftopic78882.html


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    •   Alt14th November 2004, 14:41

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    colpitts vs hartley

    Colpitts has much better phase noise.In fact you could construct one differential Colpitts OSC. For Hartley OSC, the difficult thing is that you must use inductor instead of caps in Colpitts configuration.Inductor is always area consuming.


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    •   Alt15th November 2004, 02:22

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    hartley osc

    It is not true that Colpitts topology has any inherent advantage over Hartley, phase noise or whatever.
    Each has a resonant circuit that is connected in the same place. The only difference is that the tap on the resonant circuit is implemented with the capacitors in the Colpitts and an inductor tap in Hartley. One outcome of the inductor tap is that the Hartley has some tendency to have parasitic resonances as the inductor is divided by the tap into two parts, and the mutual inductance between them has a final value. On the other side the Hartley has less capacitors.
    I have used in the past the Hartley discrete topology many times with excellent results and performance.


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    colpitts oscillator

    okay, how about if we look at it from an IC design view point.



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    colpitts osc

    Colpitts much smaller layout size and better performance when made on IC because uses caps. Good Hartley will need extern inductors for good response.


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    Re: hartley Vs colpitts oscillator

    Using an IC like the RF2506 (see: http://electroschematics.com/756/10-...hz-oscillator/), you could make Hartley or Colpitts oscillators out of it. If the frequency is upper-VHF or above then Colpitts has an advantage in having less risk of parasitic oscillations. If it is for a VFO or VCO, rather than fixed-frequency crystal-controlled oscillator, Hartley LC circuits are somewhat easier to tune. Notice the cross-coupled LC oscillator (popular with IC implementations, and good at UHF) is basically a push-pull version of the Hartley.

    Phase noise is often a key factor: it can be made to be good with all sorts of oscillator topologies, but is difficult to get right when the signal voltage at the tuned circuit is high (which the cheap-and-nasty traditional triode or FET voltage stabilisation circuits tended to give) because the capacitance in the FET and/or diodes in the gate/grid/base circuit will vary throughout the cycle; the voltage stabilisation circuit is also important to get right if it results in AM noise (that can easily become phase noise). Even if you are after a squarewave output, varying levels of signal into the tuned circuit will move the frequency a bit.

    Mark



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    hartley Vs colpitts oscillator

    Colpitts has much better phase noise but hartley has a better perfomance in tunning bandwith.if you dont have problem to space in your design so you can apply hartley to good tunning.



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