Discussion in 'Homework Help' started by ppppp, Apr 29, 2011.

  1. ppppp

    Thread Starter New Member

    Apr 23, 2011
    how oscillator gives output without input.plz give me ans frnds
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. BillB3857

    Senior Member

    Feb 28, 2009
    In the case of many oscillators, simple random noise gets amplified repeatedly and fed back to the input until the frequency determining system takes over and allows only amplification of the desired frequency.
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    Essentially, oscillators depend on some kind of amplifying system provided with positive feedback, but this more obvious with some types than others.

    At one extreme we have simple oscillators using a single amplifying device with a frequency-selective positive feedback path. In this case it is easy to visualise random noise leading to an increasing signal building up around the feedback loop, assuming that (at least initially) the loop gain is more than one at some frequency where the signal comes back around the loop in phase with itself.

    RC oscillators like the 555 are usually analysed in terms of large-signal processes where capacitors charge until a threshold is reached, triggering some event that leads to the capacitor discharging again. That said, the comparators or other trigger devices underlying this process can be considered to be rather specialised amplifiers.

    Other oscillators are based on devices which present a negative incremental resistance or trigger characteristic between two terminals. These include tunnel diodes, some gas discharge tubes (including thyratrons) and uni-junction transistors. Here the amplification is an implicit process, a consequence of the negative incremental resistance.
  5. bertus


    Apr 5, 2008