2018-19

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Browsing 2018-19 by Subject "1NH15EE014"

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    HIGH FREQUENCY STABILITY OF TCXO FOR PHASE LOCK LOOP
    (2019-07-23T06:02:26Z) CHANDAN N; LAVAN KRISHNA K; SAI DINESH P; DAYA DIKSHITH R
    Crystal oscillators are the heartbeat of modern communication systems. For decades, the quartz crystal has been used for precise frequency control. Applications that require accurate frequency control include wireless transmitters, digital circuits, and time-based measurement instruments. In the increasingly popular field of wireless communications, available frequency spectrum is becoming very limited. Regulatory agencies have imposed tight restrictions on bandwidth and frequency stability. These requirements vary throughout the spectrum in accordance with the intended applications. Many factors affect the frequency stability of an oscillator. These include variations in voltage, time, and temperature. Specifications for frequency stability are expressed as the amount of the divergence from the nominal operating frequency, usually in terms of a percentage or in parts per million (ppm). There are generally two methods of controlling the instability of an oscillator due to temperature variations of its environment. The first is the method of temperature control. It involves the use of some kind of temperature stable chamber in which the sensitive components of the oscillator are placed. In the case of a crystal oscillator, the crystal is placed in a thermal oven that is held at a constant temperature. This circuit is called an oven-controlled crystal oscillator (OCXO). Very good stability over wide temperature ranges can be achieved. However, there are some disadvantages. The oven itself is usually a somewhat bulky unit that draws a considerable amount of current to maintain a constant temperature. This significantly restricts its use in miniature battery powered electronic devices. In addition, an oven-stabilized oscillator needs an initial warm-up period before it reaches a stable frequency. In the applications where the size, current draw, and warm-up period are tolerable, this approach to frequency stability is usually very desirable