Phase Locked Loop

Phase-Locked Loop

M Alam
Pakistan Air Force - Karachi Institute of Economics & adenosine monophosphate; Technology

Abstract Phase Locked Loop (PLL) is an old technology dating from 1930s, but has been used over the past decades and is contributing importantly towards the technology advancement in the fields of communication, instrumentation, servo force back control formations and multimedia apparatus. Inventions in PLL schemes combining with novel coordinated circuit (IC) technology have made PLL devices important governing body components. The development for better PLL ICs is continuing. As a result, it is expected that it will contribute towards improvement in system performance and reliability for future communication systems. This paper serves as an introduction to PLL and gives a concise view of what PLL is, its history, elements and techniques etc.

Keywords:PLL (Phase-Locked Loop), IC (Integrated Circuit), VCO (Voltage Controlled Oscillator), PD (Phase Detector), LPF (Low Pass Filter), LPLL (Linear Phase Lock Loop), DPLL (digital Phase Lock Loop), ADPLL (All Digital Phase Lock Loop), NCO Numerically-Controlled Oscillator, SPLL (Software Phase Lock Loop)
BACKGROUND
 Earliest research towards what became to be known as the phase-locked loop goes back to 1932.



The staple fibre concepts were published by de Bellescize when he developed an resource to Edwin Armstrongs super-heterodyne receiver, the Homodyne or direct-conversion receiver. In the homodyne or synchrodyne system, a local oscillator was tuned to the desired input frequency and multiplied with the input prognosticate. The resulting output signal included the original modulation information. The intent was to develop an alternative receiver circuit that required fewer tuned circuits than the super-heterodyne receiver. Since the local oscillator would apace drift in frequency, an automatic correction signal was use to the oscillator, maintaining it in the same phase and frequency as the desired signal [1].
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