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Phase-Locked Loop With Fast Acquisition Time

IP.com Disclosure Number: IPCOM000041379D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Hong, JH: AUTHOR [+2]

Abstract

A crystal oscillator and a phase-frequency detector are used to minimize the acquisition time of a phase-locked loop (PLL). The figure shows a block diagram for a PLL. Such PLLs are commonly used for timing recovery in many communication systems. In order to increase the transmission efficiency, it is desirable to minimize the PLL acquisition time. Each transmission burst is preceded by the acquisition time to which the PLL is synchronized with the data being received. If there is a large frequency error between the free-running voltage-controlled oscillator (VCO) in the PLL and incoming (received) data, the acquisition time is very long or, in some cases, the PLL may not achieve a lock at all. To overcome this problem the output from a local crystal oscillator is fed into a phase-frequency detector.

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Phase-Locked Loop With Fast Acquisition Time

A crystal oscillator and a phase-frequency detector are used to minimize the acquisition time of a phase-locked loop (PLL). The figure shows a block diagram for a PLL. Such PLLs are commonly used for timing recovery in many communication systems. In order to increase the transmission efficiency, it is desirable to minimize the PLL acquisition time. Each transmission burst is preceded by the acquisition time to which the PLL is synchronized with the data being received. If there is a large frequency error between the free-running voltage-controlled oscillator (VCO) in the PLL and incoming (received) data, the acquisition time is very long or, in some cases, the PLL may not achieve a lock at all. To overcome this problem the output from a local crystal oscillator is fed into a phase-frequency detector. The local crystal oscillator is usually present locally in the transmitter. Therefore, no additional crystal oscillator is needed in such cases. This technique keeps the phase-locked loop locked to the local crystal oscillator during idle periods (that is, the period when no incoming data signal is present). This ensures that the initial frequency offset error is made as small as the crystal oscillator frequency tolerance and a fast acquisition is made possible.

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