Phase locked loop operating principle and applications. In the classic books on phaselocked loops, published in 1966, such concepts as holdin, pullin, lockin, and other frequency ranges for which pll can achieve lock, were introduced. Pdf using chaos to broaden the capture range of a phase. The root locus for a typical loop transfer function is found as follows. Only the analog phaselocked loop apll is discussed in this course. Most of the monolithic pll integrated circuits use an analog phase detector and.
Through elaboration it ends at a model of an all digital and fixedpoint phase locked loop. The capture range is the range in which the phase locker loops attains the phase lock. In any feedback circuit, the possibility of instability and oscillation is a very real. Using chaos to broaden the capture range of a phaselocked loop article pdf available in ieee transactions on circuits and systems i fundamental theory and applications 4011. It is an electronic circuit consisting of a variable frequency oscillator and a. With phase comparator 1, the range of frequencies over which the pll can acquire lock. Applications of phase locked loops play an increasingly important role in modern electronic systems, and the last 25 years have seen new developments in the underlying theories as well. Apr 03, 20 what is phase locked loop pll pll is an electronic module circuit that locks the phase of the output to the input.
The pll consists of i phase detector ii lpf iii vco. Phaselocked loop is one of the most commonly used circuit in both telecommunication and measurement engineering. Through elaboration it ends at a model of an all digital and fixedpoint phaselocked loop. Phase locked loop i am a beginner in electronics hobby essentially because it has been 35 years since class and i was looking at the pll circuit and trying to understand how it works. The capture range is smaller than the locking range. Pll is widely used in communication circuits to select the desired frequency channel. A new pll system that uses adaptation algorithms is developed with the aim of improving speed of responses, robustness. Its content starts with the number n loaded in parallel from the loop filter. Since the phase comparator goes thru its full output range over only 1 cycle of mismatch between the incoming signal and the local oscillator, its output becomes effectively gibberish when the frequency difference is high. This latter band of frequencies is defined as the capture range of the pll system. N delaylocked loop delay line based phaselocked loop.
The oscillator generates a periodic signal, and the phase detector compares the. These parameters are hard to derive analytically and require simulation. As we have studied in lecture, a phaselocked loop has three blocks within. Unless the loop filter values are correctly chosen, it would take the loop too long to lock or once locked it is still unstable small variations in the input data may cause the loop unlock again. Can someone here in the forum please explain a pll and give an example circuit. Phaselocked loop is one of the most commonly used circuit in both.
Digital phase locked loop devon fernandez and sanjeev manandhar december 8, 2003 1. We are more interested in the frequency of the incoming signal, rather than how pretty it looks there is a local voltage controlled oscillator the output of the vco is compared to the input signal and the difference in phase is used to vary the vco until this phase difference is minimised. The frequency range which the pll will accept and lock on is called the capture range. Phase detector 1 is used in applications that require zero frequency and phase difference at lock. The analog and digital signals are used in the phaselocked loop. Phase locked loop tutorial file exchange matlab central. Phase locked loop pll overview of the phaselocked loop pll, pdf file. Limited by the dynamic range of the loop components. A low power cmos design of an all digital phase locked loop a thesis presented by jun zhao to the department of department of electrical and computer engineering in partial ful llment of the requirements for the degree of. The clock, fc, causes the counter to count down to 0. Capture range and lock range refer to how close the local oscillator frequency needs to be to lock onto the incoming signal. Organized in a logical format, it first introduces the subject in a qualitative manner and discusses key applications.
In any feedback circuit, the possibility of instability and oscillation is a very real threat, and must always be taken into consideration. Number of acronyms and symbols damping factor natural frequency kd phase detector gain ko gain of the vco tracking range figure. Depending on the operation principle of loop components we distinguish analog digital hybrid phaselocked loops. To understand the working of the phase locked loop system, let us consider the fm transmitter, which can be considered as one of the most frequently used pll applications. Usually in engineering literature only nonstrict definitions are given for these concepts. Jan 24, 2009ece department, winter school on nit durgapur vlsi systems design 2. A pll is a negative feedback system where an oscillatorgenerated signal is phase and frequency locked to a reference signal.
Phase locked loop fundamentals the basic form of a phase locked loop pll consists of a voltage controlled oscillator vco, a phase detector pd, and a filter. Many modern systems use direct digital synthesis, but the pll is a venerable and timetested technique. The 567 tone decoder is perhaps most famous phase locked loop pll chip. Phaselocked loop from wikipedia, the free encyclopedia a phaselocked loop or phase lock loop pll is a control system that tries to generate an output signal whose phase is related to the phase of the input reference signal. Once the pll is locked and tracking a signal the range of frequencies that the pll will follow is called the tracking range. A phaselocked loop or phase lock loop pll is a control system that generates an output signal whose phase is related to the phase of an input signal.
This tutorial starts with a simple conceptual model of an analog phase locked loop pll. The pll consists of an lctank circuit, divider, phase detector with charge pump, and an onchip passive loop. The free running frequency is usually in the middle of the capture range. Using matlab, plot the step response of the closedloop system from the scaled modulating signal x s to the vco input signal x vco.
Delaylocked loop delay line based phaselocked loop vcobased u d u d f ref f o f o f ref filter. Eine phasenregelschleife, auch als englisch phaselocked loop pll bezeichnet, ist eine. The things i have taken on board to help with my rudimentary understanding are these. The phase locked loop, pll can be used for a variety of radio frequency applications, and accordingly the pll is found in many radio receivers as well as other pieces of equipment. Thus, a pll goes through three stages i free running, ii capture and iii locked or tracking. Ordering information ta package orderable part number topside marking 55cto125c soic m tube cd74act297m c to 125 soic m act297m tape and. A 1 ghz portable digital delaylocked loop with infinite.
Phase locked loops can be used, for example, to generate stable output high. Plls are used to generate, stabilize, modulate, demodulate, filter or recover a signal from a noisy communications channel where data has been interrupted. The phase locked loop, pll, was not used in early radio equipment because of the number of different stages required. Phase locked loops presents the latest information on the basic theory and applications of plls. The phase locked loop or pll is a particularly useful circuit block that is widely used in radio frequency or wireless applications. Next, it develops basic models for components of a pll, and these are used to develop a basic pll model. Good frequency range low jitter challenges phase offset lock time startup sequence loss of lock coding dependant how to integrate. A phase locked loop or phase lock loop pll is a control system that generates an output signal whose phase is related to the phase of an input signal. I remember studying this, but also remember that i didnt really understand it back then. The negativegoing edge of v1 generates a start pulse. Once locked, pll tracks the frequency changes of the input signal. The capture range of a pll, the interval of frequencies within which it will notice an oscillation if its not currently locked onto one, is pretty narrow.
Phaselocked loop the frequency range of input signals on which the pll will lock if it was initially out of lock. Phase locked loop, pll circuits, pll theory, vco, frequency. Phase locked loop system for facts power systems, ieee. A phaselocked loop is a feedback system combining a voltage controlled oscillator vco and a phase comparator so connected that the oscillator maintains a constant phase angle relative to a reference signal. Gate cmos the mc74hc4046b is similar in function to the mc14046 metal gate cmos device. A digital delaylocked loop dll that achieves infinite phase range and 40ps worst case phase resolution at 400 mhz was developed in a 3. In view of its usefulness, the phase locked loop or pll is found in many wireless, radio, and general electronic items from mobile phones to broadcast radios, televisions to wifi routers, walkie talkie radios to professional communications systems and vey much more. Phase locked loops electrical and computer engineering. The capture range is smaller or equal to the lock range.
Sep 07, 2016 a phase locked loop pll is an electronic circuit with a voltage or voltagedriven oscillator that constantly adjusts to match the frequency of an input signal. The frequency capture range 2fc is defined as the frequency range of input signals on which the pll will lock. Phase locked loop design fundamentals application note, rev. Capture range frequency range over which pll can lock on signal lock range frequency range over which pll can track input variation role of low pass filter decreasing bandwidth increasing. The final model can serve a starting point for code generation both ansi c or synthesizable hdl. Multiple plls harmonic locking problems incoming data 10 clock generation phase detector charge pump filter delay line phase detector charge pump vco.
Pll circuit in fm transmitter is a closed loop feedback control system. Phaselocked loops presents the latest information on the basic theory and applications of plls. Total capture range is the difference between these two frequencies. Pdf phase locked loop test methodology researchgate.
Pdf in this article different types of phased locked loop technique are studied. Once this action starts, we say that the signal is in the capture range. Its primary function is to drive a load whenever a sustained frequency within its detection band is present at the self. Phase locked loop pll devices a phase locked loop pll device is a closed loop electronic circuit that controls an oscillator so that it provides an output signal that maintains a constant phase angle with respect to a reference signal, which can range from a fraction of a hz to many ghz. Phaselocked loops worksheet analog integrated circuits. The loop filter also determines phase detector loop filter voltage. Capture range depends on the time constant of the loop filter, determined by c f and a 3. The device inputs are compatible with standard cmos outputs. Vlsi apll performance metrics systems design 240109 hold range the hold range, is defined as the frequency range over which the pll is able to statically maintain phase tracking lock range the lock range, is defined as the frequency range within which the pll locks within one singlebeat note between the reference frequency and output. Phase locked loop using vlsi technology for wireless. Most of the answers can be found in the lecture notes. In its more general form figure 1, the pll may also contain a mixer and a digital divider. Basic difference between pll lock range and capture range. The capture range is the frequency range for which it will lock from an initially unlocked state.
A low power cmos design of an all digital phase locked loop a thesis presented by jun zhao to the department of department of electrical and computer engineering in partial ful llment of the requirements for the degree of doctor of philosophy in electrical engineering in the eld of electrical engineering northeastern university boston. This page describes basic difference between pll lock range and capture range. The loop filter is a simple rc filter, however, it plays a very important role in the dpll. Range of input frequencies around the vco center frequency onto which the loop will lock when starting from an unlocked condition.
Phaselocked loops plls and clock recovery circuits crcs find wide. The phaselocked loop detector compares the input frequency and the output frequency of the vco to produces a dc voltage which is directly proportional to the phase distinction of the two frequencies. But it also helps in reducing noise and in maintaining the locked loop through momentary losses of signal. With phase comparator 1, the range of frequencies over which the pll can acquire lock capture range depends on the lowpass filter. Tone decoderphase locked loop ne567se567 2002 sep 25 2 8530124 28984 description the ne567se567 tone and frequency decoder is a highly stable phaselocked loop with synchronous am lock detection and power output circuitry. Phase detector 2, if quadrature lock is desired, when detector 1 is used in the main loop, detector can also be used to indicate whether the main loop is in lock or out of lock. Together, the phaselocked loop, vco, reference oscillator and phase comparator comprise a frequency synthesizer an electronic system that produces a range of frequencies from a single fixed oscillator. One more thing must be considered in loop filter design. The pullin range is the frequency range beyond the lock capture range over which the loop will lock after losing lock skipping cycles. In view of its usefulness, the phase locked loop or pll is found in many wireless, radio, and general electronic items from mobile phones to broadcast radios, televisions to wifi routers, walkie talkie radios to. Mar 23, 2016 to combine flexibility with crystallike stability, you can use a phase locked loop pll. Phase locked loop pll the phase locked loop or pll is a feedback system used in high quality stereo decoders, frequency shift keying, telemetry applications, wide band fm discriminators, frequency multiplication applications etc. Phase locked loop pll aniruddha chandra ece department, nit durgapur, wb, india. Technical brief swra029 fractionalintegern pll basics pdf.
Pll integrated circuits are now available to minimize the component count. This phase locked loop keeps the generated signal and reference. Phase locked loop system for facts dragan jovcic, member, ieee abstract this research addresses the special requirements of phase locked loops plls for a typical application with facts elements. Sometimes a frequency detector is added to the phase detector to assist in initial acquisition of lock. Once a loop is locked, it will follow the input through the whole range of the vco, which may be larger than the capture range. When the filter bandwidth is reduced, the response time increases. Generally the tracking range is larger than the capture range. These parameters are hard to derive analytically and require. Phaselocked loop pll devices a phaselocked loop pll device is a closedloop electronic circuit that controls an oscillator so that it provides an output signal that maintains a constant phase angle with respect to a reference signal, which can range from a fraction of a hz to many ghz. The hef4046b is a phaselocked loop circuit that consists of a linear voltage. A low power cmos design of an all digital phase locked loop.
Pll lock range vs capture rangepll free running frequency. The frequency lock range 2f l is defined as the frequency range of input signals on which the loop will stay locked if it was initially in lock. Realtime control of loop bandwidth by manipulating the athroughd inputs can maximize the overall performance of the digital phaselocked loop. The terms holdin range, pullin range acquisition range, and lockin range are widely used by engineers for the concepts of frequency deviation ranges within which phase locked loop based circuits can achieve lock under various additional conditions.
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