IC Phase-locked Loops (PLL) Information

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Last revised: November 13, 2024

Reviewed by: Scott Orlosky, consulting engineer

IC phase locked loops (PLL) are closed-loop frequency controls that are based on the phase difference between the input signal and the output signal of a controlled oscillator. An IC phase-locked loop generally consists of a phase detector, a loop filter, voltage controlled oscillator (VCO) and an amplifier.

There are several ways in which IC phase locked loops (PLL) function. An IC phase-locked loop is an electronic circuit that controls an oscillator and provides an output signal. This output signal should be capable of maintaining a constant phase angle with respect to the reference signal in the range of few Hz to many GHz.

A digital phase locked loop is comprised of a serial shift register that receives digital input, a local oscillator that gives a clock pulse to the shift register, and a phase corrector circuit that produces a stable clock, which is in phase with a received signal. A digital PLL chip can interface with more than one device. Some specifications of the frequency synthesizer digital PLL includes frequency range, output power and step size.

Types of IC Phase-locked Loops (PLL)

A digital phase locked loop circuit is used if the data and clock are to be sent together over the same cable because in this circuit the receiver separates the clock from the data received.

A digital PLL chip simplifies the clock design and increases reliability of the circuit in which it is present. A current loop driver kit is a type of phase locked loop circuit in which the phase detector is not present.

A current loop chip is a programmable chip and it can directly interface to the computer.

In an ADC phase locked loop, the analog signal is converted into the digital signal.

A synthesizer digital PLL is a type of frequency synthesizer, an electronic device that is capable of producing frequency coherent to a reference frequency.

Other IC phase locked loops (PLL) are commonly available.

Applications

IC phase locked loops are used in many applications. Some examples include application in the communications field to lock the communication signals in their frequency range, frequency synthesizers, and signal regeneration. IC phase locked loops (PLL) should adhere to Institute of Electrical and Electronics Engineers (IEEE) and other industry standards.

Standards

SMD 5962-77050 — Microcircuit, linear, phase-locked loop system, monolithic silicon

IC Phase-locked Loops FAQs

How do PLLs contribute to signal integrity and stability in communication systems?

PLLs are essential for synchronizing clocks within communication systems. They ensure that different parts of the system operate in harmony, which is critical for maintaining signal integrity. For example, in digital communication links, PLLs are used to extract clock information from the received signal, ensuring that the data is correctly timed and synchronized.

PLLs are used to generate stable and accurate frequencies required for communication systems. They convert reference clock frequencies into new frequencies without losing accuracy, which is vital for maintaining signal stability. This is particularly important in systems like cellular networks where frequency accuracy and clock purity are key design parameters.

In many communication systems, data is transmitted without an additional timing reference. PLLs are used to recover the clock from the transmitted signal, ensuring that the data can be correctly interpreted at the receiving end. This maintains the integrity of the transmitted data.

PLLs have the ability to extract signals from noisy environments. They can filter out noise and provide a clean, stable signal, which is particularly important in communication systems where noise can degrade signal quality.

PLLs are used for retiming signals, which can help in reduce jitter. By ensuring that signals are correctly timed, PLLs help in minimizing errors and improving the overall performance of communication systems.

PLLs are part of frequency synthesizers that provide highly stable frequencies required in communication systems. These synthesizers ensure that the generated frequencies are stable and accurate.

How do PLLs help in reducing noise in communication systems?

PLLs have the ability to extract signals from extremely noisy environments. This is particularly useful in communication systems where the input signal may be superimposed with noise. The PLL can filter out this noise, providing a cleaner and more stable signal. This property is extensively utilized in the field of communications

PLLs are part of frequency synthesizers that provide highly stable frequencies required in communication systems. These synthesizers ensure that the generated frequencies are stable, and accurate..

In many communication systems, data is transmitted without a timing reference. PLLs are used to recover the clock from the transmitted signal, ensuring that the data can be correctly interpreted at the receiving end. This reduces phase noise, which can degrade signal quality.

PLLs are used to retime signals, which helps in reducing jitter and maintaining signal integrity. By ensuring that signals are correctly timed, PLLs help minimize errors and improving the overall performance of communication systems.

When used as frequency synthesizers, PLLs often rely on high-quality quartz crystal oscillators. These oscillators are exceptional in minimizing noise, including thermal noise from transistors and resistors within the oscillator circuit

What is the role of PLLs in clock recovery?

PLLs are used in almost every digital communication link to extract clock information from the received signal. Digital data is often sent without a clock signal, so the receiver must extract this clock information to correctly interpret the data. This process is known as clock recovery

There are two primary methods of transmitting digital data: baseband and carrier-based transmission. In baseband transmission, the digital signal is sent directly over the link. In carrier-based systems, the digital signal is modulated onto a high-frequency carrier signal. PLLs are used in both methods to recover the clock signal from the transmitted data.

As part of clock recovery the digital data is also synchronized correctly. Both recovery of the clock signal plus synchronization must be executed to recapture and maintain the integrity of the transmitted data. Without these measures, the transmission cannot be correctly interpreted at the receiving end..

PLLs help in reducing phase noise, which can degrade signal quality. Phase noise is a critical factor in digital processing, as it affects the dynamic range of analog-to-digital converters by adding noise..

PLLs are also used for retiming signals, which helps in reducing jitter. By ensuring that signals are correctly timed, PLLs minimize errors and improve the overall performance of communication systems.

What are the challenges in designing PLLs for modern communication systems?

Among the many challenges, modern PLLs are often realized as single-chip ICs, which requires significant miniaturization. This trend towards miniaturization must balance with maintaining performance and functionality. The integration of PLLs into CMOS RFICs (Radio Frequency Integrated Circuits) is particularly challenging due to the need for seamless integration between RF and digital functionalities.

PLLs must generate highly stable and accurate frequencies. In systems like GSM (Global System for Mobile) the frequency must be agile and accurate to within a few parts per million. Achieving this level of precision requires high-quality reference oscillators and sophisticated feedback control mechanisms.

Noise is a critical factor in PLL design. Every building block of the PLL can contribute to noise, and the reference signal itself is often a significant source of noise. Designers must carefully manage and minimize noise to ensure signal integrity and system performance.

Clock recovery in digital communication systems is imperative. PLLs must accurately extract and synchronize clock information from the received signal. The transmission methods (baseband and carrier-based) plus the presence of noise make this challenging.

PLLs are used for frequency synthesis, converting reference clock frequencies into new frequencies without losing accuracy. In cellular networks, for example, the frequency switching speed is a critical parameter. The PLL must quickly and accurately switch frequencies to avoid drop outs.

Phase noise affects the dynamic range of analog-to-digital converters and overall system performance. PLLs must minimize phase noise to ensure equally spaced time samples and preserve the digital signal.

Retiming signals to reduce jitter requires PLLs. Without retiming, signals will get out of synchronization and communication will fail.

What are the different configurations of PLL synthesizers used in communication systems?

Analog PLLs were the first type to be used in digital circuits and are still found in many systems. They are treated as if they were fully digital and are known for their simplicity and reliability. However, they are gradually being replaced by more advanced digital configurations.

As digital PLLs have become more prevalent they can incorporate digital phase comparators and loop filters, which improve performance and allow for miniaturization. Digital PLLs are often integrated into CMOS RFICs (Radio Frequency Integrated Circuits) for seamless integration between RF and digital functionalities.

Mixed-signal PLLs combine both analog and digital components. They are particularly useful for frequency synthesis, retiming, and clock signal recovery. These PLLs are used in almost every digital communication link to extract clock information from the received signal, whether the data is transmitted over serial or parallel data channels.

Frequency synthesizers are a specific type of PLL used to generate stable and accurate frequencies required in communication systems. They convert reference clock frequencies into new frequencies without losing accuracy. These synthesizers are essential in systems like cellular networks, where frequency accuracy, clock purity, and switching speed are critical design parameters.

CMOS PLLs are widely used in modern communication systems due to their ability to integrate RF and digital functionalities seamlessly. These PLLs must be highly stable, quickly and accurately set channel frequencies, and minimize generated noise. They are particularly important in systems like GSM, where frequency agility and accuracy are crucial.

Ring-type oscillators are another configuration used in PLLs. These oscillators have been digitalized and are part of the continuing miniaturization of PLLs. They are often used in modern PLLs realized as single-chip ICs.