Phase-Locked Loops

Publish Date: Dec 05, 2011 | 9 Ratings | 2.22 out of 5 |  PDF

Overview

This tutorial is part of the National Instruments Measurement Fundamentals series. Each tutorial in this series teaches you a specific topic of common measurement applications by explaining the theory and giving practical examples. This tutorial covers an introduction to RF, wireless, and high-frequency signals and systems.

For the complete list of tutorials, return to the NI Measurement Fundamentals main page, or for more RF tutorials, refer to the NI RF Fundamentals main subpage. For more information about National Instruments RF products, visit www.ni.com/rf.

A phase-locked loop (PLL) is a feedback control circuit that synchronizes the phase of a generated signal with that of a reference signal. It is important to keep in mind that a PLL can generate signals that are only integer multiples of the reference signal.

Table of Contents

  1. Phase-Locked Loop Operation
  2. Conclusion
  3. Related Products

1. Phase-Locked Loop Operation

The basic components of a phase-locked loop (PLL) are a stable reference oscillator, a phase detector, a frequency divider, a voltage-controlled oscillator (VCO), amplifiers, and filters. The following figure shows a simplified PLL block diagram.


Figure 1. PLL Block Diagram

PLLs work by comparing the generated signal phase to the reference oscillator signal phase and then using the difference to adjust the generated signal. To compare the two waves, both signals must be of the same frequency. The frequency divider is used to divide down the generated signal. Because the frequency divider can divide down only an integer number of times, the generated signal must be an integer multiple of the reference oscillator signal. The phase detector returns a voltage depending on the phase difference between the two waves. This voltage is amplified, filtered, and then fed into the VCO. The VCO adjusts the signal it outputs based on this voltage.

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2. Conclusion

Phase-locked loops play a vital part in many modern-day circuits. They are used to demodulate amplitude and frequency modulated signals, synchronize clocks, recover small signals from noise, and they are used in devices such as dual-tone multiple frequency decoders and modems.

For the complete list of tutorials, return to the NI Measurement Fundamentals main page, or for more RF tutorials, refer to the NI RF Fundamentals main subpage. For more information about National Instruments RF products, visit  www.ni.com/rf.

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3. Related Products

NI PXIe-5663 6.6 GHz RF Vector Signal Analyzer
The National Instruments PXIe-5663 is a modular 6.6 GHz RF vector signal analyzer with 50 MHz of instantaneous bandwidth optimized for automated test.

NI PXIe-5673 6.6 GHz RF Vector Signal Generator
The National Instruments PXIe-5673 is a 4-slot 6.6 GHz RF vector signal generator that delivers signal generation from 85 MHz to 6.6 GHz, 100 MHz of instantaneous bandwidth, and up to 512 MB of memory.

NI PXI-5660 2.7 GHz RF Vector Signal Analyzer
The National Instruments PXI-5660 is a modular 2.7 GHz RF vector signal analyzer with 20 MHz of instantaneous bandwidth optimized for automated test.

NI PXI-5671 2.7 GHz RF Vector Signal Generator
The National Instruments PXI-5671 module is a 3-slot RF vector signal generator that delivers signal generation from 250 kHz to 2.7 GHz, 20 MHz of instantaneous bandwidth, and up to 512 MB of memory.

NI PXI-5652 6.6 GHz RF and Microwave Signal Generator
The National Instruments PXI-5652 6.6 GHz RF and microwave signal generator is continuous-wave with modulation capability. It is excellent for setting up stimulus response applications with RF signal analyzers.

NI RF Switches
The National Instruments RF switch modules are ideal for expanding the channel count or increasing the flexibility of systems with signal bandwidths greater than 10 MHz to bandwidths as high as 26.5 GHz.

NI LabVIEW
National Instruments LabVIEW is an industry-leading graphical software tool for designing test, measurement, and automation systems.

NI Modulation Toolkit
The National Instruments Modulation Toolkit extends the built-in analysis capability of LabVIEW with functions and tools for signal generation, analysis, visualization, and processing of standard and custom digital and analog modulation formats.

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