Phase Locked Loops for Wireless Communication Systems

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TECHNOLOGY FOCUS
Phase Locked Loop frequency synthesizers are key buildingblocks in wireless communication systems. Today, the industry is making huge progress towards total integration into one piece of silicon together with other building-blocks needed for a complete radio, all with the goal to make wireless products affordable and comfortable in use.

COURSE OBJECTIVES
This course enables engineers to understand the principles of PLL circuits and its applications and to design PLL synthesizers optimized for a given application. It introduces advanced technologies of frequency synthesis used in modern communication devices. 

Monday- LUTZ KONSTROFFER
CONTROL LOOP BASICS 
Control loop basics are the foundation of any detailed PLL consideration. The concepts of open and closed loop gain, phase and amplitude margin and their link to the dynamical behavior are introduced. The Z-transformation as a method to describe and optimize the behavior of time discrete control loops is explained.

• Open and Closed Loop Gain and Phase Transfer Function
• Bode Plot, Phase Margin, Amplitude Margin
• Poles and Zeros, Characteristic Function
• Closed Loop Transfer Function, 3dB-Bandwith, Dynamic Control Behavior
• Describing Time Discrete Control Loops by Z-Transformation
• Principals of Modulators

Phase Noise in a Wireless System 
Parameters that describe the phase fluctuations and establish relationships 
between different sets of parameters are introduced. The impact of the noise behavior of a PLL on the receiver and transmitter performance in a wireless system is discussed.

• The Phase Angle as a Random Process
• Parameters Describing Phase Fluctuations and Relations between them
• SSB Phase Noise, Phase and Frequency Error
• Effect of the Phase Noise on the Blocking and Adjacent Channel Power Performance

PLL Components
We focus on the components that build a PLL. All building-blocks of a PLL are described in terms of their linear transfer functions.

• VCOs
• Phase Noise in VCOs
• Phase Detector Types
• Charge Pumps
• Use of Op-Amps
• Dividers and Mixers in a PLL

Tuesday - LUTZ KONSTROFFER 
PLL FUNDAMENTALS 
Based on the linear description of the building-blocks, we will derive the transfer functions of a PLL and its implications on the system performance, such as switching time and spurious suppression. A discussion of the noise behavior of the PLL will complete this section.

• The Phase Transfer Function
• Transfer Functions for Noise and Spurious Signals
• Lock Time, Natural Frequency, Damping Factor, and Phase Margin
• 2nd-, 3rd-, and High-order Filters
• Correlation between Phase Comparison Frequency and Loop Bandwidth 
  Requirement
• Phase and Frequency Modulation in a PLL
• Sources of Phase Noise in a PLL and its Simulation

The Integer N PLL in a Wireless IC 
As the loop filter is a key element in any PLL, its dimensioning is based on lock time and spurious requirements.

• Loop Filter Dimensioning from Lock Time Requirements
• Compromise between Spurs, Noise and Lock Time
• Sources of PFD Spurs
• Charge Pump Issues
• Problems Linked to Speed-up Circuits

The Fractional N PLL in a Wireless IC 
An approach to overcome the constraints of lock time, phase noise, and spurious suppression is the fractional N concept.

• Basics of Operation
• Spurs Due to the Fractional Concept
• Analog and Digital Fractional Compensation
• Limits of Fractional Compensation Circuits
• The Impact of Phase Detector Linearity
• The Measurement of PLL Parameters
• Phase Noise Measurement with a Spectrum Analyzer
• Phase Noise Measurement by Down Conversion
• Delayed Self Homodyne Phase Noise Measurement
• Simple and High Precision Lock Time Measurement Methods
• Measuring the PLL Phase Transfer Function

Practical Demonstrations 
The effect of PLL settings and loop filter parameters on the performance in the frequency domain and in the time domain is demonstrated on PLL ICs of two different vendors.

• PLL stability
• Impact of the loop filter on the spurious suppression
• Impact of the loop filter on the switching speed

Wednesday - BERND SCHEFFLER 
SYNTHESIZER CONCEPTS 
We review various transceiver/synthesizer concepts. Special focus is on how to modulate a carrier for TX and maximize reuse HW for RX in half-duplex systems.

• On-channel Modulation
• Offset-loop
• Open-loop Modulation
• Closed-loop Modulation

Direct Digital Synthesis 
The architecture of a DDS is analyzed in detail. The noise and spurious response of the system is considered for each building-block. Other system parameters like lock-time and frequency resolution will be touched.

• Accumulators
• Phase and Amplitude Quantization
• Frequency Resolution
• Spurious Analysis
• DAC

Sigma-Delta PLL 
Starting from a classical PLL, the mathematical description of the noise behavior of a Sigma-Delta PLL with multi-modulus divider is developed. 
The digital fractional spurious compensation is modelled, and in a second step we perform a quantization noise simulation and extract a rule of thumb for practical usage. Frequency resolution and other key parameters are treated before advantages are summarized.

• Sigma-Delta Modulator
• MASH
• Divider Control
• Quantization Noise
• SSB Phase Noise
• Frequency Resolution

Thursday - BERND SCHEFFLER 
Generate Modulated Signals with digital PLLs 
The advantage of this PLL architecture to generate phase- and frequency 
modulated signals is presented. For vector modulated signals the sigma-rho concept is compared to a classical on-channel modulation concept.

• In-Band and 2-Point Modulation
• Modulation Bandwidth
• Sigma-Rho Modulation
• Vector Modulation
• Impairments
• IQ Modulator
• On-Channel Modulation

Complete Digital PLL - Digital Controlled Oscillator (DCO) 
Silicon technology trends allow new PLL architectures and increase its digital content. Starting point is the analysis of a DCO and its application in a closed loop system. Means to increase frequency resolution and quantization noise will be treated on an architectural level.

• DCO
• Digital Loop Filter
• All Digital Loop
• Quantization
• Non-linear Control Loop

Said about the course from previous participants:
"Practical examples and exercises."
"A lot of interaction, good depth in material."
"Practical measurements on hardware."
"The level of the course has been chosen correctly / properly matched with the audience level."
"Instructors with plenty of real-life practical knowledge."