Phase locked loop simulations
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PHASE LOCKED LOOP SIMULATIONS. By, R.Vikram Reddy(0104445). Talk Outline. History Introduction PLL Basics PLL Types Loop Components -Phase Detectors -Voltage controlled Oscillators -Loop Filters Applications.

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Phase locked loop simulations



R.Vikram Reddy(0104445)

Talk outline

Talk Outline



PLL Basics

PLL Types

Loop Components

-Phase Detectors

-Voltage controlled Oscillators

-Loop Filters




  • Coincides with invention of “coherent communication” (DeBellescize, 1932).

  • The earliest widespread use of PLLs was to the horizontal and vertical sweeps used in television, where a continuous clocking signal had to be synchronized with a periodic synch pulse.

  • PLLs were critical to development of color television

  • The first PLL IC arrived around 1965. This created an explosion in the use of PLLs.

Plls today

PLLs Today

– PLLs in every cell phone, television, radio, pager, computer, all telephony, ...

– The most prolific feedback system built by engineers.

– At low end: all software PLLs implement entire PLL functionality on sampled data.

– At high end: optical PLLs used in clock recovery for 160 Gbps data (OFC 2002).

Pll basics

PLL Basics

  • Definition:

    A phase-locked loop (PLL) is an electronic circuit with a voltage- or current-driven oscillator that is constantly adjusted to match in phase (and thus lock on) the frequency of an input signal.

Basic idea of a phase locked loop

Basic idea of a Phase Locked Loop

Components of pll

Components Of PLL

  • Phase Detector (PD):A nonlinear device whose output contains the phase difference between the two oscillating input signals.

  • Voltage controlled oscillator (VCO): Another nonlinear device which produces oscillations whose frequency is controlled by a lower frequency input voltage.

  • Loop filter

Phase locked loop simulations

  • General sinusoid at reference input can be written as:


  • Assume VCO output signal is

    Vosc=Eoscsin(ωt- Ød+90)

    =Eosccos(ωot - Ød)……(2)

  • Phase Detector output:


    where Km is the multiplication constant

Phase locked loop simulations

  • Vpd=KmEinEoscsin(ωt)cos(ωt-Ød)

  • Using the familiar trigonometric identity in terms of the PLL:

    Vpd=0.5KmEinEosc[sin(Ød) + sin(2ωt-Ød)]

  • The output of the low pass filter :


    For small Ød


How a pll works

How A PLL Works:

Capture range

Capture Range:

  • The maximum difference between the input signals frequency and oscillators free running frequency where lock can eventually be attained is defined as the capture range.

  • The Phenomenon of “Beating”.

Lock range

Lock Range:

  • The maximum frequency excursions over which the output remains locked with the input is called the lock range.

  • The maximum output of the low pass filter is given by

    Vcntl-max=0.5 KlpKmEinEosc

    when Ød=90.

    Therefore lock range is given by


Types of plls

Types Of PLLs

  • Analog or Linear PLL (LPLL)

    • Digital PLL (DPLL)

    • All digital PLL (ADPLL)

Phase locked loop simulations


  • The LPLL (Best) or analog PLL is the classical form of PLL. All components in the LPLL operate in the continuous-time domain.

Phase locked loop simulations


Phase locked loop simulations

  • The phase detector is typically some form of analog multiplier.

  • The phase error function is of the form

    φ(t) = KmK1Asin [θ(t) − θ^(t)]

    ≈ KD[θ(t) − θ^(t)]

  • The loop filter may be active or passive, but it typically results in the loop being either first-order or second-order.

  • The design/analysis of the loop filter makes use of the Laplace transform.

Phase locked loop simulations


The digital PLL is just an analog PLL with a digital phase detector.

  • The DPLL is a hybrid system

  • The DPLL is very popular in synthesizer


Phase locked loop simulations

In the below figure the optional digital divider, and variations on it, are used in frequency synthesis applications.

Phase locked loop simulations

  • Popular types of digital phase detectors include:

    – Exclusive or gate (EXOR)

    – Edge-triggered JK-flip flop

    – Phase frequency detector (PFD)



  • The all-digital PLL (classical all-digital) is distinctly different from the other two PLLs

  • The ADPLL is a digital loop in two senses:

    – All digital components

    – All digital (discrete-time) signals

  • There are many ADPLL building blocks, and many variations on putting them together.



  • The VCO is replaced by a Digitally Controlled Oscillator (DCO) or also called a Numerically Controlled Oscillator (NCO)

Loop components


Phase detector

Phase Detector

  • A phase detector is a circuit that normally has an output voltage with an average value proportional to the phase difference between the input signal and output of VCO.


  • Phase detectors can be a simple EX-OR gate, a sample and hold, an analog multiplier or a combination of D-flip flops.

Phase locked loop simulations


  • The simplest phase detector is xor

Phase locked loop simulations

  • An exclusive OR gate gives a high output when the signals are of opposite sign and a low output when they are of the same sign.

Phase frequency detector

Phase Frequency Detector

  • It is a combination of tri state phase frequency detector and a charge pump.

Sample and hold phase detector

Sample and Hold Phase Detector

  • A sample and hold circuit samples an input signal and holds on to its last sampled value until the input is sampled again.



Design circuit xor ttl logic gate

Design Circuit:XOR (TTL Logic) gate:

Phase locked loop simulations


VCC 4 0 5V

VINA 1 0 PULSE(0V 5V 0US 0.1US 0.1US 2US 5US)

VINB 9 0 PULSE(0V 5V 0US 0.1US 0.1US 3US 5US)

RBA 4 3 4K

RBB 4 8 4K

RCSA 4 5 1.9K

RCSB 4 11 1.9K

RSDA 7 0 1.2K

RSDB 12 0 1.2K

RCX 4 14 3K

RC 4 15 1.6K

RCP 4 16 120

RX 18 0 1K





DX 17 19 DIODE

Q1A 2 3 1 QM

Q1B 10 8 9 QM

QS2A 5 2 7 QM

QS2B 11 10 12 QM

QSDA 6 7 0 QM

QSDB 13 12 0 QM

QX1 14 13 6 QM

QX2 14 6 13 QM

QS 15 14 18 QM

QP 16 15 17 QM

QO 19 18 0 QM


.MODEL QM NPN (IS=1E-14 BF=50 BR=1 RB=70 RC=4 TF=0.1NS TR=1NS)

.TRAN 0.1US 15US

.PLOT V(1) V(9) V(19)


Voltage controlled oscillators vcos

Voltage Controlled Oscillators (VCOs)

  • The function of a VCO is to generate a stable and periodic waveform whose frequency can be varied with the applied control voltage.

  • The actual clock from PLL is the VCO output.

  • VCO’s frequency is modulated by the input voltage

Classification of vco

Classification of VCO

Depending on the type of output waveform, VCOs are classified as

  • Harmonic Oscillators

  • Relaxation Oscillators

Phase locked loop simulations

Some of the commonly used VCOs-Ring Oscillators:Common in monolithic topologies and it uses odd number of inverters connected in feedback loop.-Other forms of VCOs, such as crytal oscillators and resonant oscillators essentially run on the same principle

Vco circuit design

VCO Circuit Design:

  • A simple design of VCO consists of a collector coupled astable multivibrator using n-p-n transistor with a control voltage.

    Step 1

Step 2 f 1 2rcln 1 vcc v

Step 2f=1/2RCln (1+Vcc/V)

Step 3

Step 3:

Phase locked loop simulations

*Voltage controlled Oscillator

VCC 6 0 DC 5V

VI 7 0 PULSE(0 5 0US 30US 30US 30US 40US)

RC1 6 1 1K

RC2 6 2 1K

RE1 7 10 1K

RE2 7 11 1K

R3 7 8 2K

R4 7 9 2K

R5 8 0 4.7K

R6 9 0 4.7K

C1 1 4 150PF

C2 2 3 150PF

Q1 1 3 0 QM

Q2 2 4 0 QM

.MODEL QM NPN (IS=2E-16 BF=50 BR=1 RB=5 RC=1 RE=0 TF=0.2NS TR=5NS)

Q3 3 8 10 QM1

Q4 4 9 11 QM1

.MODEL QM1 PNP (IS=2E-16 BF=100 BR=1 RB=5 RC=1 RE=0 TF=0.2NS TR=5NS)

.IC V(1)=0 V(3)=0

.TRAN 0.1US 90US

.PLOT TRAN V(2) V(7)


Loop filter

Loop filter:

  • The loop filter may be active or passive, but it typically results.

  • In the loop being either first-order or second-order.

  • A 1st order filter having a low frequency pole and high frequency zero is recommended.

  • Loop filter system functions, F(s), include:

    Filter Type Filter F(s)

    perfect integrator 1+sτ2/sτ1

    imperfect integrator 1+sτ2/1+sτ1

    lag or low pass 1/1+sτ

Filter design

Filter Design

  • Design circuit is a simple RC low-pass filter which can extract the average value from the output of the phase detector.

  • This average value is used to drive the VCO







Phase locked loop simulations

low pass filter

R1 1 2 86K

C1 2 3 5PF

R2 3 0 2K

VIN 1 0 PULSE(0V 9V 0US 0US 0US 2US 5US)

.TRAN 0.01US 15US

.PLOT TRAN V(2) V(1)


Pll applications


Phase locked loop simulations

  • The earliest widespread use of PLLs was for the horizontal and

  • vertical sweeps used in televisions.

  • PLLs were critical to development of color televisions also.

  • PLLs today:

  • –Cell phones, televisions, radios, pagers, computers, all

  • telephony,

  • – At low end: all software PLLs implement entire PLL functionality

  • on sampled data.

  • – At high end: optical PLLs used in clock recovery for 160 Gbps

  • data

Phase locked loop simulations

  • Phase-locked loops are widely used for synchronization purposes

  • Space communications for coherent carrier tracking

  • and threshold extension

  • Bit and symbol synchronization

  • They are also used for:

  • Demodulation of frequency modulated signals

  • To synthesize new frequencies which are multiples of a

  • reference frequency, with the same stability as the

  • reference frequency.

Phase locked loop simulations

  • Deskewing

  • the clock must be received and amplified

  • finite delay dependent on process,temperature and voltage between detected clock edge and the received data

  • delay limits the frequency at which data can be sent

  • deskew PLL on the receiver side phase-matches the clock at each data flip-flop to the received clock.

  • 2. Clock generation

  • multiplies lower-frequency reference clock (usually 50 or 100 MHz) up to the operating frequency of the processor that operate at Gigahertz

Phase locked loop simulations

  • 3. Spread spectrum

  • All electronic systems emit some unwanted radio

  • frequency energy

  • limits on this emitted energy and any interference

  • caused

  • spreading the energy over a larger portion of the

  • spectrum

  • 4. Jitter and noise reduction

  • reference and feedback clock edges can be brought into very

  • close alignment

  • phase and frequency of generated clock is unaffected by rapid

  • changes in voltages of the power supply lines and of the

  • substrate on which the PLL circuits are fabricated

Phase locked loop simulations

1. Carrier Recovery

• General block diagram of frequency recovery from a modulated


• When carrier has strong component in signal spectrum, PLL

can lock.

• When carrier is missing from signal spectrum, PLL must be

preceded by a nonlinear element.

Phase locked loop simulations

2. Costas Loop

  • A Costas loop can both recover the carrier and demodulate the data from a

  • signal.

  • If there were no modulation, the upper arm is simply a PLL lock to a carrier.

  • The effect of the lower arm of the loop is to lock to the modulation and cancel it

  • out of the upper arm of the loop.

  • Does the same thing as squaring loop, but down converts signal to baseband &

  • does filtering there.

Phase locked loop simulations

3. Clock distribution

Phase locked loop simulations

4. Frequency Synthesis

In wireless applications, frequency synthesizers provide local oscillators ability for up and down conversion of modulated signals

Phase locked loop simulations

A basic PLL synthesizer

Phase locked loop simulations

5. Disk Drive Control

Amplitude encoded position error signal (PES) in a hard disk.

PLLs are used to time the acquisition

of the readback signal.

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