Load Pull Pres

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Load Pull Simulation Using ADSAndy Howard

Applications Engineer

28 May, 2002



Page

Outline

2

• Overview

• Specifyingand generatingdesired load reflection coefficients

• Assigningarbitrary reflection coefficients atthe harmonic freqs.

• iasing the deviceand runninga simulation

• !alculating desiredresponses "deliveredpower#PA$# etc.%

• &enerating contourlines

Load Pull

Simulation

Using ADS20 May, 2002



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Load pull simulation varies the load reflectioncoefficient presented to a device...

3

Vary load

reflectioncoefficient

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Simulation




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'to find the optimal value to ma(imi)e power orPA$# etc.

4

Load Pull

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Specify the load reflection coefficients

5

Simulation set up iscomplicated, but

region is sampled

more uniformly

Simulation set up

is trivial

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Sweeping rho over a circular region

6

Specify circular region, via s11_rho and s11_centervariables

This is just a

static figure. It

does not get updatednor correspond

to the values in the

equations.

adius of circle

!enter of circle

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Simulation




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Use *eflection!oefUtility data display to helpset s++,center and s++,rho

7

The circle center and

radius are updated "hen

you move either or bothof the mar#ers

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-wo variables are swept to generate the points within the desired circle

8

These initiali$e the

s"ept variables

inde%s11 is the reflection

coefficient

&ill e%plain Start

and Stop equations

later

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Simulation




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ore on the swept variables

9

Variable 'imag_inde%s11( is

the y)a%is value of simulated

reflection coefficient.

Variable 'real_inde%s11( is

the %)a%is value. The

imag_inde%s11 variable is

stepped uniformly, "hereas

real_inde%s11 is stepped

non)uniformly.

*ach point is a data pair+

real_inde%s11, imag_inde%s11-

m is at appro%imately+ )/.0/, /.2-

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Sweep limits for /imag,inde(s++0

0

3rro" points to s11_center

imags11_center-

3

4

5istance '3(65istance '4(6ma%_rho)ma%_rho7lines81-

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1hat is /ma(,rho02

9ength of vector !

6mags11_center-

!

5

9ength of vector 5

61)mags11_center-

The ma%_rho equation reduces the radius of the circle of simulated

reflection coefficients if any part of the circle "ould other"ise beoutside the Smith chart, "hich "ould imply an active load.

'ma%_rho( "ill be the smaller of

the length of vector 5 and the user)entered circle radius, s11_rho.

Load Pull

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1hat about the /ma(,rho3"lines4+%0 term2

2

Including this term prevents the first

and last line from being tangent tothe circle at a single point. This allo"s

real_inde%s11 to be s"ept along the first

and last lines defined by imag_inde%s11.Load Pull

Simulation




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Sweep limits for /real,inde(s++0

3

ma%imum value of

c_limit


reals11_center- c_limit is the distance fromthe

vertical center line of the circleto the edges, along each of the

hori$ontal lines. It is different

for each hori$ontal line.

min. value

of c_limit

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5ow is c,limit calculated2

4


imags11_center-

c_limit is calculated from+

r::;6c_limit::;8<::;,

"here

<6imag_inde%s11)imags11_center-,

and r6ma%_rho

!ircle radius is ma%_rho

imag_inde%s11

c_limit

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5ow are the number of lines and the points perline calculated2

5

=ser sets this value

The 'lines( equation ta#es the

square root of 'pts(, then computes

the integer part. The ma%- function

ensures that at least one line is used.

The number of points per line is

computed by #eeping the integer

part of pts7lines.

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Simulation




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Alternate reflection coefficient sweep

6

S"eep the phase of the reflectioncoefficient '>hi_rho( in degrees,

and s"eep the magnitude '?ag_rho(.

'rho( belo" becomes the s"ept

reflection coefficient, instead of

inde%s11.

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Outline

7

• Overview






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6ou could ma7e the load independent offrequency8

8

4ut this "ould model an unrealistically

simple situation and "ould give

sub)optimal results.

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Set source and load impedances at harmonicfrequencies arbitrarily

9

These default values are some"hat

sub)optimal, as using opens or shortsto terminate the harmonics should

give better performance.

@_l_; is the load impedance at

;nd harmonicA other load andsource impedances defined similarly

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Defining a single# frequency9dependentreflection coefficient "+%

20

The 'brute force( "ay, using a giant if)then)else equation+

This is from e%amples7B_4oard7C35!_>3_prj7C35!_>3_Test

These are frequency brea# points, mid"ay bet"een

the fundamental and ;nd harmonic, bet"een the

;nd and rd harmonics, etc. Bfreq is thefundamental frequency.

These equations convert harmonic

impedances to reflection coefficients.

...

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Defining a single# frequency9dependentreflection coefficient ":%

2

=sing an array, defined via the 'list -( function+

The list function defines an array of reflection coefficients, the first

value being /, the second value inde%s11, the third value fg@_l_;-,

etc.

The function fg%- converts an impedance

% into a reflection coefficient.Load Pull

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Defining a single# frequency9dependentreflection coefficient ": continued%

22

iload is the inde% into the array.

"hen iload61, 9oadTuner 6 9oad3rrayD1E 6/

"hen iload6;, 9oadTuner 6 9oad3rrayD;E 6inde%s11

"hen iload6, 9oadTuner 6 9oad3rrayDE 6fg@_l_;-

etc.

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5ow is iload calculated2

23

'freq( is an internal simulator variable. Bor a 1)tone load)pullsimulation it "ill have values /, Bfreq, ;:Bfreq, :Bfreq,

etc., "here Bfreq is defined to be the fundamental analysis

frequency.

length9oad3rray-6 in this case.

So "hen freq6/,iload 6 intmin/7Bfreq 81.F, -- 6 intmin1.F, -- 6 int1.F- 61

&hen freq6Bfreq,

iload 6intminBfreq7Bfreq81.F, -- 6intmin;.F, -- 6int;.F- 6;Load Pull

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ore details

24

&hen freq6/, analysis at 5! is being carried out, and iload61,

so 9oadTuner 69oad3rrayD1E6/. So the reflection coefficient at5! is /.

&hen freq6Bfreq, analysis at the fundamental frequency is

being carried out, and iload6;,

so 9oadTuner69oad3rrayD;E6inde%s11, "hich is the load

reflection coefficient at the fundamental frequency.

&hen freq6;:Bfreq, analysis at the ;nd harmonic frequency

is being carried out, and iload6,

so 9oadTuner69oad3rrayDE6fg@_l_;-, "hich is the load

reflection coefficient at the ;nd harmonic frequency. *tc.Load Pull

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Load pull at a harmonic frequency

25

5efine a ne" variable, @_l_fund, to fi% the load impedance atthe fundamental frequency. Then change the 9oad3rray equation

to+

9oad3rray 6 list/, fg@_l_fund-, inde%s11, fg@_l_-,G-

The reflection coefficient at "hich harmonic frequency is beings"eptH

&hat if you "anted to s"eep the reflection coefficient at the third

harmonicHLoad Pull

Simulation




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Outline

26

• Overview






Load Pull

Simulation

Using ADS

20 May, 2002



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odify the bias networ7 as desired

27

4ut if you delete both current probes and voltage labels

'Vs_lo"( and 'Vs_high( then the >3* calculations on thedata display "ont "or#.

Load Pull

Simulation

Using ADS

20 May, 2002



Page

Outline

28

• Overview






Load Pull

Simulation

Using ADS

20 May, 2002



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!alculate the D! power consumption

29

The e%ists - function returns / if the variable in quotes

is not in the dataset. So, for e%ample, you could delete the

"ire label Vs_lo", re)run the simulation, and the po"er"ould still be calculated. If you alter the device biasing and

still "ant to calculate the 5! po"er consumption, you may

need to modify the equation for >dc.

The D/E inde%

means use the

5! component.

Load Pull

Simulation

Using ADS

20 May, 2002



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!alculate the power delivered and PA$

30

>avs is the po"er available from the source, in d4m.

The user sets this value on the schematic, and it is passed

into the dataset.

>o"er)added efficiency is calculated as the po"er delivered

to the load minus the po"er available from the source divided

by the 5! po"er consumption.

/.F:realV:conjI-- isa standard equation

for calculating po"er

delivered to a comple%

load. efer to 5esoer and

Juh, 4asic !ircuit Theory.

Load Pull

Simulation

Using ADS

20 May, 2002



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Pdel,1atts and PA$ are functions of the twoswept variables

3

The ma%imum values are computed by finding the

ma%ima across one dimension real_inde%s11- first,then finding the ma%imum of the remaining array.

Load Pull

Simulation

Using ADS

20 May, 2002



Page

Outline

32

• Overview

• Specifyingand generatingdesired load reflectioncoefficients

• Assigning arbitrary reflectioncoefficients at theharmonic freqs.

• iasingthedeviceandrunninga simulation

• !alculatingdesired responses "delivered power# PA$#etc.%

• &eneratingcontour lines

Load Pull

Simulation

Using ADS

20 May, 2002



Page

ost simple contour lines

33

Simplest case is to just use

contour_polar - function "ith

defaults. Kenerates si% equally)

spaced levels bet"een the

minimum and ma%imum of

the data.

4ut you cant easily find the

ma%imum by moving the

mar#er or quic#ly change

the number of lines or their

spacing.

Load Pull

Simulation

Using ADS

20 May, 2002



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ay specify specific contour values

34

=se curly braces L M to specify

specific contour values.

4ut you cant easily find the

ma%imum by moving the

mar#er, and you may have

to modify the values by

hand if you change the

simulation.

Load Pull

Simulation

Using ADS

20 May, 2002



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ore comple( but more fle(ible contourequations

35

Specify step in N >3* bet"een lines

Specify number of contour lines

Birst contour line "ill be for >3*ma%)/.1. This )/.1 term

is included so the first line "ill be a small circle that you cansee, rather than being a single pi%el that you cant.

If Cum>3*_lines6F, then D/++Cum>3*_lines)1-E generates

an array from / to O, in steps of 1.

So the second >3* line "ill be for >3*ma%)/.1 )1:>3*_step.

The third >3* line "ill be for >3*ma%)/.1 );:>3*_step.*tc.

&ith this approach, you can quic#ly change the number of

lines and the spacing bet"een them.Load Pull

Simulation

Using ADS

20 May, 2002



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&enerating contour lines for rectangular plots

36

The contour - function generates contours for a rectangular

plot, "hich may give you more resolution than a Smith chart.

These pairs

of points

define the

left)mostarc

3lthough the right column and y)a%is are

labeled '>3*_contours(, they are really

'imag_inde%s11(Load Pull

Simulation

Using ADS

20 May, 2002



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&enerating contour lines for Smith chart

37

The contour - function generates y)a%is coordinates >3*_contours

) really imag_inde%s11- paired "ith %)a%is coordinates

real_inde%s11-. 4ut you have to convert these to comple% numbersfor plotting on the Smith chart.

The >3*_contours_p equation ta#es the P and < coordinate pairs of the

contour lines and converts them to comple% numbers, P 8j:<, "hichcan be plotted on a Smith chart.

This equation generates contour lines for the Smith chart directly+

Load Pull

Simulation

Using ADS

20 May, 2002



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&enerating contours after sweeping magnitudeand phase of rho

38

>3*_contours can be plotted on a rectangular plot. The P)a%is

"ill be the magnitude of the reflection coefficient, and the <)a%is"ill be the phase of the reflection coefficient, in degrees.

These must be converted to comple% numbers via the

>3*_conts_forSmith!h equation, for plotting on a Smith chart.Load Pull

Simulation

Using ADS

20 May, 2002



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Plotting the actually9simulated reflectioncoefficients

39

This data sho"s the simulation

results "hen the reflection

coefficient is the value selectedby the mar#ers location.

These 'surface_samples( are computed from the s"ept variables,

real_inde%s11 and imag_inde%s11+

The 'e%pand -( function just adds an e%tra independent variable

to the imag_inde%s11 variable so it can be added to real_inde%s11.Load Pull

Simulation

Using ADS

20 May, 2002



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PA$ and power delivered are functions ofthe swept variables

40

Bind the indices of imag_inde%s11 and real_inde%s11 thatcorrespond to mar#er ms location

Load Pull

Simulation

Using ADS

20 May, 2002



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Summary

4

•

35S offers much fle%ibility for simulating load pull•Set)up and post)processing equations are comple%, but you

dont have to #no" them to run simulations. The set)up

and post)processing can be simplified.

•Qther, more advanced capabilities are available, including

source)pull, t"o)tone intermodulation distortion "hiledoing a load pull, and optimi$ation "ithin a load pull s"eep.

Load Pull

Simulation

Using ADS

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